GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-11+1


rfc:rfc4918

Network Working Group L. Dusseault, Ed. Request for Comments: 4918 CommerceNet Obsoletes: 2518 June 2007 Category: Standards Track

HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 Web Distributed Authoring and Versioning (WebDAV) consists of a set
 of methods, headers, and content-types ancillary to HTTP/1.1 for the
 management of resource properties, creation and management of
 resource collections, URL namespace manipulation, and resource
 locking (collision avoidance).
 RFC 2518 was published in February 1999, and this specification
 obsoletes RFC 2518 with minor revisions mostly due to
 interoperability experience.

Dusseault Standards Track [Page 1] RFC 4918 WebDAV June 2007

Table of Contents

 1. Introduction ....................................................7
 2. Notational Conventions ..........................................8
 3. Terminology .....................................................8
 4. Data Model for Resource Properties .............................10
    4.1. The Resource Property Model ...............................10
    4.2. Properties and HTTP Headers ...............................10
    4.3. Property Values ...........................................10
         4.3.1. Example - Property with Mixed Content ..............12
    4.4. Property Names ............................................14
    4.5. Source Resources and Output Resources .....................14
 5. Collections of Web Resources ...................................14
    5.1. HTTP URL Namespace Model ..................................15
    5.2. Collection Resources ......................................15
 6. Locking ........................................................17
    6.1. Lock Model ................................................18
    6.2. Exclusive vs. Shared Locks ................................19
    6.3. Required Support ..........................................20
    6.4. Lock Creator and Privileges ...............................20
    6.5. Lock Tokens ...............................................21
    6.6. Lock Timeout ..............................................21
    6.7. Lock Capability Discovery .................................22
    6.8. Active Lock Discovery .....................................22
 7. Write Lock .....................................................23
    7.1. Write Locks and Properties ................................24
    7.2. Avoiding Lost Updates .....................................24
    7.3. Write Locks and Unmapped URLs .............................25
    7.4. Write Locks and Collections ...............................26
    7.5. Write Locks and the If Request Header .....................28
         7.5.1. Example - Write Lock and COPY ......................28
         7.5.2. Example - Deleting a Member of a Locked
                Collection .........................................29
    7.6. Write Locks and COPY/MOVE .................................30
    7.7. Refreshing Write Locks ....................................30
 8. General Request and Response Handling ..........................31
    8.1. Precedence in Error Handling ..............................31
    8.2. Use of XML ................................................31
    8.3. URL Handling ..............................................32
         8.3.1. Example - Correct URL Handling .....................32
    8.4. Required Bodies in Requests ...............................33
    8.5. HTTP Headers for Use in WebDAV ............................33
    8.6. ETag ......................................................33
    8.7. Including Error Response Bodies ...........................34
    8.8. Impact of Namespace Operations on Cache Validators ........34
 9. HTTP Methods for Distributed Authoring .........................35
    9.1. PROPFIND Method ...........................................35
         9.1.1. PROPFIND Status Codes ..............................37

Dusseault Standards Track [Page 2] RFC 4918 WebDAV June 2007

         9.1.2. Status Codes for Use in 'propstat' Element .........37
         9.1.3. Example - Retrieving Named Properties ..............38
         9.1.4. Example - Using 'propname' to Retrieve All
                Property Names .....................................39
         9.1.5. Example - Using So-called 'allprop' ................41
         9.1.6. Example - Using 'allprop' with 'include' ...........43
    9.2. PROPPATCH Method ..........................................44
         9.2.1. Status Codes for Use in 'propstat' Element .........44
         9.2.2. Example - PROPPATCH ................................45
    9.3. MKCOL Method ..............................................46
         9.3.1. MKCOL Status Codes .................................47
         9.3.2. Example - MKCOL ....................................47
    9.4. GET, HEAD for Collections .................................48
    9.5. POST for Collections ......................................48
    9.6. DELETE Requirements .......................................48
         9.6.1. DELETE for Collections .............................49
         9.6.2. Example - DELETE ...................................49
    9.7. PUT Requirements ..........................................50
         9.7.1. PUT for Non-Collection Resources ...................50
         9.7.2. PUT for Collections ................................51
    9.8. COPY Method ...............................................51
         9.8.1. COPY for Non-collection Resources ..................51
         9.8.2. COPY for Properties ................................52
         9.8.3. COPY for Collections ...............................52
         9.8.4. COPY and Overwriting Destination Resources .........53
         9.8.5. Status Codes .......................................54
         9.8.6. Example - COPY with Overwrite ......................55
         9.8.7. Example - COPY with No Overwrite ...................55
         9.8.8. Example - COPY of a Collection .....................56
    9.9. MOVE Method ...............................................56
         9.9.1. MOVE for Properties ................................57
         9.9.2. MOVE for Collections ...............................57
         9.9.3. MOVE and the Overwrite Header ......................58
         9.9.4. Status Codes .......................................59
         9.9.5. Example - MOVE of a Non-Collection .................60
         9.9.6. Example - MOVE of a Collection .....................60
    9.10. LOCK Method ..............................................61
         9.10.1. Creating a Lock on an Existing Resource ...........61
         9.10.2. Refreshing Locks ..................................62
         9.10.3. Depth and Locking .................................62
         9.10.4. Locking Unmapped URLs .............................63
         9.10.5. Lock Compatibility Table ..........................63
         9.10.6. LOCK Responses ....................................63
         9.10.7. Example - Simple Lock Request .....................64
         9.10.8. Example - Refreshing a Write Lock .................65
         9.10.9. Example - Multi-Resource Lock Request .............66
    9.11. UNLOCK Method ............................................68
         9.11.1. Status Codes ......................................68

Dusseault Standards Track [Page 3] RFC 4918 WebDAV June 2007

         9.11.2. Example - UNLOCK ..................................69
 10. HTTP Headers for Distributed Authoring ........................69
    10.1. DAV Header ...............................................69
    10.2. Depth Header .............................................70
    10.3. Destination Header .......................................71
    10.4. If Header ................................................72
         10.4.1. Purpose ...........................................72
         10.4.2. Syntax ............................................72
         10.4.3. List Evaluation ...................................73
         10.4.4. Matching State Tokens and ETags ...................74
         10.4.5. If Header and Non-DAV-Aware Proxies ...............74
         10.4.6. Example - No-tag Production .......................75
         10.4.7. Example - Using "Not" with No-tag Production ......75
         10.4.8. Example - Causing a Condition to Always
                 Evaluate to True ..................................75
         10.4.9. Example - Tagged List If Header in COPY ...........76
         10.4.10. Example - Matching Lock Tokens with
                  Collection Locks .................................76
         10.4.11. Example - Matching ETags on Unmapped URLs ........76
    10.5. Lock-Token Header ........................................77
    10.6. Overwrite Header .........................................77
    10.7. Timeout Request Header ...................................78
 11. Status Code Extensions to HTTP/1.1 ............................78
    11.1. 207 Multi-Status .........................................78
    11.2. 422 Unprocessable Entity .................................78
    11.3. 423 Locked ...............................................78
    11.4. 424 Failed Dependency ....................................79
    11.5. 507 Insufficient Storage .................................79
 12. Use of HTTP Status Codes ......................................79
    12.1. 412 Precondition Failed ..................................79
    12.2. 414 Request-URI Too Long .................................79
 13. Multi-Status Response .........................................80
    13.1. Response Headers .........................................80
    13.2. Handling Redirected Child Resources ......................81
    13.3. Internal Status Codes ....................................81
 14. XML Element Definitions .......................................81
    14.1. activelock XML Element ...................................81
    14.2. allprop XML Element ......................................82
    14.3. collection XML Element ...................................82
    14.4. depth XML Element ........................................82
    14.5. error XML Element ........................................82
    14.6. exclusive XML Element ....................................83
    14.7. href XML Element .........................................83
    14.8. include XML Element ......................................83
    14.9. location XML Element .....................................83
    14.10. lockentry XML Element ...................................84
    14.11. lockinfo XML Element ....................................84
    14.12. lockroot XML Element ....................................84

Dusseault Standards Track [Page 4] RFC 4918 WebDAV June 2007

    14.13. lockscope XML Element ...................................84
    14.14. locktoken XML Element ...................................85
    14.15. locktype XML Element ....................................85
    14.16. multistatus XML Element .................................85
    14.17. owner XML Element .......................................85
    14.18. prop XML Element ........................................86
    14.19. propertyupdate XML Element ..............................86
    14.20. propfind XML Element ....................................86
    14.21. propname XML Element ....................................87
    14.22. propstat XML Element ....................................87
    14.23. remove XML Element ......................................87
    14.24. response XML Element ....................................88
    14.25. responsedescription XML Element .........................88
    14.26. set XML Element .........................................88
    14.27. shared XML Element ......................................89
    14.28. status XML Element ......................................89
    14.29. timeout XML Element .....................................89
    14.30. write XML Element .......................................89
 15. DAV Properties ................................................90
 16. Precondition/Postcondition XML Elements .......................98
 17. XML Extensibility in DAV .....................................101
 18. DAV Compliance Classes .......................................103
    18.1. Class 1 .................................................103
    18.2. Class 2 .................................................103
    18.3. Class 3 .................................................103
 19. Internationalization Considerations ..........................104
 20. Security Considerations ......................................105
    20.1. Authentication of Clients ...............................105
    20.2. Denial of Service .......................................106
    20.3. Security through Obscurity ..............................106
    20.4. Privacy Issues Connected to Locks .......................106
    20.5. Privacy Issues Connected to Properties ..................107
    20.6. Implications of XML Entities ............................107
    20.7. Risks Connected with Lock Tokens ........................108
    20.8. Hosting Malicious Content ...............................108
 21. IANA Considerations ..........................................109
    21.1. New URI Schemes .........................................109
    21.2. XML Namespaces ..........................................109
    21.3. Message Header Fields ...................................109
         21.3.1. DAV ..............................................109
         21.3.2. Depth ............................................110
         21.3.3. Destination ......................................110
         21.3.4. If ...............................................110
         21.3.5. Lock-Token .......................................110
         21.3.6. Overwrite ........................................111
         21.3.7. Timeout ..........................................111
    21.4. HTTP Status Codes .......................................111
 22. Acknowledgements .............................................112

Dusseault Standards Track [Page 5] RFC 4918 WebDAV June 2007

 23. Contributors to This Specification ...........................113
 24. Authors of RFC 2518 ..........................................113
 25. References ...................................................114
    25.1. Normative References.....................................114
    25.2. Informative References ..................................115
 Appendix A.  Notes on Processing XML Elements ....................117
    A.1. Notes on Empty XML Elements ..............................117
    A.2. Notes on Illegal XML Processing ..........................117
    A.3. Example - XML Syntax Error ...............................117
    A.4. Example - Unexpected XML Element .........................118
 Appendix B. Notes on HTTP Client Compatibility ...................119
 Appendix C. The 'opaquelocktoken' Scheme and URIs ................120
 Appendix D. Lock-null Resources ..................................120
    D.1. Guidance for Clients Using LOCK to Create Resources ......121
 Appendix E. Guidance for Clients Desiring to Authenticate ........121
 Appendix F. Summary of Changes from RFC 2518 .....................123
    F.1. Changes for Both Client and Server Implementations .......123
    F.2. Changes for Server Implementations .......................125
    F.3. Other Changes ............................................126

Dusseault Standards Track [Page 6] RFC 4918 WebDAV June 2007

1. Introduction

 This document describes an extension to the HTTP/1.1 protocol that
 allows clients to perform remote Web content authoring operations.
 This extension provides a coherent set of methods, headers, request
 entity body formats, and response entity body formats that provide
 operations for:
 Properties: The ability to create, remove, and query information
 about Web pages, such as their authors, creation dates, etc.
 Collections: The ability to create sets of documents and to retrieve
 a hierarchical membership listing (like a directory listing in a file
 system).
 Locking: The ability to keep more than one person from working on a
 document at the same time.  This prevents the "lost update problem",
 in which modifications are lost as first one author, then another,
 writes changes without merging the other author's changes.
 Namespace Operations: The ability to instruct the server to copy and
 move Web resources, operations that change the mapping from URLs to
 resources.
 Requirements and rationale for these operations are described in a
 companion document, "Requirements for a Distributed Authoring and
 Versioning Protocol for the World Wide Web" [RFC2291].
 This document does not specify the versioning operations suggested by
 [RFC2291].  That work was done in a separate document, "Versioning
 Extensions to WebDAV" [RFC3253].
 The sections below provide a detailed introduction to various WebDAV
 abstractions: resource properties (Section 4), collections of
 resources (Section 5), locks (Section 6) in general, and write locks
 (Section 7) specifically.
 These abstractions are manipulated by the WebDAV-specific HTTP
 methods (Section 9) and the extra HTTP headers (Section 10) used with
 WebDAV methods.  General considerations for handling HTTP requests
 and responses in WebDAV are found in Section 8.
 While the status codes provided by HTTP/1.1 are sufficient to
 describe most error conditions encountered by WebDAV methods, there
 are some errors that do not fall neatly into the existing categories.
 This specification defines extra status codes developed for WebDAV
 methods (Section 11) and describes existing HTTP status codes
 (Section 12) as used in WebDAV.  Since some WebDAV methods may

Dusseault Standards Track [Page 7] RFC 4918 WebDAV June 2007

 operate over many resources, the Multi-Status response (Section 13)
 has been introduced to return status information for multiple
 resources.  Finally, this version of WebDAV introduces precondition
 and postcondition (Section 16) XML elements in error response bodies.
 WebDAV uses XML ([REC-XML]) for property names and some values, and
 also uses XML to marshal complicated requests and responses.  This
 specification contains DTD and text definitions of all properties
 (Section 15) and all other XML elements (Section 14) used in
 marshalling.  WebDAV includes a few special rules on extending WebDAV
 XML marshalling in backwards-compatible ways (Section 17).
 Finishing off the specification are sections on what it means for a
 resource to be compliant with this specification (Section 18), on
 internationalization support (Section 19), and on security
 (Section 20).

2. Notational Conventions

 Since this document describes a set of extensions to the HTTP/1.1
 protocol, the augmented BNF used herein to describe protocol elements
 is exactly the same as described in Section 2.1 of [RFC2616],
 including the rules about implied linear whitespace.  Since this
 augmented BNF uses the basic production rules provided in Section 2.2
 of [RFC2616], these rules apply to this document as well.  Note this
 is not the standard BNF syntax used in other RFCs.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].
 Note that in natural language, a property like the "creationdate"
 property in the "DAV:" XML namespace is sometimes referred to as
 "DAV:creationdate" for brevity.

3. Terminology

 URI/URL - A Uniform Resource Identifier and Uniform Resource Locator,
 respectively.  These terms (and the distinction between them) are
 defined in [RFC3986].
 URI/URL Mapping - A relation between an absolute URI and a resource.
 Since a resource can represent items that are not network
 retrievable, as well as those that are, it is possible for a resource
 to have zero, one, or many URI mappings.  Mapping a resource to an
 "http" scheme URI makes it possible to submit HTTP protocol requests
 to the resource using the URI.

Dusseault Standards Track [Page 8] RFC 4918 WebDAV June 2007

 Path Segment - Informally, the characters found between slashes ("/")
 in a URI.  Formally, as defined in Section 3.3 of [RFC3986].
 Collection - Informally, a resource that also acts as a container of
 references to child resources.  Formally, a resource that contains a
 set of mappings between path segments and resources and meets the
 requirements defined in Section 5.
 Internal Member (of a Collection) - Informally, a child resource of a
 collection.  Formally, a resource referenced by a path segment
 mapping contained in the collection.
 Internal Member URL (of a Collection) - A URL of an internal member,
 consisting of the URL of the collection (including trailing slash)
 plus the path segment identifying the internal member.
 Member (of a Collection) - Informally, a "descendant" of a
 collection.  Formally, an internal member of the collection, or,
 recursively, a member of an internal member.
 Member URL (of a Collection) - A URL that is either an internal
 member URL of the collection itself, or is an internal member URL of
 a member of that collection.
 Property - A name/value pair that contains descriptive information
 about a resource.
 Live Property - A property whose semantics and syntax are enforced by
 the server.  For example, the live property DAV:getcontentlength has
 its value, the length of the entity returned by a GET request,
 automatically calculated by the server.
 Dead Property - A property whose semantics and syntax are not
 enforced by the server.  The server only records the value of a dead
 property; the client is responsible for maintaining the consistency
 of the syntax and semantics of a dead property.
 Principal - A distinct human or computational actor that initiates
 access to network resources.
 State Token - A URI that represents a state of a resource.  Lock
 tokens are the only state tokens defined in this specification.

Dusseault Standards Track [Page 9] RFC 4918 WebDAV June 2007

4. Data Model for Resource Properties

4.1. The Resource Property Model

 Properties are pieces of data that describe the state of a resource.
 Properties are data about data.
 Properties are used in distributed authoring environments to provide
 for efficient discovery and management of resources.  For example, a
 'subject' property might allow for the indexing of all resources by
 their subject, and an 'author' property might allow for the discovery
 of what authors have written which documents.
 The DAV property model consists of name/value pairs.  The name of a
 property identifies the property's syntax and semantics, and provides
 an address by which to refer to its syntax and semantics.
 There are two categories of properties: "live" and "dead".  A live
 property has its syntax and semantics enforced by the server.  Live
 properties include cases where a) the value of a property is
 protected and maintained by the server, and b) the value of the
 property is maintained by the client, but the server performs syntax
 checking on submitted values.  All instances of a given live property
 MUST comply with the definition associated with that property name.
 A dead property has its syntax and semantics enforced by the client;
 the server merely records the value of the property verbatim.

4.2. Properties and HTTP Headers

 Properties already exist, in a limited sense, in HTTP message
 headers.  However, in distributed authoring environments, a
 relatively large number of properties are needed to describe the
 state of a resource, and setting/returning them all through HTTP
 headers is inefficient.  Thus, a mechanism is needed that allows a
 principal to identify a set of properties in which the principal is
 interested and to set or retrieve just those properties.

4.3. Property Values

 The value of a property is always a (well-formed) XML fragment.
 XML has been chosen because it is a flexible, self-describing,
 structured data format that supports rich schema definitions, and
 because of its support for multiple character sets.  XML's self-
 describing nature allows any property's value to be extended by
 adding elements.  Clients will not break when they encounter
 extensions because they will still have the data specified in the
 original schema and MUST ignore elements they do not understand.

Dusseault Standards Track [Page 10] RFC 4918 WebDAV June 2007

 XML's support for multiple character sets allows any human-readable
 property to be encoded and read in a character set familiar to the
 user.  XML's support for multiple human languages, using the "xml:
 lang" attribute, handles cases where the same character set is
 employed by multiple human languages.  Note that xml:lang scope is
 recursive, so an xml:lang attribute on any element containing a
 property name element applies to the property value unless it has
 been overridden by a more locally scoped attribute.  Note that a
 property only has one value, in one language (or language MAY be left
 undefined); a property does not have multiple values in different
 languages or a single value in multiple languages.
 A property is always represented with an XML element consisting of
 the property name, called the "property name element".  The simplest
 example is an empty property, which is different from a property that
 does not exist:
    <R:title xmlns:R="http://www.example.com/ns/"></R:title>
 The value of the property appears inside the property name element.
 The value may be any kind of well-formed XML content, including both
 text-only and mixed content.  Servers MUST preserve the following XML
 Information Items (using the terminology from [REC-XML-INFOSET]) in
 storage and transmission of dead properties:
 For the property name Element Information Item itself:
    [namespace name]
    [local name]
    [attributes] named "xml:lang" or any such attribute in scope
    [children] of type element or character
 On all Element Information Items in the property value:
    [namespace name]
    [local name]
    [attributes]
    [children] of type element or character

Dusseault Standards Track [Page 11] RFC 4918 WebDAV June 2007

 On Attribute Information Items in the property value:
    [namespace name]
    [local name]
    [normalized value]
 On Character Information Items in the property value:
    [character code]
 Since prefixes are used in some XML vocabularies (XPath and XML
 Schema, for example), servers SHOULD preserve, for any Information
 Item in the value:
    [prefix]
 XML Infoset attributes not listed above MAY be preserved by the
 server, but clients MUST NOT rely on them being preserved.  The above
 rules would also apply by default to live properties, unless defined
 otherwise.
 Servers MUST ignore the XML attribute xml:space if present and never
 use it to change whitespace handling.  Whitespace in property values
 is significant.

4.3.1. Example - Property with Mixed Content

 Consider a dead property 'author' created by the client as follows:
   <D:prop xml:lang="en" xmlns:D="DAV:">
     <x:author xmlns:x='http://example.com/ns'>
       <x:name>Jane Doe</x:name>
       <!-- Jane's contact info -->
       <x:uri type='email'
              added='2005-11-26'>mailto:jane.doe@example.com</x:uri>
       <x:uri type='web'
              added='2005-11-27'>http://www.example.com</x:uri>
       <x:notes xmlns:h='http://www.w3.org/1999/xhtml'>
         Jane has been working way <h:em>too</h:em> long on the
         long-awaited revision of <![CDATA[<RFC2518>]]>.
       </x:notes>
     </x:author>
   </D:prop>

Dusseault Standards Track [Page 12] RFC 4918 WebDAV June 2007

 When this property is requested, a server might return:
   <D:prop xmlns:D='DAV:'><author
           xml:lang='en'
           xmlns:x='http://example.com/ns'
           xmlns='http://example.com/ns'
           xmlns:h='http://www.w3.org/1999/xhtml'>
       <x:name>Jane Doe</x:name>
       <x:uri   added="2005-11-26" type="email"
         >mailto:jane.doe@example.com</x:uri>
       <x:uri   added="2005-11-27" type="web"
         >http://www.example.com</x:uri>
       <x:notes>
         Jane has been working way <h:em>too</h:em> long on the
         long-awaited revision of &lt;RFC2518&gt;.
       </x:notes>
     </author>
   </D:prop>
 Note in this example:
 o  The [prefix] for the property name itself was not preserved, being
    non-significant, whereas all other [prefix] values have been
    preserved,
 o  attribute values have been rewritten with double quotes instead of
    single quotes (quoting style is not significant), and attribute
    order has not been preserved,
 o  the xml:lang attribute has been returned on the property name
    element itself (it was in scope when the property was set, but the
    exact position in the response is not considered significant as
    long as it is in scope),
 o  whitespace between tags has been preserved everywhere (whitespace
    between attributes not so),
 o  CDATA encapsulation was replaced with character escaping (the
    reverse would also be legal),
 o  the comment item was stripped (as would have been a processing
    instruction item).
 Implementation note: there are cases such as editing scenarios where
 clients may require that XML content is preserved character by
 character (such as attribute ordering or quoting style).  In this
 case, clients should consider using a text-only property value by
 escaping all characters that have a special meaning in XML parsing.

Dusseault Standards Track [Page 13] RFC 4918 WebDAV June 2007

4.4. Property Names

 A property name is a universally unique identifier that is associated
 with a schema that provides information about the syntax and
 semantics of the property.
 Because a property's name is universally unique, clients can depend
 upon consistent behavior for a particular property across multiple
 resources, on the same and across different servers, so long as that
 property is "live" on the resources in question, and the
 implementation of the live property is faithful to its definition.
 The XML namespace mechanism, which is based on URIs ([RFC3986]), is
 used to name properties because it prevents namespace collisions and
 provides for varying degrees of administrative control.
 The property namespace is flat; that is, no hierarchy of properties
 is explicitly recognized.  Thus, if a property A and a property A/B
 exist on a resource, there is no recognition of any relationship
 between the two properties.  It is expected that a separate
 specification will eventually be produced that will address issues
 relating to hierarchical properties.
 Finally, it is not possible to define the same property twice on a
 single resource, as this would cause a collision in the resource's
 property namespace.

4.5. Source Resources and Output Resources

 Some HTTP resources are dynamically generated by the server.  For
 these resources, there presumably exists source code somewhere
 governing how that resource is generated.  The relationship of source
 files to output HTTP resources may be one to one, one to many, many
 to one, or many to many.  There is no mechanism in HTTP to determine
 whether a resource is even dynamic, let alone where its source files
 exist or how to author them.  Although this problem would usefully be
 solved, interoperable WebDAV implementations have been widely
 deployed without actually solving this problem, by dealing only with
 static resources.  Thus, the source vs. output problem is not solved
 in this specification and has been deferred to a separate document.

5. Collections of Web Resources

 This section provides a description of a type of Web resource, the
 collection, and discusses its interactions with the HTTP URL
 namespace and with HTTP methods.  The purpose of a collection
 resource is to model collection-like objects (e.g., file system
 directories) within a server's namespace.

Dusseault Standards Track [Page 14] RFC 4918 WebDAV June 2007

 All DAV-compliant resources MUST support the HTTP URL namespace model
 specified herein.

5.1. HTTP URL Namespace Model

 The HTTP URL namespace is a hierarchical namespace where the
 hierarchy is delimited with the "/" character.
 An HTTP URL namespace is said to be consistent if it meets the
 following conditions: for every URL in the HTTP hierarchy there
 exists a collection that contains that URL as an internal member URL.
 The root, or top-level collection of the namespace under
 consideration, is exempt from the previous rule.  The top-level
 collection of the namespace under consideration is not necessarily
 the collection identified by the absolute path '/' -- it may be
 identified by one or more path segments (e.g., /servlets/webdav/...)
 Neither HTTP/1.1 nor WebDAV requires that the entire HTTP URL
 namespace be consistent -- a WebDAV-compatible resource may not have
 a parent collection.  However, certain WebDAV methods are prohibited
 from producing results that cause namespace inconsistencies.
 As is implicit in [RFC2616] and [RFC3986], any resource, including
 collection resources, MAY be identified by more than one URI.  For
 example, a resource could be identified by multiple HTTP URLs.

5.2. Collection Resources

 Collection resources differ from other resources in that they also
 act as containers.  Some HTTP methods apply only to a collection, but
 some apply to some or all of the resources inside the container
 defined by the collection.  When the scope of a method is not clear,
 the client can specify what depth to apply.  Depth can be either zero
 levels (only the collection), one level (the collection and directly
 contained resources), or infinite levels (the collection and all
 contained resources recursively).
 A collection's state consists of at least a set of mappings between
 path segments and resources, and a set of properties on the
 collection itself.  In this document, a resource B will be said to be
 contained in the collection resource A if there is a path segment
 mapping that maps to B and that is contained in A.  A collection MUST
 contain at most one mapping for a given path segment, i.e., it is
 illegal to have the same path segment mapped to more than one
 resource.

Dusseault Standards Track [Page 15] RFC 4918 WebDAV June 2007

 Properties defined on collections behave exactly as do properties on
 non-collection resources.  A collection MAY have additional state
 such as entity bodies returned by GET.
 For all WebDAV-compliant resources A and B, identified by URLs "U"
 and "V", respectively, such that "V" is equal to "U/SEGMENT", A MUST
 be a collection that contains a mapping from "SEGMENT" to B.  So, if
 resource B with URL "http://example.com/bar/blah" is WebDAV compliant
 and if resource A with URL "http://example.com/bar/" is WebDAV
 compliant, then resource A must be a collection and must contain
 exactly one mapping from "blah" to B.
 Although commonly a mapping consists of a single segment and a
 resource, in general, a mapping consists of a set of segments and a
 resource.  This allows a server to treat a set of segments as
 equivalent (i.e., either all of the segments are mapped to the same
 resource, or none of the segments are mapped to a resource).  For
 example, a server that performs case-folding on segments will treat
 the segments "ab", "Ab", "aB", and "AB" as equivalent.  A client can
 then use any of these segments to identify the resource.  Note that a
 PROPFIND result will select one of these equivalent segments to
 identify the mapping, so there will be one PROPFIND response element
 per mapping, not one per segment in the mapping.
 Collection resources MAY have mappings to non-WebDAV-compliant
 resources in the HTTP URL namespace hierarchy but are not required to
 do so.  For example, if resource X with URL
 "http://example.com/bar/blah" is not WebDAV compliant and resource A
 with "URL http://example.com/bar/" identifies a WebDAV collection,
 then A may or may not have a mapping from "blah" to X.
 If a WebDAV-compliant resource has no WebDAV-compliant internal
 members in the HTTP URL namespace hierarchy, then the WebDAV-
 compliant resource is not required to be a collection.
 There is a standing convention that when a collection is referred to
 by its name without a trailing slash, the server MAY handle the
 request as if the trailing slash were present.  In this case, it
 SHOULD return a Content-Location header in the response, pointing to
 the URL ending with the "/".  For example, if a client invokes a
 method on http://example.com/blah (no trailing slash), the server may
 respond as if the operation were invoked on http://example.com/blah/
 (trailing slash), and should return a Content-Location header with
 the value http://example.com/blah/.  Wherever a server produces a URL
 referring to a collection, the server SHOULD include the trailing
 slash.  In general, clients SHOULD use the trailing slash form of
 collection names.  If clients do not use the trailing slash form the
 client needs to be prepared to see a redirect response.  Clients will

Dusseault Standards Track [Page 16] RFC 4918 WebDAV June 2007

 find the DAV:resourcetype property more reliable than the URL to find
 out if a resource is a collection.
 Clients MUST be able to support the case where WebDAV resources are
 contained inside non-WebDAV resources.  For example, if an OPTIONS
 response from "http://example.com/servlet/dav/collection" indicates
 WebDAV support, the client cannot assume that
 "http://example.com/servlet/dav/" or its parent necessarily are
 WebDAV collections.
 A typical scenario in which mapped URLs do not appear as members of
 their parent collection is the case where a server allows links or
 redirects to non-WebDAV resources.  For instance, "/col/link" might
 not appear as a member of "/col/", although the server would respond
 with a 302 status to a GET request to "/col/link"; thus, the URL
 "/col/link" would indeed be mapped.  Similarly, a dynamically-
 generated page might have a URL mapping from "/col/index.html", thus
 this resource might respond with a 200 OK to a GET request yet not
 appear as a member of "/col/".
 Some mappings to even WebDAV-compliant resources might not appear in
 the parent collection.  An example for this case are servers that
 support multiple alias URLs for each WebDAV-compliant resource.  A
 server may implement case-insensitive URLs, thus "/col/a" and
 "/col/A" identify the same resource, yet only either "a" or "A" is
 reported upon listing the members of "/col".  In cases where a server
 treats a set of segments as equivalent, the server MUST expose only
 one preferred segment per mapping, consistently chosen, in PROPFIND
 responses.

6. Locking

 The ability to lock a resource provides a mechanism for serializing
 access to that resource.  Using a lock, an authoring client can
 provide a reasonable guarantee that another principal will not modify
 a resource while it is being edited.  In this way, a client can
 prevent the "lost update" problem.
 This specification allows locks to vary over two client-specified
 parameters, the number of principals involved (exclusive vs. shared)
 and the type of access to be granted.  This document defines locking
 for only one access type, write.  However, the syntax is extensible,
 and permits the eventual specification of locking for other access
 types.

Dusseault Standards Track [Page 17] RFC 4918 WebDAV June 2007

6.1. Lock Model

 This section provides a concise model for how locking behaves.  Later
 sections will provide more detail on some of the concepts and refer
 back to these model statements.  Normative statements related to LOCK
 and UNLOCK method handling can be found in the sections on those
 methods, whereas normative statements that cover any method are
 gathered here.
 1.  A lock either directly or indirectly locks a resource.
 2.  A resource becomes directly locked when a LOCK request to a URL
     of that resource creates a new lock.  The "lock-root" of the new
     lock is that URL.  If at the time of the request, the URL is not
     mapped to a resource, a new empty resource is created and
     directly locked.
 3.  An exclusive lock (Section 6.2) conflicts with any other kind of
     lock on the same resource, whether either lock is direct or
     indirect.  A server MUST NOT create conflicting locks on a
     resource.
 4.  For a collection that is locked with a depth-infinity lock L, all
     member resources are indirectly locked.  Changes in membership of
     such a collection affect the set of indirectly locked resources:
  • If a member resource is added to the collection, the new

member resource MUST NOT already have a conflicting lock,

        because the new resource MUST become indirectly locked by L.
  • If a member resource stops being a member of the collection,

then the resource MUST no longer be indirectly locked by L.

 5.  Each lock is identified by a single globally unique lock token
     (Section 6.5).
 6.  An UNLOCK request deletes the lock with the specified lock token.
     After a lock is deleted, no resource is locked by that lock.
 7.  A lock token is "submitted" in a request when it appears in an
     "If" header (Section 7, "Write Lock", discusses when token
     submission is required for write locks).
 8.  If a request causes the lock-root of any lock to become an
     unmapped URL, then the lock MUST also be deleted by that request.

Dusseault Standards Track [Page 18] RFC 4918 WebDAV June 2007

6.2. Exclusive vs. Shared Locks

 The most basic form of lock is an exclusive lock.  Exclusive locks
 avoid having to deal with content change conflicts, without requiring
 any coordination other than the methods described in this
 specification.
 However, there are times when the goal of a lock is not to exclude
 others from exercising an access right but rather to provide a
 mechanism for principals to indicate that they intend to exercise
 their access rights.  Shared locks are provided for this case.  A
 shared lock allows multiple principals to receive a lock.  Hence any
 principal that has both access privileges and a valid lock can use
 the locked resource.
 With shared locks, there are two trust sets that affect a resource.
 The first trust set is created by access permissions.  Principals who
 are trusted, for example, may have permission to write to the
 resource.  Among those who have access permission to write to the
 resource, the set of principals who have taken out a shared lock also
 must trust each other, creating a (typically) smaller trust set
 within the access permission write set.
 Starting with every possible principal on the Internet, in most
 situations the vast majority of these principals will not have write
 access to a given resource.  Of the small number who do have write
 access, some principals may decide to guarantee their edits are free
 from overwrite conflicts by using exclusive write locks.  Others may
 decide they trust their collaborators will not overwrite their work
 (the potential set of collaborators being the set of principals who
 have write permission) and use a shared lock, which informs their
 collaborators that a principal may be working on the resource.
 The WebDAV extensions to HTTP do not need to provide all of the
 communications paths necessary for principals to coordinate their
 activities.  When using shared locks, principals may use any out-of-
 band communication channel to coordinate their work (e.g., face-to-
 face interaction, written notes, post-it notes on the screen,
 telephone conversation, email, etc.)  The intent of a shared lock is
 to let collaborators know who else may be working on a resource.
 Shared locks are included because experience from Web-distributed
 authoring systems has indicated that exclusive locks are often too
 rigid.  An exclusive lock is used to enforce a particular editing
 process: take out an exclusive lock, read the resource, perform
 edits, write the resource, release the lock.  This editing process
 has the problem that locks are not always properly released, for
 example, when a program crashes or when a lock creator leaves without

Dusseault Standards Track [Page 19] RFC 4918 WebDAV June 2007

 unlocking a resource.  While both timeouts (Section 6.6) and
 administrative action can be used to remove an offending lock,
 neither mechanism may be available when needed; the timeout may be
 long or the administrator may not be available.
 A successful request for a new shared lock MUST result in the
 generation of a unique lock associated with the requesting principal.
 Thus, if five principals have taken out shared write locks on the
 same resource, there will be five locks and five lock tokens, one for
 each principal.

6.3. Required Support

 A WebDAV-compliant resource is not required to support locking in any
 form.  If the resource does support locking, it may choose to support
 any combination of exclusive and shared locks for any access types.
 The reason for this flexibility is that locking policy strikes to the
 very heart of the resource management and versioning systems employed
 by various storage repositories.  These repositories require control
 over what sort of locking will be made available.  For example, some
 repositories only support shared write locks, while others only
 provide support for exclusive write locks, while yet others use no
 locking at all.  As each system is sufficiently different to merit
 exclusion of certain locking features, this specification leaves
 locking as the sole axis of negotiation within WebDAV.

6.4. Lock Creator and Privileges

 The creator of a lock has special privileges to use the lock to
 modify the resource.  When a locked resource is modified, a server
 MUST check that the authenticated principal matches the lock creator
 (in addition to checking for valid lock token submission).
 The server MAY allow privileged users other than the lock creator to
 destroy a lock (for example, the resource owner or an administrator).
 The 'unlock' privilege in [RFC3744] was defined to provide that
 permission.
 There is no requirement for servers to accept LOCK requests from all
 users or from anonymous users.
 Note that having a lock does not confer full privilege to modify the
 locked resource.  Write access and other privileges MUST be enforced
 through normal privilege or authentication mechanisms, not based on
 the possible obscurity of lock token values.

Dusseault Standards Track [Page 20] RFC 4918 WebDAV June 2007

6.5. Lock Tokens

 A lock token is a type of state token that identifies a particular
 lock.  Each lock has exactly one unique lock token generated by the
 server.  Clients MUST NOT attempt to interpret lock tokens in any
 way.
 Lock token URIs MUST be unique across all resources for all time.
 This uniqueness constraint allows lock tokens to be submitted across
 resources and servers without fear of confusion.  Since lock tokens
 are unique, a client MAY submit a lock token in an If header on a
 resource other than the one that returned it.
 When a LOCK operation creates a new lock, the new lock token is
 returned in the Lock-Token response header defined in Section 10.5,
 and also in the body of the response.
 Servers MAY make lock tokens publicly readable (e.g., in the DAV:
 lockdiscovery property).  One use case for making lock tokens
 readable is so that a long-lived lock can be removed by the resource
 owner (the client that obtained the lock might have crashed or
 disconnected before cleaning up the lock).  Except for the case of
 using UNLOCK under user guidance, a client SHOULD NOT use a lock
 token created by another client instance.
 This specification encourages servers to create Universally Unique
 Identifiers (UUIDs) for lock tokens, and to use the URI form defined
 by "A Universally Unique Identifier (UUID) URN Namespace"
 ([RFC4122]).  However, servers are free to use any URI (e.g., from
 another scheme) so long as it meets the uniqueness requirements.  For
 example, a valid lock token might be constructed using the
 "opaquelocktoken" scheme defined in Appendix C.
 Example: "urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6"

6.6. Lock Timeout

 A lock MAY have a limited lifetime.  The lifetime is suggested by the
 client when creating or refreshing the lock, but the server
 ultimately chooses the timeout value.  Timeout is measured in seconds
 remaining until lock expiration.
 The timeout counter MUST be restarted if a refresh lock request is
 successful (see Section 9.10.2).  The timeout counter SHOULD NOT be
 restarted at any other time.
 If the timeout expires, then the lock SHOULD be removed.  In this
 case the server SHOULD act as if an UNLOCK method was executed by the

Dusseault Standards Track [Page 21] RFC 4918 WebDAV June 2007

 server on the resource using the lock token of the timed-out lock,
 performed with its override authority.
 Servers are advised to pay close attention to the values submitted by
 clients, as they will be indicative of the type of activity the
 client intends to perform.  For example, an applet running in a
 browser may need to lock a resource, but because of the instability
 of the environment within which the applet is running, the applet may
 be turned off without warning.  As a result, the applet is likely to
 ask for a relatively small timeout value so that if the applet dies,
 the lock can be quickly harvested.  However, a document management
 system is likely to ask for an extremely long timeout because its
 user may be planning on going offline.
 A client MUST NOT assume that just because the timeout has expired,
 the lock has immediately been removed.
 Likewise, a client MUST NOT assume that just because the timeout has
 not expired, the lock still exists.  Clients MUST assume that locks
 can arbitrarily disappear at any time, regardless of the value given
 in the Timeout header.  The Timeout header only indicates the
 behavior of the server if extraordinary circumstances do not occur.
 For example, a sufficiently privileged user may remove a lock at any
 time, or the system may crash in such a way that it loses the record
 of the lock's existence.

6.7. Lock Capability Discovery

 Since server lock support is optional, a client trying to lock a
 resource on a server can either try the lock and hope for the best,
 or perform some form of discovery to determine what lock capabilities
 the server supports.  This is known as lock capability discovery.  A
 client can determine what lock types the server supports by
 retrieving the DAV:supportedlock property.
 Any DAV-compliant resource that supports the LOCK method MUST support
 the DAV:supportedlock property.

6.8. Active Lock Discovery

 If another principal locks a resource that a principal wishes to
 access, it is useful for the second principal to be able to find out
 who the first principal is.  For this purpose the DAV:lockdiscovery
 property is provided.  This property lists all outstanding locks,
 describes their type, and MAY even provide the lock tokens.
 Any DAV-compliant resource that supports the LOCK method MUST support
 the DAV:lockdiscovery property.

Dusseault Standards Track [Page 22] RFC 4918 WebDAV June 2007

7. Write Lock

 This section describes the semantics specific to the write lock type.
 The write lock is a specific instance of a lock type, and is the only
 lock type described in this specification.
 An exclusive write lock protects a resource: it prevents changes by
 any principal other than the lock creator and in any case where the
 lock token is not submitted (e.g., by a client process other than the
 one holding the lock).
 Clients MUST submit a lock-token they are authorized to use in any
 request that modifies a write-locked resource.  The list of
 modifications covered by a write-lock include:
 1.  A change to any of the following aspects of any write-locked
     resource:
  • any variant,
  • any dead property,
  • any live property that is lockable (a live property is

lockable unless otherwise defined.)

 2.  For collections, any modification of an internal member URI.  An
     internal member URI of a collection is considered to be modified
     if it is added, removed, or identifies a different resource.
     More discussion on write locks and collections is found in
     Section 7.4.
 3.  A modification of the mapping of the root of the write lock,
     either to another resource or to no resource (e.g., DELETE).
 Of the methods defined in HTTP and WebDAV, PUT, POST, PROPPATCH,
 LOCK, UNLOCK, MOVE, COPY (for the destination resource), DELETE, and
 MKCOL are affected by write locks.  All other HTTP/WebDAV methods
 defined so far -- GET in particular -- function independently of a
 write lock.
 The next few sections describe in more specific terms how write locks
 interact with various operations.

Dusseault Standards Track [Page 23] RFC 4918 WebDAV June 2007

7.1. Write Locks and Properties

 While those without a write lock may not alter a property on a
 resource it is still possible for the values of live properties to
 change, even while locked, due to the requirements of their schemas.
 Only dead properties and live properties defined as lockable are
 guaranteed not to change while write locked.

7.2. Avoiding Lost Updates

 Although the write locks provide some help in preventing lost
 updates, they cannot guarantee that updates will never be lost.
 Consider the following scenario:
 Two clients A and B are interested in editing the resource
 'index.html'.  Client A is an HTTP client rather than a WebDAV
 client, and so does not know how to perform locking.
 Client A doesn't lock the document, but does a GET, and begins
 editing.
 Client B does LOCK, performs a GET and begins editing.
 Client B finishes editing, performs a PUT, then an UNLOCK.
 Client A performs a PUT, overwriting and losing all of B's changes.
 There are several reasons why the WebDAV protocol itself cannot
 prevent this situation.  First, it cannot force all clients to use
 locking because it must be compatible with HTTP clients that do not
 comprehend locking.  Second, it cannot require servers to support
 locking because of the variety of repository implementations, some of
 which rely on reservations and merging rather than on locking.
 Finally, being stateless, it cannot enforce a sequence of operations
 like LOCK / GET / PUT / UNLOCK.
 WebDAV servers that support locking can reduce the likelihood that
 clients will accidentally overwrite each other's changes by requiring
 clients to lock resources before modifying them.  Such servers would
 effectively prevent HTTP 1.0 and HTTP 1.1 clients from modifying
 resources.
 WebDAV clients can be good citizens by using a lock / retrieve /
 write /unlock sequence of operations (at least by default) whenever
 they interact with a WebDAV server that supports locking.

Dusseault Standards Track [Page 24] RFC 4918 WebDAV June 2007

 HTTP 1.1 clients can be good citizens, avoiding overwriting other
 clients' changes, by using entity tags in If-Match headers with any
 requests that would modify resources.
 Information managers may attempt to prevent overwrites by
 implementing client-side procedures requiring locking before
 modifying WebDAV resources.

7.3. Write Locks and Unmapped URLs

 WebDAV provides the ability to send a LOCK request to an unmapped URL
 in order to reserve the name for use.  This is a simple way to avoid
 the lost-update problem on the creation of a new resource (another
 way is to use If-None-Match header specified in Section 14.26 of
 [RFC2616]).  It has the side benefit of locking the new resource
 immediately for use of the creator.
 Note that the lost-update problem is not an issue for collections
 because MKCOL can only be used to create a collection, not to
 overwrite an existing collection.  When trying to lock a collection
 upon creation, clients can attempt to increase the likelihood of
 getting the lock by pipelining the MKCOL and LOCK requests together
 (but because this doesn't convert two separate operations into one
 atomic operation, there's no guarantee this will work).
 A successful lock request to an unmapped URL MUST result in the
 creation of a locked (non-collection) resource with empty content.
 Subsequently, a successful PUT request (with the correct lock token)
 provides the content for the resource.  Note that the LOCK request
 has no mechanism for the client to provide Content-Type or Content-
 Language, thus the server will use defaults or empty values and rely
 on the subsequent PUT request for correct values.
 A resource created with a LOCK is empty but otherwise behaves in
 every way as a normal resource.  It behaves the same way as a
 resource created by a PUT request with an empty body (and where a
 Content-Type and Content-Language was not specified), followed by a
 LOCK request to the same resource.  Following from this model, a
 locked empty resource:
 o  Can be read, deleted, moved, and copied, and in all ways behaves
    as a regular non-collection resource.
 o  Appears as a member of its parent collection.
 o  SHOULD NOT disappear when its lock goes away (clients must
    therefore be responsible for cleaning up their own mess, as with
    any other operation or any non-empty resource).

Dusseault Standards Track [Page 25] RFC 4918 WebDAV June 2007

 o  MAY NOT have values for properties like DAV:getcontentlanguage
    that haven't been specified yet by the client.
 o  Can be updated (have content added) with a PUT request.
 o  MUST NOT be converted into a collection.  The server MUST fail a
    MKCOL request (as it would with a MKCOL request to any existing
    non-collection resource).
 o  MUST have defined values for DAV:lockdiscovery and DAV:
    supportedlock properties.
 o  The response MUST indicate that a resource was created, by use of
    the "201 Created" response code (a LOCK request to an existing
    resource instead will result in 200 OK).  The body must still
    include the DAV:lockdiscovery property, as with a LOCK request to
    an existing resource.
 The client is expected to update the locked empty resource shortly
 after locking it, using PUT and possibly PROPPATCH.
 Alternatively and for backwards compatibility to [RFC2518], servers
 MAY implement Lock-Null Resources (LNRs) instead (see definition in
 Appendix D).  Clients can easily interoperate both with servers that
 support the old model LNRs and the recommended model of "locked empty
 resources" by only attempting PUT after a LOCK to an unmapped URL,
 not MKCOL or GET, and by not relying on specific properties of LNRs.

7.4. Write Locks and Collections

 There are two kinds of collection write locks.  A depth-0 write lock
 on a collection protects the collection properties plus the internal
 member URLs of that one collection, while not protecting the content
 or properties of member resources (if the collection itself has any
 entity bodies, those are also protected).  A depth-infinity write
 lock on a collection provides the same protection on that collection
 and also provides write lock protection on every member resource.
 Expressed otherwise, a write lock of either kind protects any request
 that would create a new resource in a write locked collection, any
 request that would remove an internal member URL of a write locked
 collection, and any request that would change the segment name of any
 internal member.
 Thus, a collection write lock protects all the following actions:
 o  DELETE a collection's direct internal member,

Dusseault Standards Track [Page 26] RFC 4918 WebDAV June 2007

 o  MOVE an internal member out of the collection,
 o  MOVE an internal member into the collection,
 o  MOVE to rename an internal member within a collection,
 o  COPY an internal member into a collection, and
 o  PUT or MKCOL request that would create a new internal member.
 The collection's lock token is required in addition to the lock token
 on the internal member itself, if it is locked separately.
 In addition, a depth-infinity lock affects all write operations to
 all members of the locked collection.  With a depth-infinity lock,
 the resource identified by the root of the lock is directly locked,
 and all its members are indirectly locked.
 o  Any new resource added as a descendant of a depth-infinity locked
    collection becomes indirectly locked.
 o  Any indirectly locked resource moved out of the locked collection
    into an unlocked collection is thereafter unlocked.
 o  Any indirectly locked resource moved out of a locked source
    collection into a depth-infinity locked target collection remains
    indirectly locked but is now protected by the lock on the target
    collection (the target collection's lock token will thereafter be
    required to make further changes).
 If a depth-infinity write LOCK request is issued to a collection
 containing member URLs identifying resources that are currently
 locked in a manner that conflicts with the new lock (see Section 6.1,
 point 3), the request MUST fail with a 423 (Locked) status code, and
 the response SHOULD contain the 'no-conflicting-lock' precondition.
 If a lock request causes the URL of a resource to be added as an
 internal member URL of a depth-infinity locked collection, then the
 new resource MUST be automatically protected by the lock.  For
 example, if the collection /a/b/ is write locked and the resource /c
 is moved to /a/b/c, then resource /a/b/c will be added to the write
 lock.

Dusseault Standards Track [Page 27] RFC 4918 WebDAV June 2007

7.5. Write Locks and the If Request Header

 A user agent has to demonstrate knowledge of a lock when requesting
 an operation on a locked resource.  Otherwise, the following scenario
 might occur.  In the scenario, program A, run by User A, takes out a
 write lock on a resource.  Program B, also run by User A, has no
 knowledge of the lock taken out by program A, yet performs a PUT to
 the locked resource.  In this scenario, the PUT succeeds because
 locks are associated with a principal, not a program, and thus
 program B, because it is acting with principal A's credential, is
 allowed to perform the PUT.  However, had program B known about the
 lock, it would not have overwritten the resource, preferring instead
 to present a dialog box describing the conflict to the user.  Due to
 this scenario, a mechanism is needed to prevent different programs
 from accidentally ignoring locks taken out by other programs with the
 same authorization.
 In order to prevent these collisions, a lock token MUST be submitted
 by an authorized principal for all locked resources that a method may
 change or the method MUST fail.  A lock token is submitted when it
 appears in an If header.  For example, if a resource is to be moved
 and both the source and destination are locked, then two lock tokens
 must be submitted in the If header, one for the source and the other
 for the destination.

7.5.1. Example - Write Lock and COPY

 >>Request
   COPY /~fielding/index.html HTTP/1.1
   Host: www.example.com
   Destination: http://www.example.com/users/f/fielding/index.html
   If: <http://www.example.com/users/f/fielding/index.html>
       (<urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6>)
 >>Response
   HTTP/1.1 204 No Content
 In this example, even though both the source and destination are
 locked, only one lock token must be submitted (the one for the lock
 on the destination).  This is because the source resource is not
 modified by a COPY, and hence unaffected by the write lock.  In this
 example, user agent authentication has previously occurred via a
 mechanism outside the scope of the HTTP protocol, in the underlying
 transport layer.

Dusseault Standards Track [Page 28] RFC 4918 WebDAV June 2007

7.5.2. Example - Deleting a Member of a Locked Collection

 Consider a collection "/locked" with an exclusive, depth-infinity
 write lock, and an attempt to delete an internal member "/locked/
 member":
 >>Request
   DELETE /locked/member HTTP/1.1
   Host: example.com
 >>Response
   HTTP/1.1 423 Locked
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:error xmlns:D="DAV:">
     <D:lock-token-submitted>
       <D:href>/locked/</D:href>
     </D:lock-token-submitted>
   </D:error>
 Thus, the client would need to submit the lock token with the request
 to make it succeed.  To do that, various forms of the If header (see
 Section 10.4) could be used.
 "No-Tag-List" format:
   If: (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
 "Tagged-List" format, for "http://example.com/locked/":
   If: <http://example.com/locked/>
       (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
 "Tagged-List" format, for "http://example.com/locked/member":
   If: <http://example.com/locked/member>
       (<urn:uuid:150852e2-3847-42d5-8cbe-0f4f296f26cf>)
 Note that, for the purpose of submitting the lock token, the actual
 form doesn't matter; what's relevant is that the lock token appears
 in the If header, and that the If header itself evaluates to true.

Dusseault Standards Track [Page 29] RFC 4918 WebDAV June 2007

7.6. Write Locks and COPY/MOVE

 A COPY method invocation MUST NOT duplicate any write locks active on
 the source.  However, as previously noted, if the COPY copies the
 resource into a collection that is locked with a depth-infinity lock,
 then the resource will be added to the lock.
 A successful MOVE request on a write locked resource MUST NOT move
 the write lock with the resource.  However, if there is an existing
 lock at the destination, the server MUST add the moved resource to
 the destination lock scope.  For example, if the MOVE makes the
 resource a child of a collection that has a depth-infinity lock, then
 the resource will be added to that collection's lock.  Additionally,
 if a resource with a depth-infinity lock is moved to a destination
 that is within the scope of the same lock (e.g., within the URL
 namespace tree covered by the lock), the moved resource will again be
 added to the lock.  In both these examples, as specified in
 Section 7.5, an If header must be submitted containing a lock token
 for both the source and destination.

7.7. Refreshing Write Locks

 A client MUST NOT submit the same write lock request twice.  Note
 that a client is always aware it is resubmitting the same lock
 request because it must include the lock token in the If header in
 order to make the request for a resource that is already locked.
 However, a client may submit a LOCK request with an If header but
 without a body.  A server receiving a LOCK request with no body MUST
 NOT create a new lock -- this form of the LOCK request is only to be
 used to "refresh" an existing lock (meaning, at minimum, that any
 timers associated with the lock MUST be reset).
 Clients may submit Timeout headers of arbitrary value with their lock
 refresh requests.  Servers, as always, may ignore Timeout headers
 submitted by the client, and a server MAY refresh a lock with a
 timeout period that is different than the previous timeout period
 used for the lock, provided it advertises the new value in the LOCK
 refresh response.
 If an error is received in response to a refresh LOCK request, the
 client MUST NOT assume that the lock was refreshed.

Dusseault Standards Track [Page 30] RFC 4918 WebDAV June 2007

8. General Request and Response Handling

8.1. Precedence in Error Handling

 Servers MUST return authorization errors in preference to other
 errors.  This avoids leaking information about protected resources
 (e.g., a client that finds that a hidden resource exists by seeing a
 423 Locked response to an anonymous request to the resource).

8.2. Use of XML

 In HTTP/1.1, method parameter information was exclusively encoded in
 HTTP headers.  Unlike HTTP/1.1, WebDAV encodes method parameter
 information either in an XML ([REC-XML]) request entity body, or in
 an HTTP header.  The use of XML to encode method parameters was
 motivated by the ability to add extra XML elements to existing
 structures, providing extensibility; and by XML's ability to encode
 information in ISO 10646 character sets, providing
 internationalization support.
 In addition to encoding method parameters, XML is used in WebDAV to
 encode the responses from methods, providing the extensibility and
 internationalization advantages of XML for method output, as well as
 input.
 When XML is used for a request or response body, the Content-Type
 type SHOULD be application/xml.  Implementations MUST accept both
 text/xml and application/xml in request and response bodies.  Use of
 text/xml is deprecated.
 All DAV-compliant clients and resources MUST use XML parsers that are
 compliant with [REC-XML] and [REC-XML-NAMES].  All XML used in either
 requests or responses MUST be, at minimum, well formed and use
 namespaces correctly.  If a server receives XML that is not well-
 formed, then the server MUST reject the entire request with a 400
 (Bad Request).  If a client receives XML that is not well-formed in a
 response, then the client MUST NOT assume anything about the outcome
 of the executed method and SHOULD treat the server as malfunctioning.
 Note that processing XML submitted by an untrusted source may cause
 risks connected to privacy, security, and service quality (see
 Section 20).  Servers MAY reject questionable requests (even though
 they consist of well-formed XML), for instance, with a 400 (Bad
 Request) status code and an optional response body explaining the
 problem.

Dusseault Standards Track [Page 31] RFC 4918 WebDAV June 2007

8.3. URL Handling

 URLs appear in many places in requests and responses.
 Interoperability experience with [RFC2518] showed that many clients
 parsing Multi-Status responses did not fully implement the full
 Reference Resolution defined in Section 5 of [RFC3986].  Thus,
 servers in particular need to be careful in handling URLs in
 responses, to ensure that clients have enough context to be able to
 interpret all the URLs.  The rules in this section apply not only to
 resource URLs in the 'href' element in Multi-Status responses, but
 also to the Destination and If header resource URLs.
 The sender has a choice between two approaches: using a relative
 reference, which is resolved against the Request-URI, or a full URI.
 A server MUST ensure that every 'href' value within a Multi-Status
 response uses the same format.
 WebDAV only uses one form of relative reference in its extensions,
 the absolute path.
    Simple-ref = absolute-URI | ( path-absolute [ "?" query ] )
 The absolute-URI, path-absolute and query productions are defined in
 Sections 4.3, 3.3, and 3.4 of [RFC3986].
 Within Simple-ref productions, senders MUST NOT:
 o  use dot-segments ("." or ".."), or
 o  have prefixes that do not match the Request-URI (using the
    comparison rules defined in Section 3.2.3 of [RFC2616]).
 Identifiers for collections SHOULD end in a '/' character.

8.3.1. Example - Correct URL Handling

 Consider the collection http://example.com/sample/ with the internal
 member URL http://example.com/sample/a%20test and the PROPFIND
 request below:
 >>Request:
   PROPFIND /sample/ HTTP/1.1
   Host: example.com
   Depth: 1

Dusseault Standards Track [Page 32] RFC 4918 WebDAV June 2007

 In this case, the server should return two 'href' elements containing
 either
 o  'http://example.com/sample/' and
    'http://example.com/sample/a%20test', or
 o  '/sample/' and '/sample/a%20test'
 Note that even though the server may be storing the member resource
 internally as 'a test', it has to be percent-encoded when used inside
 a URI reference (see Section 2.1 of [RFC3986]).  Also note that a
 legal URI may still contain characters that need to be escaped within
 XML character data, such as the ampersand character.

8.4. Required Bodies in Requests

 Some of these new methods do not define bodies.  Servers MUST examine
 all requests for a body, even when a body was not expected.  In cases
 where a request body is present but would be ignored by a server, the
 server MUST reject the request with 415 (Unsupported Media Type).
 This informs the client (which may have been attempting to use an
 extension) that the body could not be processed as the client
 intended.

8.5. HTTP Headers for Use in WebDAV

 HTTP defines many headers that can be used in WebDAV requests and
 responses.  Not all of these are appropriate in all situations and
 some interactions may be undefined.  Note that HTTP 1.1 requires the
 Date header in all responses if possible (see Section 14.18,
 [RFC2616]).
 The server MUST do authorization checks before checking any HTTP
 conditional header.

8.6. ETag

 HTTP 1.1 recommends the use of ETags rather than modification dates,
 for cache control, and there are even stronger reasons to prefer
 ETags for authoring.  Correct use of ETags is even more important in
 a distributed authoring environment, because ETags are necessary
 along with locks to avoid the lost-update problem.  A client might
 fail to renew a lock, for example, when the lock times out and the
 client is accidentally offline or in the middle of a long upload.
 When a client fails to renew the lock, it's quite possible the
 resource can still be relocked and the user can go on editing, as
 long as no changes were made in the meantime.  ETags are required for
 the client to be able to distinguish this case.  Otherwise, the

Dusseault Standards Track [Page 33] RFC 4918 WebDAV June 2007

 client is forced to ask the user whether to overwrite the resource on
 the server without even being able to tell the user if it has
 changed.  Timestamps do not solve this problem nearly as well as
 ETags.
 Strong ETags are much more useful for authoring use cases than weak
 ETags (see Section 13.3.3 of [RFC2616]).  Semantic equivalence can be
 a useful concept but that depends on the document type and the
 application type, and interoperability might require some agreement
 or standard outside the scope of this specification and HTTP.  Note
 also that weak ETags have certain restrictions in HTTP, e.g., these
 cannot be used in If-Match headers.
 Note that the meaning of an ETag in a PUT response is not clearly
 defined either in this document or in RFC 2616 (i.e., whether the
 ETag means that the resource is octet-for-octet equivalent to the
 body of the PUT request, or whether the server could have made minor
 changes in the formatting or content of the document upon storage).
 This is an HTTP issue, not purely a WebDAV issue.
 Because clients may be forced to prompt users or throw away changed
 content if the ETag changes, a WebDAV server SHOULD NOT change the
 ETag (or the Last-Modified time) for a resource that has an unchanged
 body and location.  The ETag represents the state of the body or
 contents of the resource.  There is no similar way to tell if
 properties have changed.

8.7. Including Error Response Bodies

 HTTP and WebDAV did not use the bodies of most error responses for
 machine-parsable information until the specification for Versioning
 Extensions to WebDAV introduced a mechanism to include more specific
 information in the body of an error response (Section 1.6 of
 [RFC3253]).  The error body mechanism is appropriate to use with any
 error response that may take a body but does not already have a body
 defined.  The mechanism is particularly appropriate when a status
 code can mean many things (for example, 400 Bad Request can mean
 required headers are missing, headers are incorrectly formatted, or
 much more).  This error body mechanism is covered in Section 16.

8.8. Impact of Namespace Operations on Cache Validators

 Note that the HTTP response headers "Etag" and "Last-Modified" (see
 [RFC2616], Sections 14.19 and 14.29) are defined per URL (not per
 resource), and are used by clients for caching.  Therefore servers
 must ensure that executing any operation that affects the URL
 namespace (such as COPY, MOVE, DELETE, PUT, or MKCOL) does preserve
 their semantics, in particular:

Dusseault Standards Track [Page 34] RFC 4918 WebDAV June 2007

 o  For any given URL, the "Last-Modified" value MUST increment every
    time the representation returned upon GET changes (within the
    limits of timestamp resolution).
 o  For any given URL, an "ETag" value MUST NOT be reused for
    different representations returned by GET.
 In practice this means that servers
 o  might have to increment "Last-Modified" timestamps for every
    resource inside the destination namespace of a namespace operation
    unless it can do so more selectively, and
 o  similarly, might have to re-assign "ETag" values for these
    resources (unless the server allocates entity tags in a way so
    that they are unique across the whole URL namespace managed by the
    server).
 Note that these considerations also apply to specific use cases, such
 as using PUT to create a new resource at a URL that has been mapped
 before, but has been deleted since then.
 Finally, WebDAV properties (such as DAV:getetag and DAV:
 getlastmodified) that inherit their semantics from HTTP headers must
 behave accordingly.

9. HTTP Methods for Distributed Authoring

9.1. PROPFIND Method

 The PROPFIND method retrieves properties defined on the resource
 identified by the Request-URI, if the resource does not have any
 internal members, or on the resource identified by the Request-URI
 and potentially its member resources, if the resource is a collection
 that has internal member URLs.  All DAV-compliant resources MUST
 support the PROPFIND method and the propfind XML element
 (Section 14.20) along with all XML elements defined for use with that
 element.
 A client MUST submit a Depth header with a value of "0", "1", or
 "infinity" with a PROPFIND request.  Servers MUST support "0" and "1"
 depth requests on WebDAV-compliant resources and SHOULD support
 "infinity" requests.  In practice, support for infinite-depth
 requests MAY be disabled, due to the performance and security
 concerns associated with this behavior.  Servers SHOULD treat a
 request without a Depth header as if a "Depth: infinity" header was
 included.

Dusseault Standards Track [Page 35] RFC 4918 WebDAV June 2007

 A client may submit a 'propfind' XML element in the body of the
 request method describing what information is being requested.  It is
 possible to:
 o  Request particular property values, by naming the properties
    desired within the 'prop' element (the ordering of properties in
    here MAY be ignored by the server),
 o  Request property values for those properties defined in this
    specification (at a minimum) plus dead properties, by using the
    'allprop' element (the 'include' element can be used with
    'allprop' to instruct the server to also include additional live
    properties that may not have been returned otherwise),
 o  Request a list of names of all the properties defined on the
    resource, by using the 'propname' element.
 A client may choose not to submit a request body.  An empty PROPFIND
 request body MUST be treated as if it were an 'allprop' request.
 Note that 'allprop' does not return values for all live properties.
 WebDAV servers increasingly have expensively-calculated or lengthy
 properties (see [RFC3253] and [RFC3744]) and do not return all
 properties already.  Instead, WebDAV clients can use propname
 requests to discover what live properties exist, and request named
 properties when retrieving values.  For a live property defined
 elsewhere, that definition can specify whether or not that live
 property would be returned in 'allprop' requests.
 All servers MUST support returning a response of content type text/
 xml or application/xml that contains a multistatus XML element that
 describes the results of the attempts to retrieve the various
 properties.
 If there is an error retrieving a property, then a proper error
 result MUST be included in the response.  A request to retrieve the
 value of a property that does not exist is an error and MUST be noted
 with a 'response' XML element that contains a 404 (Not Found) status
 value.
 Consequently, the 'multistatus' XML element for a collection resource
 MUST include a 'response' XML element for each member URL of the
 collection, to whatever depth was requested.  It SHOULD NOT include
 any 'response' elements for resources that are not WebDAV-compliant.
 Each 'response' element MUST contain an 'href' element that contains
 the URL of the resource on which the properties in the prop XML
 element are defined.  Results for a PROPFIND on a collection resource
 are returned as a flat list whose order of entries is not

Dusseault Standards Track [Page 36] RFC 4918 WebDAV June 2007

 significant.  Note that a resource may have only one value for a
 property of a given name, so the property may only show up once in
 PROPFIND responses.
 Properties may be subject to access control.  In the case of
 'allprop' and 'propname' requests, if a principal does not have the
 right to know whether a particular property exists, then the property
 MAY be silently excluded from the response.
 Some PROPFIND results MAY be cached, with care, as there is no cache
 validation mechanism for most properties.  This method is both safe
 and idempotent (see Section 9.1 of [RFC2616]).

9.1.1. PROPFIND Status Codes

 This section, as with similar sections for other methods, provides
 some guidance on error codes and preconditions or postconditions
 (defined in Section 16) that might be particularly useful with
 PROPFIND.
 403 Forbidden - A server MAY reject PROPFIND requests on collections
 with depth header of "Infinity", in which case it SHOULD use this
 error with the precondition code 'propfind-finite-depth' inside the
 error body.

9.1.2. Status Codes for Use in 'propstat' Element

 In PROPFIND responses, information about individual properties is
 returned inside 'propstat' elements (see Section 14.22), each
 containing an individual 'status' element containing information
 about the properties appearing in it.  The list below summarizes the
 most common status codes used inside 'propstat'; however, clients
 should be prepared to handle other 2/3/4/5xx series status codes as
 well.
 200 OK - A property exists and/or its value is successfully returned.
 401 Unauthorized - The property cannot be viewed without appropriate
 authorization.
 403 Forbidden - The property cannot be viewed regardless of
 authentication.
 404 Not Found - The property does not exist.

Dusseault Standards Track [Page 37] RFC 4918 WebDAV June 2007

9.1.3. Example - Retrieving Named Properties

 >>Request
   PROPFIND /file HTTP/1.1
   Host: www.example.com
   Content-type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop xmlns:R="http://ns.example.com/boxschema/">
       <R:bigbox/>
       <R:author/>
       <R:DingALing/>
       <R:Random/>
     </D:prop>
   </D:propfind>
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response xmlns:R="http://ns.example.com/boxschema/">
       <D:href>http://www.example.com/file</D:href>
       <D:propstat>
         <D:prop>
           <R:bigbox>
             <R:BoxType>Box type A</R:BoxType>
           </R:bigbox>
           <R:author>
             <R:Name>J.J. Johnson</R:Name>
           </R:author>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
       <D:propstat>
         <D:prop><R:DingALing/><R:Random/></D:prop>
         <D:status>HTTP/1.1 403 Forbidden</D:status>
         <D:responsedescription> The user does not have access to the
    DingALing property.
         </D:responsedescription>
       </D:propstat>

Dusseault Standards Track [Page 38] RFC 4918 WebDAV June 2007

     </D:response>
     <D:responsedescription> There has been an access violation error.
     </D:responsedescription>
   </D:multistatus>
 In this example, PROPFIND is executed on a non-collection resource
 http://www.example.com/file.  The propfind XML element specifies the
 name of four properties whose values are being requested.  In this
 case, only two properties were returned, since the principal issuing
 the request did not have sufficient access rights to see the third
 and fourth properties.

9.1.4. Example - Using 'propname' to Retrieve All Property Names

 >>Request
   PROPFIND /container/ HTTP/1.1
   Host: www.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <propfind xmlns="DAV:">
     <propname/>
   </propfind>
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <multistatus xmlns="DAV:">
     <response>
       <href>http://www.example.com/container/</href>
       <propstat>
         <prop xmlns:R="http://ns.example.com/boxschema/">
           <R:bigbox/>
           <R:author/>
           <creationdate/>
           <displayname/>
           <resourcetype/>
           <supportedlock/>
         </prop>
         <status>HTTP/1.1 200 OK</status>

Dusseault Standards Track [Page 39] RFC 4918 WebDAV June 2007

       </propstat>
     </response>
     <response>
       <href>http://www.example.com/container/front.html</href>
       <propstat>
         <prop xmlns:R="http://ns.example.com/boxschema/">
           <R:bigbox/>
           <creationdate/>
           <displayname/>
           <getcontentlength/>
           <getcontenttype/>
           <getetag/>
           <getlastmodified/>
           <resourcetype/>
           <supportedlock/>
         </prop>
         <status>HTTP/1.1 200 OK</status>
       </propstat>
     </response>
   </multistatus>
 In this example, PROPFIND is invoked on the collection resource
 http://www.example.com/container/, with a propfind XML element
 containing the propname XML element, meaning the name of all
 properties should be returned.  Since no Depth header is present, it
 assumes its default value of "infinity", meaning the name of the
 properties on the collection and all its descendants should be
 returned.
 Consistent with the previous example, resource
 http://www.example.com/container/ has six properties defined on it:
 bigbox and author in the "http://ns.example.com/boxschema/"
 namespace, and creationdate, displayname, resourcetype, and
 supportedlock in the "DAV:" namespace.
 The resource http://www.example.com/container/index.html, a member of
 the "container" collection, has nine properties defined on it, bigbox
 in the "http://ns.example.com/boxschema/" namespace and creationdate,
 displayname, getcontentlength, getcontenttype, getetag,
 getlastmodified, resourcetype, and supportedlock in the "DAV:"
 namespace.
 This example also demonstrates the use of XML namespace scoping and
 the default namespace.  Since the "xmlns" attribute does not contain
 a prefix, the namespace applies by default to all enclosed elements.
 Hence, all elements that do not explicitly state the namespace to
 which they belong are members of the "DAV:" namespace.

Dusseault Standards Track [Page 40] RFC 4918 WebDAV June 2007

9.1.5. Example - Using So-called 'allprop'

 Note that 'allprop', despite its name, which remains for backward-
 compatibility, does not return every property, but only dead
 properties and the live properties defined in this specification.
 >>Request
   PROPFIND /container/ HTTP/1.1
   Host: www.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:allprop/>
   </D:propfind>
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>/container/</D:href>
       <D:propstat>
         <D:prop xmlns:R="http://ns.example.com/boxschema/">
           <R:bigbox><R:BoxType>Box type A</R:BoxType></R:bigbox>
           <R:author><R:Name>Hadrian</R:Name></R:author>
           <D:creationdate>1997-12-01T17:42:21-08:00</D:creationdate>
           <D:displayname>Example collection</D:displayname>
           <D:resourcetype><D:collection/></D:resourcetype>
           <D:supportedlock>
             <D:lockentry>
               <D:lockscope><D:exclusive/></D:lockscope>
               <D:locktype><D:write/></D:locktype>
             </D:lockentry>
             <D:lockentry>
               <D:lockscope><D:shared/></D:lockscope>
               <D:locktype><D:write/></D:locktype>
             </D:lockentry>
           </D:supportedlock>
         </D:prop>

Dusseault Standards Track [Page 41] RFC 4918 WebDAV June 2007

         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
     <D:response>
       <D:href>/container/front.html</D:href>
       <D:propstat>
         <D:prop xmlns:R="http://ns.example.com/boxschema/">
           <R:bigbox><R:BoxType>Box type B</R:BoxType>
           </R:bigbox>
           <D:creationdate>1997-12-01T18:27:21-08:00</D:creationdate>
           <D:displayname>Example HTML resource</D:displayname>
           <D:getcontentlength>4525</D:getcontentlength>
           <D:getcontenttype>text/html</D:getcontenttype>
           <D:getetag>"zzyzx"</D:getetag>
           <D:getlastmodified
             >Mon, 12 Jan 1998 09:25:56 GMT</D:getlastmodified>
           <D:resourcetype/>
           <D:supportedlock>
             <D:lockentry>
               <D:lockscope><D:exclusive/></D:lockscope>
               <D:locktype><D:write/></D:locktype>
             </D:lockentry>
             <D:lockentry>
               <D:lockscope><D:shared/></D:lockscope>
               <D:locktype><D:write/></D:locktype>
             </D:lockentry>
           </D:supportedlock>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>
 In this example, PROPFIND was invoked on the resource
 http://www.example.com/container/ with a Depth header of 1, meaning
 the request applies to the resource and its children, and a propfind
 XML element containing the allprop XML element, meaning the request
 should return the name and value of all the dead properties defined
 on the resources, plus the name and value of all the properties
 defined in this specification.  This example illustrates the use of
 relative references in the 'href' elements of the response.
 The resource http://www.example.com/container/ has six properties
 defined on it: 'bigbox' and 'author in the
 "http://ns.example.com/boxschema/" namespace, DAV:creationdate, DAV:
 displayname, DAV:resourcetype, and DAV:supportedlock.

Dusseault Standards Track [Page 42] RFC 4918 WebDAV June 2007

 The last four properties are WebDAV-specific, defined in Section 15.
 Since GET is not supported on this resource, the get* properties
 (e.g., DAV:getcontentlength) are not defined on this resource.  The
 WebDAV-specific properties assert that "container" was created on
 December 1, 1997, at 5:42:21PM, in a time zone 8 hours west of GMT
 (DAV:creationdate), has a name of "Example collection" (DAV:
 displayname), a collection resource type (DAV:resourcetype), and
 supports exclusive write and shared write locks (DAV:supportedlock).
 The resource http://www.example.com/container/front.html has nine
 properties defined on it:
 'bigbox' in the "http://ns.example.com/boxschema/" namespace (another
 instance of the "bigbox" property type), DAV:creationdate, DAV:
 displayname, DAV:getcontentlength, DAV:getcontenttype, DAV:getetag,
 DAV:getlastmodified, DAV:resourcetype, and DAV:supportedlock.
 The DAV-specific properties assert that "front.html" was created on
 December 1, 1997, at 6:27:21PM, in a time zone 8 hours west of GMT
 (DAV:creationdate), has a name of "Example HTML resource" (DAV:
 displayname), a content length of 4525 bytes (DAV:getcontentlength),
 a MIME type of "text/html" (DAV:getcontenttype), an entity tag of
 "zzyzx" (DAV:getetag), was last modified on Monday, January 12, 1998,
 at 09:25:56 GMT (DAV:getlastmodified), has an empty resource type,
 meaning that it is not a collection (DAV:resourcetype), and supports
 both exclusive write and shared write locks (DAV:supportedlock).

9.1.6. Example - Using 'allprop' with 'include'

 >>Request
   PROPFIND /mycol/ HTTP/1.1
   Host: www.example.com
   Depth: 1
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:allprop/>
     <D:include>
       <D:supported-live-property-set/>
       <D:supported-report-set/>
     </D:include>
   </D:propfind>

Dusseault Standards Track [Page 43] RFC 4918 WebDAV June 2007

 In this example, PROPFIND is executed on the resource
 http://www.example.com/mycol/ and its internal member resources.  The
 client requests the values of all live properties defined in this
 specification, plus all dead properties, plus two more live
 properties defined in [RFC3253].  The response is not shown.

9.2. PROPPATCH Method

 The PROPPATCH method processes instructions specified in the request
 body to set and/or remove properties defined on the resource
 identified by the Request-URI.
 All DAV-compliant resources MUST support the PROPPATCH method and
 MUST process instructions that are specified using the
 propertyupdate, set, and remove XML elements.  Execution of the
 directives in this method is, of course, subject to access control
 constraints.  DAV-compliant resources SHOULD support the setting of
 arbitrary dead properties.
 The request message body of a PROPPATCH method MUST contain the
 propertyupdate XML element.
 Servers MUST process PROPPATCH instructions in document order (an
 exception to the normal rule that ordering is irrelevant).
 Instructions MUST either all be executed or none executed.  Thus, if
 any error occurs during processing, all executed instructions MUST be
 undone and a proper error result returned.  Instruction processing
 details can be found in the definition of the set and remove
 instructions in Sections 14.23 and 14.26.
 If a server attempts to make any of the property changes in a
 PROPPATCH request (i.e., the request is not rejected for high-level
 errors before processing the body), the response MUST be a Multi-
 Status response as described in Section 9.2.1.
 This method is idempotent, but not safe (see Section 9.1 of
 [RFC2616]).  Responses to this method MUST NOT be cached.

9.2.1. Status Codes for Use in 'propstat' Element

 In PROPPATCH responses, information about individual properties is
 returned inside 'propstat' elements (see Section 14.22), each
 containing an individual 'status' element containing information
 about the properties appearing in it.  The list below summarizes the
 most common status codes used inside 'propstat'; however, clients
 should be prepared to handle other 2/3/4/5xx series status codes as
 well.

Dusseault Standards Track [Page 44] RFC 4918 WebDAV June 2007

 200 (OK) - The property set or change succeeded.  Note that if this
 appears for one property, it appears for every property in the
 response, due to the atomicity of PROPPATCH.
 403 (Forbidden) - The client, for reasons the server chooses not to
 specify, cannot alter one of the properties.
 403 (Forbidden): The client has attempted to set a protected
 property, such as DAV:getetag.  If returning this error, the server
 SHOULD use the precondition code 'cannot-modify-protected-property'
 inside the response body.
 409 (Conflict) - The client has provided a value whose semantics are
 not appropriate for the property.
 424 (Failed Dependency) - The property change could not be made
 because of another property change that failed.
 507 (Insufficient Storage) - The server did not have sufficient space
 to record the property.

9.2.2. Example - PROPPATCH

 >>Request
   PROPPATCH /bar.html HTTP/1.1
   Host: www.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:propertyupdate xmlns:D="DAV:"
           xmlns:Z="http://ns.example.com/standards/z39.50/">
     <D:set>
       <D:prop>
         <Z:Authors>
           <Z:Author>Jim Whitehead</Z:Author>
           <Z:Author>Roy Fielding</Z:Author>
         </Z:Authors>
       </D:prop>
     </D:set>
     <D:remove>
       <D:prop><Z:Copyright-Owner/></D:prop>
     </D:remove>
   </D:propertyupdate>

Dusseault Standards Track [Page 45] RFC 4918 WebDAV June 2007

 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
           xmlns:Z="http://ns.example.com/standards/z39.50/">
     <D:response>
       <D:href>http://www.example.com/bar.html</D:href>
       <D:propstat>
         <D:prop><Z:Authors/></D:prop>
         <D:status>HTTP/1.1 424 Failed Dependency</D:status>
       </D:propstat>
       <D:propstat>
         <D:prop><Z:Copyright-Owner/></D:prop>
         <D:status>HTTP/1.1 409 Conflict</D:status>
       </D:propstat>
       <D:responsedescription> Copyright Owner cannot be deleted or
         altered.</D:responsedescription>
     </D:response>
   </D:multistatus>
 In this example, the client requests the server to set the value of
 the "Authors" property in the
 "http://ns.example.com/standards/z39.50/" namespace, and to remove
 the property "Copyright-Owner" in the same namespace.  Since the
 Copyright-Owner property could not be removed, no property
 modifications occur.  The 424 (Failed Dependency) status code for the
 Authors property indicates this action would have succeeded if it
 were not for the conflict with removing the Copyright-Owner property.

9.3. MKCOL Method

 MKCOL creates a new collection resource at the location specified by
 the Request-URI.  If the Request-URI is already mapped to a resource,
 then the MKCOL MUST fail.  During MKCOL processing, a server MUST
 make the Request-URI an internal member of its parent collection,
 unless the Request-URI is "/".  If no such ancestor exists, the
 method MUST fail.  When the MKCOL operation creates a new collection
 resource, all ancestors MUST already exist, or the method MUST fail
 with a 409 (Conflict) status code.  For example, if a request to
 create collection /a/b/c/d/ is made, and /a/b/c/ does not exist, the
 request must fail.
 When MKCOL is invoked without a request body, the newly created
 collection SHOULD have no members.

Dusseault Standards Track [Page 46] RFC 4918 WebDAV June 2007

 A MKCOL request message may contain a message body.  The precise
 behavior of a MKCOL request when the body is present is undefined,
 but limited to creating collections, members of a collection, bodies
 of members, and properties on the collections or members.  If the
 server receives a MKCOL request entity type it does not support or
 understand, it MUST respond with a 415 (Unsupported Media Type)
 status code.  If the server decides to reject the request based on
 the presence of an entity or the type of an entity, it should use the
 415 (Unsupported Media Type) status code.
 This method is idempotent, but not safe (see Section 9.1 of
 [RFC2616]).  Responses to this method MUST NOT be cached.

9.3.1. MKCOL Status Codes

 In addition to the general status codes possible, the following
 status codes have specific applicability to MKCOL:
 201 (Created) - The collection was created.
 403 (Forbidden) - This indicates at least one of two conditions: 1)
 the server does not allow the creation of collections at the given
 location in its URL namespace, or 2) the parent collection of the
 Request-URI exists but cannot accept members.
 405 (Method Not Allowed) - MKCOL can only be executed on an unmapped
 URL.
 409 (Conflict) - A collection cannot be made at the Request-URI until
 one or more intermediate collections have been created.  The server
 MUST NOT create those intermediate collections automatically.
 415 (Unsupported Media Type) - The server does not support the
 request body type (although bodies are legal on MKCOL requests, since
 this specification doesn't define any, the server is likely not to
 support any given body type).
 507 (Insufficient Storage) - The resource does not have sufficient
 space to record the state of the resource after the execution of this
 method.

9.3.2. Example - MKCOL

 This example creates a collection called /webdisc/xfiles/ on the
 server www.example.com.

Dusseault Standards Track [Page 47] RFC 4918 WebDAV June 2007

 >>Request
   MKCOL /webdisc/xfiles/ HTTP/1.1
   Host: www.example.com
 >>Response
   HTTP/1.1 201 Created

9.4. GET, HEAD for Collections

 The semantics of GET are unchanged when applied to a collection,
 since GET is defined as, "retrieve whatever information (in the form
 of an entity) is identified by the Request-URI" [RFC2616].  GET, when
 applied to a collection, may return the contents of an "index.html"
 resource, a human-readable view of the contents of the collection, or
 something else altogether.  Hence, it is possible that the result of
 a GET on a collection will bear no correlation to the membership of
 the collection.
 Similarly, since the definition of HEAD is a GET without a response
 message body, the semantics of HEAD are unmodified when applied to
 collection resources.

9.5. POST for Collections

 Since by definition the actual function performed by POST is
 determined by the server and often depends on the particular
 resource, the behavior of POST when applied to collections cannot be
 meaningfully modified because it is largely undefined.  Thus, the
 semantics of POST are unmodified when applied to a collection.

9.6. DELETE Requirements

 DELETE is defined in [RFC2616], Section 9.7, to "delete the resource
 identified by the Request-URI".  However, WebDAV changes some DELETE
 handling requirements.
 A server processing a successful DELETE request:
    MUST destroy locks rooted on the deleted resource
    MUST remove the mapping from the Request-URI to any resource.
 Thus, after a successful DELETE operation (and in the absence of
 other actions), a subsequent GET/HEAD/PROPFIND request to the target
 Request-URI MUST return 404 (Not Found).

Dusseault Standards Track [Page 48] RFC 4918 WebDAV June 2007

9.6.1. DELETE for Collections

 The DELETE method on a collection MUST act as if a "Depth: infinity"
 header was used on it.  A client MUST NOT submit a Depth header with
 a DELETE on a collection with any value but infinity.
 DELETE instructs that the collection specified in the Request-URI and
 all resources identified by its internal member URLs are to be
 deleted.
 If any resource identified by a member URL cannot be deleted, then
 all of the member's ancestors MUST NOT be deleted, so as to maintain
 URL namespace consistency.
 Any headers included with DELETE MUST be applied in processing every
 resource to be deleted.
 When the DELETE method has completed processing, it MUST result in a
 consistent URL namespace.
 If an error occurs deleting a member resource (a resource other than
 the resource identified in the Request-URI), then the response can be
 a 207 (Multi-Status).  Multi-Status is used here to indicate which
 internal resources could NOT be deleted, including an error code,
 which should help the client understand which resources caused the
 failure.  For example, the Multi-Status body could include a response
 with status 423 (Locked) if an internal resource was locked.
 The server MAY return a 4xx status response, rather than a 207, if
 the request failed completely.
 424 (Failed Dependency) status codes SHOULD NOT be in the 207 (Multi-
 Status) response for DELETE.  They can be safely left out because the
 client will know that the ancestors of a resource could not be
 deleted when the client receives an error for the ancestor's progeny.
 Additionally, 204 (No Content) errors SHOULD NOT be returned in the
 207 (Multi-Status).  The reason for this prohibition is that 204 (No
 Content) is the default success code.

9.6.2. Example - DELETE

 >>Request
   DELETE  /container/ HTTP/1.1
   Host: www.example.com

Dusseault Standards Track [Page 49] RFC 4918 WebDAV June 2007

 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <d:multistatus xmlns:d="DAV:">
     <d:response>
       <d:href>http://www.example.com/container/resource3</d:href>
       <d:status>HTTP/1.1 423 Locked</d:status>
       <d:error><d:lock-token-submitted/></d:error>
     </d:response>
   </d:multistatus>
 In this example, the attempt to delete
 http://www.example.com/container/resource3 failed because it is
 locked, and no lock token was submitted with the request.
 Consequently, the attempt to delete http://www.example.com/container/
 also failed.  Thus, the client knows that the attempt to delete
 http://www.example.com/container/ must have also failed since the
 parent cannot be deleted unless its child has also been deleted.
 Even though a Depth header has not been included, a depth of infinity
 is assumed because the method is on a collection.

9.7. PUT Requirements

9.7.1. PUT for Non-Collection Resources

 A PUT performed on an existing resource replaces the GET response
 entity of the resource.  Properties defined on the resource may be
 recomputed during PUT processing but are not otherwise affected.  For
 example, if a server recognizes the content type of the request body,
 it may be able to automatically extract information that could be
 profitably exposed as properties.
 A PUT that would result in the creation of a resource without an
 appropriately scoped parent collection MUST fail with a 409
 (Conflict).
 A PUT request allows a client to indicate what media type an entity
 body has, and whether it should change if overwritten.  Thus, a
 client SHOULD provide a Content-Type for a new resource if any is
 known.  If the client does not provide a Content-Type for a new
 resource, the server MAY create a resource with no Content-Type
 assigned, or it MAY attempt to assign a Content-Type.

Dusseault Standards Track [Page 50] RFC 4918 WebDAV June 2007

 Note that although a recipient ought generally to treat metadata
 supplied with an HTTP request as authoritative, in practice there's
 no guarantee that a server will accept client-supplied metadata
 (e.g., any request header beginning with "Content-").  Many servers
 do not allow configuring the Content-Type on a per-resource basis in
 the first place.  Thus, clients can't always rely on the ability to
 directly influence the content type by including a Content-Type
 request header.

9.7.2. PUT for Collections

 This specification does not define the behavior of the PUT method for
 existing collections.  A PUT request to an existing collection MAY be
 treated as an error (405 Method Not Allowed).
 The MKCOL method is defined to create collections.

9.8. COPY Method

 The COPY method creates a duplicate of the source resource identified
 by the Request-URI, in the destination resource identified by the URI
 in the Destination header.  The Destination header MUST be present.
 The exact behavior of the COPY method depends on the type of the
 source resource.
 All WebDAV-compliant resources MUST support the COPY method.
 However, support for the COPY method does not guarantee the ability
 to copy a resource.  For example, separate programs may control
 resources on the same server.  As a result, it may not be possible to
 copy a resource to a location that appears to be on the same server.
 This method is idempotent, but not safe (see Section 9.1 of
 [RFC2616]).  Responses to this method MUST NOT be cached.

9.8.1. COPY for Non-collection Resources

 When the source resource is not a collection, the result of the COPY
 method is the creation of a new resource at the destination whose
 state and behavior match that of the source resource as closely as
 possible.  Since the environment at the destination may be different
 than at the source due to factors outside the scope of control of the
 server, such as the absence of resources required for correct
 operation, it may not be possible to completely duplicate the
 behavior of the resource at the destination.  Subsequent alterations
 to the destination resource will not modify the source resource.
 Subsequent alterations to the source resource will not modify the
 destination resource.

Dusseault Standards Track [Page 51] RFC 4918 WebDAV June 2007

9.8.2. COPY for Properties

 After a successful COPY invocation, all dead properties on the source
 resource SHOULD be duplicated on the destination resource.  Live
 properties described in this document SHOULD be duplicated as
 identically behaving live properties at the destination resource, but
 not necessarily with the same values.  Servers SHOULD NOT convert
 live properties into dead properties on the destination resource,
 because clients may then draw incorrect conclusions about the state
 or functionality of a resource.  Note that some live properties are
 defined such that the absence of the property has a specific meaning
 (e.g., a flag with one meaning if present, and the opposite if
 absent), and in these cases, a successful COPY might result in the
 property being reported as "Not Found" in subsequent requests.
 When the destination is an unmapped URL, a COPY operation creates a
 new resource much like a PUT operation does.  Live properties that
 are related to resource creation (such as DAV:creationdate) should
 have their values set accordingly.

9.8.3. COPY for Collections

 The COPY method on a collection without a Depth header MUST act as if
 a Depth header with value "infinity" was included.  A client may
 submit a Depth header on a COPY on a collection with a value of "0"
 or "infinity".  Servers MUST support the "0" and "infinity" Depth
 header behaviors on WebDAV-compliant resources.
 An infinite-depth COPY instructs that the collection resource
 identified by the Request-URI is to be copied to the location
 identified by the URI in the Destination header, and all its internal
 member resources are to be copied to a location relative to it,
 recursively through all levels of the collection hierarchy.  Note
 that an infinite-depth COPY of /A/ into /A/B/ could lead to infinite
 recursion if not handled correctly.
 A COPY of "Depth: 0" only instructs that the collection and its
 properties, but not resources identified by its internal member URLs,
 are to be copied.
 Any headers included with a COPY MUST be applied in processing every
 resource to be copied with the exception of the Destination header.
 The Destination header only specifies the destination URI for the
 Request-URI.  When applied to members of the collection identified by
 the Request-URI, the value of Destination is to be modified to
 reflect the current location in the hierarchy.  So, if the Request-
 URI is /a/ with Host header value http://example.com/ and the

Dusseault Standards Track [Page 52] RFC 4918 WebDAV June 2007

 Destination is http://example.com/b/, then when
 http://example.com/a/c/d is processed, it must use a Destination of
 http://example.com/b/c/d.
 When the COPY method has completed processing, it MUST have created a
 consistent URL namespace at the destination (see Section 5.1 for the
 definition of namespace consistency).  However, if an error occurs
 while copying an internal collection, the server MUST NOT copy any
 resources identified by members of this collection (i.e., the server
 must skip this subtree), as this would create an inconsistent
 namespace.  After detecting an error, the COPY operation SHOULD try
 to finish as much of the original copy operation as possible (i.e.,
 the server should still attempt to copy other subtrees and their
 members that are not descendants of an error-causing collection).
 So, for example, if an infinite-depth copy operation is performed on
 collection /a/, which contains collections /a/b/ and /a/c/, and an
 error occurs copying /a/b/, an attempt should still be made to copy
 /a/c/.  Similarly, after encountering an error copying a non-
 collection resource as part of an infinite-depth copy, the server
 SHOULD try to finish as much of the original copy operation as
 possible.
 If an error in executing the COPY method occurs with a resource other
 than the resource identified in the Request-URI, then the response
 MUST be a 207 (Multi-Status), and the URL of the resource causing the
 failure MUST appear with the specific error.
 The 424 (Failed Dependency) status code SHOULD NOT be returned in the
 207 (Multi-Status) response from a COPY method.  These responses can
 be safely omitted because the client will know that the progeny of a
 resource could not be copied when the client receives an error for
 the parent.  Additionally, 201 (Created)/204 (No Content) status
 codes SHOULD NOT be returned as values in 207 (Multi-Status)
 responses from COPY methods.  They, too, can be safely omitted
 because they are the default success codes.

9.8.4. COPY and Overwriting Destination Resources

 If a COPY request has an Overwrite header with a value of "F", and a
 resource exists at the Destination URL, the server MUST fail the
 request.
 When a server executes a COPY request and overwrites a destination
 resource, the exact behavior MAY depend on many factors, including
 WebDAV extension capabilities (see particularly [RFC3253]).  For

Dusseault Standards Track [Page 53] RFC 4918 WebDAV June 2007

 example, when an ordinary resource is overwritten, the server could
 delete the target resource before doing the copy, or could do an in-
 place overwrite to preserve live properties.
 When a collection is overwritten, the membership of the destination
 collection after the successful COPY request MUST be the same
 membership as the source collection immediately before the COPY.
 Thus, merging the membership of the source and destination
 collections together in the destination is not a compliant behavior.
 In general, if clients require the state of the destination URL to be
 wiped out prior to a COPY (e.g., to force live properties to be
 reset), then the client could send a DELETE to the destination before
 the COPY request to ensure this reset.

9.8.5. Status Codes

 In addition to the general status codes possible, the following
 status codes have specific applicability to COPY:
 201 (Created) - The source resource was successfully copied.  The
 COPY operation resulted in the creation of a new resource.
 204 (No Content) - The source resource was successfully copied to a
 preexisting destination resource.
 207 (Multi-Status) - Multiple resources were to be affected by the
 COPY, but errors on some of them prevented the operation from taking
 place.  Specific error messages, together with the most appropriate
 of the source and destination URLs, appear in the body of the multi-
 status response.  For example, if a destination resource was locked
 and could not be overwritten, then the destination resource URL
 appears with the 423 (Locked) status.
 403 (Forbidden) - The operation is forbidden.  A special case for
 COPY could be that the source and destination resources are the same
 resource.
 409 (Conflict) - A resource cannot be created at the destination
 until one or more intermediate collections have been created.  The
 server MUST NOT create those intermediate collections automatically.
 412 (Precondition Failed) - A precondition header check failed, e.g.,
 the Overwrite header is "F" and the destination URL is already mapped
 to a resource.

Dusseault Standards Track [Page 54] RFC 4918 WebDAV June 2007

 423 (Locked) - The destination resource, or resource within the
 destination collection, was locked.  This response SHOULD contain the
 'lock-token-submitted' precondition element.
 502 (Bad Gateway) - This may occur when the destination is on another
 server, repository, or URL namespace.  Either the source namespace
 does not support copying to the destination namespace, or the
 destination namespace refuses to accept the resource.  The client may
 wish to try GET/PUT and PROPFIND/PROPPATCH instead.
 507 (Insufficient Storage) - The destination resource does not have
 sufficient space to record the state of the resource after the
 execution of this method.

9.8.6. Example - COPY with Overwrite

 This example shows resource
 http://www.example.com/~fielding/index.html being copied to the
 location http://www.example.com/users/f/fielding/index.html.  The 204
 (No Content) status code indicates that the existing resource at the
 destination was overwritten.
 >>Request
   COPY /~fielding/index.html HTTP/1.1
   Host: www.example.com
   Destination: http://www.example.com/users/f/fielding/index.html
 >>Response
   HTTP/1.1 204 No Content

9.8.7. Example - COPY with No Overwrite

 The following example shows the same copy operation being performed,
 but with the Overwrite header set to "F." A response of 412
 (Precondition Failed) is returned because the destination URL is
 already mapped to a resource.
 >>Request
   COPY /~fielding/index.html HTTP/1.1
   Host: www.example.com
   Destination: http://www.example.com/users/f/fielding/index.html
   Overwrite: F

Dusseault Standards Track [Page 55] RFC 4918 WebDAV June 2007

 >>Response
   HTTP/1.1 412 Precondition Failed

9.8.8. Example - COPY of a Collection

 >>Request
   COPY /container/ HTTP/1.1
   Host: www.example.com
   Destination: http://www.example.com/othercontainer/
   Depth: infinity
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <d:multistatus xmlns:d="DAV:">
     <d:response>
       <d:href>http://www.example.com/othercontainer/R2/</d:href>
       <d:status>HTTP/1.1 423 Locked</d:status>
       <d:error><d:lock-token-submitted/></d:error>
     </d:response>
   </d:multistatus>
 The Depth header is unnecessary as the default behavior of COPY on a
 collection is to act as if a "Depth: infinity" header had been
 submitted.  In this example, most of the resources, along with the
 collection, were copied successfully.  However, the collection R2
 failed because the destination R2 is locked.  Because there was an
 error copying R2, none of R2's members were copied.  However, no
 errors were listed for those members due to the error minimization
 rules.

9.9. MOVE Method

 The MOVE operation on a non-collection resource is the logical
 equivalent of a copy (COPY), followed by consistency maintenance
 processing, followed by a delete of the source, where all three
 actions are performed in a single operation.  The consistency
 maintenance step allows the server to perform updates caused by the
 move, such as updating all URLs, other than the Request-URI that
 identifies the source resource, to point to the new destination
 resource.

Dusseault Standards Track [Page 56] RFC 4918 WebDAV June 2007

 The Destination header MUST be present on all MOVE methods and MUST
 follow all COPY requirements for the COPY part of the MOVE method.
 All WebDAV-compliant resources MUST support the MOVE method.
 Support for the MOVE method does not guarantee the ability to move a
 resource to a particular destination.  For example, separate programs
 may actually control different sets of resources on the same server.
 Therefore, it may not be possible to move a resource within a
 namespace that appears to belong to the same server.
 If a resource exists at the destination, the destination resource
 will be deleted as a side-effect of the MOVE operation, subject to
 the restrictions of the Overwrite header.
 This method is idempotent, but not safe (see Section 9.1 of
 [RFC2616]).  Responses to this method MUST NOT be cached.

9.9.1. MOVE for Properties

 Live properties described in this document SHOULD be moved along with
 the resource, such that the resource has identically behaving live
 properties at the destination resource, but not necessarily with the
 same values.  Note that some live properties are defined such that
 the absence of the property has a specific meaning (e.g., a flag with
 one meaning if present, and the opposite if absent), and in these
 cases, a successful MOVE might result in the property being reported
 as "Not Found" in subsequent requests.  If the live properties will
 not work the same way at the destination, the server MAY fail the
 request.
 MOVE is frequently used by clients to rename a file without changing
 its parent collection, so it's not appropriate to reset all live
 properties that are set at resource creation.  For example, the DAV:
 creationdate property value SHOULD remain the same after a MOVE.
 Dead properties MUST be moved along with the resource.

9.9.2. MOVE for Collections

 A MOVE with "Depth: infinity" instructs that the collection
 identified by the Request-URI be moved to the address specified in
 the Destination header, and all resources identified by its internal
 member URLs are to be moved to locations relative to it, recursively
 through all levels of the collection hierarchy.
 The MOVE method on a collection MUST act as if a "Depth: infinity"
 header was used on it.  A client MUST NOT submit a Depth header on a
 MOVE on a collection with any value but "infinity".

Dusseault Standards Track [Page 57] RFC 4918 WebDAV June 2007

 Any headers included with MOVE MUST be applied in processing every
 resource to be moved with the exception of the Destination header.
 The behavior of the Destination header is the same as given for COPY
 on collections.
 When the MOVE method has completed processing, it MUST have created a
 consistent URL namespace at both the source and destination (see
 Section 5.1 for the definition of namespace consistency).  However,
 if an error occurs while moving an internal collection, the server
 MUST NOT move any resources identified by members of the failed
 collection (i.e., the server must skip the error-causing subtree), as
 this would create an inconsistent namespace.  In this case, after
 detecting the error, the move operation SHOULD try to finish as much
 of the original move as possible (i.e., the server should still
 attempt to move other subtrees and the resources identified by their
 members that are not descendants of an error-causing collection).
 So, for example, if an infinite-depth move is performed on collection
 /a/, which contains collections /a/b/ and /a/c/, and an error occurs
 moving /a/b/, an attempt should still be made to try moving /a/c/.
 Similarly, after encountering an error moving a non-collection
 resource as part of an infinite-depth move, the server SHOULD try to
 finish as much of the original move operation as possible.
 If an error occurs with a resource other than the resource identified
 in the Request-URI, then the response MUST be a 207 (Multi-Status),
 and the errored resource's URL MUST appear with the specific error.
 The 424 (Failed Dependency) status code SHOULD NOT be returned in the
 207 (Multi-Status) response from a MOVE method.  These errors can be
 safely omitted because the client will know that the progeny of a
 resource could not be moved when the client receives an error for the
 parent.  Additionally, 201 (Created)/204 (No Content) responses
 SHOULD NOT be returned as values in 207 (Multi-Status) responses from
 a MOVE.  These responses can be safely omitted because they are the
 default success codes.

9.9.3. MOVE and the Overwrite Header

 If a resource exists at the destination and the Overwrite header is
 "T", then prior to performing the move, the server MUST perform a
 DELETE with "Depth: infinity" on the destination resource.  If the
 Overwrite header is set to "F", then the operation will fail.

Dusseault Standards Track [Page 58] RFC 4918 WebDAV June 2007

9.9.4. Status Codes

 In addition to the general status codes possible, the following
 status codes have specific applicability to MOVE:
 201 (Created) - The source resource was successfully moved, and a new
 URL mapping was created at the destination.
 204 (No Content) - The source resource was successfully moved to a
 URL that was already mapped.
 207 (Multi-Status) - Multiple resources were to be affected by the
 MOVE, but errors on some of them prevented the operation from taking
 place.  Specific error messages, together with the most appropriate
 of the source and destination URLs, appear in the body of the multi-
 status response.  For example, if a source resource was locked and
 could not be moved, then the source resource URL appears with the 423
 (Locked) status.
 403 (Forbidden) - Among many possible reasons for forbidding a MOVE
 operation, this status code is recommended for use when the source
 and destination resources are the same.
 409 (Conflict) - A resource cannot be created at the destination
 until one or more intermediate collections have been created.  The
 server MUST NOT create those intermediate collections automatically.
 Or, the server was unable to preserve the behavior of the live
 properties and still move the resource to the destination (see
 'preserved-live-properties' postcondition).
 412 (Precondition Failed) - A condition header failed.  Specific to
 MOVE, this could mean that the Overwrite header is "F" and the
 destination URL is already mapped to a resource.
 423 (Locked) - The source or the destination resource, the source or
 destination resource parent, or some resource within the source or
 destination collection, was locked.  This response SHOULD contain the
 'lock-token-submitted' precondition element.
 502 (Bad Gateway) - This may occur when the destination is on another
 server and the destination server refuses to accept the resource.
 This could also occur when the destination is on another sub-section
 of the same server namespace.

Dusseault Standards Track [Page 59] RFC 4918 WebDAV June 2007

9.9.5. Example - MOVE of a Non-Collection

 This example shows resource
 http://www.example.com/~fielding/index.html being moved to the
 location http://www.example.com/users/f/fielding/index.html.  The
 contents of the destination resource would have been overwritten if
 the destination URL was already mapped to a resource.  In this case,
 since there was nothing at the destination resource, the response
 code is 201 (Created).
 >>Request
   MOVE /~fielding/index.html HTTP/1.1
   Host: www.example.com
   Destination: http://www.example/users/f/fielding/index.html
 >>Response
   HTTP/1.1 201 Created
   Location: http://www.example.com/users/f/fielding/index.html

9.9.6. Example - MOVE of a Collection

 >>Request
   MOVE /container/ HTTP/1.1
   Host: www.example.com
   Destination: http://www.example.com/othercontainer/
   Overwrite: F
   If: (<urn:uuid:fe184f2e-6eec-41d0-c765-01adc56e6bb4>)
      (<urn:uuid:e454f3f3-acdc-452a-56c7-00a5c91e4b77>)
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <d:multistatus xmlns:d='DAV:'>
     <d:response>
       <d:href>http://www.example.com/othercontainer/C2/</d:href>
       <d:status>HTTP/1.1 423 Locked</d:status>
       <d:error><d:lock-token-submitted/></d:error>
     </d:response>
   </d:multistatus>

Dusseault Standards Track [Page 60] RFC 4918 WebDAV June 2007

 In this example, the client has submitted a number of lock tokens
 with the request.  A lock token will need to be submitted for every
 resource, both source and destination, anywhere in the scope of the
 method, that is locked.  In this case, the proper lock token was not
 submitted for the destination
 http://www.example.com/othercontainer/C2/.  This means that the
 resource /container/C2/ could not be moved.  Because there was an
 error moving /container/C2/, none of /container/C2's members were
 moved.  However, no errors were listed for those members due to the
 error minimization rules.  User agent authentication has previously
 occurred via a mechanism outside the scope of the HTTP protocol, in
 an underlying transport layer.

9.10. LOCK Method

 The following sections describe the LOCK method, which is used to
 take out a lock of any access type and to refresh an existing lock.
 These sections on the LOCK method describe only those semantics that
 are specific to the LOCK method and are independent of the access
 type of the lock being requested.
 Any resource that supports the LOCK method MUST, at minimum, support
 the XML request and response formats defined herein.
 This method is neither idempotent nor safe (see Section 9.1 of
 [RFC2616]).  Responses to this method MUST NOT be cached.

9.10.1. Creating a Lock on an Existing Resource

 A LOCK request to an existing resource will create a lock on the
 resource identified by the Request-URI, provided the resource is not
 already locked with a conflicting lock.  The resource identified in
 the Request-URI becomes the root of the lock.  LOCK method requests
 to create a new lock MUST have an XML request body.  The server MUST
 preserve the information provided by the client in the 'owner'
 element in the LOCK request.  The LOCK request MAY have a Timeout
 header.
 When a new lock is created, the LOCK response:
 o  MUST contain a body with the value of the DAV:lockdiscovery
    property in a prop XML element.  This MUST contain the full
    information about the lock just granted, while information about
    other (shared) locks is OPTIONAL.
 o  MUST include the Lock-Token response header with the token
    associated with the new lock.

Dusseault Standards Track [Page 61] RFC 4918 WebDAV June 2007

9.10.2. Refreshing Locks

 A lock is refreshed by sending a LOCK request to the URL of a
 resource within the scope of the lock.  This request MUST NOT have a
 body and it MUST specify which lock to refresh by using the 'If'
 header with a single lock token (only one lock may be refreshed at a
 time).  The request MAY contain a Timeout header, which a server MAY
 accept to change the duration remaining on the lock to the new value.
 A server MUST ignore the Depth header on a LOCK refresh.
 If the resource has other (shared) locks, those locks are unaffected
 by a lock refresh.  Additionally, those locks do not prevent the
 named lock from being refreshed.
 The Lock-Token header is not returned in the response for a
 successful refresh LOCK request, but the LOCK response body MUST
 contain the new value for the DAV:lockdiscovery property.

9.10.3. Depth and Locking

 The Depth header may be used with the LOCK method.  Values other than
 0 or infinity MUST NOT be used with the Depth header on a LOCK
 method.  All resources that support the LOCK method MUST support the
 Depth header.
 A Depth header of value 0 means to just lock the resource specified
 by the Request-URI.
 If the Depth header is set to infinity, then the resource specified
 in the Request-URI along with all its members, all the way down the
 hierarchy, are to be locked.  A successful result MUST return a
 single lock token.  Similarly, if an UNLOCK is successfully executed
 on this token, all associated resources are unlocked.  Hence, partial
 success is not an option for LOCK or UNLOCK.  Either the entire
 hierarchy is locked or no resources are locked.
 If the lock cannot be granted to all resources, the server MUST
 return a Multi-Status response with a 'response' element for at least
 one resource that prevented the lock from being granted, along with a
 suitable status code for that failure (e.g., 403 (Forbidden) or 423
 (Locked)).  Additionally, if the resource causing the failure was not
 the resource requested, then the server SHOULD include a 'response'
 element for the Request-URI as well, with a 'status' element
 containing 424 Failed Dependency.
 If no Depth header is submitted on a LOCK request, then the request
 MUST act as if a "Depth:infinity" had been submitted.

Dusseault Standards Track [Page 62] RFC 4918 WebDAV June 2007

9.10.4. Locking Unmapped URLs

 A successful LOCK method MUST result in the creation of an empty
 resource that is locked (and that is not a collection) when a
 resource did not previously exist at that URL.  Later on, the lock
 may go away but the empty resource remains.  Empty resources MUST
 then appear in PROPFIND responses including that URL in the response
 scope.  A server MUST respond successfully to a GET request to an
 empty resource, either by using a 204 No Content response, or by
 using 200 OK with a Content-Length header indicating zero length

9.10.5. Lock Compatibility Table

 The table below describes the behavior that occurs when a lock
 request is made on a resource.
   +--------------------------+----------------+-------------------+
   | Current State            | Shared Lock OK | Exclusive Lock OK |
   +--------------------------+----------------+-------------------+
   | None                     | True           | True              |
   | Shared Lock              | True           | False             |
   | Exclusive Lock           | False          | False*            |
   +--------------------------+----------------+-------------------+
 Legend: True = lock may be granted.  False = lock MUST NOT be
 granted. *=It is illegal for a principal to request the same lock
 twice.
 The current lock state of a resource is given in the leftmost column,
 and lock requests are listed in the first row.  The intersection of a
 row and column gives the result of a lock request.  For example, if a
 shared lock is held on a resource, and an exclusive lock is
 requested, the table entry is "false", indicating that the lock must
 not be granted.

9.10.6. LOCK Responses

 In addition to the general status codes possible, the following
 status codes have specific applicability to LOCK:
 200 (OK) - The LOCK request succeeded and the value of the DAV:
 lockdiscovery property is included in the response body.
 201 (Created) - The LOCK request was to an unmapped URL, the request
 succeeded and resulted in the creation of a new resource, and the
 value of the DAV:lockdiscovery property is included in the response
 body.

Dusseault Standards Track [Page 63] RFC 4918 WebDAV June 2007

 409 (Conflict) - A resource cannot be created at the destination
 until one or more intermediate collections have been created.  The
 server MUST NOT create those intermediate collections automatically.
 423 (Locked), potentially with 'no-conflicting-lock' precondition
 code - There is already a lock on the resource that is not compatible
 with the requested lock (see lock compatibility table above).
 412 (Precondition Failed), with 'lock-token-matches-request-uri'
 precondition code - The LOCK request was made with an If header,
 indicating that the client wishes to refresh the given lock.
 However, the Request-URI did not fall within the scope of the lock
 identified by the token.  The lock may have a scope that does not
 include the Request-URI, or the lock could have disappeared, or the
 token may be invalid.

9.10.7. Example - Simple Lock Request

 >>Request
   LOCK /workspace/webdav/proposal.doc HTTP/1.1
   Host: example.com
   Timeout: Infinite, Second-4100000000
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   Authorization: Digest username="ejw",
     realm="ejw@example.com", nonce="...",
     uri="/workspace/webdav/proposal.doc",
     response="...", opaque="..."
   <?xml version="1.0" encoding="utf-8" ?>
   <D:lockinfo xmlns:D='DAV:'>
     <D:lockscope><D:exclusive/></D:lockscope>
     <D:locktype><D:write/></D:locktype>
     <D:owner>
       <D:href>http://example.org/~ejw/contact.html</D:href>
     </D:owner>
   </D:lockinfo>
 >>Response
   HTTP/1.1 200 OK
   Lock-Token: <urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:prop xmlns:D="DAV:">

Dusseault Standards Track [Page 64] RFC 4918 WebDAV June 2007

     <D:lockdiscovery>
       <D:activelock>
         <D:locktype><D:write/></D:locktype>
         <D:lockscope><D:exclusive/></D:lockscope>
         <D:depth>infinity</D:depth>
         <D:owner>
           <D:href>http://example.org/~ejw/contact.html</D:href>
         </D:owner>
         <D:timeout>Second-604800</D:timeout>
         <D:locktoken>
           <D:href
           >urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
         </D:locktoken>
         <D:lockroot>
           <D:href
           >http://example.com/workspace/webdav/proposal.doc</D:href>
         </D:lockroot>
       </D:activelock>
     </D:lockdiscovery>
   </D:prop>
 This example shows the successful creation of an exclusive write lock
 on resource http://example.com/workspace/webdav/proposal.doc.  The
 resource http://example.org/~ejw/contact.html contains contact
 information for the creator of the lock.  The server has an activity-
 based timeout policy in place on this resource, which causes the lock
 to automatically be removed after 1 week (604800 seconds).  Note that
 the nonce, response, and opaque fields have not been calculated in
 the Authorization request header.

9.10.8. Example - Refreshing a Write Lock

 >>Request
   LOCK /workspace/webdav/proposal.doc HTTP/1.1
   Host: example.com
   Timeout: Infinite, Second-4100000000
   If: (<urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4>)
   Authorization: Digest username="ejw",
     realm="ejw@example.com", nonce="...",
     uri="/workspace/webdav/proposal.doc",
     response="...", opaque="..."

Dusseault Standards Track [Page 65] RFC 4918 WebDAV June 2007

 >>Response
   HTTP/1.1 200 OK
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:prop xmlns:D="DAV:">
     <D:lockdiscovery>
       <D:activelock>
         <D:locktype><D:write/></D:locktype>
         <D:lockscope><D:exclusive/></D:lockscope>
         <D:depth>infinity</D:depth>
         <D:owner>
           <D:href>http://example.org/~ejw/contact.html</D:href>
         </D:owner>
         <D:timeout>Second-604800</D:timeout>
         <D:locktoken>
           <D:href
           >urn:uuid:e71d4fae-5dec-22d6-fea5-00a0c91e6be4</D:href>
         </D:locktoken>
         <D:lockroot>
           <D:href
           >http://example.com/workspace/webdav/proposal.doc</D:href>
         </D:lockroot>
       </D:activelock>
     </D:lockdiscovery>
   </D:prop>
 This request would refresh the lock, attempting to reset the timeout
 to the new value specified in the timeout header.  Notice that the
 client asked for an infinite time out but the server choose to ignore
 the request.  In this example, the nonce, response, and opaque fields
 have not been calculated in the Authorization request header.

9.10.9. Example - Multi-Resource Lock Request

 >>Request
   LOCK /webdav/ HTTP/1.1
   Host: example.com
   Timeout: Infinite, Second-4100000000
   Depth: infinity
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   Authorization: Digest username="ejw",
     realm="ejw@example.com", nonce="...",

Dusseault Standards Track [Page 66] RFC 4918 WebDAV June 2007

     uri="/workspace/webdav/proposal.doc",
     response="...", opaque="..."
   <?xml version="1.0" encoding="utf-8" ?>
   <D:lockinfo xmlns:D="DAV:">
     <D:locktype><D:write/></D:locktype>
     <D:lockscope><D:exclusive/></D:lockscope>
     <D:owner>
       <D:href>http://example.org/~ejw/contact.html</D:href>
     </D:owner>
   </D:lockinfo>
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://example.com/webdav/secret</D:href>
       <D:status>HTTP/1.1 403 Forbidden</D:status>
     </D:response>
     <D:response>
       <D:href>http://example.com/webdav/</D:href>
       <D:status>HTTP/1.1 424 Failed Dependency</D:status>
     </D:response>
   </D:multistatus>
 This example shows a request for an exclusive write lock on a
 collection and all its children.  In this request, the client has
 specified that it desires an infinite-length lock, if available,
 otherwise a timeout of 4.1 billion seconds, if available.  The
 request entity body contains the contact information for the
 principal taking out the lock -- in this case, a Web page URL.
 The error is a 403 (Forbidden) response on the resource
 http://example.com/webdav/secret.  Because this resource could not be
 locked, none of the resources were locked.  Note also that the a
 'response' element for the Request-URI itself has been included as
 required.
 In this example, the nonce, response, and opaque fields have not been
 calculated in the Authorization request header.

Dusseault Standards Track [Page 67] RFC 4918 WebDAV June 2007

9.11. UNLOCK Method

 The UNLOCK method removes the lock identified by the lock token in
 the Lock-Token request header.  The Request-URI MUST identify a
 resource within the scope of the lock.
 Note that use of the Lock-Token header to provide the lock token is
 not consistent with other state-changing methods, which all require
 an If header with the lock token.  Thus, the If header is not needed
 to provide the lock token.  Naturally, when the If header is present,
 it has its normal meaning as a conditional header.
 For a successful response to this method, the server MUST delete the
 lock entirely.
 If all resources that have been locked under the submitted lock token
 cannot be unlocked, then the UNLOCK request MUST fail.
 A successful response to an UNLOCK method does not mean that the
 resource is necessarily unlocked.  It means that the specific lock
 corresponding to the specified token no longer exists.
 Any DAV-compliant resource that supports the LOCK method MUST support
 the UNLOCK method.
 This method is idempotent, but not safe (see Section 9.1 of
 [RFC2616]).  Responses to this method MUST NOT be cached.

9.11.1. Status Codes

 In addition to the general status codes possible, the following
 status codes have specific applicability to UNLOCK:
 204 (No Content) - Normal success response (rather than 200 OK, since
 200 OK would imply a response body, and an UNLOCK success response
 does not normally contain a body).
 400 (Bad Request) - No lock token was provided.
 403 (Forbidden) - The currently authenticated principal does not have
 permission to remove the lock.
 409 (Conflict), with 'lock-token-matches-request-uri' precondition -
 The resource was not locked, or the request was made to a Request-URI
 that was not within the scope of the lock.

Dusseault Standards Track [Page 68] RFC 4918 WebDAV June 2007

9.11.2. Example - UNLOCK

 >>Request
   UNLOCK /workspace/webdav/info.doc HTTP/1.1
   Host: example.com
   Lock-Token: <urn:uuid:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7>
   Authorization: Digest username="ejw"
     realm="ejw@example.com", nonce="...",
     uri="/workspace/webdav/proposal.doc",
     response="...", opaque="..."
 >>Response
   HTTP/1.1 204 No Content
 In this example, the lock identified by the lock token
 "urn:uuid:a515cfa4-5da4-22e1-f5b5-00a0451e6bf7" is successfully
 removed from the resource
 http://example.com/workspace/webdav/info.doc.  If this lock included
 more than just one resource, the lock is removed from all resources
 included in the lock.
 In this example, the nonce, response, and opaque fields have not been
 calculated in the Authorization request header.

10. HTTP Headers for Distributed Authoring

 All DAV headers follow the same basic formatting rules as HTTP
 headers.  This includes rules like line continuation and how to
 combine (or separate) multiple instances of the same header using
 commas.
 WebDAV adds two new conditional headers to the set defined in HTTP:
 the If and Overwrite headers.

10.1. DAV Header

  DAV              = "DAV" ":" #( compliance-class )
  compliance-class = ( "1" | "2" | "3" | extend )
  extend           = Coded-URL | token
                     ; token is defined in RFC 2616, Section 2.2
  Coded-URL        = "<" absolute-URI ">"
                     ; No linear whitespace (LWS) allowed in Coded-URL
                     ; absolute-URI defined in RFC 3986, Section 4.3

Dusseault Standards Track [Page 69] RFC 4918 WebDAV June 2007

 This general-header appearing in the response indicates that the
 resource supports the DAV schema and protocol as specified.  All DAV-
 compliant resources MUST return the DAV header with compliance-class
 "1" on all OPTIONS responses.  In cases where WebDAV is only
 supported in part of the server namespace, an OPTIONS request to non-
 WebDAV resources (including "/") SHOULD NOT advertise WebDAV support.
 The value is a comma-separated list of all compliance class
 identifiers that the resource supports.  Class identifiers may be
 Coded-URLs or tokens (as defined by [RFC2616]).  Identifiers can
 appear in any order.  Identifiers that are standardized through the
 IETF RFC process are tokens, but other identifiers SHOULD be Coded-
 URLs to encourage uniqueness.
 A resource must show class 1 compliance if it shows class 2 or 3
 compliance.  In general, support for one compliance class does not
 entail support for any other, and in particular, support for
 compliance class 3 does not require support for compliance class 2.
 Please refer to Section 18 for more details on compliance classes
 defined in this specification.
 Note that many WebDAV servers do not advertise WebDAV support in
 response to "OPTIONS *".
 As a request header, this header allows the client to advertise
 compliance with named features when the server needs that
 information.  Clients SHOULD NOT send this header unless a standards
 track specification requires it.  Any extension that makes use of
 this as a request header will need to carefully consider caching
 implications.

10.2. Depth Header

    Depth = "Depth" ":" ("0" | "1" | "infinity")
 The Depth request header is used with methods executed on resources
 that could potentially have internal members to indicate whether the
 method is to be applied only to the resource ("Depth: 0"), to the
 resource and its internal members only ("Depth: 1"), or the resource
 and all its members ("Depth: infinity").
 The Depth header is only supported if a method's definition
 explicitly provides for such support.
 The following rules are the default behavior for any method that
 supports the Depth header.  A method may override these defaults by
 defining different behavior in its definition.

Dusseault Standards Track [Page 70] RFC 4918 WebDAV June 2007

 Methods that support the Depth header may choose not to support all
 of the header's values and may define, on a case-by-case basis, the
 behavior of the method if a Depth header is not present.  For
 example, the MOVE method only supports "Depth: infinity", and if a
 Depth header is not present, it will act as if a "Depth: infinity"
 header had been applied.
 Clients MUST NOT rely upon methods executing on members of their
 hierarchies in any particular order or on the execution being atomic
 unless the particular method explicitly provides such guarantees.
 Upon execution, a method with a Depth header will perform as much of
 its assigned task as possible and then return a response specifying
 what it was able to accomplish and what it failed to do.
 So, for example, an attempt to COPY a hierarchy may result in some of
 the members being copied and some not.
 By default, the Depth header does not interact with other headers.
 That is, each header on a request with a Depth header MUST be applied
 only to the Request-URI if it applies to any resource, unless
 specific Depth behavior is defined for that header.
 If a source or destination resource within the scope of the Depth
 header is locked in such a way as to prevent the successful execution
 of the method, then the lock token for that resource MUST be
 submitted with the request in the If request header.
 The Depth header only specifies the behavior of the method with
 regards to internal members.  If a resource does not have internal
 members, then the Depth header MUST be ignored.

10.3. Destination Header

 The Destination request header specifies the URI that identifies a
 destination resource for methods such as COPY and MOVE, which take
 two URIs as parameters.
    Destination = "Destination" ":" Simple-ref
 If the Destination value is an absolute-URI (Section 4.3 of
 [RFC3986]), it may name a different server (or different port or
 scheme).  If the source server cannot attempt a copy to the remote
 server, it MUST fail the request.  Note that copying and moving
 resources to remote servers is not fully defined in this
 specification (e.g., specific error conditions).

Dusseault Standards Track [Page 71] RFC 4918 WebDAV June 2007

 If the Destination value is too long or otherwise unacceptable, the
 server SHOULD return 400 (Bad Request), ideally with helpful
 information in an error body.

10.4. If Header

 The If request header is intended to have similar functionality to
 the If-Match header defined in Section 14.24 of [RFC2616].  However,
 the If header handles any state token as well as ETags.  A typical
 example of a state token is a lock token, and lock tokens are the
 only state tokens defined in this specification.

10.4.1. Purpose

 The If header has two distinct purposes:
 o  The first purpose is to make a request conditional by supplying a
    series of state lists with conditions that match tokens and ETags
    to a specific resource.  If this header is evaluated and all state
    lists fail, then the request MUST fail with a 412 (Precondition
    Failed) status.  On the other hand, the request can succeed only
    if one of the described state lists succeeds.  The success
    criteria for state lists and matching functions are defined in
    Sections 10.4.3 and 10.4.4.
 o  Additionally, the mere fact that a state token appears in an If
    header means that it has been "submitted" with the request.  In
    general, this is used to indicate that the client has knowledge of
    that state token.  The semantics for submitting a state token
    depend on its type (for lock tokens, please refer to Section 6).
 Note that these two purposes need to be treated distinctly: a state
 token counts as being submitted independently of whether the server
 actually has evaluated the state list it appears in, and also
 independently of whether or not the condition it expressed was found
 to be true.

10.4.2. Syntax

   If = "If" ":" ( 1*No-tag-list | 1*Tagged-list )
   No-tag-list = List
   Tagged-list = Resource-Tag 1*List
   List = "(" 1*Condition ")"
   Condition = ["Not"] (State-token | "[" entity-tag "]")
   ; entity-tag: see Section 3.11 of [RFC2616]
   ; No LWS allowed between "[", entity-tag and "]"

Dusseault Standards Track [Page 72] RFC 4918 WebDAV June 2007

   State-token = Coded-URL
   Resource-Tag = "<" Simple-ref ">"
   ; Simple-ref: see Section 8.3
   ; No LWS allowed in Resource-Tag
 The syntax distinguishes between untagged lists ("No-tag-list") and
 tagged lists ("Tagged-list").  Untagged lists apply to the resource
 identified by the Request-URI, while tagged lists apply to the
 resource identified by the preceding Resource-Tag.
 A Resource-Tag applies to all subsequent Lists, up to the next
 Resource-Tag.
 Note that the two list types cannot be mixed within an If header.
 This is not a functional restriction because the No-tag-list syntax
 is just a shorthand notation for a Tagged-list production with a
 Resource-Tag referring to the Request-URI.
 Each List consists of one or more Conditions.  Each Condition is
 defined in terms of an entity-tag or state-token, potentially negated
 by the prefix "Not".
 Note that the If header syntax does not allow multiple instances of
 If headers in a single request.  However, the HTTP header syntax
 allows extending single header values across multiple lines, by
 inserting a line break followed by whitespace (see [RFC2616], Section
 4.2).

10.4.3. List Evaluation

 A Condition that consists of a single entity-tag or state-token
 evaluates to true if the resource matches the described state (where
 the individual matching functions are defined below in
 Section 10.4.4).  Prefixing it with "Not" reverses the result of the
 evaluation (thus, the "Not" applies only to the subsequent entity-tag
 or state-token).
 Each List production describes a series of conditions.  The whole
 list evaluates to true if and only if each condition evaluates to
 true (that is, the list represents a logical conjunction of
 Conditions).
 Each No-tag-list and Tagged-list production may contain one or more
 Lists.  They evaluate to true if and only if any of the contained
 lists evaluates to true (that is, if there's more than one List, that
 List sequence represents a logical disjunction of the Lists).

Dusseault Standards Track [Page 73] RFC 4918 WebDAV June 2007

 Finally, the whole If header evaluates to true if and only if at
 least one of the No-tag-list or Tagged-list productions evaluates to
 true.  If the header evaluates to false, the server MUST reject the
 request with a 412 (Precondition Failed) status.  Otherwise,
 execution of the request can proceed as if the header wasn't present.

10.4.4. Matching State Tokens and ETags

 When performing If header processing, the definition of a matching
 state token or entity tag is as follows:
 Identifying a resource: The resource is identified by the URI along
 with the token, in tagged list production, or by the Request-URI in
 untagged list production.
 Matching entity tag: Where the entity tag matches an entity tag
 associated with the identified resource.  Servers MUST use either the
 weak or the strong comparison function defined in Section 13.3.3 of
 [RFC2616].
 Matching state token: Where there is an exact match between the state
 token in the If header and any state token on the identified
 resource.  A lock state token is considered to match if the resource
 is anywhere in the scope of the lock.
 Handling unmapped URLs: For both ETags and state tokens, treat as if
 the URL identified a resource that exists but does not have the
 specified state.

10.4.5. If Header and Non-DAV-Aware Proxies

 Non-DAV-aware proxies will not honor the If header, since they will
 not understand the If header, and HTTP requires non-understood
 headers to be ignored.  When communicating with HTTP/1.1 proxies, the
 client MUST use the "Cache-Control: no-cache" request header so as to
 prevent the proxy from improperly trying to service the request from
 its cache.  When dealing with HTTP/1.0 proxies, the "Pragma: no-
 cache" request header MUST be used for the same reason.
 Because in general clients may not be able to reliably detect non-
 DAV-aware intermediates, they are advised to always prevent caching
 using the request directives mentioned above.

Dusseault Standards Track [Page 74] RFC 4918 WebDAV June 2007

10.4.6. Example - No-tag Production

   If: (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
     ["I am an ETag"])
     (["I am another ETag"])
 The previous header would require that the resource identified in the
 Request-URI be locked with the specified lock token and be in the
 state identified by the "I am an ETag" ETag or in the state
 identified by the second ETag "I am another ETag".
 To put the matter more plainly one can think of the previous If
 header as expressing the condition below:
   (
     is-locked-with(urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2) AND
     matches-etag("I am an ETag")
   )
   OR
   (
     matches-etag("I am another ETag")
   )

10.4.7. Example - Using "Not" with No-tag Production

   If: (Not <urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
   <urn:uuid:58f202ac-22cf-11d1-b12d-002035b29092>)
 This If header requires that the resource must not be locked with a
 lock having the lock token
 urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2 and must be locked by a
 lock with the lock token
 urn:uuid:58f202ac-22cf-11d1-b12d-002035b29092.

10.4.8. Example - Causing a Condition to Always Evaluate to True

 There may be cases where a client wishes to submit state tokens, but
 doesn't want the request to fail just because the state token isn't
 current anymore.  One simple way to do this is to include a Condition
 that is known to always evaluate to true, such as in:
   If: (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>)
     (Not <DAV:no-lock>)
 "DAV:no-lock" is known to never represent a current lock token.  Lock
 tokens are assigned by the server, following the uniqueness
 requirements described in Section 6.5, therefore cannot use the
 "DAV:" scheme.  Thus, by applying "Not" to a state token that is

Dusseault Standards Track [Page 75] RFC 4918 WebDAV June 2007

 known not to be current, the Condition always evaluates to true.
 Consequently, the whole If header will always evaluate to true, and
 the lock token urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2 will be
 submitted in any case.

10.4.9. Example - Tagged List If Header in COPY

 >>Request
   COPY /resource1 HTTP/1.1
   Host: www.example.com
   Destination: /resource2
   If: </resource1>
     (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>
     [W/"A weak ETag"]) (["strong ETag"])
 In this example, http://www.example.com/resource1 is being copied to
 http://www.example.com/resource2.  When the method is first applied
 to http://www.example.com/resource1, resource1 must be in the state
 specified by "(<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2> [W/"A
 weak ETag"]) (["strong ETag"])".  That is, either it must be locked
 with a lock token of "urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2"
 and have a weak entity tag W/"A weak ETag" or it must have a strong
 entity tag "strong ETag".

10.4.10. Example - Matching Lock Tokens with Collection Locks

   DELETE /specs/rfc2518.txt HTTP/1.1
   Host: www.example.com
   If: <http://www.example.com/specs/>
     (<urn:uuid:181d4fae-7d8c-11d0-a765-00a0c91e6bf2>)
 For this example, the lock token must be compared to the identified
 resource, which is the 'specs' collection identified by the URL in
 the tagged list production.  If the 'specs' collection is not locked
 by a lock with the specified lock token, the request MUST fail.
 Otherwise, this request could succeed, because the If header
 evaluates to true, and because the lock token for the lock affecting
 the affected resource has been submitted.

10.4.11. Example - Matching ETags on Unmapped URLs

 Consider a collection "/specs" that does not contain the member
 "/specs/rfc2518.doc".  In this case, the If header
   If: </specs/rfc2518.doc> (["4217"])

Dusseault Standards Track [Page 76] RFC 4918 WebDAV June 2007

 will evaluate to false (the URI isn't mapped, thus the resource
 identified by the URI doesn't have an entity matching the ETag
 "4217").
 On the other hand, an If header of
   If: </specs/rfc2518.doc> (Not ["4217"])
 will consequently evaluate to true.
 Note that, as defined above in Section 10.4.4, the same
 considerations apply to matching state tokens.

10.5. Lock-Token Header

    Lock-Token = "Lock-Token" ":" Coded-URL
 The Lock-Token request header is used with the UNLOCK method to
 identify the lock to be removed.  The lock token in the Lock-Token
 request header MUST identify a lock that contains the resource
 identified by Request-URI as a member.
 The Lock-Token response header is used with the LOCK method to
 indicate the lock token created as a result of a successful LOCK
 request to create a new lock.

10.6. Overwrite Header

    Overwrite = "Overwrite" ":" ("T" | "F")
 The Overwrite request header specifies whether the server should
 overwrite a resource mapped to the destination URL during a COPY or
 MOVE.  A value of "F" states that the server must not perform the
 COPY or MOVE operation if the destination URL does map to a resource.
 If the overwrite header is not included in a COPY or MOVE request,
 then the resource MUST treat the request as if it has an overwrite
 header of value "T".  While the Overwrite header appears to duplicate
 the functionality of using an "If-Match: *" header (see [RFC2616]),
 If-Match applies only to the Request-URI, and not to the Destination
 of a COPY or MOVE.
 If a COPY or MOVE is not performed due to the value of the Overwrite
 header, the method MUST fail with a 412 (Precondition Failed) status
 code.  The server MUST do authorization checks before checking this
 or any conditional header.
 All DAV-compliant resources MUST support the Overwrite header.

Dusseault Standards Track [Page 77] RFC 4918 WebDAV June 2007

10.7. Timeout Request Header

    TimeOut = "Timeout" ":" 1#TimeType
    TimeType = ("Second-" DAVTimeOutVal | "Infinite")
               ; No LWS allowed within TimeType
    DAVTimeOutVal = 1*DIGIT
 Clients MAY include Timeout request headers in their LOCK requests.
 However, the server is not required to honor or even consider these
 requests.  Clients MUST NOT submit a Timeout request header with any
 method other than a LOCK method.
 The "Second" TimeType specifies the number of seconds that will
 elapse between granting of the lock at the server, and the automatic
 removal of the lock.  The timeout value for TimeType "Second" MUST
 NOT be greater than 2^32-1.
 See Section 6.6 for a description of lock timeout behavior.

11. Status Code Extensions to HTTP/1.1

 The following status codes are added to those defined in HTTP/1.1
 [RFC2616].

11.1. 207 Multi-Status

 The 207 (Multi-Status) status code provides status for multiple
 independent operations (see Section 13 for more information).

11.2. 422 Unprocessable Entity

 The 422 (Unprocessable Entity) status code means the server
 understands the content type of the request entity (hence a
 415(Unsupported Media Type) status code is inappropriate), and the
 syntax of the request entity is correct (thus a 400 (Bad Request)
 status code is inappropriate) but was unable to process the contained
 instructions.  For example, this error condition may occur if an XML
 request body contains well-formed (i.e., syntactically correct), but
 semantically erroneous, XML instructions.

11.3. 423 Locked

 The 423 (Locked) status code means the source or destination resource
 of a method is locked.  This response SHOULD contain an appropriate
 precondition or postcondition code, such as 'lock-token-submitted' or
 'no-conflicting-lock'.

Dusseault Standards Track [Page 78] RFC 4918 WebDAV June 2007

11.4. 424 Failed Dependency

 The 424 (Failed Dependency) status code means that the method could
 not be performed on the resource because the requested action
 depended on another action and that action failed.  For example, if a
 command in a PROPPATCH method fails, then, at minimum, the rest of
 the commands will also fail with 424 (Failed Dependency).

11.5. 507 Insufficient Storage

 The 507 (Insufficient Storage) status code means the method could not
 be performed on the resource because the server is unable to store
 the representation needed to successfully complete the request.  This
 condition is considered to be temporary.  If the request that
 received this status code was the result of a user action, the
 request MUST NOT be repeated until it is requested by a separate user
 action.

12. Use of HTTP Status Codes

 These HTTP codes are not redefined, but their use is somewhat
 extended by WebDAV methods and requirements.  In general, many HTTP
 status codes can be used in response to any request, not just in
 cases described in this document.  Note also that WebDAV servers are
 known to use 300-level redirect responses (and early interoperability
 tests found clients unprepared to see those responses).  A 300-level
 response MUST NOT be used when the server has created a new resource
 in response to the request.

12.1. 412 Precondition Failed

 Any request can contain a conditional header defined in HTTP (If-
 Match, If-Modified-Since, etc.) or the "If" or "Overwrite"
 conditional headers defined in this specification.  If the server
 evaluates a conditional header, and if that condition fails to hold,
 then this error code MUST be returned.  On the other hand, if the
 client did not include a conditional header in the request, then the
 server MUST NOT use this status code.

12.2. 414 Request-URI Too Long

 This status code is used in HTTP 1.1 only for Request-URIs, not URIs
 in other locations.

Dusseault Standards Track [Page 79] RFC 4918 WebDAV June 2007

13. Multi-Status Response

 A Multi-Status response conveys information about multiple resources
 in situations where multiple status codes might be appropriate.  The
 default Multi-Status response body is a text/xml or application/xml
 HTTP entity with a 'multistatus' root element.  Further elements
 contain 200, 300, 400, and 500 series status codes generated during
 the method invocation. 100 series status codes SHOULD NOT be recorded
 in a 'response' XML element.
 Although '207' is used as the overall response status code, the
 recipient needs to consult the contents of the multistatus response
 body for further information about the success or failure of the
 method execution.  The response MAY be used in success, partial
 success and also in failure situations.
 The 'multistatus' root element holds zero or more 'response' elements
 in any order, each with information about an individual resource.
 Each 'response' element MUST have an 'href' element to identify the
 resource.
 A Multi-Status response uses one out of two distinct formats for
 representing the status:
 1.  A 'status' element as child of the 'response' element indicates
     the status of the message execution for the identified resource
     as a whole (for instance, see Section 9.6.2).  Some method
     definitions provide information about specific status codes
     clients should be prepared to see in a response.  However,
     clients MUST be able to handle other status codes, using the
     generic rules defined in Section 10 of [RFC2616].
 2.  For PROPFIND and PROPPATCH, the format has been extended using
     the 'propstat' element instead of 'status', providing information
     about individual properties of a resource.  This format is
     specific to PROPFIND and PROPPATCH, and is described in detail in
     Sections 9.1 and 9.2.

13.1. Response Headers

 HTTP defines the Location header to indicate a preferred URL for the
 resource that was addressed in the Request-URI (e.g., in response to
 successful PUT requests or in redirect responses).  However, use of
 this header creates ambiguity when there are URLs in the body of the
 response, as with Multi-Status.  Thus, use of the Location header
 with the Multi-Status response is intentionally undefined.

Dusseault Standards Track [Page 80] RFC 4918 WebDAV June 2007

13.2. Handling Redirected Child Resources

 Redirect responses (300-303, 305, and 307) defined in HTTP 1.1
 normally take a Location header to indicate the new URI for the
 single resource redirected from the Request-URI.  Multi-Status
 responses contain many resource addresses, but the original
 definition in [RFC2518] did not have any place for the server to
 provide the new URI for redirected resources.  This specification
 does define a 'location' element for this information (see
 Section 14.9).  Servers MUST use this new element with redirect
 responses in Multi-Status.
 Clients encountering redirected resources in Multi-Status MUST NOT
 rely on the 'location' element being present with a new URI.  If the
 element is not present, the client MAY reissue the request to the
 individual redirected resource, because the response to that request
 can be redirected with a Location header containing the new URI.

13.3. Internal Status Codes

 Sections 9.2.1, 9.1.2, 9.6.1, 9.8.3, and 9.9.2 define various status
 codes used in Multi-Status responses.  This specification does not
 define the meaning of other status codes that could appear in these
 responses.

14. XML Element Definitions

 In this section, the final line of each section gives the element
 type declaration using the format defined in [REC-XML].  The "Value"
 field, where present, specifies further restrictions on the allowable
 contents of the XML element using BNF (i.e., to further restrict the
 values of a PCDATA element).  Note that all of the elements defined
 here may be extended according to the rules defined in Section 17.
 All elements defined here are in the "DAV:" namespace.

14.1. activelock XML Element

 Name:   activelock
 Purpose:   Describes a lock on a resource.
 <!ELEMENT activelock (lockscope, locktype, depth, owner?, timeout?,
           locktoken?, lockroot)>

Dusseault Standards Track [Page 81] RFC 4918 WebDAV June 2007

14.2. allprop XML Element

 Name:   allprop
 Purpose:   Specifies that all names and values of dead properties and
    the live properties defined by this document existing on the
    resource are to be returned.
 <!ELEMENT allprop EMPTY >

14.3. collection XML Element

 Name:   collection
 Purpose:   Identifies the associated resource as a collection.  The
    DAV:resourcetype property of a collection resource MUST contain
    this element.  It is normally empty but extensions may add sub-
    elements.
 <!ELEMENT collection EMPTY >

14.4. depth XML Element

 Name:   depth
 Purpose:   Used for representing depth values in XML content (e.g.,
    in lock information).
 Value:   "0" | "1" | "infinity"
 <!ELEMENT depth (#PCDATA) >

14.5. error XML Element

 Name:   error
 Purpose:   Error responses, particularly 403 Forbidden and 409
    Conflict, sometimes need more information to indicate what went
    wrong.  In these cases, servers MAY return an XML response body
    with a document element of 'error', containing child elements
    identifying particular condition codes.
 Description:   Contains at least one XML element, and MUST NOT
    contain text or mixed content.  Any element that is a child of the
    'error' element is considered to be a precondition or
    postcondition code.  Unrecognized elements MUST be ignored.
 <!ELEMENT error ANY >

Dusseault Standards Track [Page 82] RFC 4918 WebDAV June 2007

14.6. exclusive XML Element

 Name:   exclusive
 Purpose:   Specifies an exclusive lock.
 <!ELEMENT exclusive EMPTY >

14.7. href XML Element

 Name:   href
 Purpose:   MUST contain a URI or a relative reference.
 Description:   There may be limits on the value of 'href' depending
    on the context of its use.  Refer to the specification text where
    'href' is used to see what limitations apply in each case.
 Value:   Simple-ref
 <!ELEMENT href (#PCDATA)>

14.8. include XML Element

 Name:   include
 Purpose:   Any child element represents the name of a property to be
    included in the PROPFIND response.  All elements inside an
    'include' XML element MUST define properties related to the
    resource, although possible property names are in no way limited
    to those property names defined in this document or other
    standards.  This element MUST NOT contain text or mixed content.
 <!ELEMENT include ANY >

14.9. location XML Element

 Name:   location
 Purpose:   HTTP defines the "Location" header (see [RFC2616], Section
    14.30) for use with some status codes (such as 201 and the 300
    series codes).  When these codes are used inside a 'multistatus'
    element, the 'location' element can be used to provide the
    accompanying Location header value.

Dusseault Standards Track [Page 83] RFC 4918 WebDAV June 2007

 Description:   Contains a single href element with the same value
    that would be used in a Location header.
 <!ELEMENT location (href)>

14.10. lockentry XML Element

 Name:   lockentry
 Purpose:   Defines the types of locks that can be used with the
    resource.
 <!ELEMENT lockentry (lockscope, locktype) >

14.11. lockinfo XML Element

 Name:   lockinfo
 Purpose:   The 'lockinfo' XML element is used with a LOCK method to
    specify the type of lock the client wishes to have created.
 <!ELEMENT lockinfo (lockscope, locktype, owner?)  >

14.12. lockroot XML Element

 Name:   lockroot
 Purpose:   Contains the root URL of the lock, which is the URL
    through which the resource was addressed in the LOCK request.
 Description:   The href element contains the root of the lock.  The
    server SHOULD include this in all DAV:lockdiscovery property
    values and the response to LOCK requests.
 <!ELEMENT lockroot (href) >

14.13. lockscope XML Element

 Name:   lockscope
 Purpose:   Specifies whether a lock is an exclusive lock, or a shared
    lock.
   <!ELEMENT lockscope (exclusive | shared) >

Dusseault Standards Track [Page 84] RFC 4918 WebDAV June 2007

14.14. locktoken XML Element

 Name:   locktoken
 Purpose:   The lock token associated with a lock.
 Description:   The href contains a single lock token URI, which
    refers to the lock.
 <!ELEMENT locktoken (href) >

14.15. locktype XML Element

 Name:   locktype
 Purpose:   Specifies the access type of a lock.  At present, this
    specification only defines one lock type, the write lock.
 <!ELEMENT locktype (write) >

14.16. multistatus XML Element

 Name:   multistatus
 Purpose:   Contains multiple response messages.
 Description:   The 'responsedescription' element at the top level is
    used to provide a general message describing the overarching
    nature of the response.  If this value is available, an
    application may use it instead of presenting the individual
    response descriptions contained within the responses.
 <!ELEMENT multistatus (response*, responsedescription?)  >

14.17. owner XML Element

 Name:   owner
 Purpose:   Holds client-supplied information about the creator of a
    lock.
 Description:   Allows a client to provide information sufficient for
    either directly contacting a principal (such as a telephone number
    or Email URI), or for discovering the principal (such as the URL

Dusseault Standards Track [Page 85] RFC 4918 WebDAV June 2007

    of a homepage) who created a lock.  The value provided MUST be
    treated as a dead property in terms of XML Information Item
    preservation.  The server MUST NOT alter the value unless the
    owner value provided by the client is empty.  For a certain amount
    of interoperability between different client implementations, if
    clients have URI-formatted contact information for the lock
    creator suitable for user display, then clients SHOULD put those
    URIs in 'href' child elements of the 'owner' element.
 Extensibility:   MAY be extended with child elements, mixed content,
    text content or attributes.
 <!ELEMENT owner ANY >

14.18. prop XML Element

 Name:   prop
 Purpose:   Contains properties related to a resource.
 Description:   A generic container for properties defined on
    resources.  All elements inside a 'prop' XML element MUST define
    properties related to the resource, although possible property
    names are in no way limited to those property names defined in
    this document or other standards.  This element MUST NOT contain
    text or mixed content.
 <!ELEMENT prop ANY >

14.19. propertyupdate XML Element

 Name:   propertyupdate
 Purpose:   Contains a request to alter the properties on a resource.
 Description:   This XML element is a container for the information
    required to modify the properties on the resource.
 <!ELEMENT propertyupdate (remove | set)+ >

14.20. propfind XML Element

 Name:   propfind

Dusseault Standards Track [Page 86] RFC 4918 WebDAV June 2007

 Purpose:   Specifies the properties to be returned from a PROPFIND
    method.  Four special elements are specified for use with
    'propfind': 'prop', 'allprop', 'include', and 'propname'.  If
    'prop' is used inside 'propfind', it MUST NOT contain property
    values.
 <!ELEMENT propfind ( propname | (allprop, include?) | prop ) >

14.21. propname XML Element

 Name:   propname
 Purpose:   Specifies that only a list of property names on the
    resource is to be returned.
 <!ELEMENT propname EMPTY >

14.22. propstat XML Element

 Name:   propstat
 Purpose:   Groups together a prop and status element that is
    associated with a particular 'href' element.
 Description:   The propstat XML element MUST contain one prop XML
    element and one status XML element.  The contents of the prop XML
    element MUST only list the names of properties to which the result
    in the status element applies.  The optional precondition/
    postcondition element and 'responsedescription' text also apply to
    the properties named in 'prop'.
 <!ELEMENT propstat (prop, status, error?, responsedescription?) >

14.23. remove XML Element

 Name:   remove
 Purpose:   Lists the properties to be removed from a resource.
 Description:   Remove instructs that the properties specified in prop
    should be removed.  Specifying the removal of a property that does
    not exist is not an error.  All the XML elements in a 'prop' XML
    element inside of a 'remove' XML element MUST be empty, as only
    the names of properties to be removed are required.
 <!ELEMENT remove (prop) >

Dusseault Standards Track [Page 87] RFC 4918 WebDAV June 2007

14.24. response XML Element

 Name:   response
 Purpose:   Holds a single response describing the effect of a method
    on resource and/or its properties.
 Description:   The 'href' element contains an HTTP URL pointing to a
    WebDAV resource when used in the 'response' container.  A
    particular 'href' value MUST NOT appear more than once as the
    child of a 'response' XML element under a 'multistatus' XML
    element.  This requirement is necessary in order to keep
    processing costs for a response to linear time.  Essentially, this
    prevents having to search in order to group together all the
    responses by 'href'.  There are, however, no requirements
    regarding ordering based on 'href' values.  The optional
    precondition/postcondition element and 'responsedescription' text
    can provide additional information about this resource relative to
    the request or result.
 <!ELEMENT response (href, ((href*, status)|(propstat+)),
                     error?, responsedescription? , location?) >

14.25. responsedescription XML Element

 Name:   responsedescription
 Purpose:   Contains information about a status response within a
    Multi-Status.
 Description:   Provides information suitable to be presented to a
    user.
 <!ELEMENT responsedescription (#PCDATA) >

14.26. set XML Element

 Name:   set
 Purpose:   Lists the property values to be set for a resource.
 Description:   The 'set' element MUST contain only a 'prop' element.
    The elements contained by the 'prop' element inside the 'set'
    element MUST specify the name and value of properties that are set
    on the resource identified by Request-URI.  If a property already
    exists, then its value is replaced.  Language tagging information
    appearing in the scope of the 'prop' element (in the "xml:lang"

Dusseault Standards Track [Page 88] RFC 4918 WebDAV June 2007

    attribute, if present) MUST be persistently stored along with the
    property, and MUST be subsequently retrievable using PROPFIND.
 <!ELEMENT set (prop) >

14.27. shared XML Element

 Name:   shared
 Purpose:   Specifies a shared lock.
 <!ELEMENT shared EMPTY >

14.28. status XML Element

 Name:   status
 Purpose:   Holds a single HTTP status-line.
 Value:   status-line (defined in Section 6.1 of [RFC2616])
 <!ELEMENT status (#PCDATA) >

14.29. timeout XML Element

 Name:   timeout
 Purpose:   The number of seconds remaining before a lock expires.
 Value:   TimeType (defined in Section 10.7)
    <!ELEMENT timeout (#PCDATA) >

14.30. write XML Element

 Name:   write
 Purpose:   Specifies a write lock.
 <!ELEMENT write EMPTY >

Dusseault Standards Track [Page 89] RFC 4918 WebDAV June 2007

15. DAV Properties

 For DAV properties, the name of the property is also the same as the
 name of the XML element that contains its value.  In the section
 below, the final line of each section gives the element type
 declaration using the format defined in [REC-XML].  The "Value"
 field, where present, specifies further restrictions on the allowable
 contents of the XML element using BNF (i.e., to further restrict the
 values of a PCDATA element).
 A protected property is one that cannot be changed with a PROPPATCH
 request.  There may be other requests that would result in a change
 to a protected property (as when a LOCK request affects the value of
 DAV:lockdiscovery).  Note that a given property could be protected on
 one type of resource, but not protected on another type of resource.
 A computed property is one with a value defined in terms of a
 computation (based on the content and other properties of that
 resource, or even of some other resource).  A computed property is
 always a protected property.
 COPY and MOVE behavior refers to local COPY and MOVE operations.
 For properties defined based on HTTP GET response headers (DAV:get*),
 the header value could include LWS as defined in [RFC2616], Section
 4.2.  Server implementors SHOULD strip LWS from these values before
 using as WebDAV property values.

15.1. creationdate Property

 Name:   creationdate
 Purpose:   Records the time and date the resource was created.
 Value:   date-time (defined in [RFC3339], see the ABNF in Section
    5.6.)
 Protected:   MAY be protected.  Some servers allow DAV:creationdate
    to be changed to reflect the time the document was created if that
    is more meaningful to the user (rather than the time it was
    uploaded).  Thus, clients SHOULD NOT use this property in
    synchronization logic (use DAV:getetag instead).
 COPY/MOVE behavior:   This property value SHOULD be kept during a
    MOVE operation, but is normally re-initialized when a resource is
    created with a COPY.  It should not be set in a COPY.

Dusseault Standards Track [Page 90] RFC 4918 WebDAV June 2007

 Description:   The DAV:creationdate property SHOULD be defined on all
    DAV compliant resources.  If present, it contains a timestamp of
    the moment when the resource was created.  Servers that are
    incapable of persistently recording the creation date SHOULD
    instead leave it undefined (i.e. report "Not Found").
 <!ELEMENT creationdate (#PCDATA) >

15.2. displayname Property

 Name:   displayname
 Purpose:   Provides a name for the resource that is suitable for
    presentation to a user.
 Value:   Any text.
 Protected:   SHOULD NOT be protected.  Note that servers implementing
    [RFC2518] might have made this a protected property as this is a
    new requirement.
 COPY/MOVE behavior:   This property value SHOULD be preserved in COPY
    and MOVE operations.
 Description:   Contains a description of the resource that is
    suitable for presentation to a user.  This property is defined on
    the resource, and hence SHOULD have the same value independent of
    the Request-URI used to retrieve it (thus, computing this property
    based on the Request-URI is deprecated).  While generic clients
    might display the property value to end users, client UI designers
    must understand that the method for identifying resources is still
    the URL.  Changes to DAV:displayname do not issue moves or copies
    to the server, but simply change a piece of meta-data on the
    individual resource.  Two resources can have the same DAV:
    displayname value even within the same collection.
 <!ELEMENT displayname (#PCDATA) >

15.3. getcontentlanguage Property

 Name:   getcontentlanguage
 Purpose:   Contains the Content-Language header value (from Section
    14.12 of [RFC2616]) as it would be returned by a GET without
    accept headers.
 Value:   language-tag (language-tag is defined in Section 3.10 of
    [RFC2616])

Dusseault Standards Track [Page 91] RFC 4918 WebDAV June 2007

 Protected:   SHOULD NOT be protected, so that clients can reset the
    language.  Note that servers implementing [RFC2518] might have
    made this a protected property as this is a new requirement.
 COPY/MOVE behavior:   This property value SHOULD be preserved in COPY
    and MOVE operations.
 Description:   The DAV:getcontentlanguage property MUST be defined on
    any DAV-compliant resource that returns the Content-Language
    header on a GET.
 <!ELEMENT getcontentlanguage (#PCDATA) >

15.4. getcontentlength Property

 Name:   getcontentlength
 Purpose:   Contains the Content-Length header returned by a GET
    without accept headers.
 Value:   See Section 14.13 of [RFC2616].
 Protected:   This property is computed, therefore protected.
 Description:   The DAV:getcontentlength property MUST be defined on
    any DAV-compliant resource that returns the Content-Length header
    in response to a GET.
 COPY/MOVE behavior:   This property value is dependent on the size of
    the destination resource, not the value of the property on the
    source resource.
 <!ELEMENT getcontentlength (#PCDATA) >

15.5. getcontenttype Property

 Name:   getcontenttype
 Purpose:   Contains the Content-Type header value (from Section 14.17
    of [RFC2616]) as it would be returned by a GET without accept
    headers.
 Value:   media-type (defined in Section 3.7 of [RFC2616])
 Protected:   Potentially protected if the server prefers to assign
    content types on its own (see also discussion in Section 9.7.1).

Dusseault Standards Track [Page 92] RFC 4918 WebDAV June 2007

 COPY/MOVE behavior:   This property value SHOULD be preserved in COPY
    and MOVE operations.
 Description:   This property MUST be defined on any DAV-compliant
    resource that returns the Content-Type header in response to a
    GET.
 <!ELEMENT getcontenttype (#PCDATA) >

15.6. getetag Property

 Name:   getetag
 Purpose:   Contains the ETag header value (from Section 14.19 of
    [RFC2616]) as it would be returned by a GET without accept
    headers.
 Value:   entity-tag (defined in Section 3.11 of [RFC2616])
 Protected:  MUST be protected because this value is created and
    controlled by the server.
 COPY/MOVE behavior:   This property value is dependent on the final
    state of the destination resource, not the value of the property
    on the source resource.  Also note the considerations in
    Section 8.8.
 Description:   The getetag property MUST be defined on any DAV-
    compliant resource that returns the Etag header.  Refer to Section
    3.11 of RFC 2616 for a complete definition of the semantics of an
    ETag, and to Section 8.6 for a discussion of ETags in WebDAV.
 <!ELEMENT getetag (#PCDATA) >

15.7. getlastmodified Property

 Name:   getlastmodified
 Purpose:   Contains the Last-Modified header value (from Section
    14.29 of [RFC2616]) as it would be returned by a GET method
    without accept headers.
 Value:   rfc1123-date (defined in Section 3.3.1 of [RFC2616])
 Protected:   SHOULD be protected because some clients may rely on the
    value for appropriate caching behavior, or on the value of the
    Last-Modified header to which this property is linked.

Dusseault Standards Track [Page 93] RFC 4918 WebDAV June 2007

 COPY/MOVE behavior:   This property value is dependent on the last
    modified date of the destination resource, not the value of the
    property on the source resource.  Note that some server
    implementations use the file system date modified value for the
    DAV:getlastmodified value, and this can be preserved in a MOVE
    even when the HTTP Last-Modified value SHOULD change.  Note that
    since [RFC2616] requires clients to use ETags where provided, a
    server implementing ETags can count on clients using a much better
    mechanism than modification dates for offline synchronization or
    cache control.  Also note the considerations in Section 8.8.
 Description:   The last-modified date on a resource SHOULD only
    reflect changes in the body (the GET responses) of the resource.
    A change in a property only SHOULD NOT cause the last-modified
    date to change, because clients MAY rely on the last-modified date
    to know when to overwrite the existing body.  The DAV:
    getlastmodified property MUST be defined on any DAV-compliant
    resource that returns the Last-Modified header in response to a
    GET.
 <!ELEMENT getlastmodified (#PCDATA) >

15.8. lockdiscovery Property

 Name:   lockdiscovery
 Purpose:   Describes the active locks on a resource
 Protected:   MUST be protected.  Clients change the list of locks
    through LOCK and UNLOCK, not through PROPPATCH.
 COPY/MOVE behavior:   The value of this property depends on the lock
    state of the destination, not on the locks of the source resource.
    Recall that locks are not moved in a MOVE operation.
 Description:   Returns a listing of who has a lock, what type of lock
    he has, the timeout type and the time remaining on the timeout,
    and the associated lock token.  Owner information MAY be omitted
    if it is considered sensitive.  If there are no locks, but the
    server supports locks, the property will be present but contain
    zero 'activelock' elements.  If there are one or more locks, an
    'activelock' element appears for each lock on the resource.  This
    property is NOT lockable with respect to write locks (Section 7).
 <!ELEMENT lockdiscovery (activelock)* >

Dusseault Standards Track [Page 94] RFC 4918 WebDAV June 2007

15.8.1. Example - Retrieving DAV:lockdiscovery

 >>Request
   PROPFIND /container/ HTTP/1.1
   Host: www.example.com
   Content-Length: xxxx
   Content-Type: application/xml; charset="utf-8"
   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D='DAV:'>
     <D:prop><D:lockdiscovery/></D:prop>
   </D:propfind>
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D='DAV:'>
     <D:response>
       <D:href>http://www.example.com/container/</D:href>
       <D:propstat>
         <D:prop>
           <D:lockdiscovery>
            <D:activelock>
             <D:locktype><D:write/></D:locktype>
             <D:lockscope><D:exclusive/></D:lockscope>
             <D:depth>0</D:depth>
             <D:owner>Jane Smith</D:owner>
             <D:timeout>Infinite</D:timeout>
             <D:locktoken>
               <D:href
           >urn:uuid:f81de2ad-7f3d-a1b2-4f3c-00a0c91a9d76</D:href>
             </D:locktoken>
             <D:lockroot>
               <D:href>http://www.example.com/container/</D:href>
             </D:lockroot>
            </D:activelock>
           </D:lockdiscovery>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

Dusseault Standards Track [Page 95] RFC 4918 WebDAV June 2007

 This resource has a single exclusive write lock on it, with an
 infinite timeout.

15.9. resourcetype Property

 Name:   resourcetype
 Purpose:   Specifies the nature of the resource.
 Protected:   SHOULD be protected.  Resource type is generally decided
    through the operation creating the resource (MKCOL vs PUT), not by
    PROPPATCH.
 COPY/MOVE behavior:   Generally a COPY/MOVE of a resource results in
    the same type of resource at the destination.
 Description:   MUST be defined on all DAV-compliant resources.  Each
    child element identifies a specific type the resource belongs to,
    such as 'collection', which is the only resource type defined by
    this specification (see Section 14.3).  If the element contains
    the 'collection' child element plus additional unrecognized
    elements, it should generally be treated as a collection.  If the
    element contains no recognized child elements, it should be
    treated as a non-collection resource.  The default value is empty.
    This element MUST NOT contain text or mixed content.  Any custom
    child element is considered to be an identifier for a resource
    type.
 Example: (fictional example to show extensibility)
     <x:resourcetype xmlns:x="DAV:">
         <x:collection/>
         <f:search-results xmlns:f="http://www.example.com/ns"/>
     </x:resourcetype>

15.10. supportedlock Property

 Name:   supportedlock
 Purpose:   To provide a listing of the lock capabilities supported by
    the resource.
 Protected:   MUST be protected.  Servers, not clients, determine what
    lock mechanisms are supported.

Dusseault Standards Track [Page 96] RFC 4918 WebDAV June 2007

 COPY/MOVE behavior:   This property value is dependent on the kind of
    locks supported at the destination, not on the value of the
    property at the source resource.  Servers attempting to COPY to a
    destination should not attempt to set this property at the
    destination.
 Description:   Returns a listing of the combinations of scope and
    access types that may be specified in a lock request on the
    resource.  Note that the actual contents are themselves controlled
    by access controls, so a server is not required to provide
    information the client is not authorized to see.  This property is
    NOT lockable with respect to write locks (Section 7).
 <!ELEMENT supportedlock (lockentry)* >

15.10.1. Example - Retrieving DAV:supportedlock

 >>Request
   PROPFIND /container/ HTTP/1.1
   Host: www.example.com
   Content-Length: xxxx
   Content-Type: application/xml; charset="utf-8"
   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">
     <D:prop><D:supportedlock/></D:prop>
   </D:propfind>
 >>Response
   HTTP/1.1 207 Multi-Status
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx
   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">
     <D:response>
       <D:href>http://www.example.com/container/</D:href>
       <D:propstat>
         <D:prop>
           <D:supportedlock>
             <D:lockentry>
               <D:lockscope><D:exclusive/></D:lockscope>
               <D:locktype><D:write/></D:locktype>
             </D:lockentry>
             <D:lockentry>
               <D:lockscope><D:shared/></D:lockscope>

Dusseault Standards Track [Page 97] RFC 4918 WebDAV June 2007

               <D:locktype><D:write/></D:locktype>
             </D:lockentry>
           </D:supportedlock>
         </D:prop>
         <D:status>HTTP/1.1 200 OK</D:status>
       </D:propstat>
     </D:response>
   </D:multistatus>

16. Precondition/Postcondition XML Elements

 As introduced in Section 8.7, extra information on error conditions
 can be included in the body of many status responses.  This section
 makes requirements on the use of the error body mechanism and
 introduces a number of precondition and postcondition codes.
 A "precondition" of a method describes the state of the server that
 must be true for that method to be performed.  A "postcondition" of a
 method describes the state of the server that must be true after that
 method has been completed.
 Each precondition and postcondition has a unique XML element
 associated with it.  In a 207 Multi-Status response, the XML element
 MUST appear inside an 'error' element in the appropriate 'propstat or
 'response' element depending on whether the condition applies to one
 or more properties or to the resource as a whole.  In all other error
 responses where this specification's 'error' body is used, the
 precondition/postcondition XML element MUST be returned as the child
 of a top-level 'error' element in the response body, unless otherwise
 negotiated by the request, along with an appropriate response status.
 The most common response status codes are 403 (Forbidden) if the
 request should not be repeated because it will always fail, and 409
 (Conflict) if it is expected that the user might be able to resolve
 the conflict and resubmit the request.  The 'error' element MAY
 contain child elements with specific error information and MAY be
 extended with any custom child elements.
 This mechanism does not take the place of using a correct numeric
 status code as defined here or in HTTP, because the client must
 always be able to take a reasonable course of action based only on
 the numeric code.  However, it does remove the need to define new
 numeric codes.  The new machine-readable codes used for this purpose
 are XML elements classified as preconditions and postconditions, so
 naturally, any group defining a new condition code can use their own
 namespace.  As always, the "DAV:" namespace is reserved for use by
 IETF-chartered WebDAV working groups.

Dusseault Standards Track [Page 98] RFC 4918 WebDAV June 2007

 A server supporting this specification SHOULD use the XML error
 whenever a precondition or postcondition defined in this document is
 violated.  For error conditions not specified in this document, the
 server MAY simply choose an appropriate numeric status and leave the
 response body blank.  However, a server MAY instead use a custom
 condition code and other supporting text, because even when clients
 do not automatically recognize condition codes, they can be quite
 useful in interoperability testing and debugging.
 Example - Response with precondition code
 >>Response
    HTTP/1.1 423 Locked
    Content-Type: application/xml; charset="utf-8"
    Content-Length: xxxx
    <?xml version="1.0" encoding="utf-8" ?>
    <D:error xmlns:D="DAV:">
      <D:lock-token-submitted>
        <D:href>/workspace/webdav/</D:href>
      </D:lock-token-submitted>
    </D:error>
 In this example, a client unaware of a depth-infinity lock on the
 parent collection "/workspace/webdav/" attempted to modify the
 collection member "/workspace/webdav/proposal.doc".
 Some other useful preconditions and postconditions have been defined
 in other specifications extending WebDAV, such as [RFC3744] (see
 particularly Section 7.1.1), [RFC3253], and [RFC3648].
 All these elements are in the "DAV:" namespace.  If not specified
 otherwise, the content for each condition's XML element is defined to
 be empty.
 Name:  lock-token-matches-request-uri
 Use with:  409 Conflict
 Purpose:  (precondition) -- A request may include a Lock-Token header
    to identify a lock for the UNLOCK method.  However, if the
    Request-URI does not fall within the scope of the lock identified
    by the token, the server SHOULD use this error.  The lock may have
    a scope that does not include the Request-URI, or the lock could
    have disappeared, or the token may be invalid.

Dusseault Standards Track [Page 99] RFC 4918 WebDAV June 2007

 Name:  lock-token-submitted (precondition)
 Use with:  423 Locked
 Purpose:  The request could not succeed because a lock token should
    have been submitted.  This element, if present, MUST contain at
    least one URL of a locked resource that prevented the request.  In
    cases of MOVE, COPY, and DELETE where collection locks are
    involved, it can be difficult for the client to find out which
    locked resource made the request fail -- but the server is only
    responsible for returning one such locked resource.  The server
    MAY return every locked resource that prevented the request from
    succeeding if it knows them all.
 <!ELEMENT lock-token-submitted (href+) >
 Name:  no-conflicting-lock (precondition)
 Use with:  Typically 423 Locked
 Purpose:  A LOCK request failed due the presence of an already
    existing conflicting lock.  Note that a lock can be in conflict
    although the resource to which the request was directed is only
    indirectly locked.  In this case, the precondition code can be
    used to inform the client about the resource that is the root of
    the conflicting lock, avoiding a separate lookup of the
    "lockdiscovery" property.
 <!ELEMENT no-conflicting-lock (href)* >
 Name:  no-external-entities
 Use with:  403 Forbidden
 Purpose:  (precondition) -- If the server rejects a client request
    because the request body contains an external entity, the server
    SHOULD use this error.
 Name:  preserved-live-properties
 Use with:  409 Conflict
 Purpose:  (postcondition) -- The server received an otherwise-valid
    MOVE or COPY request, but cannot maintain the live properties with
    the same behavior at the destination.  It may be that the server

Dusseault Standards Track [Page 100] RFC 4918 WebDAV June 2007

    only supports some live properties in some parts of the
    repository, or simply has an internal error.
 Name:  propfind-finite-depth
 Use with:  403 Forbidden
 Purpose:  (precondition) -- This server does not allow infinite-depth
    PROPFIND requests on collections.
 Name:  cannot-modify-protected-property
 Use with:  403 Forbidden
 Purpose:  (precondition) -- The client attempted to set a protected
    property in a PROPPATCH (such as DAV:getetag).  See also
    [RFC3253], Section 3.12.

17. XML Extensibility in DAV

 The XML namespace extension ([REC-XML-NAMES]) is used in this
 specification in order to allow for new XML elements to be added
 without fear of colliding with other element names.  Although WebDAV
 request and response bodies can be extended by arbitrary XML
 elements, which can be ignored by the message recipient, an XML
 element in the "DAV:" namespace SHOULD NOT be used in the request or
 response body unless that XML element is explicitly defined in an
 IETF RFC reviewed by a WebDAV working group.
 For WebDAV to be both extensible and backwards-compatible, both
 clients and servers need to know how to behave when unexpected or
 unrecognized command extensions are received.  For XML processing,
 this means that clients and servers MUST process received XML
 documents as if unexpected elements and attributes (and all children
 of unrecognized elements) were not there.  An unexpected element or
 attribute includes one that may be used in another context but is not
 expected here.  Ignoring such items for purposes of processing can of
 course be consistent with logging all information or presenting for
 debugging.
 This restriction also applies to the processing, by clients, of DAV
 property values where unexpected XML elements SHOULD be ignored
 unless the property's schema declares otherwise.
 This restriction does not apply to setting dead DAV properties on the
 server where the server MUST record all XML elements.

Dusseault Standards Track [Page 101] RFC 4918 WebDAV June 2007

 Additionally, this restriction does not apply to the use of XML where
 XML happens to be the content type of the entity body, for example,
 when used as the body of a PUT.
 Processing instructions in XML SHOULD be ignored by recipients.
 Thus, specifications extending WebDAV SHOULD NOT use processing
 instructions to define normative behavior.
 XML DTD fragments are included for all the XML elements defined in
 this specification.  However, correct XML will not be valid according
 to any DTD due to namespace usage and extension rules.  In
 particular:
 o  Elements (from this specification) are in the "DAV:" namespace,
 o  Element ordering is irrelevant unless otherwise stated,
 o  Extension attributes MAY be added,
 o  For element type definitions of "ANY", the normative text
    definition for that element defines what can be in it and what
    that means.
 o  For element type definitions of "#PCDATA", extension elements MUST
    NOT be added.
 o  For other element type definitions, including "EMPTY", extension
    elements MAY be added.
 Note that this means that elements containing elements cannot be
 extended to contain text, and vice versa.
 With DTD validation relaxed by the rules above, the constraints
 described by the DTD fragments are normative (see for example
 Appendix A).  A recipient of a WebDAV message with an XML body MUST
 NOT validate the XML document according to any hard-coded or
 dynamically-declared DTD.
 Note that this section describes backwards-compatible extensibility
 rules.  There might also be times when an extension is designed not
 to be backwards-compatible, for example, defining an extension that
 reuses an XML element defined in this document but omitting one of
 the child elements required by the DTDs in this specification.

Dusseault Standards Track [Page 102] RFC 4918 WebDAV June 2007

18. DAV Compliance Classes

 A DAV-compliant resource can advertise several classes of compliance.
 A client can discover the compliance classes of a resource by
 executing OPTIONS on the resource and examining the "DAV" header
 which is returned.  Note particularly that resources, rather than
 servers, are spoken of as being compliant.  That is because
 theoretically some resources on a server could support different
 feature sets.  For example, a server could have a sub-repository
 where an advanced feature like versioning was supported, even if that
 feature was not supported on all sub-repositories.
 Since this document describes extensions to the HTTP/1.1 protocol,
 minimally all DAV-compliant resources, clients, and proxies MUST be
 compliant with [RFC2616].
 A resource that is class 2 or class 3 compliant must also be class 1
 compliant.

18.1. Class 1

 A class 1 compliant resource MUST meet all "MUST" requirements in all
 sections of this document.
 Class 1 compliant resources MUST return, at minimum, the value "1" in
 the DAV header on all responses to the OPTIONS method.

18.2. Class 2

 A class 2 compliant resource MUST meet all class 1 requirements and
 support the LOCK method, the DAV:supportedlock property, the DAV:
 lockdiscovery property, the Time-Out response header and the Lock-
 Token request header.  A class 2 compliant resource SHOULD also
 support the Timeout request header and the 'owner' XML element.
 Class 2 compliant resources MUST return, at minimum, the values "1"
 and "2" in the DAV header on all responses to the OPTIONS method.

18.3. Class 3

 A resource can explicitly advertise its support for the revisions to
 [RFC2518] made in this document.  Class 1 MUST be supported as well.
 Class 2 MAY be supported.  Advertising class 3 support in addition to
 class 1 and 2 means that the server supports all the requirements in
 this specification.  Advertising class 3 and class 1 support, but not
 class 2, means that the server supports all the requirements in this
 specification except possibly those that involve locking support.

Dusseault Standards Track [Page 103] RFC 4918 WebDAV June 2007

 Example:
          DAV: 1, 3

19. Internationalization Considerations

 In the realm of internationalization, this specification complies
 with the IETF Character Set Policy [RFC2277].  In this specification,
 human-readable fields can be found either in the value of a property,
 or in an error message returned in a response entity body.  In both
 cases, the human-readable content is encoded using XML, which has
 explicit provisions for character set tagging and encoding, and
 requires that XML processors read XML elements encoded, at minimum,
 using the UTF-8 [RFC3629] and UTF-16 [RFC2781] encodings of the ISO
 10646 multilingual plane.  XML examples in this specification
 demonstrate use of the charset parameter of the Content-Type header
 (defined in [RFC3023]), as well as XML charset declarations.
 XML also provides a language tagging capability for specifying the
 language of the contents of a particular XML element.  The "xml:lang"
 attribute appears on an XML element to identify the language of its
 content and attributes.  See [REC-XML] for definitions of values and
 scoping.
 WebDAV applications MUST support the character set tagging, character
 set encoding, and the language tagging functionality of the XML
 specification.  Implementors of WebDAV applications are strongly
 encouraged to read "XML Media Types" [RFC3023] for instruction on
 which MIME media type to use for XML transport, and on use of the
 charset parameter of the Content-Type header.
 Names used within this specification fall into four categories: names
 of protocol elements such as methods and headers, names of XML
 elements, names of properties, and names of conditions.  Naming of
 protocol elements follows the precedent of HTTP, using English names
 encoded in US-ASCII for methods and headers.  Since these protocol
 elements are not visible to users, and are simply long token
 identifiers, they do not need to support multiple languages.
 Similarly, the names of XML elements used in this specification are
 not visible to the user and hence do not need to support multiple
 languages.
 WebDAV property names are qualified XML names (pairs of XML namespace
 name and local name).  Although some applications (e.g., a generic
 property viewer) will display property names directly to their users,
 it is expected that the typical application will use a fixed set of
 properties, and will provide a mapping from the property name and
 namespace to a human-readable field when displaying the property name

Dusseault Standards Track [Page 104] RFC 4918 WebDAV June 2007

 to a user.  It is only in the case where the set of properties is not
 known ahead of time that an application need display a property name
 to a user.  We recommend that applications provide human-readable
 property names wherever feasible.
 For error reporting, we follow the convention of HTTP/1.1 status
 codes, including with each status code a short, English description
 of the code (e.g., 423 (Locked)).  While the possibility exists that
 a poorly crafted user agent would display this message to a user,
 internationalized applications will ignore this message, and display
 an appropriate message in the user's language and character set.
 Since interoperation of clients and servers does not require locale
 information, this specification does not specify any mechanism for
 transmission of this information.

20. Security Considerations

 This section is provided to detail issues concerning security
 implications of which WebDAV applications need to be aware.
 All of the security considerations of HTTP/1.1 (discussed in
 [RFC2616]) and XML (discussed in [RFC3023]) also apply to WebDAV.  In
 addition, the security risks inherent in remote authoring require
 stronger authentication technology, introduce several new privacy
 concerns, and may increase the hazards from poor server design.
 These issues are detailed below.

20.1. Authentication of Clients

 Due to their emphasis on authoring, WebDAV servers need to use
 authentication technology to protect not just access to a network
 resource, but the integrity of the resource as well.  Furthermore,
 the introduction of locking functionality requires support for
 authentication.
 A password sent in the clear over an insecure channel is an
 inadequate means for protecting the accessibility and integrity of a
 resource as the password may be intercepted.  Since Basic
 authentication for HTTP/1.1 performs essentially clear text
 transmission of a password, Basic authentication MUST NOT be used to
 authenticate a WebDAV client to a server unless the connection is
 secure.  Furthermore, a WebDAV server MUST NOT send a Basic
 authentication challenge in a WWW-Authenticate header unless the
 connection is secure.  An example of a secure connection would be a
 Transport Layer Security (TLS) connection employing a strong cipher
 suite and server authentication.

Dusseault Standards Track [Page 105] RFC 4918 WebDAV June 2007

 WebDAV applications MUST support the Digest authentication scheme
 [RFC2617].  Since Digest authentication verifies that both parties to
 a communication know a shared secret, a password, without having to
 send that secret in the clear, Digest authentication avoids the
 security problems inherent in Basic authentication while providing a
 level of authentication that is useful in a wide range of scenarios.

20.2. Denial of Service

 Denial-of-service attacks are of special concern to WebDAV servers.
 WebDAV plus HTTP enables denial-of-service attacks on every part of a
 system's resources.
 o  The underlying storage can be attacked by PUTting extremely large
    files.
 o  Asking for recursive operations on large collections can attack
    processing time.
 o  Making multiple pipelined requests on multiple connections can
    attack network connections.
 WebDAV servers need to be aware of the possibility of a denial-of-
 service attack at all levels.  The proper response to such an attack
 MAY be to simply drop the connection.  Or, if the server is able to
 make a response, the server MAY use a 400-level status request such
 as 400 (Bad Request) and indicate why the request was refused (a 500-
 level status response would indicate that the problem is with the
 server, whereas unintentional DoS attacks are something the client is
 capable of remedying).

20.3. Security through Obscurity

 WebDAV provides, through the PROPFIND method, a mechanism for listing
 the member resources of a collection.  This greatly diminishes the
 effectiveness of security or privacy techniques that rely only on the
 difficulty of discovering the names of network resources.  Users of
 WebDAV servers are encouraged to use access control techniques to
 prevent unwanted access to resources, rather than depending on the
 relative obscurity of their resource names.

20.4. Privacy Issues Connected to Locks

 When submitting a lock request, a user agent may also submit an
 'owner' XML field giving contact information for the person taking
 out the lock (for those cases where a person, rather than a robot, is
 taking out the lock).  This contact information is stored in a DAV:
 lockdiscovery property on the resource, and can be used by other

Dusseault Standards Track [Page 106] RFC 4918 WebDAV June 2007

 collaborators to begin negotiation over access to the resource.
 However, in many cases, this contact information can be very private,
 and should not be widely disseminated.  Servers SHOULD limit read
 access to the DAV:lockdiscovery property as appropriate.
 Furthermore, user agents SHOULD provide control over whether contact
 information is sent at all, and if contact information is sent,
 control over exactly what information is sent.

20.5. Privacy Issues Connected to Properties

 Since property values are typically used to hold information such as
 the author of a document, there is the possibility that privacy
 concerns could arise stemming from widespread access to a resource's
 property data.  To reduce the risk of inadvertent release of private
 information via properties, servers are encouraged to develop access
 control mechanisms that separate read access to the resource body and
 read access to the resource's properties.  This allows a user to
 control the dissemination of their property data without overly
 restricting access to the resource's contents.

20.6. Implications of XML Entities

 XML supports a facility known as "external entities", defined in
 Section 4.2.2 of [REC-XML], which instructs an XML processor to
 retrieve and include additional XML.  An external XML entity can be
 used to append or modify the document type declaration (DTD)
 associated with an XML document.  An external XML entity can also be
 used to include XML within the content of an XML document.  For non-
 validating XML, such as the XML used in this specification, including
 an external XML entity is not required by XML.  However, XML does
 state that an XML processor may, at its discretion, include the
 external XML entity.
 External XML entities have no inherent trustworthiness and are
 subject to all the attacks that are endemic to any HTTP GET request.
 Furthermore, it is possible for an external XML entity to modify the
 DTD, and hence affect the final form of an XML document, in the worst
 case, significantly modifying its semantics or exposing the XML
 processor to the security risks discussed in [RFC3023].  Therefore,
 implementers must be aware that external XML entities should be
 treated as untrustworthy.  If a server chooses not to handle external
 XML entities, it SHOULD respond to requests containing external
 entities with the 'no-external-entities' condition code.
 There is also the scalability risk that would accompany a widely
 deployed application that made use of external XML entities.  In this
 situation, it is possible that there would be significant numbers of
 requests for one external XML entity, potentially overloading any

Dusseault Standards Track [Page 107] RFC 4918 WebDAV June 2007

 server that fields requests for the resource containing the external
 XML entity.
 Furthermore, there's also a risk based on the evaluation of "internal
 entities" as defined in Section 4.2.2 of [REC-XML].  A small,
 carefully crafted request using nested internal entities may require
 enormous amounts of memory and/or processing time to process.  Server
 implementers should be aware of this risk and configure their XML
 parsers so that requests like these can be detected and rejected as
 early as possible.

20.7. Risks Connected with Lock Tokens

 This specification encourages the use of "A Universally Unique
 Identifier (UUID) URN Namespace" ([RFC4122]) for lock tokens
 (Section 6.5), in order to guarantee their uniqueness across space
 and time.  Version 1 UUIDs (defined in Section 4) MAY contain a
 "node" field that "consists of an IEEE 802 MAC address, usually the
 host address.  For systems with multiple IEEE addresses, any
 available one can be used".  Since a WebDAV server will issue many
 locks over its lifetime, the implication is that it may also be
 publicly exposing its IEEE 802 address.
 There are several risks associated with exposure of IEEE 802
 addresses.  Using the IEEE 802 address:
 o  It is possible to track the movement of hardware from subnet to
    subnet.
 o  It may be possible to identify the manufacturer of the hardware
    running a WebDAV server.
 o  It may be possible to determine the number of each type of
    computer running WebDAV.
 This risk only applies to host-address-based UUID versions.  Section
 4 of [RFC4122] describes several other mechanisms for generating
 UUIDs that do not involve the host address and therefore do not
 suffer from this risk.

20.8. Hosting Malicious Content

 HTTP has the ability to host programs that are executed on client
 machines.  These programs can take many forms including Web scripts,
 executables, plug-in modules, and macros in documents.  WebDAV does
 not change any of the security concerns around these programs, yet
 often WebDAV is used in contexts where a wide range of users can
 publish documents on a server.  The server might not have a close

Dusseault Standards Track [Page 108] RFC 4918 WebDAV June 2007

 trust relationship with the author that is publishing the document.
 Servers that allow clients to publish arbitrary content can usefully
 implement precautions to check that content published to the server
 is not harmful to other clients.  Servers could do this by techniques
 such as restricting the types of content that is allowed to be
 published and running virus and malware detection software on
 published content.  Servers can also mitigate the risk by having
 appropriate access restriction and authentication of users that are
 allowed to publish content to the server.

21. IANA Considerations

21.1. New URI Schemes

 This specification defines two URI schemes:
 1.  the "opaquelocktoken" scheme defined in Appendix C, and
 2.  the "DAV" URI scheme, which historically was used in [RFC2518] to
     disambiguate WebDAV property and XML element names and which
     continues to be used for that purpose in this specification and
     others extending WebDAV.  Creation of identifiers in the "DAV:"
     namespace is controlled by the IETF.
 Note that defining new URI schemes for XML namespaces is now
 discouraged.  "DAV:" was defined before standard best practices
 emerged.

21.2. XML Namespaces

 XML namespaces disambiguate WebDAV property names and XML elements.
 Any WebDAV user or application can define a new namespace in order to
 create custom properties or extend WebDAV XML syntax.  IANA does not
 need to manage such namespaces, property names, or element names.

21.3. Message Header Fields

 The message header fields below should be added to the permanent
 registry (see [RFC3864]).

21.3.1. DAV

 Header field name: DAV
 Applicable protocol: http
 Status: standard

Dusseault Standards Track [Page 109] RFC 4918 WebDAV June 2007

 Author/Change controller: IETF
 Specification document: this specification (Section 10.1)

21.3.2. Depth

 Header field name: Depth
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document: this specification (Section 10.2)

21.3.3. Destination

 Header field name: Destination
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document: this specification (Section 10.3)

21.3.4. If

 Header field name: If
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document: this specification (Section 10.4)

21.3.5. Lock-Token

 Header field name: Lock-Token
 Applicable protocol: http
 Status: standard

Dusseault Standards Track [Page 110] RFC 4918 WebDAV June 2007

 Author/Change controller: IETF
 Specification document: this specification (Section 10.5)

21.3.6. Overwrite

 Header field name: Overwrite
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document: this specification (Section 10.6)

21.3.7. Timeout

 Header field name: Timeout
 Applicable protocol: http
 Status: standard
 Author/Change controller: IETF
 Specification document: this specification (Section 10.7)

21.4. HTTP Status Codes

 This specification defines the HTTP status codes
 o  207 Multi-Status (Section 11.1)
 o  422 Unprocessable Entity (Section 11.2),
 o  423 Locked (Section 11.3),
 o  424 Failed Dependency (Section 11.4) and
 o  507 Insufficient Storage (Section 11.5),
 to be updated in the registry at
 <http://www.iana.org/assignments/http-status-codes>.
 Note: the HTTP status code 102 (Processing) has been removed in this
 specification; its IANA registration should continue to reference RFC
 2518.

Dusseault Standards Track [Page 111] RFC 4918 WebDAV June 2007

22. Acknowledgements

 A specification such as this thrives on piercing critical review and
 withers from apathetic neglect.  The authors gratefully acknowledge
 the contributions of the following people, whose insights were so
 valuable at every stage of our work.
 Contributors to RFC 2518
 Terry Allen, Harald Alvestrand, Jim Amsden, Becky Anderson, Alan
 Babich, Sanford Barr, Dylan Barrell, Bernard Chester, Tim Berners-
 Lee, Dan Connolly, Jim Cunningham, Ron Daniel, Jr., Jim Davis, Keith
 Dawson, Mark Day, Brian Deen, Martin Duerst, David Durand, Lee
 Farrell, Chuck Fay, Wesley Felter, Roy Fielding, Mark Fisher, Alan
 Freier, George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis
 Hamilton, Steve Henning, Mead Himelstein, Alex Hopmann, Andre van der
 Hoek, Ben Laurie, Paul Leach, Ora Lassila, Karen MacArthur, Steven
 Martin, Larry Masinter, Michael Mealling, Keith Moore, Thomas Narten,
 Henrik Nielsen, Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff,
 Saveen Reddy, Henry Sanders, Christopher Seiwald, Judith Slein, Mike
 Spreitzer, Einar Stefferud, Greg Stein, Ralph Swick, Kenji Takahashi,
 Richard N. Taylor, Robert Thau, John Turner, Sankar Virdhagriswaran,
 Fabio Vitali, Gregory Woodhouse, and Lauren Wood.
 Two from this list deserve special mention.  The contributions by
 Larry Masinter have been invaluable; he both helped the formation of
 the working group and patiently coached the authors along the way.
 In so many ways he has set high standards that we have toiled to
 meet.  The contributions of Judith Slein were also invaluable; by
 clarifying the requirements and in patiently reviewing version after
 version, she both improved this specification and expanded our minds
 on document management.
 We would also like to thank John Turner for developing the XML DTD.
 The authors of RFC 2518 were Yaron Goland, Jim Whitehead, A. Faizi,
 Steve Carter, and D. Jensen.  Although their names had to be removed
 due to IETF author count restrictions, they can take credit for the
 majority of the design of WebDAV.
 Additional Acknowledgements for This Specification
 Significant contributors of text for this specification are listed as
 contributors in the section below.  We must also gratefully
 acknowledge Geoff Clemm, Joel Soderberg, and Dan Brotsky for hashing
 out specific text on the list or in meetings.  Joe Hildebrand and
 Cullen Jennings helped close many issues.  Barry Lind described an
 additional security consideration and Cullen Jennings provided text

Dusseault Standards Track [Page 112] RFC 4918 WebDAV June 2007

 for that consideration.  Jason Crawford tracked issue status for this
 document for a period of years, followed by Elias Sinderson.

23. Contributors to This Specification

 Julian Reschke
 <green/>bytes GmbH
 Hafenweg 16, 48155 Muenster, Germany
 EMail: julian.reschke@greenbytes.de
 Elias Sinderson
 University of California, Santa Cruz
 1156 High Street, Santa Cruz, CA 95064
 EMail: elias@cse.ucsc.edu
 Jim Whitehead
 University of California, Santa Cruz
 1156 High Street, Santa Cruz, CA 95064
 EMail: ejw@soe.ucsc.edu

24. Authors of RFC 2518

 Y. Y. Goland
 Microsoft Corporation
 One Microsoft Way
 Redmond, WA 98052-6399
 EMail: yarong@microsoft.com
 E. J. Whitehead, Jr.
 Dept. Of Information and Computer Science
 University of California, Irvine
 Irvine, CA 92697-3425
 EMail: ejw@ics.uci.edu
 A. Faizi
 Netscape
 685 East Middlefield Road
 Mountain View, CA 94043
 EMail: asad@netscape.com

Dusseault Standards Track [Page 113] RFC 4918 WebDAV June 2007

 S. R. Carter
 Novell
 1555 N. Technology Way
 M/S ORM F111
 Orem, UT 84097-2399
 EMail: srcarter@novell.com
 D. Jensen
 Novell
 1555 N. Technology Way
 M/S ORM F111
 Orem, UT 84097-2399
 EMail: dcjensen@novell.com

25. References

25.1. Normative References

 [REC-XML]          Bray, T., Paoli, J., Sperberg-McQueen, C., Maler,
                    E., and F. Yergeau, "Extensible Markup Language
                    (XML) 1.0 (Fourth Edition)", W3C REC-xml-20060816,
                    August 2006,
                    <http://www.w3.org/TR/2006/REC-xml-20060816/>.
 [REC-XML-INFOSET]  Cowan, J. and R. Tobin, "XML Information Set
                    (Second Edition)", W3C REC-xml-infoset-20040204,
                    February 2004, <http://www.w3.org/TR/2004/
                    REC-xml-infoset-20040204/>.
 [REC-XML-NAMES]    Bray, T., Hollander, D., Layman, A., and R. Tobin,
                    "Namespaces in XML 1.0 (Second Edition)", W3C REC-
                    xml-names-20060816, August 2006, <http://
                    www.w3.org/TR/2006/REC-xml-names-20060816/>.
 [RFC2119]          Bradner, S., "Key words for use in RFCs to
                    Indicate Requirement Levels", BCP 14, RFC 2119,
                    March 1997.
 [RFC2277]          Alvestrand, H., "IETF Policy on Character Sets and
                    Languages", BCP 18, RFC 2277, January 1998.
 [RFC2616]          Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                    Masinter, L., Leach, P., and T. Berners-Lee,
                    "Hypertext Transfer Protocol -- HTTP/1.1",
                    RFC 2616, June 1999.

Dusseault Standards Track [Page 114] RFC 4918 WebDAV June 2007

 [RFC2617]          Franks, J., Hallam-Baker, P., Hostetler, J.,
                    Lawrence, S., Leach, P., Luotonen, A., and L.
                    Stewart, "HTTP Authentication: Basic and Digest
                    Access Authentication", RFC 2617, June 1999.
 [RFC3339]          Klyne, G., Ed. and C. Newman, "Date and Time on
                    the Internet: Timestamps", RFC 3339, July 2002.
 [RFC3629]          Yergeau, F., "UTF-8, a transformation format of
                    ISO 10646", STD 63, RFC 3629, November 2003.
 [RFC3986]          Berners-Lee, T., Fielding, R., and L. Masinter,
                    "Uniform Resource Identifier (URI): Generic
                    Syntax", STD 66, RFC 3986, January 2005.
 [RFC4122]          Leach, P., Mealling, M., and R. Salz, "A
                    Universally Unique IDentifier (UUID) URN
                    Namespace", RFC 4122, July 2005.

25.2. Informative References

 [RFC2291]          Slein, J., Vitali, F., Whitehead, E., and D.
                    Durand, "Requirements for a Distributed Authoring
                    and Versioning Protocol for the World Wide Web",
                    RFC 2291, February 1998.
 [RFC2518]          Goland, Y., Whitehead, E., Faizi, A., Carter, S.,
                    and D. Jensen, "HTTP Extensions for Distributed
                    Authoring -- WEBDAV", RFC 2518, February 1999.
 [RFC2781]          Hoffman, P. and F. Yergeau, "UTF-16, an encoding
                    of ISO 10646", RFC 2781, February 2000.
 [RFC3023]          Murata, M., St. Laurent, S., and D. Kohn, "XML
                    Media Types", RFC 3023, January 2001.
 [RFC3253]          Clemm, G., Amsden, J., Ellison, T., Kaler, C., and
                    J. Whitehead, "Versioning Extensions to WebDAV
                    (Web Distributed Authoring and Versioning)",
                    RFC 3253, March 2002.
 [RFC3648]          Whitehead, J. and J. Reschke, Ed., "Web
                    Distributed Authoring and Versioning (WebDAV)
                    Ordered Collections Protocol", RFC 3648,
                    December 2003.

Dusseault Standards Track [Page 115] RFC 4918 WebDAV June 2007

 [RFC3744]          Clemm, G., Reschke, J., Sedlar, E., and J.
                    Whitehead, "Web Distributed Authoring and
                    Versioning (WebDAV) Access Control Protocol",
                    RFC 3744, May 2004.
 [RFC3864]          Klyne, G., Nottingham, M., and J. Mogul,
                    "Registration Procedures for Message Header
                    Fields", BCP 90, RFC 3864, September 2004.

Dusseault Standards Track [Page 116] RFC 4918 WebDAV June 2007

Appendix A. Notes on Processing XML Elements

A.1. Notes on Empty XML Elements

 XML supports two mechanisms for indicating that an XML element does
 not have any content.  The first is to declare an XML element of the
 form <A></A>.  The second is to declare an XML element of the form
 <A/>.  The two XML elements are semantically identical.

A.2. Notes on Illegal XML Processing

 XML is a flexible data format that makes it easy to submit data that
 appears legal but in fact is not.  The philosophy of "Be flexible in
 what you accept and strict in what you send" still applies, but it
 must not be applied inappropriately.  XML is extremely flexible in
 dealing with issues of whitespace, element ordering, inserting new
 elements, etc.  This flexibility does not require extension,
 especially not in the area of the meaning of elements.
 There is no kindness in accepting illegal combinations of XML
 elements.  At best, it will cause an unwanted result and at worst it
 can cause real damage.

A.3. Example - XML Syntax Error

 The following request body for a PROPFIND method is illegal.
    <?xml version="1.0" encoding="utf-8" ?>
    <D:propfind xmlns:D="DAV:">
     <D:allprop/>
     <D:propname/>
    </D:propfind>
 The definition of the propfind element only allows for the allprop or
 the propname element, not both.  Thus, the above is an error and must
 be responded to with a 400 (Bad Request).
 Imagine, however, that a server wanted to be "kind" and decided to
 pick the allprop element as the true element and respond to it.  A
 client running over a bandwidth limited line who intended to execute
 a propname would be in for a big surprise if the server treated the
 command as an allprop.
 Additionally, if a server were lenient and decided to reply to this
 request, the results would vary randomly from server to server, with
 some servers executing the allprop directive, and others executing
 the propname directive.  This reduces interoperability rather than
 increasing it.

Dusseault Standards Track [Page 117] RFC 4918 WebDAV June 2007

A.4. Example - Unexpected XML Element

 The previous example was illegal because it contained two elements
 that were explicitly banned from appearing together in the propfind
 element.  However, XML is an extensible language, so one can imagine
 new elements being defined for use with propfind.  Below is the
 request body of a PROPFIND and, like the previous example, must be
 rejected with a 400 (Bad Request) by a server that does not
 understand the expired-props element.
    <?xml version="1.0" encoding="utf-8" ?>
    <D:propfind xmlns:D="DAV:"
    xmlns:E="http://www.example.com/standards/props/">
     <E:expired-props/>
    </D:propfind>
 To understand why a 400 (Bad Request) is returned, let us look at the
 request body as the server unfamiliar with expired-props sees it.
    <?xml version="1.0" encoding="utf-8" ?>
    <D:propfind xmlns:D="DAV:"
                xmlns:E="http://www.example.com/standards/props/">
    </D:propfind>
 As the server does not understand the 'expired-props' element,
 according to the WebDAV-specific XML processing rules specified in
 Section 17, it must process the request as if the element were not
 there.  Thus, the server sees an empty propfind, which by the
 definition of the propfind element is illegal.
 Please note that had the extension been additive, it would not
 necessarily have resulted in a 400 (Bad Request).  For example,
 imagine the following request body for a PROPFIND:
    <?xml version="1.0" encoding="utf-8" ?>
    <D:propfind xmlns:D="DAV:"
                xmlns:E="http://www.example.com/standards/props/">
     <D:propname/>
     <E:leave-out>*boss*</E:leave-out>
    </D:propfind>
 The previous example contains the fictitious element leave-out.  Its
 purpose is to prevent the return of any property whose name matches
 the submitted pattern.  If the previous example were submitted to a
 server unfamiliar with 'leave-out', the only result would be that the
 'leave-out' element would be ignored and a propname would be
 executed.

Dusseault Standards Track [Page 118] RFC 4918 WebDAV June 2007

Appendix B. Notes on HTTP Client Compatibility

 WebDAV was designed to be, and has been found to be, backward-
 compatible with HTTP 1.1.  The PUT and DELETE methods are defined in
 HTTP and thus may be used by HTTP clients as well as WebDAV-aware
 clients, but the responses to PUT and DELETE have been extended in
 this specification in ways that only a WebDAV client would be
 entirely prepared for.  Some theoretical concerns were raised about
 whether those responses would cause interoperability problems with
 HTTP-only clients, and this section addresses those concerns.
 Since any HTTP client ought to handle unrecognized 400-level and 500-
 level status codes as errors, the following new status codes should
 not present any issues: 422, 423, and 507 (424 is also a new status
 code but it appears only in the body of a Multistatus response.)  So,
 for example, if an HTTP client attempted to PUT or DELETE a locked
 resource, the 423 Locked response ought to result in a generic error
 presented to the user.
 The 207 Multistatus response is interesting because an HTTP client
 issuing a DELETE request to a collection might interpret a 207
 response as a success, even though it does not realize the resource
 is a collection and cannot understand that the DELETE operation might
 have been a complete or partial failure.  That interpretation isn't
 entirely justified, because a 200-level response indicates that the
 server "received, understood, and accepted" the request, not that the
 request resulted in complete success.
 One option is that a server could treat a DELETE of a collection as
 an atomic operation, and use either 204 No Content in case of
 success, or some appropriate error response (400 or 500 level) for an
 error.  This approach would indeed maximize backward compatibility.
 However, since interoperability tests and working group discussions
 have not turned up any instances of HTTP clients issuing a DELETE
 request against a WebDAV collection, this concern is more theoretical
 than practical.  Thus, servers are likely to be completely successful
 at interoperating with HTTP clients even if they treat any collection
 DELETE request as a WebDAV request and send a 207 Multi-Status
 response.
 In general, server implementations are encouraged to use the detailed
 responses and other mechanisms defined in this document rather than
 make changes for theoretical interoperability concerns.

Dusseault Standards Track [Page 119] RFC 4918 WebDAV June 2007

Appendix C. The 'opaquelocktoken' Scheme and URIs

 The 'opaquelocktoken' URI scheme was defined in [RFC2518] (and
 registered by IANA) in order to create syntactically correct and
 easy-to-generate URIs out of UUIDs, intended to be used as lock
 tokens and to be unique across all resources for all time.
 An opaquelocktoken URI is constructed by concatenating the
 'opaquelocktoken' scheme with a UUID, along with an optional
 extension.  Servers can create new UUIDs for each new lock token.  If
 a server wishes to reuse UUIDs, the server MUST add an extension, and
 the algorithm generating the extension MUST guarantee that the same
 extension will never be used twice with the associated UUID.
   OpaqueLockToken-URI = "opaquelocktoken:" UUID [Extension]
     ; UUID is defined in Section 3 of [RFC4122].  Note that LWS
     ; is not allowed between elements of
     ; this production.
   Extension = path
     ; path is defined in Section 3.3 of [RFC3986]

Appendix D. Lock-null Resources

 The original WebDAV model for locking unmapped URLs created "lock-
 null resources".  This model was over-complicated and some
 interoperability and implementation problems were discovered.  The
 new WebDAV model for locking unmapped URLs (see Section 7.3) creates
 "locked empty resources".  Lock-null resources are deprecated.  This
 section discusses the original model briefly because clients MUST be
 able to handle either model.
 In the original "lock-null resource" model, which is no longer
 recommended for implementation:
 o  A lock-null resource sometimes appeared as "Not Found".  The
    server responds with a 404 or 405 to any method except for PUT,
    MKCOL, OPTIONS, PROPFIND, LOCK, UNLOCK.
 o  A lock-null resource does however show up as a member of its
    parent collection.
 o  The server removes the lock-null resource entirely (its URI
    becomes unmapped) if its lock goes away before it is converted to
    a regular resource.  Recall that locks go away not only when they
    expire or are unlocked, but are also removed if a resource is
    renamed or moved, or if any parent collection is renamed or moved.

Dusseault Standards Track [Page 120] RFC 4918 WebDAV June 2007

 o  The server converts the lock-null resource into a regular resource
    if a PUT request to the URL is successful.
 o  The server converts the lock-null resource into a collection if a
    MKCOL request to the URL is successful (though interoperability
    experience showed that not all servers followed this requirement).
 o  Property values were defined for DAV:lockdiscovery and DAV:
    supportedlock properties but not necessarily for other properties
    like DAV:getcontenttype.
 Clients can easily interoperate both with servers that support the
 old model "lock-null resources" and the recommended model of "locked
 empty resources" by only attempting PUT after a LOCK to an unmapped
 URL, not MKCOL or GET.

D.1. Guidance for Clients Using LOCK to Create Resources

 A WebDAV client implemented to this specification might find servers
 that create lock-null resources (implemented before this
 specification using [RFC2518]) as well as servers that create locked
 empty resources.  The response to the LOCK request will not indicate
 what kind of resource was created.  There are a few techniques that
 help the client deal with either type.
    If the client wishes to avoid accidentally creating either lock-
    null or empty locked resources, an "If-Match: *" header can be
    included with LOCK requests to prevent the server from creating a
    new resource.
    If a LOCK request creates a resource and the client subsequently
    wants to overwrite that resource using a COPY or MOVE request, the
    client should include an "Overwrite: T" header.
    If a LOCK request creates a resource and the client then decides
    to get rid of that resource, a DELETE request is supposed to fail
    on a lock-null resource and UNLOCK should be used instead.  But
    with a locked empty resource, UNLOCK doesn't make the resource
    disappear.  Therefore, the client might have to try both requests
    and ignore an error in one of the two requests.

Appendix E. Guidance for Clients Desiring to Authenticate

 Many WebDAV clients that have already been implemented have account
 settings (similar to the way email clients store IMAP account
 settings).  Thus, the WebDAV client would be able to authenticate
 with its first couple requests to the server, provided it had a way
 to get the authentication challenge from the server with realm name,

Dusseault Standards Track [Page 121] RFC 4918 WebDAV June 2007

 nonce, and other challenge information.  Note that the results of
 some requests might vary according to whether or not the client is
 authenticated -- a PROPFIND might return more visible resources if
 the client is authenticated, yet not fail if the client is anonymous.
 There are a number of ways the client might be able to trigger the
 server to provide an authentication challenge.  This appendix
 describes a couple approaches that seem particularly likely to work.
 The first approach is to perform a request that ought to require
 authentication.  However, it's possible that a server might handle
 any request even without authentication, so to be entirely safe, the
 client could add a conditional header to ensure that even if the
 request passes permissions checks, it's not actually handled by the
 server.  An example of following this approach would be to use a PUT
 request with an "If-Match" header with a made-up ETag value.  This
 approach might fail to result in an authentication challenge if the
 server does not test authorization before testing conditionals as is
 required (see Section 8.5), or if the server does not need to test
 authorization.
 Example - forcing auth challenge with write request
 >>Request
   PUT /forceauth.txt HTTP/1.1
   Host: www.example.com
   If-Match: "xxx"
   Content-Type: text/plain
   Content-Length: 0
 The second approach is to use an Authorization header (defined in
 [RFC2617]), which is likely to be rejected by the server but which
 will then prompt a proper authentication challenge.  For example, the
 client could start with a PROPFIND request containing an
 Authorization header containing a made-up Basic userid:password
 string or with actual plausible credentials.  This approach relies on
 the server responding with a "401 Unauthorized" along with a
 challenge if it receives an Authorization header with an unrecognized
 username, invalid password, or if it doesn't even handle Basic
 authentication.  This seems likely to work because of the
 requirements of RFC 2617:

Dusseault Standards Track [Page 122] RFC 4918 WebDAV June 2007

 "If the origin server does not wish to accept the credentials sent
 with a request, it SHOULD return a 401 (Unauthorized) response.  The
 response MUST include a WWW-Authenticate header field containing at
 least one (possibly new) challenge applicable to the requested
 resource."
 There's a slight problem with implementing that recommendation in
 some cases, because some servers do not even have challenge
 information for certain resources.  Thus, when there's no way to
 authenticate to a resource or the resource is entirely publicly
 available over all accepted methods, the server MAY ignore the
 Authorization header, and the client will presumably try again later.
 Example - forcing auth challenge with Authorization header
 >>Request
   PROPFIND /docs/ HTTP/1.1
   Host: www.example.com
   Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
   Content-type: application/xml; charset="utf-8"
   Content-Length: xxxx
   [body omitted]

Appendix F. Summary of Changes from RFC 2518

 This section lists major changes between this document and RFC 2518,
 starting with those that are likely to result in implementation
 changes.  Servers will advertise support for all changes in this
 specification by returning the compliance class "3" in the DAV
 response header (see Sections 10.1 and 18.3).

F.1. Changes for Both Client and Server Implementations

 Collections and Namespace Operations
 o  The semantics of PROPFIND 'allprop' (Section 9.1) have been
    relaxed so that servers return results including, at a minimum,
    the live properties defined in this specification, but not
    necessarily return other live properties.  The 'allprop' directive
    therefore means something more like "return all properties that
    are supposed to be returned when 'allprop' is requested" -- a set
    of properties that may include custom properties and properties
    defined in other specifications if those other specifications so
    require.  Related to this, 'allprop' requests can now be extended
    with the 'include' syntax to include specific named properties,

Dusseault Standards Track [Page 123] RFC 4918 WebDAV June 2007

    thereby avoiding additional requests due to changed 'allprop'
    semantics.
 o  Servers are now allowed to reject PROPFIND requests with Depth:
    Infinity.  Clients that used this will need to be able to do a
    series of Depth:1 requests instead.
 o  Multi-Status response bodies now can transport the value of HTTP's
    Location response header in the new 'location' element.  Clients
    may use this to avoid additional roundtrips to the server when
    there is a 'response' element with a 3xx status (see
    Section 14.24).
 o  The definition of COPY has been relaxed so that it doesn't require
    servers to first delete the target resources anymore (this was a
    known incompatibility with [RFC3253]).  See Section 9.8.
 Headers and Marshalling
 o  The Destination and If request headers now allow absolute paths in
    addition to full URIs (see Section 8.3).  This may be useful for
    clients operating through a reverse proxy that does rewrite the
    Host request header, but not WebDAV-specific headers.
 o  This specification adopts the error marshalling extensions and the
    "precondition/postcondition" terminology defined in [RFC3253] (see
    Section 16).  Related to that, it adds the "error" XML element
    inside multistatus response bodies (see Section 14.5, however note
    that it uses a format different from the one recommended in RFC
    3253).
 o  Senders and recipients are now required to support the UTF-16
    character encoding in XML message bodies (see Section 19).
 o  Clients are now required to send the Depth header on PROPFIND
    requests, although servers are still encouraged to support clients
    that don't.
 Locking
 o  RFC 2518's concept of "lock-null resources" (LNRs) has been
    replaced by a simplified approach, the "locked empty resources"
    (see Section 7.3).  There are some aspects of lock-null resources
    clients cannot rely on anymore, namely, the ability to use them to
    create a locked collection or the fact that they disappear upon
    UNLOCK when no PUT or MKCOL request was issued.  Note that servers
    are still allowed to implement LNRs as per RFC 2518.

Dusseault Standards Track [Page 124] RFC 4918 WebDAV June 2007

 o  There is no implicit refresh of locks anymore.  Locks are only
    refreshed upon explicit request (see Section 9.10.2).
 o  Clarified that the DAV:owner value supplied in the LOCK request
    must be preserved by the server just like a dead property
    (Section 14.17).  Also added the DAV:lockroot element
    (Section 14.12), which allows clients to discover the root of
    lock.

F.2. Changes for Server Implementations

 Collections and Namespace Operations
 o  Due to interoperability problems, allowable formats for contents
    of 'href' elements in multistatus responses have been limited (see
    Section 8.3).
 o  Due to lack of implementation, support for the 'propertybehavior'
    request body for COPY and MOVE has been removed.  Instead,
    requirements for property preservation have been clarified (see
    Sections 9.8 and 9.9).
 Properties
 o  Strengthened server requirements for storage of property values,
    in particular persistence of language information (xml:lang),
    whitespace, and XML namespace information (see Section 4.3).
 o  Clarified requirements on which properties should be writable by
    the client; in particular, setting "DAV:displayname" should be
    supported by servers (see Section 15).
 o  Only 'rfc1123-date' productions are legal as values for DAV:
    getlastmodified (see Section 15.7).
 Headers and Marshalling
 o  Servers are now required to do authorization checks before
    processing conditional headers (see Section 8.5).
 Locking
 o  Strengthened requirement to check identity of lock creator when
    accessing locked resources (see Section 6.4).  Clients should be
    aware that lock tokens returned to other principals can only be
    used to break a lock, if at all.

Dusseault Standards Track [Page 125] RFC 4918 WebDAV June 2007

 o  Section 8.10.4 of [RFC2518] incorrectly required servers to return
    a 409 status where a 207 status was really appropriate.  This has
    been corrected (Section 9.10).

F.3. Other Changes

 The definition of collection state has been fixed so it doesn't vary
 anymore depending on the Request-URI (see Section 5.2).
 The DAV:source property introduced in Section 4.6 of [RFC2518] was
 removed due to lack of implementation experience.
 The DAV header now allows non-IETF extensions through URIs in
 addition to compliance class tokens.  It also can now be used in
 requests, although this specification does not define any associated
 semantics for the compliance classes defined in here (see
 Section 10.1).
 In RFC 2518, the definition of the Depth header (Section 9.2)
 required that, by default, request headers would be applied to each
 resource in scope.  Based on implementation experience, the default
 has now been reversed (see Section 10.2).
 The definitions of HTTP status code 102 ([RFC2518], Section 10.1) and
 the Status-URI response header (Section 9.7) have been removed due to
 lack of implementation.
 The TimeType format used in the Timeout request header and the
 "timeout" XML element used to be extensible.  Now, only the two
 formats defined by this specification are allowed (see Section 10.7).

Author's Address

 Lisa Dusseault (editor)
 CommerceNet
 2064 Edgewood Dr.
 Palo Alto, CA  94303
 US
 EMail: ldusseault@commerce.net

Dusseault Standards Track [Page 126] RFC 4918 WebDAV June 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Dusseault Standards Track [Page 127]

/data/webs/external/dokuwiki/data/pages/rfc/rfc4918.txt · Last modified: 2007/06/29 21:48 (external edit)