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rfc:rfc8040

Internet Engineering Task Force (IETF) A. Bierman Request for Comments: 8040 YumaWorks Category: Standards Track M. Bjorklund ISSN: 2070-1721 Tail-f Systems

                                                             K. Watsen
                                                      Juniper Networks
                                                          January 2017
                         RESTCONF Protocol

Abstract

 This document describes an HTTP-based protocol that provides a
 programmatic interface for accessing data defined in YANG, using the
 datastore concepts defined in the Network Configuration Protocol
 (NETCONF).

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8040.

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Bierman, et al. Standards Track [Page 1] RFC 8040 RESTCONF January 2017

Table of Contents

 1. Introduction ....................................................5
    1.1. Terminology ................................................5
         1.1.1. NETCONF .............................................6
         1.1.2. HTTP ................................................6
         1.1.3. YANG ................................................7
         1.1.4. NETCONF Notifications ...............................7
         1.1.5. Terms ...............................................8
         1.1.6. URI Template and Examples ..........................10
         1.1.7. Tree Diagrams ......................................11
    1.2. Subset of NETCONF Functionality ...........................11
    1.3. Data-Model-Driven API .....................................12
    1.4. Coexistence with NETCONF ..................................13
    1.5. RESTCONF Extensibility ....................................14
 2. Transport Protocol .............................................15
    2.1. Integrity and Confidentiality .............................15
    2.2. HTTPS with X.509v3 Certificates ...........................16
    2.3. Certificate Validation ....................................16
    2.4. Authenticated Server Identity .............................16
    2.5. Authenticated Client Identity .............................16
 3. Resources ......................................................17
    3.1. Root Resource Discovery ...................................18
    3.2. RESTCONF Media Types ......................................20
    3.3. API Resource ..............................................20
         3.3.1. {+restconf}/data ...................................21
         3.3.2. {+restconf}/operations .............................22
         3.3.3. {+restconf}/yang-library-version ...................22
    3.4. Datastore Resource ........................................23
         3.4.1. Edit Collision Prevention ..........................23
    3.5. Data Resource .............................................24
         3.5.1. Timestamp ..........................................25
         3.5.2. Entity-Tag .........................................25
         3.5.3. Encoding Data Resource Identifiers in the
                Request URI ........................................26
         3.5.4. Default Handling ...................................29
    3.6. Operation Resource ........................................30
         3.6.1. Encoding Operation Resource Input Parameters .......31
         3.6.2. Encoding Operation Resource Output Parameters ......36
         3.6.3. Encoding Operation Resource Errors .................38
    3.7. Schema Resource ...........................................40
    3.8. Event Stream Resource .....................................41
    3.9. "errors" YANG Data Template ...............................41
 4. RESTCONF Methods ...............................................42
    4.1. OPTIONS ...................................................43
    4.2. HEAD ......................................................43
    4.3. GET .......................................................43
    4.4. POST ......................................................45

Bierman, et al. Standards Track [Page 2] RFC 8040 RESTCONF January 2017

         4.4.1. Create Resource Mode ...............................45
         4.4.2. Invoke Operation Mode ..............................47
    4.5. PUT .......................................................48
    4.6. PATCH .....................................................50
         4.6.1. Plain Patch ........................................50
    4.7. DELETE ....................................................51
    4.8. Query Parameters ..........................................52
         4.8.1. The "content" Query Parameter ......................54
         4.8.2. The "depth" Query Parameter ........................54
         4.8.3. The "fields" Query Parameter .......................55
         4.8.4. The "filter" Query Parameter .......................56
         4.8.5. The "insert" Query Parameter .......................57
         4.8.6. The "point" Query Parameter ........................57
         4.8.7. The "start-time" Query Parameter ...................58
         4.8.8. The "stop-time" Query Parameter ....................58
         4.8.9. The "with-defaults" Query Parameter ................59
 5. Messages .......................................................60
    5.1. Request URI Structure .....................................61
    5.2. Message Encoding ..........................................62
    5.3. RESTCONF Metadata .........................................63
         5.3.1. XML Metadata Encoding Example ......................64
         5.3.2. JSON Metadata Encoding Example .....................65
    5.4. Return Status .............................................65
    5.5. Message Caching ...........................................66
 6. Notifications ..................................................66
    6.1. Server Support ............................................66
    6.2. Event Streams .............................................67
    6.3. Subscribing to Receive Notifications ......................68
         6.3.1. NETCONF Event Stream ...............................70
    6.4. Receiving Event Notifications .............................70
 7. Error Reporting ................................................73
    7.1. Error Response Message ....................................75
 8. RESTCONF Module ................................................79
 9. RESTCONF Monitoring ............................................85
    9.1. restconf-state/capabilities ...............................86
         9.1.1. Query Parameter URIs ...............................87
         9.1.2. The "defaults" Protocol Capability URI .............87
    9.2. restconf-state/streams ....................................88
    9.3. RESTCONF Monitoring Module ................................89
 10. YANG Module Library ...........................................93
    10.1. modules-state/module .....................................93
 11. IANA Considerations ...........................................94
    11.1. The "restconf" Relation Type .............................94
    11.2. Registrations for New URIs and YANG Modules ..............94
    11.3. Media Types ..............................................95
         11.3.1. Media Type "application/yang-data+xml" ............95
         11.3.2. Media Type "application/yang-data+json" ...........96

Bierman, et al. Standards Track [Page 3] RFC 8040 RESTCONF January 2017

    11.4. RESTCONF Capability URNs .................................97
    11.5. Registration of "restconf" URN Sub-namespace .............98
 12. Security Considerations .......................................99
 13. References ...................................................100
    13.1. Normative References ....................................100
    13.2. Informative References ..................................104
 Appendix A. Example YANG Module ..................................105
   A.1. "example-jukebox" YANG Module .............................106
 Appendix B. RESTCONF Message Examples ............................112
   B.1. Resource Retrieval Examples ...............................112
     B.1.1. Retrieve the Top-Level API Resource ...................112
     B.1.2. Retrieve the Server Module Information ................114
     B.1.3. Retrieve the Server Capability Information ............117
   B.2. Data Resource and Datastore Resource Examples .............118
     B.2.1. Create New Data Resources .............................118
     B.2.2. Detect Datastore Resource Entity-Tag Change ...........119
     B.2.3. Edit a Datastore Resource .............................121
     B.2.4. Replace a Datastore Resource ..........................122
     B.2.5. Edit a Data Resource ..................................122
   B.3. Query Parameter Examples ..................................123
     B.3.1. "content" Parameter ...................................123
     B.3.2. "depth" Parameter .....................................126
     B.3.3. "fields" Parameter ....................................130
     B.3.4. "insert" Parameter ....................................132
     B.3.5. "point" Parameter .....................................133
     B.3.6. "filter" Parameter ....................................134
     B.3.7. "start-time" Parameter ................................134
     B.3.8. "stop-time" Parameter .................................135
     B.3.9. "with-defaults" Parameter .............................135
 Acknowledgements .................................................137
 Authors' Addresses ...............................................137

Bierman, et al. Standards Track [Page 4] RFC 8040 RESTCONF January 2017

1. Introduction

 There is a need for standard mechanisms to allow Web applications to
 access the configuration data, state data, data-model-specific Remote
 Procedure Call (RPC) operations, and event notifications within a
 networking device, in a modular and extensible manner.
 This document defines a protocol based on HTTP [RFC7230] called
 "RESTCONF", for configuring data defined in YANG version 1 [RFC6020]
 or YANG version 1.1 [RFC7950], using the datastore concepts defined
 in the Network Configuration Protocol (NETCONF) [RFC6241].
 NETCONF defines configuration datastores and a set of Create, Read,
 Update, Delete (CRUD) operations that can be used to access these
 datastores.  NETCONF also defines a protocol for invoking these
 operations.  The YANG language defines the syntax and semantics of
 datastore content, configuration, state data, RPC operations, and
 event notifications.
 RESTCONF uses HTTP methods to provide CRUD operations on a conceptual
 datastore containing YANG-defined data, which is compatible with a
 server that implements NETCONF datastores.
 If a RESTCONF server is co-located with a NETCONF server, then there
 are protocol interactions with the NETCONF protocol; these
 interactions are described in Section 1.4.  The RESTCONF server MAY
 provide access to specific datastores using operation resources, as
 described in Section 3.6.  The RESTCONF protocol does not specify any
 mandatory operation resources.  The semantics of each operation
 resource determine if and how datastores are accessed.
 Configuration data and state data are exposed as resources that can
 be retrieved with the GET method.  Resources representing
 configuration data can be modified with the DELETE, PATCH, POST, and
 PUT methods.  Data is encoded with either XML [W3C.REC-xml-20081126]
 or JSON [RFC7159].
 Data-model-specific RPC operations defined with the YANG "rpc" or
 "action" statements can be invoked with the POST method.  Data-model-
 specific event notifications defined with the YANG "notification"
 statement can be accessed.

1.1. Terminology

 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].

Bierman, et al. Standards Track [Page 5] RFC 8040 RESTCONF January 2017

1.1.1. NETCONF

 The following terms are defined in [RFC6241]:
 o  candidate configuration datastore
 o  configuration data
 o  datastore
 o  configuration datastore
 o  running configuration datastore
 o  startup configuration datastore
 o  state data
 o  user

1.1.2. HTTP

 The following terms are defined in [RFC3986]:
 o  fragment
 o  path
 o  query
 The following terms are defined in [RFC7230]:
 o  header field
 o  message-body
 o  request-line
 o  request URI
 o  status-line

Bierman, et al. Standards Track [Page 6] RFC 8040 RESTCONF January 2017

 The following terms are defined in [RFC7231]:
 o  method
 o  request
 o  resource
 The following term is defined in [RFC7232]:
 o  entity-tag

1.1.3. YANG

 The following terms are defined in [RFC7950]:
 o  action
 o  container
 o  data node
 o  key leaf
 o  leaf
 o  leaf-list
 o  list
 o  mandatory node
 o  ordered-by user
 o  presence container
 o  RPC operation
 o  top-level data node

1.1.4. NETCONF Notifications

 The following term is defined in [RFC5277]:
 o  notification replay

Bierman, et al. Standards Track [Page 7] RFC 8040 RESTCONF January 2017

1.1.5. Terms

 The following terms are used within this document:
 o  API resource: the resource that models the RESTCONF root resource
    and the sub-resources to access YANG-defined content.  It is
    defined with the YANG data template named "yang-api" in the
    "ietf-restconf" module.
 o  client: a RESTCONF client.
 o  data resource: a resource that models a YANG data node.  It is
    defined with YANG data definition statements.
 o  datastore resource: the resource that models a programmatic
    interface using NETCONF datastore concepts.  By default, RESTCONF
    methods access a unified view of the underlying datastore
    implementation on the server.  It is defined as a sub-resource
    within the API resource.
 o  edit operation: a RESTCONF operation on a data resource using
    either a POST, PUT, PATCH, or DELETE method.  This is not the same
    as the NETCONF edit operation (i.e., one of the values for the
    "nc:operation" attribute: "create", "replace", "merge", "delete",
    or "remove").
 o  event stream resource: a resource that represents an SSE
    (Server-Sent Events) event stream.  The content consists of text
    using the media type "text/event-stream", as defined by the SSE
    specification [W3C.REC-eventsource-20150203].  Event stream
    contents are described in Section 3.8.
 o  media type: HTTP uses Internet media types [RFC2046] in the
    "Content-Type" and "Accept" header fields in order to provide open
    and extensible data typing and type negotiation.
 o  NETCONF client: a client that implements the NETCONF protocol.
    Called "client" in [RFC6241].
 o  NETCONF server: a server that implements the NETCONF protocol.
    Called "server" in [RFC6241].
 o  operation: the conceptual RESTCONF operation for a message,
    derived from the HTTP method, request URI, header fields, and
    message-body.

Bierman, et al. Standards Track [Page 8] RFC 8040 RESTCONF January 2017

 o  operation resource: a resource that models a data-model-specific
    operation that is in turn defined with a YANG "rpc" or "action"
    statement.  It is invoked with the POST method.
 o  patch: a PATCH method on the target datastore or data resource.
    The media type of the message-body content will identify the patch
    type in use.
 o  plain patch: a specific media type for use with the PATCH method;
    see Section 4.6.1.  It can be used for simple "merge" edit
    operations.  It is specified by a request Content-Type of
    "application/yang-data+xml" or "application/yang-data+json".
 o  query parameter: a parameter (and its value, if any), encoded
    within the query component of the request URI.
 o  resource type: one of the RESTCONF resource classes defined in
    this document.  One of "api", "datastore", "data", "operation",
    "schema", or "event stream".
 o  RESTCONF capability: an optional RESTCONF protocol feature that is
    advertised by a particular server if the feature is supported on
    that server.  The feature is identified by an IANA-registered
    NETCONF Capability URI and advertised with an entry in the
    "capability" leaf-list defined in Section 9.3.
 o  RESTCONF client: a client that implements the RESTCONF protocol.
 o  RESTCONF server: a server that implements the RESTCONF protocol.
 o  retrieval request: a request using the GET or HEAD methods.
 o  schema resource: a resource that is used by the client to retrieve
    a YANG schema with the GET method.  It has a representation with
    the media type "application/yang".
 o  server: a RESTCONF server.
 o  "stream" list: the set of data resource instances that describe
    the event stream resources available from the server.  This
    information is defined in the "ietf-restconf-monitoring" module as
    the "stream" list.  It can be retrieved using the target resource
    "{+restconf}/data/ietf-restconf-monitoring:restconf-state/streams/
    stream".  The "stream" list contains information about each
    stream, such as the URL to retrieve the event stream data.
 o  stream resource: an event stream resource.

Bierman, et al. Standards Track [Page 9] RFC 8040 RESTCONF January 2017

 o  target resource: the resource that is associated with a particular
    message, identified by the "path" component of the request URI.
 o  yang-data extension: a YANG external statement that conforms to
    the "yang-data" extension statement, found in Section 8.  The
    yang-data extension is used to define YANG data structures that
    are meant to be used as YANG data templates.  These data
    structures are not intended to be implemented as part of a
    configuration datastore or as an operational state within the
    server, so normal YANG data definition statements cannot be used.
 o  YANG data template: a schema for modeling protocol message
    components as conceptual data structures using YANG.  This allows
    the messages to be defined in an encoding-independent manner.
    Each YANG data template is defined with the "yang-data" extension,
    found in Section 8.  Representations of instances conforming to a
    particular YANG data template can be defined for YANG.  The XML
    representation is defined in YANG version 1.1 [RFC7950] and
    supported with the "application/yang-data+xml" media type.  The
    JSON representation is defined in "JSON Encoding of Data Modeled
    with YANG" [RFC7951] and supported with the
    "application/yang-data+json" media type.

1.1.6. URI Template and Examples

 Throughout this document, the URI template [RFC6570] syntax
 "{+restconf}" is used to refer to the RESTCONF root resource outside
 of an example.  See Section 3.1 for details.
 For simplicity, all of the examples in this document use "/restconf"
 as the discovered RESTCONF API root path.  Many of the examples
 throughout the document are based on the "example-jukebox" YANG
 module defined in Appendix A.1.
 Many protocol header lines and message-body text within examples
 throughout the document are split into multiple lines for display
 purposes only.  When a line ends with a backslash ("\") as the last
 character, the line is wrapped for display purposes.  It is to be
 considered to be joined to the next line by deleting the backslash,
 the following line break, and the leading whitespace of the
 next line.

Bierman, et al. Standards Track [Page 10] RFC 8040 RESTCONF January 2017

1.1.7. Tree Diagrams

 A simplified graphical representation of the data model is used in
 this document.  The meanings of the symbols in these diagrams are as
 follows:
 o  Brackets "[" and "]" enclose list keys.
 o  Abbreviations before data node names: "rw" means configuration
    data (read-write), "ro" means state data (read-only), and "x"
    means operation resource (executable).
 o  Symbols after data node names: "?" means an optional node, "!"
    means a presence container, and "*" denotes a list and leaf-list.
 o  Parentheses enclose choice and case nodes, and case nodes are also
    marked with a colon (":").
 o  Ellipsis ("...") stands for contents of subtrees that are not
    shown.

1.2. Subset of NETCONF Functionality

 RESTCONF does not need to mirror the full functionality of the
 NETCONF protocol, but it does need to be compatible with NETCONF.
 RESTCONF achieves this by implementing a subset of the interaction
 capabilities provided by the NETCONF protocol -- for instance, by
 eliminating datastores and explicit locking.
 RESTCONF uses HTTP methods to implement the equivalent of NETCONF
 operations, enabling basic CRUD operations on a hierarchy of
 conceptual resources.
 The HTTP POST, PUT, PATCH, and DELETE methods are used to edit data
 resources represented by YANG data models.  These basic edit
 operations allow the running configuration to be altered by a
 RESTCONF client.
 RESTCONF is not intended to replace NETCONF, but rather to provide an
 HTTP interface that follows Representational State Transfer (REST)
 principles [REST-Dissertation] and is compatible with the NETCONF
 datastore model.

Bierman, et al. Standards Track [Page 11] RFC 8040 RESTCONF January 2017

1.3. Data-Model-Driven API

 RESTCONF combines the simplicity of HTTP with the predictability and
 automation potential of a schema-driven API.  Knowing the YANG
 modules used by the server, a client can derive all management
 resource URLs and the proper structure of all RESTCONF requests and
 responses.  This strategy obviates the need for responses provided by
 the server to contain Hypermedia as the Engine of Application State
 (HATEOAS) links, originally described in Roy Fielding's doctoral
 dissertation [REST-Dissertation], because the client can determine
 the links it needs from the YANG modules.
 RESTCONF utilizes the YANG library [RFC7895] to allow a client to
 discover the YANG module conformance information for the server, in
 case the client wants to use it.
 The server can optionally support the retrieval of the YANG modules
 it uses, as identified in its YANG library.  See Section 3.7 for
 details.
 The URIs for data-model-specific RPC operations and datastore content
 are predictable, based on the YANG module definitions.
 The RESTCONF protocol operates on a conceptual datastore defined with
 the YANG data modeling language.  The server lists each YANG module
 it supports using the "ietf-yang-library" YANG module defined in
 [RFC7895].  The server MUST implement the "ietf-yang-library" module,
 which MUST identify all of the YANG modules used by the server, in
 the "modules-state/module" list.  The conceptual datastore contents,
 data-model-specific RPC operations, and event notifications are
 identified by this set of YANG modules.
 The classification of data as configuration data or non-configuration
 data is derived from the YANG "config" statement.  Behavior related
 to the ordering of data is derived from the YANG "ordered-by"
 statement.  Non-configuration data is also called "state data".
 The RESTCONF datastore editing model is simple and direct, similar to
 the behavior of the :writable-running capability in NETCONF.  Each
 RESTCONF edit of a data resource within the datastore resource is
 activated upon successful completion of the edit.

Bierman, et al. Standards Track [Page 12] RFC 8040 RESTCONF January 2017

1.4. Coexistence with NETCONF

 RESTCONF can be implemented on a device that supports the NETCONF
 protocol.
 The following figure shows the system components if a RESTCONF server
 is co-located with a NETCONF server:
       +-----------+           +-----------------+
       |  Web app  | <-------> |                 |
       +-----------+  RESTCONF | network device  |
                               |                 |
       +-----------+           |   +-----------+ |
       | NETCONF   | <-------> |   | datastore | |
       | Client    |  NETCONF  |   |           | |
       +-----------+           |   +-----------+ |
                               +-----------------+
 The following figure shows the system components if a RESTCONF server
 is implemented in a device that does not have a NETCONF server:
       +-----------+           +-----------------+
       |  Web app  | <-------> |                 |
       +-----------+  RESTCONF | network device  |
                               |                 |
                               +-----------------+
 There are interactions between the NETCONF protocol and RESTCONF
 protocol related to edit operations.  It is possible that locks are
 in use on a RESTCONF server, even though RESTCONF cannot manipulate
 locks.  In such a case, the RESTCONF protocol will not be granted
 write access to data resources within a datastore.
 If the NETCONF server supports :writable-running, all edits to
 configuration nodes in {+restconf}/data are performed in the running
 configuration datastore.  The URI template "{+restconf}" is defined
 in Section 1.1.6.
 Otherwise, if the device supports :candidate, all edits to
 configuration nodes in {+restconf}/data are performed in the
 candidate configuration datastore.  The candidate MUST be
 automatically committed to running immediately after each successful
 edit.  Any edits from other sources that are in the candidate
 datastore will also be committed.  If a confirmed commit procedure is
 in progress by any NETCONF client, then any new commit will act as
 the confirming commit.  If the NETCONF server is expecting a

Bierman, et al. Standards Track [Page 13] RFC 8040 RESTCONF January 2017

 "persist-id" parameter to complete the confirmed commit procedure,
 then the RESTCONF edit operation MUST fail with a "409 Conflict"
 status-line.  The error-tag "in-use" is used in this case.
 If the NETCONF server supports :startup, the RESTCONF server MUST
 automatically update the non-volatile startup configuration
 datastore, after the "running" datastore has been altered as a
 consequence of a RESTCONF edit operation.
 If a datastore that would be modified by a RESTCONF operation has an
 active lock from a NETCONF client, the RESTCONF edit operation MUST
 fail with a "409 Conflict" status-line.  The error-tag value "in-use"
 is returned in this case.

1.5. RESTCONF Extensibility

 There are two extensibility mechanisms built into RESTCONF:
 o  protocol version
 o  optional capabilities
 This document defines version 1 of the RESTCONF protocol.  If a
 future version of this protocol is defined, then that document will
 specify how the new version of RESTCONF is identified.  It is
 expected that a different RESTCONF root resource will be used, which
 will be located using a different link relation (see Section 3.1).
 The server will advertise all protocol versions that it supports in
 its host-meta data.
 In this example, the server supports both RESTCONF version 1 and a
 fictitious version 2.
 The client might send the following:
    GET /.well-known/host-meta HTTP/1.1
    Host: example.com
    Accept: application/xrd+xml

Bierman, et al. Standards Track [Page 14] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 200 OK
    Content-Type: application/xrd+xml
    Content-Length: nnn
    <XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
        <Link rel='restconf' href='/restconf'/>
        <Link rel='restconf2' href='/restconf2'/>
    </XRD>
 RESTCONF also supports a server-defined list of optional
 capabilities, which are listed by a server using the
 "ietf-restconf-monitoring" module defined in Section 9.3.  This
 document defines several query parameters in Section 4.8.  Each
 optional parameter has a corresponding capability URI, defined in
 Section 9.1.1, that is advertised by the server if supported.
 The "capability" leaf-list can identify any sort of server extension.
 Currently, this extension mechanism is used to identify optional
 query parameters that are supported, but it is not limited to that
 purpose.  For example, the "defaults" URI defined in Section 9.1.2
 specifies a mandatory URI identifying server default-handling
 behavior.
 A new sub-resource type could be identified with a capability if it
 is optional to implement.  Mandatory protocol features and new
 resource types require a new revision of the RESTCONF protocol.

2. Transport Protocol

2.1. Integrity and Confidentiality

 HTTP [RFC7230] is an application-layer protocol that may be layered
 on any reliable transport-layer protocol.  RESTCONF is defined on top
 of HTTP, but due to the sensitive nature of the information conveyed,
 RESTCONF requires that the transport-layer protocol provide both data
 integrity and confidentiality.  A RESTCONF server MUST support the
 Transport Layer Security (TLS) protocol [RFC5246] and SHOULD adhere
 to [RFC7525].  The RESTCONF protocol MUST NOT be used over HTTP
 without using the TLS protocol.
 RESTCONF does not require a specific version of HTTP.  However, it is
 RECOMMENDED that at least HTTP/1.1 [RFC7230] be supported by all
 implementations.

Bierman, et al. Standards Track [Page 15] RFC 8040 RESTCONF January 2017

2.2. HTTPS with X.509v3 Certificates

 Given the nearly ubiquitous support for HTTP over TLS [RFC7230],
 RESTCONF implementations MUST support the "https" URI scheme, which
 has the IANA-assigned default port 443.
 RESTCONF servers MUST present an X.509v3-based certificate when
 establishing a TLS connection with a RESTCONF client.  The use of
 X.509v3-based certificates is consistent with NETCONF over TLS
 [RFC7589].

2.3. Certificate Validation

 The RESTCONF client MUST either (1) use X.509 certificate path
 validation [RFC5280] to verify the integrity of the RESTCONF server's
 TLS certificate or (2) match the server's TLS certificate with a
 certificate obtained by a trusted mechanism (e.g., a pinned
 certificate).  If X.509 certificate path validation fails and the
 presented X.509 certificate does not match a certificate obtained by
 a trusted mechanism, the connection MUST be terminated, as described
 in Section 7.2.1 of [RFC5246].

2.4. Authenticated Server Identity

 The RESTCONF client MUST check the identity of the server according
 to Section 3.1 of [RFC2818].

2.5. Authenticated Client Identity

 The RESTCONF server MUST authenticate client access to any protected
 resource.  If the RESTCONF client is not authenticated, the server
 SHOULD send an HTTP response with a "401 Unauthorized" status-line,
 as defined in Section 3.1 of [RFC7235].  The error-tag value
 "access-denied" is used in this case.
 To authenticate a client, a RESTCONF server SHOULD require
 authentication based on TLS client certificates (Section 7.4.6 of
 [RFC5246]).  If certificate-based authentication is not feasible
 (e.g., because one cannot build the required PKI for clients), then
 HTTP authentication MAY be used.  In the latter case, one of the HTTP
 authentication schemes defined in the "Hypertext Transfer Protocol
 (HTTP) Authentication Scheme Registry" (Section 5.1 in [RFC7235])
 MUST be used.
 A server MAY also support the combination of both client certificates
 and an HTTP client authentication scheme, with the determination of
 how to process this combination left as an implementation decision.

Bierman, et al. Standards Track [Page 16] RFC 8040 RESTCONF January 2017

 The RESTCONF client identity derived from the authentication
 mechanism used is hereafter known as the "RESTCONF username" and
 subject to the NETCONF Access Control Model (NACM) [RFC6536].  When a
 client certificate is presented, the RESTCONF username MUST be
 derived using the algorithm defined in Section 7 of [RFC7589].  For
 all other cases, when HTTP authentication is used, the RESTCONF
 username MUST be provided by the HTTP authentication scheme used.

3. Resources

 The RESTCONF protocol operates on a hierarchy of resources, starting
 with the top-level API resource itself (Section 3.1).  Each resource
 represents a manageable component within the device.
 A resource can be considered as a collection of data and the set of
 allowed methods on that data.  It can contain nested child resources.
 The child resource types and the methods allowed on them are specific
 to the data model.
 A resource has a representation associated with a media type
 identifier, as represented by the "Content-Type" header field in the
 HTTP response message.  A resource has one or more representations,
 each associated with a different media type.  When a representation
 of a resource is sent in an HTTP message, the associated media type
 is given in the "Content-Type" header.  A resource can contain zero
 or more nested resources.  A resource can be created and deleted
 independently of its parent resource, as long as the parent resource
 exists.
 The RESTCONF resources are accessed via a set of URIs defined in this
 document.  The set of YANG modules supported by the server will
 determine the data-model-specific RPC operations, top-level data
 nodes, and event notification messages supported by the server.
 The RESTCONF protocol does not include a data resource discovery
 mechanism.  Instead, the definitions within the YANG modules
 advertised by the server are used to construct an RPC operation or
 data resource identifier.

Bierman, et al. Standards Track [Page 17] RFC 8040 RESTCONF January 2017

3.1. Root Resource Discovery

 In line with the best practices defined by [RFC7320], RESTCONF
 enables deployments to specify where the RESTCONF API is located.
 When first connecting to a RESTCONF server, a RESTCONF client MUST
 determine the root of the RESTCONF API.  There MUST be exactly one
 "restconf" link relation returned by the device.
 The client discovers this by getting the "/.well-known/host-meta"
 resource ([RFC6415]) and using the <Link> element containing the
 "restconf" attribute:
 Example returning /restconf:
 The client might send the following:
    GET /.well-known/host-meta HTTP/1.1
    Host: example.com
    Accept: application/xrd+xml
 The server might respond as follows:
    HTTP/1.1 200 OK
    Content-Type: application/xrd+xml
    Content-Length: nnn
    <XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
        <Link rel='restconf' href='/restconf'/>
    </XRD>
 After discovering the RESTCONF API root, the client MUST use this
 value as the initial part of the path in the request URI, in any
 subsequent request for a RESTCONF resource.
 In this example, the client would use the path "/restconf" as the
 RESTCONF root resource.
 Example returning /top/restconf:
 The client might send the following:
    GET /.well-known/host-meta HTTP/1.1
    Host: example.com
    Accept: application/xrd+xml

Bierman, et al. Standards Track [Page 18] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 200 OK
    Content-Type: application/xrd+xml
    Content-Length: nnn
    <XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
        <Link rel='restconf' href='/top/restconf'/>
    </XRD>
 In this example, the client would use the path "/top/restconf" as the
 RESTCONF root resource.
 The client can now determine the operation resources supported by the
 server.  In this example, a custom "play" operation is supported:
 The client might send the following:
    GET /top/restconf/operations HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Last-Modified: Thu, 26 Jan 2017 16:00:14 GMT
    Content-Type: application/yang-data+json
    { "operations" : { "example-jukebox:play" : [null] } }
 If the Extensible Resource Descriptor (XRD) contains more than one
 link relation, then only the relation named "restconf" is relevant to
 this specification.
 Note that any given endpoint (host:port) can only support one
 RESTCONF server, due to the root resource discovery mechanism.  This
 limits the number of RESTCONF servers that can run concurrently on a
 host, since each server must use a different port.

Bierman, et al. Standards Track [Page 19] RFC 8040 RESTCONF January 2017

3.2. RESTCONF Media Types

 The RESTCONF protocol defines two application-specific media types to
 identify representations of data that conforms to the schema for a
 particular YANG construct.
 This document defines media types for XML and JSON serialization
 of YANG data.  Other documents MAY define other media types for
 different serializations of YANG data.  The
 "application/yang-data+xml" media type is defined in Section 11.3.1.
 The "application/yang-data+json" media type is defined in
 Section 11.3.2.

3.3. API Resource

 The API resource contains the RESTCONF root resource for the RESTCONF
 datastore and operation resources.  It is the top-level resource
 located at {+restconf} and has the media type
 "application/yang-data+xml" or "application/yang-data+json".
 YANG tree diagram for an API resource:
   +---- {+restconf}
         +---- data
         | ...
         +---- operations?
         | ...
         +--ro yang-library-version    string
 The "yang-api" YANG data template is defined using the "yang-data"
 extension in the "ietf-restconf" module, found in Section 8.  It
 specifies the structure and syntax of the conceptual child resources
 within the API resource.
 The API resource can be retrieved with the GET method.
 The {+restconf} root resource name used in responses representing the
 root of the "ietf-restconf" module MUST identify the "ietf-restconf"
 YANG module.  For example, a request to GET the root resource
 "/restconf" in JSON format will return a representation of the API
 resource named "ietf-restconf:restconf".

Bierman, et al. Standards Track [Page 20] RFC 8040 RESTCONF January 2017

 This resource has the following child resources:
      +----------------------+---------------------------------+
      | Child Resource       | Description                     |
      +----------------------+---------------------------------+
      | data                 | Contains all data resources     |
      | operations           | Data-model-specific operations  |
      | yang-library-version | "ietf-yang-library" module date |
      +----------------------+---------------------------------+
                         RESTCONF API Resource

3.3.1. {+restconf}/data

 This mandatory resource represents the combined configuration and
 state data resources that can be accessed by a client.  It cannot be
 created or deleted by the client.  The datastore resource type is
 defined in Section 3.4.
 Example:
 This example request by the client would retrieve only the
 non-configuration data nodes that exist within the "library"
 resource, using the "content" query parameter (see Section 4.8.1).
    GET /restconf/data/example-jukebox:jukebox/library\
        ?content=nonconfig HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+xml
    <library xmlns="https://example.com/ns/example-jukebox">
      <artist-count>42</artist-count>
      <album-count>59</album-count>
      <song-count>374</song-count>
    </library>

Bierman, et al. Standards Track [Page 21] RFC 8040 RESTCONF January 2017

3.3.2. {+restconf}/operations

 This optional resource is a container that provides access to the
 data-model-specific RPC operations supported by the server.  The
 server MAY omit this resource if no data-model-specific RPC
 operations are advertised.
 Any data-model-specific RPC operations defined in the YANG modules
 advertised by the server MUST be available as child nodes of this
 resource.
 The access point for each RPC operation is represented as an empty
 leaf.  If an operation resource is retrieved, the empty leaf
 representation is returned by the server.
 Operation resources are defined in Section 3.6.

3.3.3. {+restconf}/yang-library-version

 This mandatory leaf identifies the revision date of the
 "ietf-yang-library" YANG module that is implemented by this server.
 In the example that follows, the revision date for the module version
 found in [RFC7895] is used.
 Example:
    GET /restconf/yang-library-version HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+xml
    <yang-library-version
      xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">\
      2016-06-21\
    </yang-library-version>

Bierman, et al. Standards Track [Page 22] RFC 8040 RESTCONF January 2017

3.4. Datastore Resource

 The "{+restconf}/data" subtree represents the datastore resource,
 which is a collection of configuration data and state data nodes.
 This resource type is an abstraction of the system's underlying
 datastore implementation.  The client uses it to edit and retrieve
 data resources, as the conceptual root of all configuration and state
 data that is present on the device.
 Configuration edit transaction management and configuration
 persistence are handled by the server and not controlled by the
 client.  A datastore resource can be written directly with the POST
 and PATCH methods.  Each RESTCONF edit of a datastore resource is
 saved to non-volatile storage by the server if the server supports
 non-volatile storage of configuration data, as described in
 Section 1.4.
 If the datastore resource represented by the "{+restconf}/data"
 subtree is retrieved, then the datastore and its contents are
 returned by the server.  The datastore is represented by a node named
 "data" in the "ietf-restconf" module namespace.

3.4.1. Edit Collision Prevention

 Two edit collision detection and prevention mechanisms are provided
 in RESTCONF for the datastore resource: a timestamp and an
 entity-tag.  Any change to configuration data resources updates the
 timestamp and entity-tag of the datastore resource.  In addition, the
 RESTCONF server MUST return an error if the datastore is locked by an
 external source (e.g., NETCONF server).

3.4.1.1. Timestamp

 The last change time is maintained, and the "Last-Modified" header
 field (Section 2.2 of [RFC7232]) is returned in the response for a
 retrieval request.  The "If-Unmodified-Since" header field
 (Section 3.4 of [RFC7232]) can be used in edit operation requests to
 cause the server to reject the request if the resource has been
 modified since the specified timestamp.
 The server SHOULD maintain a last-modified timestamp for the
 datastore resource, defined in Section 3.4.  This timestamp is only
 affected by configuration child data resources and MUST NOT be
 updated for changes to non-configuration child data resources.
 Last-modified timestamps for data resources are discussed in
 Section 3.5.

Bierman, et al. Standards Track [Page 23] RFC 8040 RESTCONF January 2017

 If the RESTCONF server is co-located with a NETCONF server, then the
 last-modified timestamp MUST be for the "running" datastore.  Note
 that it is possible that other protocols can cause the last-modified
 timestamp to be updated.  Such mechanisms are out of scope for this
 document.

3.4.1.2. Entity-Tag

 The server MUST maintain a unique opaque entity-tag for the datastore
 resource and MUST return it in the "ETag" (Section 2.3 of [RFC7232])
 header in the response for a retrieval request.  The client MAY use
 an "If-Match" header in edit operation requests to cause the server
 to reject the request if the resource entity-tag does not match the
 specified value.
 The server MUST maintain an entity-tag for the top-level
 {+restconf}/data resource.  This entity-tag is only affected by
 configuration data resources and MUST NOT be updated for changes to
 non-configuration data.  Entity-tags for data resources are discussed
 in Section 3.5.  Note that each representation (e.g., XML vs. JSON)
 requires a different entity-tag.
 If the RESTCONF server is co-located with a NETCONF server, then this
 entity-tag MUST be for the "running" datastore.  Note that it is
 possible that other protocols can cause the entity-tag to be updated.
 Such mechanisms are out of scope for this document.

3.4.1.3. Update Procedure

 Changes to configuration data resources affect the timestamp and
 entity-tag for that resource, any ancestor data resources, and the
 datastore resource.
 For example, an edit to disable an interface might be done by setting
 the leaf "/interfaces/interface/enabled" to "false".  The "enabled"
 data node and its ancestors (one "interface" list instance, and the
 "interfaces" container) are considered to be changed.  The datastore
 is considered to be changed when any top-level configuration data
 node is changed (e.g., "interfaces").

3.5. Data Resource

 A data resource represents a YANG data node that is a descendant node
 of a datastore resource.  Each YANG-defined data node can be uniquely
 targeted by the request-line of an HTTP method.  Containers, leafs,
 leaf-list entries, list entries, anydata nodes, and anyxml nodes are
 data resources.

Bierman, et al. Standards Track [Page 24] RFC 8040 RESTCONF January 2017

 The representation maintained for each data resource is the
 YANG-defined subtree for that node.  HTTP methods on a data resource
 affect both the targeted data node and all of its descendants,
 if any.
 A data resource can be retrieved with the GET method.  Data resources
 are accessed via the "{+restconf}/data" URI.  This subtree is used to
 retrieve and edit data resources.

3.5.1. Timestamp

 For configuration data resources, the server MAY maintain a
 last-modified timestamp for the resource and return the
 "Last-Modified" header field when it is retrieved with the GET or
 HEAD methods.
 The "Last-Modified" header field can be used by a RESTCONF client in
 subsequent requests, within the "If-Modified-Since" and
 "If-Unmodified-Since" header fields.
 If maintained, the resource timestamp MUST be set to the current time
 whenever the resource or any configuration resource within the
 resource is altered.  If not maintained, then the resource timestamp
 for the datastore MUST be used instead.  If the RESTCONF server is
 co-located with a NETCONF server, then the last-modified timestamp
 for a configuration data resource MUST represent the instance within
 the "running" datastore.
 This timestamp is only affected by configuration data resources and
 MUST NOT be updated for changes to non-configuration data.

3.5.2. Entity-Tag

 For configuration data resources, the server SHOULD maintain a
 resource entity-tag for each resource and return the "ETag" header
 field when it is retrieved as the target resource with the GET or
 HEAD methods.  If maintained, the resource entity-tag MUST be updated
 whenever the resource or any configuration resource within the
 resource is altered.  If not maintained, then the resource entity-tag
 for the datastore MUST be used instead.
 The "ETag" header field can be used by a RESTCONF client in
 subsequent requests, within the "If-Match" and "If-None-Match" header
 fields.

Bierman, et al. Standards Track [Page 25] RFC 8040 RESTCONF January 2017

 This entity-tag is only affected by configuration data resources and
 MUST NOT be updated for changes to non-configuration data.  If the
 RESTCONF server is co-located with a NETCONF server, then the
 entity-tag for a configuration data resource MUST represent the
 instance within the "running" datastore.

3.5.3. Encoding Data Resource Identifiers in the Request URI

 In YANG, data nodes can be identified with an absolute XPath
 expression, defined in [XPath], starting from the document root to
 the target resource.  In RESTCONF, URI-encoded path expressions are
 used instead.
 A predictable location for a data resource is important, since
 applications will code to the YANG data model module, which uses
 static naming and defines an absolute path location for all data
 nodes.
 A RESTCONF data resource identifier is encoded from left to right,
 starting with the top-level data node, according to the "api-path"
 rule in Section 3.5.3.1.  The node name of each ancestor of the
 target resource node is encoded in order, ending with the node name
 for the target resource.  If a node in the path is defined in a
 module other than its parent node or its parent is the datastore,
 then the module name followed by a colon character (":") MUST be
 prepended to the node name in the resource identifier.  See
 Section 3.5.3.1 for details.
 If a data node in the path expression is a YANG leaf-list node, then
 the leaf-list value MUST be encoded according to the following rules:
 o  The identifier for the leaf-list MUST be encoded using one path
    segment [RFC3986].
 o  The path segment is constructed by having the leaf-list name,
    followed by an "=" character, followed by the leaf-list value
    (e.g., /restconf/data/top-leaflist=fred).
 o  The leaf-list value is specified as a string, using the canonical
    representation for the YANG data type.  Any reserved characters
    MUST be percent-encoded, according to Sections 2.1 and 2.5 of
    [RFC3986].

Bierman, et al. Standards Track [Page 26] RFC 8040 RESTCONF January 2017

 o  YANG 1.1 allows duplicate leaf-list values for non-configuration
    data.  In this case, there is no mechanism to specify the exact
    matching leaf-list instance.
 o  The comma (",") character is percent-encoded [RFC3986], even
    though multiple key values are not possible for a leaf-list.  This
    is more consistent and avoids special processing rules.
 If a data node in the path expression is a YANG list node, then the
 key values for the list (if any) MUST be encoded according to the
 following rules:
 o  The key leaf values for a data resource representing a YANG list
    MUST be encoded using one path segment [RFC3986].
 o  If there is only one key leaf value, the path segment is
    constructed by having the list name, followed by an "=" character,
    followed by the single key leaf value.
 o  If there are multiple key leaf values, the path segment is
    constructed by having the list name, followed by the value of each
    leaf identified in the "key" statement, encoded in the order
    specified in the YANG "key" statement.  Each key leaf value except
    the last one is followed by a comma character.
 o  The key value is specified as a string, using the canonical
    representation for the YANG data type.  Any reserved characters
    MUST be percent-encoded, according to Sections 2.1 and 2.5 of
    [RFC3986].  The comma (",") character MUST be percent-encoded if
    it is present in the key value.
 o  All of the components in the "key" statement MUST be encoded.
    Partial instance identifiers are not supported.
 o  Missing key values are not allowed, so two consecutive commas are
    interpreted as a comma, followed by a zero-length string, followed
    by a comma.  For example, "list1=foo,,baz" would be interpreted as
    a list named "list1" with three key values, and the second key
    value is a zero-length string.
 o  Note that non-configuration lists are not required to define keys.
    In this case, a single list instance cannot be accessed.
 o  The "list-instance" Augmented Backus-Naur Form (ABNF) [RFC5234]
    rule defined in Section 3.5.3.1 represents the syntax of a list
    instance identifier.

Bierman, et al. Standards Track [Page 27] RFC 8040 RESTCONF January 2017

 Examples:
    container top {
        list list1 {
            key "key1 key2 key3";
             ...
             list list2 {
                 key "key4 key5";
                 ...
                 leaf X { type string; }
             }
         }
         leaf-list Y {
           type uint32;
         }
     }
 For the above YANG definition, the container "top" is defined in the
 "example-top" YANG module, and a target resource URI for leaf "X"
 would be encoded as follows:
     /restconf/data/example-top:top/list1=key1,key2,key3/\
        list2=key4,key5/X
 For the above YANG definition, a target resource URI for
 leaf-list "Y" would be encoded as follows:
     /restconf/data/example-top:top/Y=instance-value
 The following example shows how reserved characters are
 percent-encoded within a key value.  The value of "key1" contains
 a comma, single-quote, double-quote, colon, double-quote, space,
 and forward slash (,'":" /).  Note that double-quote is not a
 reserved character and does not need to be percent-encoded.  The
 value of "key2" is the empty string, and the value of "key3" is the
 string "foo".
 Example URL:
    /restconf/data/example-top:top/list1=%2C%27"%3A"%20%2F,,foo

3.5.3.1. ABNF for Data Resource Identifiers

 The "api-path" ABNF [RFC5234] syntax is used to construct RESTCONF
 path identifiers.  Note that this syntax is used for all resources,
 and the API path starts with the RESTCONF root resource.  Data
 resources are required to be identified under the "{+restconf}/data"
 subtree.

Bierman, et al. Standards Track [Page 28] RFC 8040 RESTCONF January 2017

 An identifier is not allowed to start with the case-insensitive
 string "XML", according to YANG identifier rules.  The syntax for
 "api-identifier" and "key-value" MUST conform to the JSON identifier
 encoding rules in Section 4 of [RFC7951]: The RESTCONF root resource
 path is required.  Additional sub-resource identifiers are optional.
 The characters in a key value string are constrained, and some
 characters need to be percent-encoded, as described in Section 3.5.3.
 api-path = root *("/" (api-identifier / list-instance))
 root = string  ;; replacement string for {+restconf}
 api-identifier = [module-name ":"] identifier
 module-name = identifier
 list-instance = api-identifier "=" key-value *("," key-value)
 key-value = string  ;; constrained chars are percent-encoded
 string = <an unquoted string>
 identifier = (ALPHA / "_")
              *(ALPHA / DIGIT / "_" / "-" / ".")

3.5.4. Default Handling

 RESTCONF requires that a server report its default-handling mode (see
 Section 9.1.2 for details).  If the optional "with-defaults" query
 parameter is supported by the server, a client may use it to control
 the retrieval of default values (see Section 4.8.9 for details).
 If a leaf or leaf-list is missing from the configuration and there is
 a YANG-defined default for that data resource, then the server MUST
 use the YANG-defined default as the configured value.
 If the target of a GET method is a data node that represents a leaf
 or leaf-list that has a default value and the leaf or leaf-list has
 not been instantiated yet, the server MUST return the default value
 or values that are in use by the server.  In this case, the server
 MUST ignore its "basic-mode", described in Section 4.8.9, and return
 the default value.
 If the target of a GET method is a data node that represents a
 container or list that has any child resources with default values,
 for the child resources that have not been given values yet, the

Bierman, et al. Standards Track [Page 29] RFC 8040 RESTCONF January 2017

 server MAY return the default values that are in use by the server in
 accordance with its reported default-handling mode and query
 parameters passed by the client.

3.6. Operation Resource

 An operation resource represents an RPC operation defined with the
 YANG "rpc" statement or a data-model-specific action defined with a
 YANG "action" statement.  It is invoked using a POST method on the
 operation resource.
 An RPC operation is invoked as:
    POST {+restconf}/operations/<operation>
 The <operation> field identifies the module name and rpc identifier
 string for the desired operation.
 For example, if "module-A" defined a "reset" RPC operation, then
 invoking the operation would be requested as follows:
    POST /restconf/operations/module-A:reset HTTP/1.1
    Server: example.com
 An action is invoked as:
    POST {+restconf}/data/<data-resource-identifier>/<action>
 where <data-resource-identifier> contains the path to the data node
 where the action is defined, and <action> is the name of the action.
 For example, if "module-A" defined a "reset-all" action in the
 container "interfaces", then invoking this action would be requested
 as follows:
    POST /restconf/data/module-A:interfaces/reset-all HTTP/1.1
    Server: example.com
 If the RPC operation is invoked without errors and if the "rpc" or
 "action" statement has no "output" section, the response message
 MUST NOT include a message-body and MUST send a "204 No Content"
 status-line instead.
 All operation resources representing RPC operations supported by the
 server MUST be identified in the "{+restconf}/operations" subtree,
 defined in Section 3.3.2.  Operation resources representing YANG
 actions are not identified in this subtree, since they are invoked
 using a URI within the "{+restconf}/data" subtree.

Bierman, et al. Standards Track [Page 30] RFC 8040 RESTCONF January 2017

3.6.1. Encoding Operation Resource Input Parameters

 If the "rpc" or "action" statement has an "input" section, then
 instances of these input parameters are encoded in the module
 namespace where the "rpc" or "action" statement is defined, in an XML
 element or JSON object named "input", which is in the module
 namespace where the "rpc" or "action" statement is defined.
 If the "rpc" or "action" statement has an "input" section and the
 "input" object tree contains any child data nodes that are considered
 mandatory nodes, then a message-body MUST be sent by the client in
 the request.
 If the "rpc" or "action" statement has an "input" section and the
 "input" object tree does not contain any child nodes that are
 considered mandatory nodes, then a message-body MAY be sent by the
 client in the request.
 If the "rpc" or "action" statement has no "input" section, the
 request message MUST NOT include a message-body.
 Examples:
 The following YANG module is used for the RPC operation examples in
 this section.
 module example-ops {
   namespace "https://example.com/ns/example-ops";
   prefix "ops";
   organization "Example, Inc.";
   contact "support at example.com";
   description "Example Operations Data Model Module.";
   revision "2016-07-07" {
     description "Initial version.";
     reference "example.com document 3-3373.";
   }

Bierman, et al. Standards Track [Page 31] RFC 8040 RESTCONF January 2017

   rpc reboot {
     description "Reboot operation.";
     input {
       leaf delay {
         type uint32;
         units "seconds";
         default 0;
         description
           "Number of seconds to wait before initiating the
            reboot operation.";
       }
       leaf message {
         type string;
         description
           "Log message to display when reboot is started.";
       }
       leaf language {
         type string;
         description "Language identifier string.";
         reference "RFC 5646.";
       }
     }
   }

Bierman, et al. Standards Track [Page 32] RFC 8040 RESTCONF January 2017

   rpc get-reboot-info {
     description
       "Retrieve parameters used in the last reboot operation.";
     output {
       leaf reboot-time {
         type uint32;
         description
           "The 'delay' parameter used in the last reboot
            operation.";
       }
       leaf message {
         type string;
         description
           "The 'message' parameter used in the last reboot
            operation.";
       }
       leaf language {
         type string;
         description
           "The 'language' parameter used in the last reboot
            operation.";
       }
     }
   }
 }
 The following YANG module is used for the YANG action examples in
 this section.
 module example-actions {
   yang-version 1.1;
   namespace "https://example.com/ns/example-actions";
   prefix "act";
   import ietf-yang-types { prefix yang; }
   organization "Example, Inc.";
   contact "support at example.com";
   description "Example Actions Data Model Module.";
   revision "2016-07-07" {
     description "Initial version.";
     reference "example.com document 2-9973.";
   }

Bierman, et al. Standards Track [Page 33] RFC 8040 RESTCONF January 2017

   container interfaces {
     description "System interfaces.";
     list interface {
       key name;
       description "One interface entry.";
       leaf name {
         type string;
         description "Interface name.";
       }
       action reset {
         description "Reset an interface.";
         input {
           leaf delay {
             type uint32;
             units "seconds";
             default 0;
             description
               "Number of seconds to wait before starting the
                interface reset.";
           }
         }
       }
       action get-last-reset-time {
         description
           "Retrieve the last interface reset time.";
         output {
           leaf last-reset {
             type yang:date-and-time;
             mandatory true;
             description
               "Date and time of the last interface reset, or
                the last reboot time of the device.";
           }
         }
       }
     }
   }
 }

Bierman, et al. Standards Track [Page 34] RFC 8040 RESTCONF January 2017

 RPC Input Example:
 The client might send the following POST request message to invoke
 the "reboot" RPC operation:
    POST /restconf/operations/example-ops:reboot HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <input xmlns="https://example.com/ns/example-ops">
     <delay>600</delay>
     <message>Going down for system maintenance</message>
     <language>en-US</language>
    </input>
 The server might respond as follows:
    HTTP/1.1 204 No Content
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
 The same example request message is shown here using JSON encoding:
    POST /restconf/operations/example-ops:reboot HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    {
      "example-ops:input" : {
        "delay" : 600,
        "message" : "Going down for system maintenance",
        "language" : "en-US"
      }
    }
 Action Input Example:
 The client might send the following POST request message to invoke
 the "reset" action:
    POST /restconf/data/example-actions:interfaces/\
       interface=eth0/reset HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <input xmlns="https://example.com/ns/example-actions">
      <delay>600</delay>
    </input>

Bierman, et al. Standards Track [Page 35] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 204 No Content
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
 The same example request message is shown here using JSON encoding:
    POST /restconf/data/example-actions:interfaces/\
      interface=eth0/reset HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    { "example-actions:input" : {
        "delay" : 600
      }
    }

3.6.2. Encoding Operation Resource Output Parameters

 If the "rpc" or "action" statement has an "output" section, then
 instances of these output parameters are encoded in the module
 namespace where the "rpc" or "action" statement is defined, in an XML
 element or JSON object named "output", which is in the module
 namespace where the "rpc" or "action" statement is defined.
 If the RPC operation is invoked without errors, and if the "rpc" or
 "action" statement has an "output" section and the "output" object
 tree contains any child data nodes that are considered mandatory
 nodes, then a response message-body MUST be sent by the server in the
 response.
 If the RPC operation is invoked without errors, and if the "rpc" or
 "action" statement has an "output" section and the "output" object
 tree does not contain any child nodes that are considered mandatory
 nodes, then a response message-body MAY be sent by the server in the
 response.
 The request URI is not returned in the response.  Knowledge of the
 request URI may be needed to associate the output with the specific
 "rpc" or "action" statement used in the request.

Bierman, et al. Standards Track [Page 36] RFC 8040 RESTCONF January 2017

 Examples:
 RPC Output Example:
 The "example-ops" YANG module defined in Section 3.6.1 is used for
 this example.
 The client might send the following POST request message to invoke
 the "get-reboot-info" operation:
    POST /restconf/operations/example-ops:get-reboot-info HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "example-ops:output" : {
        "reboot-time" : 30,
        "message" : "Going down for system maintenance",
        "language" : "en-US"
      }
    }
 The same response is shown here using XML encoding:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+xml
    <output xmlns="https://example.com/ns/example-ops">
      <reboot-time>30</reboot-time>
      <message>Going down for system maintenance</message>
      <language>en-US</language>
    </output>

Bierman, et al. Standards Track [Page 37] RFC 8040 RESTCONF January 2017

 Action Output Example:
 The "example-actions" YANG module defined in Section 3.6.1 is used
 for this example.
 The client might send the following POST request message to invoke
 the "get-last-reset-time" action:
    POST /restconf/data/example-actions:interfaces/\
       interface=eth0/get-last-reset-time HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "example-actions:output" : {
        "last-reset" : "2015-10-10T02:14:11Z"
      }
    }

3.6.3. Encoding Operation Resource Errors

 If any errors occur while attempting to invoke the operation or
 action, then an "errors" media type is returned with the appropriate
 error status.
 If (1) the RPC operation input is not valid or (2) the RPC operation
 is invoked but errors occur, then a message-body containing an
 "errors" resource MUST be sent by the server, as defined in
 Section 3.9.

Bierman, et al. Standards Track [Page 38] RFC 8040 RESTCONF January 2017

 Using the "reboot" RPC operation from the example in Section 3.6.1,
 the client might send the following POST request message:
    POST /restconf/operations/example-ops:reboot HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <input xmlns="https://example.com/ns/example-ops">
      <delay>-33</delay>
      <message>Going down for system maintenance</message>
      <language>en-US</language>
    </input>
 The server might respond with an "invalid-value" error:
    HTTP/1.1 400 Bad Request
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+xml
    <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
      <error>
        <error-type>protocol</error-type>
        <error-tag>invalid-value</error-tag>
        <error-path xmlns:ops="https://example.com/ns/example-ops">
          /ops:input/ops:delay
        </error-path>
        <error-message>Invalid input parameter</error-message>
      </error>
    </errors>

Bierman, et al. Standards Track [Page 39] RFC 8040 RESTCONF January 2017

 The same response is shown here using JSON encoding:
    HTTP/1.1 400 Bad Request
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    { "ietf-restconf:errors" : {
        "error" : [
          {
            "error-type" : "protocol",
            "error-tag" : "invalid-value",
            "error-path" : "/example-ops:input/delay",
            "error-message" : "Invalid input parameter"
          }
        ]
      }
    }

3.7. Schema Resource

 The server can optionally support the retrieval of the YANG modules
 it uses.  If retrieval is supported, then the "schema" leaf MUST be
 present in the associated "module" list entry, defined in [RFC7895].
 To retrieve a YANG module, a client first needs to get the URL for
 retrieving the schema, which is stored in the "schema" leaf.  Note
 that there is no required structure for this URL.  The URL value
 shown below is just an example.
 The client might send the following GET request message:
    GET /restconf/data/ietf-yang-library:modules-state/\
        module=example-jukebox,2016-08-15/schema HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "ietf-yang-library:schema" :
       "https://example.com/mymodules/example-jukebox/2016-08-15"
    }

Bierman, et al. Standards Track [Page 40] RFC 8040 RESTCONF January 2017

 Next, the client needs to retrieve the actual YANG schema.
 The client might send the following GET request message:
    GET https://example.com/mymodules/example-jukebox/\
       2016-08-15 HTTP/1.1
    Host: example.com
    Accept: application/yang
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang
       // entire YANG module contents deleted for this example...

3.8. Event Stream Resource

 An event stream resource represents a source for system-generated
 event notifications.  Each stream is created and modified by the
 server only.  A client can retrieve a stream resource or initiate a
 long-poll server-sent event stream [W3C.REC-eventsource-20150203],
 using the procedure specified in Section 6.3.
 An event stream functions according to the "NETCONF Event
 Notifications" specification [RFC5277].  The available streams can be
 retrieved from the "stream" list, which specifies the syntax and
 semantics of the stream resources.

3.9. "errors" YANG Data Template

 The "errors" YANG data template models a collection of error
 information that is sent as the message-body in a server response
 message if an error occurs while processing a request message.  It is
 not considered as a resource type because no instances can be
 retrieved with a GET request.
 The "ietf-restconf" YANG module contains the "yang-errors" YANG data
 template, which specifies the syntax and semantics of an "errors"
 container within a RESTCONF response.  RESTCONF error-handling
 behavior is defined in Section 7.

Bierman, et al. Standards Track [Page 41] RFC 8040 RESTCONF January 2017

4. RESTCONF Methods

 The RESTCONF protocol uses HTTP methods to identify the CRUD
 operations requested for a particular resource.
 The following table shows how the RESTCONF operations relate to
 NETCONF protocol operations.
 +----------+-------------------------------------------------------+
 | RESTCONF | NETCONF                                               |
 +----------+-------------------------------------------------------+
 | OPTIONS  | none                                                  |
 |          |                                                       |
 | HEAD     | <get-config>, <get>                                   |
 |          |                                                       |
 | GET      | <get-config>, <get>                                   |
 |          |                                                       |
 | POST     | <edit-config> (nc:operation="create")                 |
 |          |                                                       |
 | POST     | invoke an RPC operation                               |
 |          |                                                       |
 | PUT      | <copy-config> (PUT on datastore)                      |
 |          |                                                       |
 | PUT      | <edit-config> (nc:operation="create/replace")         |
 |          |                                                       |
 | PATCH    | <edit-config> (nc:operation depends on PATCH content) |
 |          |                                                       |
 | DELETE   | <edit-config> (nc:operation="delete")                 |
 +----------+-------------------------------------------------------+
                       CRUD Methods in RESTCONF
 The "remove" edit operation attribute for the NETCONF <edit-config>
 RPC operation is not supported by the HTTP DELETE method.  The
 resource must exist or the DELETE method will fail.  The PATCH method
 is equivalent to a "merge" edit operation when using a plain patch
 (see Section 4.6.1); other media types may provide more granular
 control.
 Access control mechanisms are used to limit what CRUD operations can
 be used.  In particular, RESTCONF is compatible with the NETCONF
 Access Control Model (NACM) [RFC6536], as there is a specific mapping
 between RESTCONF and NETCONF operations.  The resource path needs to
 be converted internally by the server to the corresponding YANG
 instance identifier.  Using this information, the server can apply
 the NACM access control rules to RESTCONF messages.

Bierman, et al. Standards Track [Page 42] RFC 8040 RESTCONF January 2017

 The server MUST NOT allow any RESTCONF operation for any resources
 that the client is not authorized to access.
 The implementation of all methods (except PATCH [RFC5789]) is defined
 in [RFC7231].  This section defines the RESTCONF protocol usage for
 each HTTP method.

4.1. OPTIONS

 The OPTIONS method is sent by the client to discover which methods
 are supported by the server for a specific resource (e.g., GET, POST,
 DELETE).  The server MUST implement this method.
 The "Accept-Patch" header field MUST be supported and returned in the
 response to the OPTIONS request, as defined in [RFC5789].

4.2. HEAD

 The RESTCONF server MUST support the HEAD method.  The HEAD method is
 sent by the client to retrieve just the header fields (which contain
 the metadata for a resource) that would be returned for the
 comparable GET method, without the response message-body.  It is
 supported for all resources that support the GET method.
 The request MUST contain a request URI that contains at least the
 root resource.  The same query parameters supported by the GET method
 are supported by the HEAD method.
 The access control behavior is enforced as if the method was GET
 instead of HEAD.  The server MUST respond the same as if the method
 was GET instead of HEAD, except that no response message-body is
 included.

4.3. GET

 The RESTCONF server MUST support the GET method.  The GET method is
 sent by the client to retrieve data and metadata for a resource.  It
 is supported for all resource types, except operation resources.  The
 request MUST contain a request URI that contains at least the root
 resource.
 The server MUST NOT return any data resources for which the user does
 not have read privileges.  If the user is not authorized to read the
 target resource, an error response containing a "401 Unauthorized"
 status-line SHOULD be returned.  The error-tag value "access-denied"
 is returned in this case.  A server MAY return a "404 Not Found"
 status-line, as described in Section 6.5.4 in [RFC7231].  The
 error-tag value "invalid-value" is returned in this case.

Bierman, et al. Standards Track [Page 43] RFC 8040 RESTCONF January 2017

 If the user is authorized to read some but not all of the target
 resource, the unauthorized content is omitted from the response
 message-body, and the authorized content is returned to the client.
 If any content is returned to the client, then the server MUST send a
 valid response message-body.  More than one element MUST NOT be
 returned for XML encoding.  If multiple elements are sent in a JSON
 message-body, then they MUST be sent as a JSON array.  In this case,
 any timestamp or entity-tag returned in the response MUST be
 associated with the first element returned.
 If a retrieval request for a data resource representing a YANG
 leaf-list or list object identifies more than one instance and XML
 encoding is used in the response, then an error response containing a
 "400 Bad Request" status-line MUST be returned by the server.  The
 error-tag value "invalid-value" is used in this case.  Note that a
 non-configuration list is not required to define any keys.  In this
 case, the retrieval of a single list instance is not possible.
 If a retrieval request for a data resource represents an instance
 that does not exist, then an error response containing a "404 Not
 Found" status-line MUST be returned by the server.  The error-tag
 value "invalid-value" is used in this case.
 If the target resource of a retrieval request is for an operation
 resource, then a "405 Method Not Allowed" status-line MUST be
 returned by the server.  The error-tag value
 "operation-not-supported" is used in this case.
 Note that the way that access control is applied to data resources
 may not be completely compatible with HTTP caching.  The
 "Last-Modified" and "ETag" header fields maintained for a data
 resource are not affected by changes to the access control rules for
 that data resource.  It is possible for the representation of a data
 resource that is visible to a particular client to be changed without
 detection via the "Last-Modified" or "ETag" values.
 Example:
 The client might request the response header fields for an XML
 representation of a specific "album" resource:
    GET /restconf/data/example-jukebox:jukebox/\
       library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml

Bierman, et al. Standards Track [Page 44] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+xml
    Cache-Control: no-cache
    ETag: "a74eefc993a2b"
    Last-Modified: Thu, 26 Jan 2017 14:02:14 GMT
    <album xmlns="http://example.com/ns/example-jukebox"
           xmlns:jbox="http://example.com/ns/example-jukebox">
      <name>Wasting Light</name>
      <genre>jbox:alternative</genre>
      <year>2011</year>
    </album>
 Refer to Appendix B.1 for more resource retrieval examples.

4.4. POST

 The RESTCONF server MUST support the POST method.  The POST method is
 sent by the client to create a data resource or invoke an operation
 resource.  The server uses the target resource type to determine how
 to process the request.
    +-----------+------------------------------------------------+
    | Type      | Description                                    |
    +-----------+------------------------------------------------+
    | Datastore | Create a top-level configuration data resource |
    | Data      | Create a configuration data child resource     |
    | Operation | Invoke an RPC operation                        |
    +-----------+------------------------------------------------+
                   Resource Types That Support POST

4.4.1. Create Resource Mode

 If the target resource type is a datastore or data resource, then the
 POST is treated as a request to create a top-level resource or child
 resource, respectively.  The message-body is expected to contain the
 content of a child resource to create within the parent (target
 resource).  The message-body MUST contain exactly one instance of the
 expected data resource.  The data model for the child tree is the
 subtree, as defined by YANG for the child resource.

Bierman, et al. Standards Track [Page 45] RFC 8040 RESTCONF January 2017

 The "insert" (Section 4.8.5) and "point" (Section 4.8.6) query
 parameters MUST be supported by the POST method for datastore and
 data resources.  These parameters are only allowed if the list or
 leaf-list is "ordered-by user".
 If the POST method succeeds, a "201 Created" status-line is returned
 and there is no response message-body.  A "Location" header field
 identifying the child resource that was created MUST be present in
 the response in this case.
 If the data resource already exists, then the POST request MUST fail
 and a "409 Conflict" status-line MUST be returned.  The error-tag
 value "resource-denied" is used in this case.
 If the user is not authorized to create the target resource, an error
 response containing a "403 Forbidden" status-line SHOULD be returned.
 The error-tag value "access-denied" is used in this case.  A server
 MAY return a "404 Not Found" status-line, as described in
 Section 6.5.4 in [RFC7231].  The error-tag value "invalid-value" is
 used in this case.  All other error responses are handled according
 to the procedures defined in Section 7.
 Example:
 To create a new "jukebox" resource, the client might send the
 following:
    POST /restconf/data HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    { "example-jukebox:jukebox" : {} }
 If the resource is created, the server might respond as follows:
    HTTP/1.1 201 Created
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Location: https://example.com/restconf/data/\
        example-jukebox:jukebox
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    ETag: "b3a3e673be2"
 Refer to Appendix B.2.1 for more resource creation examples.

Bierman, et al. Standards Track [Page 46] RFC 8040 RESTCONF January 2017

4.4.2. Invoke Operation Mode

 If the target resource type is an operation resource, then the POST
 method is treated as a request to invoke that operation.  The
 message-body (if any) is processed as the operation input parameters.
 Refer to Section 3.6 for details on operation resources.
 If the POST request succeeds, a "200 OK" status-line is returned if
 there is a response message-body, and a "204 No Content" status-line
 is returned if there is no response message-body.
 If the user is not authorized to invoke the target operation, an
 error response containing a "403 Forbidden" status-line SHOULD be
 returned.  The error-tag value "access-denied" is used in this case.
 A server MAY return a "404 Not Found" status-line, as described in
 Section 6.5.4 in [RFC7231].  All other error responses are handled
 according to the procedures defined in Section 7.
 Example:
 In this example, the client is invoking the "play" operation defined
 in the "example-jukebox" YANG module.
 A client might send a "play" request as follows:
    POST /restconf/operations/example-jukebox:play HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    {
      "example-jukebox:input" : {
        "playlist" : "Foo-One",
        "song-number" : 2
      }
    }
 The server might respond as follows:
    HTTP/1.1 204 No Content
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server

Bierman, et al. Standards Track [Page 47] RFC 8040 RESTCONF January 2017

4.5. PUT

 The RESTCONF server MUST support the PUT method.  The PUT method is
 sent by the client to create or replace the target data resource.  A
 request message-body MUST be present, representing the new data
 resource, or the server MUST return a "400 Bad Request" status-line.
 The error-tag value "invalid-value" is used in this case.
 Both the POST and PUT methods can be used to create data resources.
 The difference is that for POST, the client does not provide the
 resource identifier for the resource that will be created.  The
 target resource for the POST method for resource creation is the
 parent of the new resource.  The target resource for the PUT method
 for resource creation is the new resource.
 The PUT method MUST be supported for data and datastore resources.  A
 PUT on the datastore resource is used to replace the entire contents
 of the datastore.  A PUT on a data resource only replaces that data
 resource within the datastore.
 The "insert" (Section 4.8.5) and "point" (Section 4.8.6) query
 parameters MUST be supported by the PUT method for data resources.
 These parameters are only allowed if the list or leaf-list is
 "ordered-by user".
 Consistent with [RFC7231], if the PUT request creates a new resource,
 a "201 Created" status-line is returned.  If an existing resource is
 modified, a "204 No Content" status-line is returned.
 If the user is not authorized to create or replace the target
 resource, an error response containing a "403 Forbidden" status-line
 SHOULD be returned.  The error-tag value "access-denied" is used in
 this case.
 A server MAY return a "404 Not Found" status-line, as described in
 Section 6.5.4 in [RFC7231].  The error-tag value "invalid-value" is
 used in this case.  All other error responses are handled according
 to the procedures defined in Section 7.
 If the target resource represents a YANG leaf-list, then the PUT
 method MUST NOT change the value of the leaf-list instance.
 If the target resource represents a YANG list instance, then the key
 leaf values, in message-body representation, MUST be the same as the
 key leaf values in the request URI.  The PUT method MUST NOT be used
 to change the key leaf values for a data resource instance.

Bierman, et al. Standards Track [Page 48] RFC 8040 RESTCONF January 2017

 Example:
 An "album" child resource defined in the "example-jukebox" YANG
 module is replaced, or it is created if it does not already exist.
 To replace the "album" resource contents, the client might send the
 following:
    PUT /restconf/data/example-jukebox:jukebox/\
        library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    {
      "example-jukebox:album" : [
        {
          "name" : "Wasting Light",
          "genre" : "example-jukebox:alternative",
          "year" : 2011
        }
      ]
    }
 If the resource is updated, the server might respond as follows:
    HTTP/1.1 204 No Content
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    ETag: "b27480aeda4c"
 The same request is shown here using XML encoding:
    PUT /restconf/data/example-jukebox:jukebox/\
        library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <album xmlns="http://example.com/ns/example-jukebox"
           xmlns:jbox="http://example.com/ns/example-jukebox">
      <name>Wasting Light</name>
      <genre>jbox:alternative</genre>
      <year>2011</year>
    </album>
 Refer to Appendix B.2.4 for an example using the PUT method to
 replace the contents of the datastore resource.

Bierman, et al. Standards Track [Page 49] RFC 8040 RESTCONF January 2017

4.6. PATCH

 The RESTCONF server MUST support the PATCH method for a plain patch
 and MAY support additional media types.  The media types for the
 PATCH method supported by the server can be discovered by the client
 by sending an OPTIONS request and examining the "Accept-Patch" header
 field in the response (see Section 4.1).
 RESTCONF uses the HTTP PATCH method defined in [RFC5789] to provide
 an extensible framework for resource patching mechanisms.  Each patch
 mechanism needs a unique media type.
 This document defines one patch mechanism (Section 4.6.1).  Another
 patch mechanism, the YANG Patch mechanism, is defined in
 [YANG-Patch].  Other patch mechanisms may be defined by future
 specifications.
 If the target resource instance does not exist, the server MUST NOT
 create it.
 If the PATCH request succeeds, a "200 OK" status-line is returned if
 there is a message-body, and "204 No Content" is returned if no
 response message-body is sent.
 If the user is not authorized to alter the target resource, an error
 response containing a "403 Forbidden" status-line SHOULD be returned.
 A server MAY return a "404 Not Found" status-line, as described in
 Section 6.5.4 in [RFC7231].  The error-tag value "invalid-value" is
 used in this case.  All other error responses are handled according
 to the procedures defined in Section 7.

4.6.1. Plain Patch

 The plain patch mechanism merges the contents of the message-body
 with the target resource.  The message-body for a plain patch MUST be
 present and MUST be represented by the media type
 "application/yang-data+xml" or "application/yang-data+json".
 Plain patch can be used to create or update, but not delete, a child
 resource within the target resource.  Please see [YANG-Patch] for an
 alternate media type supporting the ability to delete child
 resources.  The YANG Patch media type allows multiple suboperations
 (e.g., "merge", "delete") within a single PATCH method.
 If the target resource represents a YANG leaf-list, then the PATCH
 method MUST NOT change the value of the leaf-list instance.

Bierman, et al. Standards Track [Page 50] RFC 8040 RESTCONF January 2017

 If the target resource represents a YANG list instance, then the key
 leaf values, in message-body representation, MUST be the same as the
 key leaf values in the request URI.  The PATCH method MUST NOT be
 used to change the key leaf values for a data resource instance.
 After the plain patch is processed by the server, a response will be
 returned to the client, as specified in Section 4.6.
 Example:
 To replace just the "year" field in the "album" resource (instead of
 replacing the entire resource with the PUT method), the client might
 send a plain patch as follows:
    PATCH /restconf/data/example-jukebox:jukebox/\
        library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
    Host: example.com
    If-Match: "b8389233a4c"
    Content-Type: application/yang-data+xml
    <album xmlns="http://example.com/ns/example-jukebox">
     <year>2011</year>
    </album>
 If the field is updated, the server might respond as follows:
    HTTP/1.1 204 No Content
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    ETag: "b2788923da4c"

4.7. DELETE

 The RESTCONF server MUST support the DELETE method.  The DELETE
 method is used to delete the target resource.  If the DELETE request
 succeeds, a "204 No Content" status-line is returned.
 If the user is not authorized to delete the target resource, then an
 error response containing a "403 Forbidden" status-line SHOULD be
 returned.  The error-tag value "access-denied" is returned in this
 case.  A server MAY return a "404 Not Found" status-line, as
 described in Section 6.5.4 in [RFC7231].  The error-tag value
 "invalid-value" is returned in this case.  All other error responses
 are handled according to the procedures defined in Section 7.

Bierman, et al. Standards Track [Page 51] RFC 8040 RESTCONF January 2017

 If the target resource represents a configuration leaf-list or list
 data node, then it MUST represent a single YANG leaf-list or list
 instance.  The server MUST NOT use the DELETE method to delete more
 than one such instance.
 Example:
 To delete the "album" resource with the key "Wasting Light", the
 client might send the following:
    DELETE /restconf/data/example-jukebox:jukebox/\
        library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
    Host: example.com
 If the resource is deleted, the server might respond as follows:
    HTTP/1.1 204 No Content
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server

4.8. Query Parameters

 Each RESTCONF operation allows zero or more query parameters to be
 present in the request URI.  Which specific parameters are allowed
 will depend on the resource type, and sometimes the specific target
 resource used, in the request.
 o  Query parameters can be given in any order.
 o  Each parameter can appear at most once in a request URI.
 o  If more than one instance of a query parameter is present, then a
    "400 Bad Request" status-line MUST be returned by the server.  The
    error-tag value "invalid-value" is returned in this case.
 o  A default value may apply if the parameter is missing.
 o  Query parameter names and values are case sensitive.
 o  A server MUST return an error with a "400 Bad Request" status-line
    if a query parameter is unexpected.  The error-tag value
    "invalid-value" is returned in this case.

Bierman, et al. Standards Track [Page 52] RFC 8040 RESTCONF January 2017

 +---------------+---------+-----------------------------------------+
 | Name          | Methods | Description                             |
 +---------------+---------+-----------------------------------------+
 | content       | GET,    | Select config and/or non-config data    |
 |               | HEAD    | resources                               |
 |               |         |                                         |
 | depth         | GET,    | Request limited subtree depth in the    |
 |               | HEAD    | reply content                           |
 |               |         |                                         |
 | fields        | GET,    | Request a subset of the target resource |
 |               | HEAD    | contents                                |
 |               |         |                                         |
 | filter        | GET,    | Boolean notification filter for event   |
 |               | HEAD    | stream resources                        |
 |               |         |                                         |
 | insert        | POST,   | Insertion mode for "ordered-by user"    |
 |               | PUT     | data resources                          |
 |               |         |                                         |
 | point         | POST,   | Insertion point for "ordered-by user"   |
 |               | PUT     | data resources                          |
 |               |         |                                         |
 | start-time    | GET,    | Replay buffer start time for event      |
 |               | HEAD    | stream resources                        |
 |               |         |                                         |
 | stop-time     | GET,    | Replay buffer stop time for event       |
 |               | HEAD    | stream resources                        |
 |               |         |                                         |
 | with-defaults | GET,    | Control the retrieval of default values |
 |               | HEAD    |                                         |
 +---------------+---------+-----------------------------------------+
                       RESTCONF Query Parameters
 Refer to Appendix B.3 for examples of query parameter usage.
 If vendors define additional query parameters, they SHOULD use a
 prefix (such as the enterprise or organization name) for query
 parameter names in order to avoid collisions with other parameters.

Bierman, et al. Standards Track [Page 53] RFC 8040 RESTCONF January 2017

4.8.1. The "content" Query Parameter

 The "content" query parameter controls how descendant nodes of the
 requested data nodes will be processed in the reply.
 The allowed values are:
  +-----------+-----------------------------------------------------+
  | Value     | Description                                         |
  +-----------+-----------------------------------------------------+
  | config    | Return only configuration descendant data nodes     |
  |           |                                                     |
  | nonconfig | Return only non-configuration descendant data nodes |
  |           |                                                     |
  | all       | Return all descendant data nodes                    |
  +-----------+-----------------------------------------------------+
 This parameter is only allowed for GET methods on datastore and data
 resources.  A "400 Bad Request" status-line is returned if used for
 other methods or resource types.
 If this query parameter is not present, the default value is "all".
 This query parameter MUST be supported by the server.

4.8.2. The "depth" Query Parameter

 The "depth" query parameter is used to limit the depth of subtrees
 returned by the server.  Data nodes with a "depth" value greater than
 the "depth" parameter are not returned in a response for a GET
 method.
 The requested data node has a depth level of "1".  If the "fields"
 parameter (Section 4.8.3) is used to select descendant data nodes,
 then these nodes and all of their ancestor nodes have a "depth" value
 of "1".  (This has the effect of including the nodes specified by the
 fields, even if the "depth" value is less than the actual depth level
 of the specified fields.)  Any other child node has a "depth" value
 that is 1 greater than its parent.
 The value of the "depth" parameter is either an integer between 1 and
 65535 or the string "unbounded".  "unbounded" is the default.
 This parameter is only allowed for GET methods on API, datastore, and
 data resources.  A "400 Bad Request" status-line is returned if used
 for other methods or resource types.

Bierman, et al. Standards Track [Page 54] RFC 8040 RESTCONF January 2017

 By default, the server will include all sub-resources within a
 retrieved resource that have the same resource type as the requested
 resource.  The exception is the datastore resource.  If this resource
 type is retrieved, then by default the datastore and all child data
 resources are returned.
 If the "depth" query parameter URI is listed in the "capability"
 leaf-list defined in Section 9.3, then the server supports the
 "depth" query parameter.

4.8.3. The "fields" Query Parameter

 The "fields" query parameter is used to optionally identify data
 nodes within the target resource to be retrieved in a GET method.
 The client can use this parameter to retrieve a subset of all nodes
 in a resource.
 The server will return a message-body representing the target
 resource, with descendant nodes pruned as specified in the
 "fields-expr" value.  The server does not return a set of separate
 sub-resources.
 A value of the "fields" query parameter matches the following rule:
  fields-expr = path "(" fields-expr ")" / path ";" fields-expr / path
  path = api-identifier [ "/" path ]
 "api-identifier" is defined in Section 3.5.3.1.
 ";" is used to select multiple nodes.  For example, to retrieve only
 the "genre" and "year" of an album, use "fields=genre;year".
 Parentheses are used to specify sub-selectors of a node.  Note that
 there is no path separator character "/" between a "path" field and a
 left parenthesis character "(".
 For example, assume that the target resource is the "album" list.  To
 retrieve only the "label" and "catalogue-number" of the "admin"
 container within an album, use
 "fields=admin(label;catalogue-number)".
 "/" is used in a path to retrieve a child node of a node.  For
 example, to retrieve only the "label" of an album, use
 "fields=admin/label".
 This parameter is only allowed for GET methods on API, datastore, and
 data resources.  A "400 Bad Request" status-line is returned if used
 for other methods or resource types.

Bierman, et al. Standards Track [Page 55] RFC 8040 RESTCONF January 2017

 If the "fields" query parameter URI is listed in the "capability"
 leaf-list defined in Section 9.3, then the server supports the
 "fields" parameter.

4.8.4. The "filter" Query Parameter

 The "filter" query parameter is used to indicate which subset of all
 possible events is of interest.  If not present, all events not
 precluded by other parameters will be sent.
 This parameter is only allowed for GET methods on an event stream
 resource.  A "400 Bad Request" status-line is returned if used for
 other methods or resource types.
 The format of this parameter is an XPath 1.0 expression [XPath] and
 is evaluated in the following context:
 o  The set of namespace declarations is the set of prefix and
    namespace pairs for all supported YANG modules, where the prefix
    is the YANG module name and the namespace is as defined by the
    "namespace" statement in the YANG module.
 o  The function library is the core function library defined in
    XPath 1.0, plus any functions defined by the data model.
 o  The set of variable bindings is empty.
 o  The context node is the root node.
 The "filter" query parameter is used as defined in Section 3.6 of
 [RFC5277].  If the boolean result of the expression is "true" when
 applied to the conceptual "notification" document root, then the
 event notification is delivered to the client.
 If the "filter" query parameter URI is listed in the "capability"
 leaf-list defined in Section 9.3, then the server supports the
 "filter" query parameter.

Bierman, et al. Standards Track [Page 56] RFC 8040 RESTCONF January 2017

4.8.5. The "insert" Query Parameter

 The "insert" query parameter is used to specify how a resource should
 be inserted within an "ordered-by user" list.
 The allowed values are:
 +--------+----------------------------------------------------------+
 | Value  | Description                                              |
 +--------+----------------------------------------------------------+
 | first  | Insert the new data as the new first entry.              |
 |        |                                                          |
 | last   | Insert the new data as the new last entry.               |
 |        |                                                          |
 | before | Insert the new data before the insertion point, as       |
 |        | specified by the value of the "point" parameter.         |
 |        |                                                          |
 | after  | Insert the new data after the insertion point, as        |
 |        | specified by the value of the "point" parameter.         |
 +--------+----------------------------------------------------------+
 The default value is "last".
 This parameter is only supported for the POST and PUT methods.  It is
 also only supported if the target resource is a data resource, and
 that data represents a YANG list or leaf-list that is
 "ordered-by user".
 If the values "before" or "after" are used, then a "point" query
 parameter for the "insert" query parameter MUST also be present, or a
 "400 Bad Request" status-line is returned.
 The "insert" query parameter MUST be supported by the server.

4.8.6. The "point" Query Parameter

 The "point" query parameter is used to specify the insertion point
 for a data resource that is being created or moved within an
 "ordered-by user" list or leaf-list.
 The value of the "point" parameter is a string that identifies the
 path to the insertion point object.  The format is the same as a
 target resource URI string.
 This parameter is only supported for the POST and PUT methods.  It is
 also only supported if the target resource is a data resource, and
 that data represents a YANG list or leaf-list that is
 "ordered-by user".

Bierman, et al. Standards Track [Page 57] RFC 8040 RESTCONF January 2017

 If the "insert" query parameter is not present or has a value other
 than "before" or "after", then a "400 Bad Request" status-line is
 returned.
 This parameter contains the instance identifier of the resource to be
 used as the insertion point for a POST or PUT method.
 The "point" query parameter MUST be supported by the server.

4.8.7. The "start-time" Query Parameter

 The "start-time" query parameter is used to trigger the notification
 replay feature defined in [RFC5277] and indicate that the replay
 should start at the time specified.  If the stream does not support
 replay per the "replay-support" attribute returned by the
 "stream" list entry for the stream resource, then the server MUST
 return a "400 Bad Request" status-line.
 The value of the "start-time" parameter is of type "date-and-time",
 defined in the "ietf-yang-types" YANG module [RFC6991].
 This parameter is only allowed for GET methods on a
 "text/event-stream" data resource.  A "400 Bad Request" status-line
 is returned if used for other methods or resource types.
 If this parameter is not present, then a replay subscription is not
 being requested.  It is not valid to specify start times that are
 later than the current time.  If the value specified is earlier than
 the log can support, the replay will begin with the earliest
 available notification.  A client can obtain a server's current time
 by examining the "Date" header field that the server returns in
 response messages, according to [RFC7231].
 If this query parameter is supported by the server, then the "replay"
 query parameter URI MUST be listed in the "capability" leaf-list
 defined in Section 9.3, and the "stop-time" query parameter MUST also
 be supported by the server.
 If the "replay-support" leaf has the value "true" in the "stream"
 entry (defined in Section 9.3), then the server MUST support the
 "start-time" and "stop-time" query parameters for that stream.

4.8.8. The "stop-time" Query Parameter

 The "stop-time" query parameter is used with the replay feature to
 indicate the newest notifications of interest.  This parameter MUST
 be used with, and have a value later than, the "start-time"
 parameter.

Bierman, et al. Standards Track [Page 58] RFC 8040 RESTCONF January 2017

 The value of the "stop-time" parameter is of type "date-and-time",
 defined in the "ietf-yang-types" YANG module [RFC6991].
 This parameter is only allowed for GET methods on a
 "text/event-stream" data resource.  A "400 Bad Request" status-line
 is returned if used for other methods or resource types.
 If this parameter is not present, the notifications will continue
 until the subscription is terminated.  Values in the future are
 valid.
 If this query parameter is supported by the server, then the "replay"
 query parameter URI MUST be listed in the "capability" leaf-list
 defined in Section 9.3, and the "start-time" query parameter MUST
 also be supported by the server.
 If the "replay-support" leaf is present in the "stream" entry
 (defined in Section 9.3), then the server MUST support the
 "start-time" and "stop-time" query parameters for that stream.

4.8.9. The "with-defaults" Query Parameter

 The "with-defaults" query parameter is used to specify how
 information about default data nodes should be returned in response
 to GET requests on data resources.
 If the server supports this capability, then it MUST implement the
 behavior described in Section 4.5.1 of [RFC6243], except applied to
 the RESTCONF GET operation instead of the NETCONF operations.
 +-------------------+-----------------------------------------------+
 | Value             | Description                                   |
 +-------------------+-----------------------------------------------+
 | report-all        | All data nodes are reported                   |
 |                   |                                               |
 | trim              | Data nodes set to the YANG default are not    |
 |                   | reported                                      |
 |                   |                                               |
 | explicit          | Data nodes set to the YANG default by the     |
 |                   | client are reported                           |
 |                   |                                               |
 | report-all-tagged | All data nodes are reported, and defaults are |
 |                   | tagged                                        |
 +-------------------+-----------------------------------------------+
 If the "with-defaults" parameter is set to "report-all", then the
 server MUST adhere to the default-reporting behavior defined in
 Section 3.1 of [RFC6243].

Bierman, et al. Standards Track [Page 59] RFC 8040 RESTCONF January 2017

 If the "with-defaults" parameter is set to "trim", then the server
 MUST adhere to the default-reporting behavior defined in Section 3.2
 of [RFC6243].
 If the "with-defaults" parameter is set to "explicit", then the
 server MUST adhere to the default-reporting behavior defined in
 Section 3.3 of [RFC6243].
 If the "with-defaults" parameter is set to "report-all-tagged", then
 the server MUST adhere to the default-reporting behavior defined in
 Section 3.4 of [RFC6243].  Metadata is reported by the server as
 specified in Section 5.3.  The XML encoding for the "default"
 attribute sent by the server for default nodes is defined in
 Section 6 of [RFC6243].  The JSON encoding for the "default"
 attribute MUST use the same values, as defined in [RFC6243], but
 encoded according to the rules in [RFC7952].  The module name
 "ietf-netconf-with-defaults" MUST be used for the "default"
 attribute.
 If the "with-defaults" parameter is not present, then the server MUST
 adhere to the default-reporting behavior defined in its "basic-mode"
 parameter for the "defaults" protocol capability URI, defined in
 Section 9.1.2.
 If the server includes the "with-defaults" query parameter URI in the
 "capability" leaf-list defined in Section 9.3, then the
 "with-defaults" query parameter MUST be supported.
 Since the server does not report the "also-supported" parameter as
 described in Section 4.3 of [RFC6243], it is possible that some
 values for the "with-defaults" parameter will not be supported.  If
 the server does not support the requested value of the
 "with-defaults" parameter, the server MUST return a response with a
 "400 Bad Request" status-line.  The error-tag value "invalid-value"
 is used in this case.

5. Messages

 The RESTCONF protocol uses HTTP messages.  A single HTTP message
 corresponds to a single protocol method.  Most messages can perform a
 single task on a single resource, such as retrieving a resource or
 editing a resource.  The exception is the PATCH method, which allows
 multiple datastore edits within a single message.

Bierman, et al. Standards Track [Page 60] RFC 8040 RESTCONF January 2017

5.1. Request URI Structure

 Resources are represented with URIs following the structure for
 generic URIs in [RFC3986].
 A RESTCONF operation is derived from the HTTP method and the request
 URI, using the following conceptual fields:
      <OP> /<restconf>/<path>?<query>
        ^       ^        ^       ^
        |       |        |       |
      method  entry  resource  query
        M       M        O        O
     M=mandatory, O=optional
     where:
       <OP> is the HTTP method
       <restconf> is the RESTCONF root resource
       <path> is the target resource URI
       <query> is the query parameter list
 o  method: the HTTP method identifying the RESTCONF operation
    requested by the client, to act upon the target resource specified
    in the request URI.  RESTCONF operation details are described in
    Section 4.
 o  entry: the root of the RESTCONF API configured on this HTTP
    server, discovered by getting the "/.well-known/host-meta"
    resource, as described in Section 3.1.
 o  resource: the path expression identifying the resource that is
    being accessed by the RESTCONF operation.  If this field is not
    present, then the target resource is the API itself, represented
    by the YANG data template named "yang-api", found in Section 8.
 o  query: the set of parameters associated with the RESTCONF message;
    see Section 3.4 of [RFC3986].  RESTCONF parameters have the
    familiar form of "name=value" pairs.  Most query parameters are
    optional to implement by the server and optional to use by the
    client.  Each optional query parameter is identified by a URI.
    The server MUST list the optional query parameter URIs it supports
    in the "capability" leaf-list defined in Section 9.3.

Bierman, et al. Standards Track [Page 61] RFC 8040 RESTCONF January 2017

 There is a specific set of parameters defined, although the server
 MAY choose to support query parameters not defined in this document.
 The contents of any query parameter value MUST be encoded according
 to Section 3.4 of [RFC3986].  Any reserved characters MUST be
 percent-encoded, according to Sections 2.1 and 2.5 of [RFC3986].
 Note that the fragment component is not used by the RESTCONF
 protocol.  The fragment is excluded from the target URI by a server,
 as described in Section 5.1 of [RFC7230].
 When new resources are created by the client, a "Location" header
 field is returned, which identifies the path of the newly created
 resource.  The client uses this exact path identifier to access the
 resource once it has been created.
 The target of a RESTCONF operation is a resource.  The "path" field
 in the request URI represents the target resource for the RESTCONF
 operation.
 Refer to Appendix B for examples of RESTCONF request URIs.

5.2. Message Encoding

 RESTCONF messages are encoded in HTTP according to [RFC7230].  The
 "utf-8" character set is used for all messages.  RESTCONF message
 content is sent in the HTTP message-body.
 Content is encoded in either JSON or XML format.  A server MUST
 support one of either XML or JSON encoding.  A server MAY support
 both XML and JSON encoding.  A client will need to support both XML
 and JSON to interoperate with all RESTCONF servers.
 XML encoding rules for data nodes are defined in [RFC7950].  The same
 encoding rules are used for all XML content.  JSON encoding rules are
 defined in [RFC7951].  Additional JSON encoding rules for metadata
 are defined in [RFC7952].  This encoding is valid JSON, but it also
 has special encoding rules to identify module namespaces and provide
 consistent type processing of YANG data.

Bierman, et al. Standards Track [Page 62] RFC 8040 RESTCONF January 2017

 The request input content encoding format is identified with the
 "Content-Type" header field.  This field MUST be present if a
 message-body is sent by the client.
 The server MUST support the "Accept" header field and the "406 Not
 Acceptable" status-line, as defined in [RFC7231].  The response
 output content encoding formats that the client will accept are
 identified with the "Accept" header field in the request.  If it is
 not specified, the request input encoding format SHOULD be used, or
 the server MAY choose any supported content encoding format.
 If there was no request input, then the default output encoding is
 XML or JSON, depending on server preference.  File extensions encoded
 in the request are not used to identify format encoding.
 A client can determine if the RESTCONF server supports an encoding
 format by sending a request using a specific format in the
 "Content-Type" and/or "Accept" header field.  If the server does not
 support the requested input encoding for a request, then it MUST
 return an error response with a "415 Unsupported Media Type"
 status-line.  If the server does not support any of the requested
 output encodings for a request, then it MUST return an error response
 with a "406 Not Acceptable" status-line.

5.3. RESTCONF Metadata

 The RESTCONF protocol needs to support the retrieval of the same
 metadata that is used in the NETCONF protocol.  Information about
 default leafs, last-modified timestamps, etc. is commonly used to
 annotate representations of the datastore contents.
 With the XML encoding, the metadata is encoded as attributes in XML,
 according to Section 3.3 of [W3C.REC-xml-20081126].  With the JSON
 encoding, the metadata is encoded as specified in [RFC7952].

Bierman, et al. Standards Track [Page 63] RFC 8040 RESTCONF January 2017

 The following examples are based on the example in Appendix B.3.9.
 The "report-all-tagged" mode for the "with-defaults" query parameter
 requires that a "default" attribute be returned for default nodes.
 These examples show that attribute for the "mtu" leaf.

5.3.1. XML Metadata Encoding Example

    GET /restconf/data/interfaces/interface=eth1
        ?with-defaults=report-all-tagged HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+xml
    <interface
      xmlns="urn:example.com:params:xml:ns:yang:example-interface">
      <name>eth1</name>
      <mtu xmlns:wd="urn:ietf:params:xml:ns:netconf:default:1.0"
        wd:default="true">1500</mtu>
      <status>up</status>
    </interface>

Bierman, et al. Standards Track [Page 64] RFC 8040 RESTCONF January 2017

5.3.2. JSON Metadata Encoding Example

 Note that RFC 6243 defines the "default" attribute with the
 XML Schema Definition (XSD), not YANG, so the YANG module name has to
 be assigned instead of derived from the YANG module.  The value
 "ietf-netconf-with-defaults" is assigned for JSON metadata encoding.
    GET /restconf/data/interfaces/interface=eth1\
        ?with-defaults=report-all-tagged HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "example:interface" : [
        {
          "name" : "eth1",
          "mtu" : 1500,
          "@mtu" : {
             "ietf-netconf-with-defaults:default" : true
          },
          "status" : "up"
        }
      ]
    }

5.4. Return Status

 Each message represents some sort of resource access.  An HTTP
 "status-line" header field is returned for each request.  If a status
 code in the "4xx" range is returned in the status-line, then the
 error information SHOULD be returned in the response, according to
 the format defined in Section 7.1.  If a status code in the "5xx"
 range is returned in the status-line, then the error information MAY
 be returned in the response, according to the format defined in
 Section 7.1.  If a status code in the "1xx", "2xx", or "3xx" range is
 returned in the status-line, then error information MUST NOT be
 returned in the response, since these ranges do not represent error
 conditions.

Bierman, et al. Standards Track [Page 65] RFC 8040 RESTCONF January 2017

5.5. Message Caching

 Since the datastore contents change at unpredictable times, responses
 from a RESTCONF server generally SHOULD NOT be cached.
 The server MUST include a "Cache-Control" header field in every
 response that specifies whether the response should be cached.
 Instead of relying on HTTP caching, the client SHOULD track the
 "ETag" and/or "Last-Modified" header fields returned by the server
 for the datastore resource (or data resource, if the server supports
 it).  A retrieval request for a resource can include the
 "If-None-Match" and/or "If-Modified-Since" header fields, which will
 cause the server to return a "304 Not Modified" status-line if the
 resource has not changed.  The client MAY use the HEAD method to
 retrieve just the message header fields, which SHOULD include the
 "ETag" and "Last-Modified" header fields, if this metadata is
 maintained for the target resource.
 Note that access control can be applied to data resources, such that
 the values in the "Last-Modified" and "ETag" headers maintained for a
 data resource may not be reliable, as described in Section 4.3.

6. Notifications

 The RESTCONF protocol supports YANG-defined event notifications.  The
 solution preserves aspects of NETCONF event notifications [RFC5277]
 while utilizing the Server-Sent Events [W3C.REC-eventsource-20150203]
 transport strategy.

6.1. Server Support

 A RESTCONF server MAY support RESTCONF notifications.  Clients may
 determine if a server supports RESTCONF notifications by using the
 HTTP OPTIONS, HEAD, or GET method on the "stream" list.  The server
 does not support RESTCONF notifications if an HTTP error code is
 returned (e.g., a "404 Not Found" status-line).

Bierman, et al. Standards Track [Page 66] RFC 8040 RESTCONF January 2017

6.2. Event Streams

 A RESTCONF server that supports notifications will populate a stream
 resource for each notification delivery service access point.  A
 RESTCONF client can retrieve the list of supported event streams from
 a RESTCONF server using the GET method on the "stream" list.
 The "restconf-state/streams" container definition in the
 "ietf-restconf-monitoring" module (defined in Section 9.3) is used to
 specify the structure and syntax of the conceptual child resources
 within the "streams" resource.
 For example:
 The client might send the following request:
    GET /restconf/data/ietf-restconf-monitoring:restconf-state/\
        streams HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml
 The server might send the following response:
    HTTP/1.1 200 OK
    Content-Type: application/yang-data+xml
    <streams
      xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
       <stream>
          <name>NETCONF</name>
          <description>default NETCONF event stream</description>
          <replay-support>true</replay-support>
          <replay-log-creation-time>\
             2007-07-08T00:00:00Z\
          </replay-log-creation-time>
          <access>
             <encoding>xml</encoding>
             <location>https://example.com/streams/NETCONF\
             </location>
          </access>
          <access>
             <encoding>json</encoding>
             <location>https://example.com/streams/NETCONF-JSON\
             </location>
          </access>
       </stream>

Bierman, et al. Standards Track [Page 67] RFC 8040 RESTCONF January 2017

       <stream>
          <name>SNMP</name>
          <description>SNMP notifications</description>
          <replay-support>false</replay-support>
          <access>
             <encoding>xml</encoding>
             <location>https://example.com/streams/SNMP</location>
          </access>
       </stream>
       <stream>
          <name>syslog-critical</name>
          <description>Critical and higher severity</description>
          <replay-support>true</replay-support>
          <replay-log-creation-time>
             2007-07-01T00:00:00Z
          </replay-log-creation-time>
          <access>
             <encoding>xml</encoding>
             <location>\
               https://example.com/streams/syslog-critical\
             </location>
          </access>
       </stream>
    </streams>

6.3. Subscribing to Receive Notifications

 RESTCONF clients can determine the URL for the subscription resource
 (to receive notifications) by sending an HTTP GET request for the
 "location" leaf with the "stream" list entry.  The value returned by
 the server can be used for the actual notification subscription.
 The client will send an HTTP GET request for the URL returned by the
 server with the "Accept" type "text/event-stream".
 The server will treat the connection as an event stream, using the
 Server-Sent Events [W3C.REC-eventsource-20150203] transport strategy.
 The server MAY support query parameters for a GET method on this
 resource.  These parameters are specific to each event stream.

Bierman, et al. Standards Track [Page 68] RFC 8040 RESTCONF January 2017

 For example:
 The client might send the following request:
    GET /restconf/data/ietf-restconf-monitoring:restconf-state/\
        streams/stream=NETCONF/access=xml/location HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml
 The server might send the following response:
    HTTP/1.1 200 OK
    Content-Type: application/yang-data+xml
    <location
      xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">\
      https://example.com/streams/NETCONF\
    </location>
 The RESTCONF client can then use this URL value to start monitoring
 the event stream:
    GET /streams/NETCONF HTTP/1.1
    Host: example.com
    Accept: text/event-stream
    Cache-Control: no-cache
    Connection: keep-alive
 A RESTCONF client MAY request that the server compress the events
 using the HTTP header field "Accept-Encoding".  For instance:
    GET /streams/NETCONF HTTP/1.1
    Host: example.com
    Accept: text/event-stream
    Cache-Control: no-cache
    Connection: keep-alive
    Accept-Encoding: gzip, deflate

Bierman, et al. Standards Track [Page 69] RFC 8040 RESTCONF January 2017

6.3.1. NETCONF Event Stream

 The server SHOULD support the NETCONF event stream defined in
 Section 3.2.3 of [RFC5277].  The notification messages for this
 stream are encoded in XML.
 The server MAY support additional streams that represent the semantic
 content of the NETCONF event stream, but using a representation with
 a different media type.
 The server MAY support the "start-time", "stop-time", and "filter"
 query parameters, defined in Section 4.8.  Refer to Appendix B.3.6
 for filter parameter examples.

6.4. Receiving Event Notifications

 RESTCONF notifications are encoded according to the definition of the
 event stream.
 The structure of the event data is based on the <notification>
 element definition in Section 4 of [RFC5277].  It MUST conform to the
 schema for the <notification> element in Section 4 of [RFC5277],
 using the XML namespace as defined in the XSD as follows:
   urn:ietf:params:xml:ns:netconf:notification:1.0
 For JSON-encoding purposes, the module name for the "notification"
 element is "ietf-restconf".
 Two child nodes within the "notification" container are expected,
 representing the event time and the event payload.  The "eventTime"
 node is defined within the same XML namespace as the <notification>
 element.  It is defined to be within the "ietf-restconf" module
 namespace for JSON-encoding purposes.
 The name and namespace of the payload element are determined by the
 YANG module containing the notification-stmt representing the
 notification message.

Bierman, et al. Standards Track [Page 70] RFC 8040 RESTCONF January 2017

 In the following example, the YANG module "example-mod" is used:
   module example-mod {
     namespace "http://example.com/event/1.0";
     prefix ex;
     organization "Example, Inc.";
     contact "support at example.com";
     description "Example Notification Data Model Module.";
     revision "2016-07-07" {
       description "Initial version.";
       reference "example.com document 2-9976.";
     }
     notification event {
       description "Example notification event.";
       leaf event-class {
         type string;
         description "Event class identifier.";
       }
       container reporting-entity {
         description "Event specific information.";
         leaf card {
           type string;
           description "Line card identifier.";
         }
       }
       leaf severity {
         type string;
         description "Event severity description.";
       }
     }
   }
 An example SSE event notification encoded using XML:
    data: <notification
    data:    xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0">
    data:    <eventTime>2013-12-21T00:01:00Z</eventTime>
    data:    <event xmlns="http://example.com/event/1.0">
    data:       <event-class>fault</event-class>
    data:       <reporting-entity>
    data:           <card>Ethernet0</card>
    data:       </reporting-entity>
    data:       <severity>major</severity>
    data:     </event>
    data: </notification>

Bierman, et al. Standards Track [Page 71] RFC 8040 RESTCONF January 2017

 An example SSE event notification encoded using JSON:
    data: {
    data:   "ietf-restconf:notification" : {
    data:     "eventTime" : "2013-12-21T00:01:00Z",
    data:     "example-mod:event" : {
    data:       "event-class" : "fault",
    data:       "reporting-entity" : { "card" : "Ethernet0" },
    data:       "severity" : "major"
    data:     }
    data:   }
    data: }
 Alternatively, since neither XML nor JSON is whitespace sensitive,
 the above messages can be encoded onto a single line.  For example:
    XML:
    data: <notification xmlns="urn:ietf:params:xml:ns:netconf:notif\
    ication:1.0"><eventTime>2013-12-21T00:01:00Z</eventTime><event \
    xmlns="http://example.com/event/1.0"><event-class>fault</event-\
    class><reportingEntity><card>Ethernet0</card></reporting-entity>\
    <severity>major</severity></event></notification>
    JSON:
    data: {"ietf-restconf:notification":{"eventTime":"2013-12-21\
    T00:01:00Z","example-mod:event":{"event-class": "fault","repor\
    tingEntity":{"card":"Ethernet0"},"severity":"major"}}}
 The SSE specification supports the following additional fields:
 "event", "id", and "retry".  A RESTCONF server MAY send the "retry"
 field, and if it does, RESTCONF clients SHOULD use it.  A RESTCONF
 server SHOULD NOT send the "event" or "id" fields, as there are no
 meaningful values that could be used for them that would not be
 redundant to the contents of the notification itself.  RESTCONF
 servers that do not send the "id" field also do not need to support
 the HTTP header field "Last-Event-ID" [W3C.REC-eventsource-20150203].
 RESTCONF servers that do send the "id" field SHOULD support the
 "start-time" query parameter as the preferred means for a client to
 specify where to restart the event stream.

Bierman, et al. Standards Track [Page 72] RFC 8040 RESTCONF January 2017

7. Error Reporting

 HTTP status codes are used to report success or failure for RESTCONF
 operations.  The error information that NETCONF error responses
 contain in the <rpc-error> element is adapted for use in RESTCONF,
 and <errors> data tree information is returned for the "4xx" and
 "5xx" classes of status codes.
 Since an operation resource is defined with a YANG "rpc" statement
 and an action is defined with a YANG "action" statement, a mapping
 from the NETCONF <error-tag> value to the HTTP status code is needed.
 The specific error-tag and response code to use are specific to the
 data model and might be contained in the YANG "description" statement
 for the "action" or "rpc" statement.

Bierman, et al. Standards Track [Page 73] RFC 8040 RESTCONF January 2017

            +-------------------------+------------------+
            | error-tag               | status code      |
            +-------------------------+------------------+
            | in-use                  | 409              |
            |                         |                  |
            | invalid-value           | 400, 404, or 406 |
            |                         |                  |
            | (request) too-big       | 413              |
            |                         |                  |
            | (response) too-big      | 400              |
            |                         |                  |
            | missing-attribute       | 400              |
            |                         |                  |
            | bad-attribute           | 400              |
            |                         |                  |
            | unknown-attribute       | 400              |
            |                         |                  |
            | bad-element             | 400              |
            |                         |                  |
            | unknown-element         | 400              |
            |                         |                  |
            | unknown-namespace       | 400              |
            |                         |                  |
            | access-denied           | 401 or 403       |
            |                         |                  |
            | lock-denied             | 409              |
            |                         |                  |
            | resource-denied         | 409              |
            |                         |                  |
            | rollback-failed         | 500              |
            |                         |                  |
            | data-exists             | 409              |
            |                         |                  |
            | data-missing            | 409              |
            |                         |                  |
            | operation-not-supported | 405 or 501       |
            |                         |                  |
            | operation-failed        | 412 or 500       |
            |                         |                  |
            | partial-operation       | 500              |
            |                         |                  |
            | malformed-message       | 400              |
            +-------------------------+------------------+
                Mapping from <error-tag> to Status Code

Bierman, et al. Standards Track [Page 74] RFC 8040 RESTCONF January 2017

7.1. Error Response Message

 When an error occurs for a request message on any resource type and
 the status code that will be returned is in the "4xx" range (except
 for status code "403 Forbidden"), the server SHOULD send a response
 message-body containing the information described by the
 "yang-errors" YANG data template within the "ietf-restconf" module
 found in Section 8.  The Content-Type of this response message MUST
 be "application/yang-data", plus, optionally, a structured syntax
 name suffix.
 The client SHOULD specify the desired encoding(s) for response
 messages by specifying the appropriate media type(s) in the
 "Accept" header.  If the client did not specify an "Accept" header,
 then the same structured syntax name suffix used in the request
 message SHOULD be used, or the server MAY choose any supported
 message-encoding format.  If there is no request message, the server
 MUST select "application/yang-data+xml" or
 "application/yang-data+json", depending on server preference.  All of
 the examples in this document, except for the one below, assume that
 XML encoding will be returned if there is an error.
 YANG tree diagram for <errors> data:
   +---- errors
         +---- error*
            +---- error-type       enumeration
            +---- error-tag        string
            +---- error-app-tag?   string
            +---- error-path?      instance-identifier
            +---- error-message?   string
            +---- error-info?
 The semantics and syntax for RESTCONF error messages are defined with
 the "yang-errors" YANG data template extension, found in Section 8.

Bierman, et al. Standards Track [Page 75] RFC 8040 RESTCONF January 2017

 Examples:
 The following example shows an error returned for a "lock-denied"
 error that can occur if a NETCONF client has locked a datastore.  The
 RESTCONF client is attempting to delete a data resource.  Note that
 an "Accept" header field is used to specify the desired encoding for
 the error message.  There would be no response message-body content
 if this operation was successful.
    DELETE /restconf/data/example-jukebox:jukebox/\
       library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json

Bierman, et al. Standards Track [Page 76] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 409 Conflict
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "ietf-restconf:errors" : {
        "error" : [
          {
            "error-type" : "protocol",
            "error-tag" : "lock-denied",
            "error-message" : "Lock failed; lock already held"
          }
        ]
      }
    }
 The following example shows an error returned for a "data-exists"
 error on a data resource.  The "jukebox" resource already exists, so
 it cannot be created.
 The client might send the following:
    POST /restconf/data/example-jukebox:jukebox HTTP/1.1
    Host: example.com

Bierman, et al. Standards Track [Page 77] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 409 Conflict
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+xml
    <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
      <error>
        <error-type>protocol</error-type>
        <error-tag>data-exists</error-tag>
        <error-path
          xmlns:rc="urn:ietf:params:xml:ns:yang:ietf-restconf"
          xmlns:jbox="https://example.com/ns/example-jukebox">\
          /rc:restconf/rc:data/jbox:jukebox
        </error-path>
        <error-message>
          Data already exists; cannot create new resource
        </error-message>
      </error>
    </errors>

Bierman, et al. Standards Track [Page 78] RFC 8040 RESTCONF January 2017

8. RESTCONF Module

 The "ietf-restconf" module defines conceptual definitions within an
 extension and two groupings, which are not meant to be implemented as
 datastore contents by a server.  For example, the "restconf"
 container is not intended to be implemented as a top-level data node
 (under the "/restconf/data" URI).
 Note that the "ietf-restconf" module does not have any
 protocol-accessible objects, so no YANG tree diagram is shown.
 <CODE BEGINS>
 file "ietf-restconf@2017-01-26.yang"
 module ietf-restconf {
   yang-version 1.1;
   namespace "urn:ietf:params:xml:ns:yang:ietf-restconf";
   prefix "rc";
   organization
     "IETF NETCONF (Network Configuration) Working Group";
   contact
     "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
      WG List:  <mailto:netconf@ietf.org>
      Author:   Andy Bierman
                <mailto:andy@yumaworks.com>
      Author:   Martin Bjorklund
                <mailto:mbj@tail-f.com>
      Author:   Kent Watsen
                <mailto:kwatsen@juniper.net>";
   description
     "This module contains conceptual YANG specifications
      for basic RESTCONF media type definitions used in
      RESTCONF protocol messages.
      Note that the YANG definitions within this module do not
      represent configuration data of any kind.
      The 'restconf-media-type' YANG extension statement
      provides a normative syntax for XML and JSON
      message-encoding purposes.

Bierman, et al. Standards Track [Page 79] RFC 8040 RESTCONF January 2017

      Copyright (c) 2017 IETF Trust and the persons identified as
      authors of the code.  All rights reserved.
      Redistribution and use in source and binary forms, with or
      without modification, is permitted pursuant to, and subject
      to the license terms contained in, the Simplified BSD License
      set forth in Section 4.c of the IETF Trust's Legal Provisions
      Relating to IETF Documents
      (http://trustee.ietf.org/license-info).
      This version of this YANG module is part of RFC 8040; see
      the RFC itself for full legal notices.";
   revision 2017-01-26 {
     description
       "Initial revision.";
     reference
       "RFC 8040: RESTCONF Protocol.";
   }
   extension yang-data {
     argument name {
       yin-element true;
     }
     description
       "This extension is used to specify a YANG data template that
        represents conceptual data defined in YANG.  It is
        intended to describe hierarchical data independent of
        protocol context or specific message-encoding format.
        Data definition statements within a yang-data extension
        specify the generic syntax for the specific YANG data
        template, whose name is the argument of the 'yang-data'
        extension statement.
        Note that this extension does not define a media type.
        A specification using this extension MUST specify the
        message-encoding rules, including the content media type.
        The mandatory 'name' parameter value identifies the YANG
        data template that is being defined.  It contains the
        template name.
        This extension is ignored unless it appears as a top-level
        statement.  It MUST contain data definition statements
        that result in exactly one container data node definition.
        An instance of a YANG data template can thus be translated
        into an XML instance document, whose top-level element
        corresponds to the top-level container.

Bierman, et al. Standards Track [Page 80] RFC 8040 RESTCONF January 2017

        The module name and namespace values for the YANG module using
        the extension statement are assigned to instance document data
        conforming to the data definition statements within
        this extension.
        The substatements of this extension MUST follow the
        'data-def-stmt' rule in the YANG ABNF.
        The XPath document root is the extension statement itself,
        such that the child nodes of the document root are
        represented by the data-def-stmt substatements within
        this extension.  This conceptual document is the context
        for the following YANG statements:
  1. must-stmt
  2. when-stmt
  3. path-stmt
  4. min-elements-stmt
  5. max-elements-stmt
  6. mandatory-stmt
  7. unique-stmt
  8. ordered-by
  9. instance-identifier data type
        The following data-def-stmt substatements are constrained
        when used within a 'yang-data' extension statement.
  1. The list-stmt is not required to have a key-stmt defined.
  2. The if-feature-stmt is ignored if present.
  3. The config-stmt is ignored if present.
  4. The available identity values for any 'identityref'

leaf or leaf-list nodes are limited to the module

            containing this extension statement and the modules
            imported into that module.
       ";
   }
   rc:yang-data yang-errors {
     uses errors;
   }
   rc:yang-data yang-api {
     uses restconf;
   }

Bierman, et al. Standards Track [Page 81] RFC 8040 RESTCONF January 2017

   grouping errors {
     description
       "A grouping that contains a YANG container
        representing the syntax and semantics of a
        YANG Patch error report within a response message.";
     container errors {
       description
         "Represents an error report returned by the server if
          a request results in an error.";
       list error {
         description
           "An entry containing information about one
            specific error that occurred while processing
            a RESTCONF request.";
         reference
           "RFC 6241, Section 4.3.";
         leaf error-type {
           type enumeration {
             enum transport {
               description
                 "The transport layer.";
             }
             enum rpc {
               description
                 "The rpc or notification layer.";
             }
             enum protocol {
               description
                 "The protocol operation layer.";
             }
             enum application {
               description
                 "The server application layer.";
             }
           }
           mandatory true;
           description
             "The protocol layer where the error occurred.";
         }

Bierman, et al. Standards Track [Page 82] RFC 8040 RESTCONF January 2017

         leaf error-tag {
           type string;
           mandatory true;
           description
             "The enumerated error-tag.";
         }
         leaf error-app-tag {
           type string;
           description
             "The application-specific error-tag.";
         }
         leaf error-path {
           type instance-identifier;
           description
             "The YANG instance identifier associated
              with the error node.";
         }
         leaf error-message {
           type string;
           description
             "A message describing the error.";
         }
         anydata error-info {
            description
              "This anydata value MUST represent a container with
               zero or more data nodes representing additional
               error information.";
         }
       }
     }
   }
   grouping restconf {
     description
       "Conceptual grouping representing the RESTCONF
        root resource.";
     container restconf {
       description
         "Conceptual container representing the RESTCONF
          root resource.";

Bierman, et al. Standards Track [Page 83] RFC 8040 RESTCONF January 2017

       container data {
         description
           "Container representing the datastore resource.
            Represents the conceptual root of all state data
            and configuration data supported by the server.
            The child nodes of this container can be any data
            resources that are defined as top-level data nodes
            from the YANG modules advertised by the server in
            the 'ietf-yang-library' module.";
       }
       container operations {
         description
           "Container for all operation resources.
            Each resource is represented as an empty leaf with the
            name of the RPC operation from the YANG 'rpc' statement.
            For example, the 'system-restart' RPC operation defined
            in the 'ietf-system' module would be represented as
            an empty leaf in the 'ietf-system' namespace.  This is
            a conceptual leaf and will not actually be found in
            the module:
               module ietf-system {
                 leaf system-reset {
                   type empty;
                 }
               }
            To invoke the 'system-restart' RPC operation:
               POST /restconf/operations/ietf-system:system-restart
            To discover the RPC operations supported by the server:
               GET /restconf/operations
            In XML, the YANG module namespace identifies the module:
              <system-restart
                 xmlns='urn:ietf:params:xml:ns:yang:ietf-system'/>
            In JSON, the YANG module name identifies the module:
              { 'ietf-system:system-restart' : [null] }
           ";
       }

Bierman, et al. Standards Track [Page 84] RFC 8040 RESTCONF January 2017

       leaf yang-library-version {
         type string {
           pattern '\d{4}-\d{2}-\d{2}';
         }
         config false;
         mandatory true;
         description
           "Identifies the revision date of the 'ietf-yang-library'
            module that is implemented by this RESTCONF server.
            Indicates the year, month, and day in YYYY-MM-DD
            numeric format.";
       }
     }
   }
 }
 <CODE ENDS>

9. RESTCONF Monitoring

 The "ietf-restconf-monitoring" module provides information about the
 RESTCONF protocol capabilities and event streams available from the
 server.  A RESTCONF server MUST implement the
 "ietf-restconf-monitoring" module.
 YANG tree diagram for the "ietf-restconf-monitoring" module:
    +--ro restconf-state
       +--ro capabilities
       |  +--ro capability*   inet:uri
       +--ro streams
          +--ro stream* [name]
             +--ro name                        string
             +--ro description?                string
             +--ro replay-support?             boolean
             +--ro replay-log-creation-time?   yang:date-and-time
             +--ro access* [encoding]
                +--ro encoding  string
                +--ro location  inet:uri

Bierman, et al. Standards Track [Page 85] RFC 8040 RESTCONF January 2017

9.1. restconf-state/capabilities

 This mandatory container holds the RESTCONF protocol capability URIs
 supported by the server.
 The server MAY maintain a last-modified timestamp for this container
 and return the "Last-Modified" header field when this data node is
 retrieved with the GET or HEAD methods.  Note that the last-modified
 timestamp for the datastore resource is not affected by changes to
 this subtree.
 The server SHOULD maintain an entity-tag for this container and
 return the "ETag" header field when this data node is retrieved with
 the GET or HEAD methods.  Note that the entity-tag for the datastore
 resource is not affected by changes to this subtree.
 The server MUST include a "capability" URI leaf-list entry for the
 "defaults" mode used by the server, defined in Section 9.1.2.
 The server MUST include a "capability" URI leaf-list entry
 identifying each supported optional protocol feature.  This includes
 optional query parameters and MAY include other capability URIs
 defined outside this document.

Bierman, et al. Standards Track [Page 86] RFC 8040 RESTCONF January 2017

9.1.1. Query Parameter URIs

 A new set of RESTCONF Capability URIs are defined to identify the
 specific query parameters (defined in Section 4.8) supported by the
 server.
 The server MUST include a "capability" leaf-list entry for each
 optional query parameter that it supports.
 +----------------+---------+---------------------------------------+
 | Name           | Section | URI                                   |
 |                |         |                                       |
 +----------------+---------+---------------------------------------+
 | depth          | 4.8.2   | urn:ietf:params:restconf:capability:  |
 |                |         | depth:1.0                             |
 |                |         |                                       |
 | fields         | 4.8.3   | urn:ietf:params:restconf:capability:  |
 |                |         | fields:1.0                            |
 |                |         |                                       |
 | filter         | 4.8.4   | urn:ietf:params:restconf:capability:  |
 |                |         | filter:1.0                            |
 |                |         |                                       |
 | replay         | 4.8.7   | urn:ietf:params:restconf:capability:  |
 |                | 4.8.8   | replay:1.0                            |
 |                |         |                                       |
 | with-defaults  | 4.8.9   | urn:ietf:params:restconf:capability:  |
 |                |         | with-defaults:1.0                     |
 +----------------+---------+---------------------------------------+
                     RESTCONF Query Parameter URIs

9.1.2. The "defaults" Protocol Capability URI

 This URI identifies the "basic-mode" default-handling mode that is
 used by the server for processing default leafs in requests for data
 resources.  This protocol capability URI MUST be supported by the
 server and MUST be listed in the "capability" leaf-list defined in
 Section 9.3.
    +----------+--------------------------------------------------+
    | Name     | URI                                              |
    +----------+--------------------------------------------------+
    | defaults | urn:ietf:params:restconf:capability:defaults:1.0 |
    +----------+--------------------------------------------------+
                  RESTCONF "defaults" Capability URI

Bierman, et al. Standards Track [Page 87] RFC 8040 RESTCONF January 2017

 The URI MUST contain a query parameter named "basic-mode" with one of
 the values listed below:
 +------------+------------------------------------------------------+
 | Value      | Description                                          |
 +------------+------------------------------------------------------+
 | report-all | No data nodes are considered default                 |
 |            |                                                      |
 | trim       | Values set to the YANG default-stmt value are        |
 |            | default                                              |
 |            |                                                      |
 | explicit   | Values set by the client are never considered        |
 |            | default                                              |
 +------------+------------------------------------------------------+
 The "basic-mode" definitions are specified in "With-defaults
 Capability for NETCONF" [RFC6243].
 If the "basic-mode" is set to "report-all", then the server MUST
 adhere to the default-handling behavior defined in Section 2.1 of
 [RFC6243].
 If the "basic-mode" is set to "trim", then the server MUST adhere to
 the default-handling behavior defined in Section 2.2 of [RFC6243].
 If the "basic-mode" is set to "explicit", then the server MUST adhere
 to the default-handling behavior defined in Section 2.3 of [RFC6243].
 Example (split for display purposes only):
    urn:ietf:params:restconf:capability:defaults:1.0?
         basic-mode=explicit

9.2. restconf-state/streams

 This optional container provides access to the event streams
 supported by the server.  The server MAY omit this container if no
 event streams are supported.
 The server will populate this container with a "stream" list entry
 for each stream type it supports.  Each stream contains a leaf called
 "events", which contains a URI that represents an event stream
 resource.
 Stream resources are defined in Section 3.8.  Notifications are
 defined in Section 6.

Bierman, et al. Standards Track [Page 88] RFC 8040 RESTCONF January 2017

9.3. RESTCONF Monitoring Module

 The "ietf-restconf-monitoring" module defines monitoring information
 for the RESTCONF protocol.
 The "ietf-yang-types" and "ietf-inet-types" modules from [RFC6991]
 are used by this module for some type definitions.
 <CODE BEGINS>
 file "ietf-restconf-monitoring@2017-01-26.yang"
 module ietf-restconf-monitoring {
   namespace "urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring";
   prefix "rcmon";
   import ietf-yang-types { prefix yang; }
   import ietf-inet-types { prefix inet; }
   organization
     "IETF NETCONF (Network Configuration) Working Group";
   contact
     "WG Web:   <https://datatracker.ietf.org/wg/netconf/>
      WG List:  <mailto:netconf@ietf.org>
      Author:   Andy Bierman
                <mailto:andy@yumaworks.com>
      Author:   Martin Bjorklund
                <mailto:mbj@tail-f.com>
      Author:   Kent Watsen
                <mailto:kwatsen@juniper.net>";

Bierman, et al. Standards Track [Page 89] RFC 8040 RESTCONF January 2017

   description
     "This module contains monitoring information for the
      RESTCONF protocol.
      Copyright (c) 2017 IETF Trust and the persons identified as
      authors of the code.  All rights reserved.
      Redistribution and use in source and binary forms, with or
      without modification, is permitted pursuant to, and subject
      to the license terms contained in, the Simplified BSD License
      set forth in Section 4.c of the IETF Trust's Legal Provisions
      Relating to IETF Documents
      (http://trustee.ietf.org/license-info).
      This version of this YANG module is part of RFC 8040; see
      the RFC itself for full legal notices.";
   revision 2017-01-26 {
     description
       "Initial revision.";
     reference
       "RFC 8040: RESTCONF Protocol.";
   }
   container restconf-state {
     config false;
     description
       "Contains RESTCONF protocol monitoring information.";
     container capabilities {
       description
         "Contains a list of protocol capability URIs.";
       leaf-list capability {
         type inet:uri;
         description
           "A RESTCONF protocol capability URI.";
       }
     }

Bierman, et al. Standards Track [Page 90] RFC 8040 RESTCONF January 2017

     container streams {
       description
         "Container representing the notification event streams
          supported by the server.";
        reference
          "RFC 5277, Section 3.4, <streams> element.";
       list stream {
         key name;
         description
           "Each entry describes an event stream supported by
            the server.";
         leaf name {
           type string;
           description
             "The stream name.";
           reference
             "RFC 5277, Section 3.4, <name> element.";
         }
         leaf description {
           type string;
           description
             "Description of stream content.";
           reference
             "RFC 5277, Section 3.4, <description> element.";
         }
         leaf replay-support {
           type boolean;
           default false;
           description
             "Indicates if replay buffer is supported for this stream.
              If 'true', then the server MUST support the 'start-time'
              and 'stop-time' query parameters for this stream.";
           reference
             "RFC 5277, Section 3.4, <replaySupport> element.";
         }

Bierman, et al. Standards Track [Page 91] RFC 8040 RESTCONF January 2017

         leaf replay-log-creation-time {
           when "../replay-support" {
             description
               "Only present if notification replay is supported.";
           }
           type yang:date-and-time;
           description
             "Indicates the time the replay log for this stream
              was created.";
           reference
             "RFC 5277, Section 3.4, <replayLogCreationTime>
              element.";
         }
         list access {
           key encoding;
           min-elements 1;
           description
             "The server will create an entry in this list for each
              encoding format that is supported for this stream.
              The media type 'text/event-stream' is expected
              for all event streams.  This list identifies the
              subtypes supported for this stream.";
           leaf encoding {
             type string;
             description
               "This is the secondary encoding format within the
                'text/event-stream' encoding used by all streams.
                The type 'xml' is supported for XML encoding.
                The type 'json' is supported for JSON encoding.";
           }

Bierman, et al. Standards Track [Page 92] RFC 8040 RESTCONF January 2017

           leaf location {
             type inet:uri;
             mandatory true;
             description
               "Contains a URL that represents the entry point
                for establishing notification delivery via
                server-sent events.";
           }
         }
       }
     }
   }
 }
 <CODE ENDS>

10. YANG Module Library

 The "ietf-yang-library" module defined in [RFC7895] provides
 information about the YANG modules and submodules used by the
 RESTCONF server.  Implementation is mandatory for RESTCONF servers.
 All YANG modules and submodules used by the server MUST be identified
 in the YANG module library.

10.1. modules-state/module

 This mandatory list contains one entry for each YANG data model
 module supported by the server.  There MUST be an instance of this
 list for every YANG module that is used by the server.
 The contents of this list are defined in the "module" YANG list
 statement in [RFC7895].
 Note that there are no protocol-accessible objects in the
 "ietf-restconf" module to implement, but it is possible that a server
 will list the "ietf-restconf" module in the YANG library if it is
 imported (directly or indirectly) by an implemented module.

Bierman, et al. Standards Track [Page 93] RFC 8040 RESTCONF January 2017

11. IANA Considerations

11.1. The "restconf" Relation Type

 This specification registers the "restconf" relation type in the
 "Link Relation Types" registry defined by [RFC5988]:
    Relation Name: restconf
    Description: Identifies the root of the RESTCONF API as configured
                 on this HTTP server.  The "restconf" relation
                 defines the root of the API defined in RFC 8040.
                 Subsequent revisions of RESTCONF will use alternate
                 relation values to support protocol versioning.
    Reference: RFC 8040

11.2. Registrations for New URIs and YANG Modules

 This document registers two URIs as namespaces in the "IETF XML
 Registry" [RFC3688]:
   URI: urn:ietf:params:xml:ns:yang:ietf-restconf
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.
   URI: urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring
   Registrant Contact: The IESG.
   XML: N/A; the requested URI is an XML namespace.
 This document registers two YANG modules in the "YANG Module Names"
 registry [RFC6020]:
   name:         ietf-restconf
   namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf
   prefix:       rc
   reference:    RFC 8040
   name:         ietf-restconf-monitoring
   namespace:    urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring
   prefix:       rcmon
   reference:    RFC 8040

Bierman, et al. Standards Track [Page 94] RFC 8040 RESTCONF January 2017

11.3. Media Types

11.3.1. Media Type "application/yang-data+xml"

 Type name: application
 Subtype name: yang-data+xml
 Required parameters: None
 Optional parameters: None
 Encoding considerations: 8-bit
    Each conceptual YANG data node is encoded according to the
    XML Encoding Rules and Canonical Format for the specific
    YANG data node type defined in [RFC7950].
 Security considerations: Security considerations related
    to the generation and consumption of RESTCONF messages
    are discussed in Section 12 of RFC 8040.
    Additional security considerations are specific to the
    semantics of particular YANG data models.  Each YANG module
    is expected to specify security considerations for the
    YANG data defined in that module.
 Interoperability considerations: RFC 8040 specifies the
    format of conforming messages and the interpretation
    thereof.
 Published specification: RFC 8040
 Applications that use this media type: Instance document
    data parsers used within a protocol or automation tool
    that utilize YANG-defined data structures.
 Fragment identifier considerations: Fragment identifiers for
    this type are not defined.  All YANG data nodes are
    accessible as resources using the path in the request URI.
 Additional information:
    Deprecated alias names for this type: N/A
    Magic number(s): N/A
    File extension(s): None
    Macintosh file type code(s): "TEXT"
 Person & email address to contact for further information: See
    the Authors' Addresses section of RFC 8040.

Bierman, et al. Standards Track [Page 95] RFC 8040 RESTCONF January 2017

 Intended usage: COMMON
 Restrictions on usage: N/A
 Author: See the Authors' Addresses section of RFC 8040.
 Change controller: Internet Engineering Task Force
    (mailto:iesg@ietf.org).
 Provisional registration? (standards tree only): no

11.3.2. Media Type "application/yang-data+json"

 Type name: application
 Subtype name: yang-data+json
 Required parameters: None
 Optional parameters: None
 Encoding considerations: 8-bit
    Each conceptual YANG data node is encoded according to
    [RFC7951].  A metadata annotation is encoded according to
    [RFC7952].
 Security considerations: Security considerations related
    to the generation and consumption of RESTCONF messages
    are discussed in Section 12 of RFC 8040.
    Additional security considerations are specific to the
    semantics of particular YANG data models.  Each YANG module
    is expected to specify security considerations for the
    YANG data defined in that module.
 Interoperability considerations: RFC 8040 specifies the format
    of conforming messages and the interpretation thereof.
 Published specification: RFC 8040
 Applications that use this media type: Instance document
    data parsers used within a protocol or automation tool
    that utilize YANG-defined data structures.
 Fragment identifier considerations: The syntax and semantics
    of fragment identifiers are the same as the syntax and semantics
    specified for the "application/json" media type.

Bierman, et al. Standards Track [Page 96] RFC 8040 RESTCONF January 2017

 Additional information:
    Deprecated alias names for this type: N/A
    Magic number(s): N/A
    File extension(s): None
    Macintosh file type code(s): "TEXT"
 Person & email address to contact for further information: See
    the Authors' Addresses section of RFC 8040.
 Intended usage: COMMON
 Restrictions on usage: N/A
 Author: See the Authors' Addresses section of RFC 8040.
 Change controller: Internet Engineering Task Force
    (mailto:iesg@ietf.org).
 Provisional registration? (standards tree only): no

11.4. RESTCONF Capability URNs

 This document defines a registry for RESTCONF capability identifiers.
 The name of the registry is "RESTCONF Capability URNs".  The review
 policy for this registry is "IETF Review" [RFC5226].  The registry
 shall record the following for each entry:
 o  the name of the RESTCONF capability.  By convention, this name
    begins with the colon (":") character.
 o  the URN for the RESTCONF capability.
 o  the reference for the document registering the value.

Bierman, et al. Standards Track [Page 97] RFC 8040 RESTCONF January 2017

 This document registers several capability identifiers in the
 "RESTCONF Capability URNs" registry:
 Index           Capability Identifier
 ---------------------------------------------------------------------
 :defaults       urn:ietf:params:restconf:capability:defaults:1.0
 :depth          urn:ietf:params:restconf:capability:depth:1.0
 :fields         urn:ietf:params:restconf:capability:fields:1.0
 :filter         urn:ietf:params:restconf:capability:filter:1.0
 :replay         urn:ietf:params:restconf:capability:replay:1.0
 :with-defaults  urn:ietf:params:restconf:capability:with-defaults:1.0

11.5. Registration of "restconf" URN Sub-namespace

 IANA has registered a new URN sub-namespace within the "IETF URN
 Sub-namespace for Registered Protocol Parameter Identifiers" registry
 defined in [RFC3553].
    Registry Name: restconf
    Specification: RFC 8040
    Repository: "RESTCONF Capability URNs" registry (Section 11.4)
    Index value:  Sub-parameters MUST be specified in UTF-8, using
       standard URI encoding where necessary.

Bierman, et al. Standards Track [Page 98] RFC 8040 RESTCONF January 2017

12. Security Considerations

 Section 2.1 states that "a RESTCONF server MUST support the TLS
 protocol [RFC5246]."  This language leaves open the possibility that
 a RESTCONF server might also support future versions of the TLS
 protocol.  Of specific concern, TLS 1.3 [TLS1.3] introduces support
 for 0-RTT handshakes that can lead to security issues for RESTCONF
 APIs, as described in Appendix B.1 of the TLS 1.3 document.  It is
 therefore RECOMMENDED that RESTCONF servers do not support 0-RTT at
 all (not even for idempotent requests) until an update to this RFC
 guides otherwise.
 Section 2.5 recommends authentication based on TLS client
 certificates but allows the use of any authentication scheme defined
 in the "Hypertext Transfer Protocol (HTTP) Authentication Scheme
 Registry".  Implementations need to be aware that the strengths of
 these methods vary greatly and that some may be considered
 experimental.  Selection of any of these schemes SHOULD be performed
 after reading the Security Considerations section of the RFC
 associated with the scheme's registry entry.
 The "ietf-restconf-monitoring" YANG module defined in this memo is
 designed to be accessed via the NETCONF protocol [RFC6241].  The
 lowest NETCONF layer is the secure transport layer, and the
 mandatory-to-implement secure transport is Secure Shell (SSH)
 [RFC6242].  The NETCONF access control model [RFC6536] provides the
 means to restrict access for particular NETCONF users to a
 preconfigured subset of all available NETCONF protocol operations and
 content.
 The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement
 secure transport is TLS [RFC5246].  The RESTCONF protocol uses the
 NETCONF access control model [RFC6536], which provides the means to
 restrict access for particular RESTCONF users to a preconfigured
 subset of all available RESTCONF protocol operations and content.
 This section provides security considerations for the resources
 defined by the RESTCONF protocol.  Security considerations for HTTPS
 are defined in [RFC7230].  Aside from the "ietf-restconf-monitoring"
 module (Section 9) and the "ietf-yang-library" module (Section 10),
 RESTCONF does not specify which YANG modules a server needs to
 support.  Security considerations for the other modules manipulated
 by RESTCONF can be found in the documents defining those YANG
 modules.
 Configuration information is by its very nature sensitive.  Its
 transmission in the clear and without integrity checking leaves
 devices open to classic eavesdropping and false data injection

Bierman, et al. Standards Track [Page 99] RFC 8040 RESTCONF January 2017

 attacks.  Configuration information often contains passwords, user
 names, service descriptions, and topological information, all of
 which are sensitive.  There are many patterns of attack that have
 been observed through operational practice with existing management
 interfaces.  It would be wise for implementers to research them and
 take them into account when implementing this protocol.
 Different environments may well allow different rights prior to, and
 then after, authentication.  When a RESTCONF operation is not
 properly authorized, the RESTCONF server MUST return a "401
 Unauthorized" status-line.  Note that authorization information can
 be exchanged in the form of configuration information, which is all
 the more reason to ensure the security of the connection.  Note that
 it is possible for a client to detect configuration changes in data
 resources it is not authorized to access by monitoring changes in the
 "ETag" and "Last-Modified" header fields returned by the server for
 the datastore resource.
 A RESTCONF server implementation SHOULD attempt to prevent system
 disruption due to excessive resource consumption required to fulfill
 edit requests via the POST, PUT, and PATCH methods.  On such an
 implementation, it may be possible to construct an attack that
 attempts to consume all available memory or other resource types.

13. References

13.1. Normative References

 [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
            Extensions (MIME) Part Two: Media Types", RFC 2046,
            DOI 10.17487/RFC2046, November 1996,
            <http://www.rfc-editor.org/info/rfc2046>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC3553]  Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
            IETF URN Sub-namespace for Registered Protocol
            Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553,
            June 2003, <http://www.rfc-editor.org/info/rfc3553>.
 [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
            DOI 10.17487/RFC3688, January 2004,
            <http://www.rfc-editor.org/info/rfc3688>.

Bierman, et al. Standards Track [Page 100] RFC 8040 RESTCONF January 2017

 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66,
            RFC 3986, DOI 10.17487/RFC3986, January 2005,
            <http://www.rfc-editor.org/info/rfc3986>.
 [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
            Syntax Specifications: ABNF", STD 68, RFC 5234,
            DOI 10.17487/RFC5234, January 2008,
            <http://www.rfc-editor.org/info/rfc5234>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246,
            DOI 10.17487/RFC5246, August 2008,
            <http://www.rfc-editor.org/info/rfc5246>.
 [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
            Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
            <http://www.rfc-editor.org/info/rfc5277>.
 [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
            Housley, R., and W. Polk, "Internet X.509 Public Key
            Infrastructure Certificate and Certificate Revocation List
            (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
            <http://www.rfc-editor.org/info/rfc5280>.
 [RFC5789]  Dusseault, L. and J. Snell, "PATCH Method for HTTP",
            RFC 5789, DOI 10.17487/RFC5789, March 2010,
            <http://www.rfc-editor.org/info/rfc5789>.
 [RFC5988]  Nottingham, M., "Web Linking", RFC 5988,
            DOI 10.17487/RFC5988, October 2010,
            <http://www.rfc-editor.org/info/rfc5988>.
 [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
            the Network Configuration Protocol (NETCONF)", RFC 6020,
            DOI 10.17487/RFC6020, October 2010,
            <http://www.rfc-editor.org/info/rfc6020>.
 [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
            and A. Bierman, Ed., "Network Configuration Protocol
            (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
            <http://www.rfc-editor.org/info/rfc6241>.
 [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
            Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
            <http://www.rfc-editor.org/info/rfc6242>.

Bierman, et al. Standards Track [Page 101] RFC 8040 RESTCONF January 2017

 [RFC6243]  Bierman, A. and B. Lengyel, "With-defaults Capability for
            NETCONF", RFC 6243, DOI 10.17487/RFC6243, June 2011,
            <http://www.rfc-editor.org/info/rfc6243>.
 [RFC6415]  Hammer-Lahav, E., Ed., and B. Cook, "Web Host Metadata",
            RFC 6415, DOI 10.17487/RFC6415, October 2011,
            <http://www.rfc-editor.org/info/rfc6415>.
 [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
            Protocol (NETCONF) Access Control Model", RFC 6536,
            DOI 10.17487/RFC6536, March 2012,
            <http://www.rfc-editor.org/info/rfc6536>.
 [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
            and D. Orchard, "URI Template", RFC 6570,
            DOI 10.17487/RFC6570, March 2012,
            <http://www.rfc-editor.org/info/rfc6570>.
 [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
            RFC 6991, DOI 10.17487/RFC6991, July 2013,
            <http://www.rfc-editor.org/info/rfc6991>.
 [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
            Interchange Format", RFC 7159, DOI 10.17487/RFC7159,
            March 2014, <http://www.rfc-editor.org/info/rfc7159>.
 [RFC7230]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
            Transfer Protocol (HTTP/1.1): Message Syntax and Routing",
            RFC 7230, DOI 10.17487/RFC7230, June 2014,
            <http://www.rfc-editor.org/info/rfc7230>.
 [RFC7231]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
            Transfer Protocol (HTTP/1.1): Semantics and Content",
            RFC 7231, DOI 10.17487/RFC7231, June 2014,
            <http://www.rfc-editor.org/info/rfc7231>.
 [RFC7232]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
            Transfer Protocol (HTTP/1.1): Conditional Requests",
            RFC 7232, DOI 10.17487/RFC7232, June 2014,
            <http://www.rfc-editor.org/info/rfc7232>.
 [RFC7235]  Fielding, R., Ed., and J. Reschke, Ed., "Hypertext
            Transfer Protocol (HTTP/1.1): Authentication", RFC 7235,
            DOI 10.17487/RFC7235, June 2014,
            <http://www.rfc-editor.org/info/rfc7235>.

Bierman, et al. Standards Track [Page 102] RFC 8040 RESTCONF January 2017

 [RFC7320]  Nottingham, M., "URI Design and Ownership", BCP 190,
            RFC 7320, DOI 10.17487/RFC7320, July 2014,
            <http://www.rfc-editor.org/info/rfc7320>.
 [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
            "Recommendations for Secure Use of Transport Layer
            Security (TLS) and Datagram Transport Layer Security
            (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525,
            May 2015, <http://www.rfc-editor.org/info/rfc7525>.
 [RFC7589]  Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
            NETCONF Protocol over Transport Layer Security (TLS) with
            Mutual X.509 Authentication", RFC 7589,
            DOI 10.17487/RFC7589, June 2015,
            <http://www.rfc-editor.org/info/rfc7589>.
 [RFC7895]  Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
            Library", RFC 7895, DOI 10.17487/RFC7895, June 2016,
            <http://www.rfc-editor.org/info/rfc7895>.
 [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
            RFC 7950, DOI 10.17487/RFC7950, August 2016,
            <http://www.rfc-editor.org/info/rfc7950>.
 [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
            RFC 7951, DOI 10.17487/RFC7951, August 2016,
            <http://www.rfc-editor.org/info/rfc7951>.
 [RFC7952]  Lhotka, L., "Defining and Using Metadata with YANG",
            RFC 7952, DOI 10.17487/RFC7952, August 2016,
            <http://www.rfc-editor.org/info/rfc7952>.
 [W3C.REC-eventsource-20150203]
            Hickson, I., "Server-Sent Events", World Wide Web
            Consortium Recommendation REC-eventsource-20150203,
            February 2015,
            <http://www.w3.org/TR/2015/REC-eventsource-20150203>.

Bierman, et al. Standards Track [Page 103] RFC 8040 RESTCONF January 2017

 [W3C.REC-xml-20081126]
            Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E.,
            and F. Yergeau, "Extensible Markup Language (XML) 1.0
            (Fifth Edition)", World Wide Web Consortium Recommendation
            REC-xml-20081126, November 2008,
            <http://www.w3.org/TR/2008/REC-xml-20081126>.
 [XPath]    Clark, J. and S. DeRose, "XML Path Language (XPath)
            Version 1.0", World Wide Web Consortium Recommendation
            REC-xpath-19991116, November 1999,
            <http://www.w3.org/TR/1999/REC-xpath-19991116>.

13.2. Informative References

 [REST-Dissertation]
            Fielding, R., "Architectural Styles and the Design of
            Network-based Software Architectures", 2000.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
            DOI 10.17487/RFC2818, May 2000,
            <http://www.rfc-editor.org/info/rfc2818>.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.
 [TLS1.3]   Rescorla, E., "The Transport Layer Security (TLS) Protocol
            Version 1.3", Work in Progress, draft-ietf-tls-tls13-18,
            October 2016.
 [YANG-Patch]
            Bierman, A., Bjorklund, M., and K. Watsen, "YANG Patch
            Media Type", Work in Progress,
            draft-ietf-netconf-yang-patch-14, November 2016.

Bierman, et al. Standards Track [Page 104] RFC 8040 RESTCONF January 2017

Appendix A. Example YANG Module

 The example YANG module used in this document represents a simple
 media jukebox interface.
 YANG tree diagram for the "example-jukebox" module:
    +--rw jukebox!
       +--rw library
       |  +--rw artist* [name]
       |  |  +--rw name     string
       |  |  +--rw album* [name]
       |  |     +--rw name     string
       |  |     +--rw genre?   identityref
       |  |     +--rw year?    uint16
       |  |     +--rw admin
       |  |     |  +--rw label?              string
       |  |     |  +--rw catalogue-number?   string
       |  |     +--rw song* [name]
       |  |        +--rw name        string
       |  |        +--rw location    string
       |  |        +--rw format?     string
       |  |        +--rw length?     uint32
       |  +--ro artist-count?   uint32
       |  +--ro album-count?    uint32
       |  +--ro song-count?     uint32
       +--rw playlist* [name]
       |  +--rw name           string
       |  +--rw description?   string
       |  +--rw song* [index]
       |     +--rw index    uint32
       |     +--rw id       instance-identifier
       +--rw player
          +--rw gap?   decimal64
   rpcs:
   +---x play
       +--ro input
          +--ro playlist       string
          +--ro song-number    uint32

Bierman, et al. Standards Track [Page 105] RFC 8040 RESTCONF January 2017

A.1. "example-jukebox" YANG Module

 module example-jukebox {
    namespace "http://example.com/ns/example-jukebox";
    prefix "jbox";
    organization "Example, Inc.";
    contact "support at example.com";
    description "Example Jukebox Data Model Module.";
    revision "2016-08-15" {
      description "Initial version.";
      reference "example.com document 1-4673.";
    }
    identity genre {
      description
        "Base for all genre types.";
    }
    // abbreviated list of genre classifications
    identity alternative {
      base genre;
      description
        "Alternative music.";
    }
    identity blues {
      base genre;
      description
        "Blues music.";
    }
    identity country {
      base genre;
      description
        "Country music.";
    }
    identity jazz {
      base genre;
      description
        "Jazz music.";
    }
    identity pop {
      base genre;
      description
        "Pop music.";
    }

Bierman, et al. Standards Track [Page 106] RFC 8040 RESTCONF January 2017

    identity rock {
      base genre;
      description
        "Rock music.";
    }
    container jukebox {
      presence
        "An empty container indicates that the jukebox
         service is available.";
      description
        "Represents a 'jukebox' resource, with a library, playlists,
         and a 'play' operation.";
      container library {
        description
          "Represents the 'jukebox' library resource.";
        list artist {
          key name;
          description
            "Represents one 'artist' resource within the
             'jukebox' library resource.";
          leaf name {
            type string {
              length "1 .. max";
            }
            description
              "The name of the artist.";
          }
          list album {
            key name;
            description
              "Represents one 'album' resource within one
               'artist' resource, within the jukebox library.";
            leaf name {
              type string {
                length "1 .. max";
              }
              description
                "The name of the album.";
            }

Bierman, et al. Standards Track [Page 107] RFC 8040 RESTCONF January 2017

            leaf genre {
              type identityref { base genre; }
              description
                "The genre identifying the type of music on
                 the album.";
            }
            leaf year {
              type uint16 {
                range "1900 .. max";
              }
              description
                "The year the album was released.";
            }
            container admin {
              description
                "Administrative information for the album.";
              leaf label {
                type string;
                description
                  "The label that released the album.";
              }
              leaf catalogue-number {
                type string;
                description
                  "The album's catalogue number.";
              }
            }
            list song {
              key name;
              description
                "Represents one 'song' resource within one
                 'album' resource, within the jukebox library.";
              leaf name {
                type string {
                   length "1 .. max";
                }
                description
                  "The name of the song.";
              }

Bierman, et al. Standards Track [Page 108] RFC 8040 RESTCONF January 2017

              leaf location {
                type string;
                mandatory true;
                description
                  "The file location string of the
                   media file for the song.";
              }
              leaf format {
                type string;
                description
                  "An identifier string for the media type
                   for the file associated with the
                   'location' leaf for this entry.";
              }
              leaf length {
                type uint32;
                units "seconds";
                description
                  "The duration of this song in seconds.";
              }
            }   // end list 'song'
          }   // end list 'album'
        }  // end list 'artist'
        leaf artist-count {
           type uint32;
           units "artists";
           config false;
           description
             "Number of artists in the library.";
        }
        leaf album-count {
           type uint32;
           units "albums";
           config false;
           description
             "Number of albums in the library.";
        }
        leaf song-count {
           type uint32;
           units "songs";
           config false;
           description
             "Number of songs in the library.";
        }
      }  // end library

Bierman, et al. Standards Track [Page 109] RFC 8040 RESTCONF January 2017

      list playlist {
        key name;
        description
          "Example configuration data resource.";
        leaf name {
          type string;
          description
            "The name of the playlist.";
        }
        leaf description {
          type string;
          description
            "A comment describing the playlist.";
        }
        list song {
          key index;
          ordered-by user;
          description
            "Example nested configuration data resource.";
          leaf index {    // not really needed
            type uint32;
            description
              "An arbitrary integer index for this playlist song.";
          }
          leaf id {
            type instance-identifier;
            mandatory true;
            description
              "Song identifier.  Must identify an instance of
               /jukebox/library/artist/album/song/name.";
          }
        }
      }

Bierman, et al. Standards Track [Page 110] RFC 8040 RESTCONF January 2017

      container player {
        description
          "Represents the jukebox player resource.";
        leaf gap {
          type decimal64 {
            fraction-digits 1;
            range "0.0 .. 2.0";
          }
          units "tenths of seconds";
          description
            "Time gap between each song.";
        }
      }
    }
    rpc play {
      description
        "Control function for the jukebox player.";
      input {
        leaf playlist {
          type string;
          mandatory true;
          description
            "The playlist name.";
        }
        leaf song-number {
          type uint32;
          mandatory true;
          description
            "Song number in playlist to play.";
        }
      }
    }
 }

Bierman, et al. Standards Track [Page 111] RFC 8040 RESTCONF January 2017

Appendix B. RESTCONF Message Examples

 The examples within this document use the normative YANG module
 "ietf-restconf" as defined in Section 8 and the non-normative example
 YANG module "example-jukebox" as defined in Appendix A.1.
 This section shows some typical RESTCONF message exchanges.

B.1. Resource Retrieval Examples

B.1.1. Retrieve the Top-Level API Resource

 The client starts by retrieving the RESTCONF root resource:
    GET /.well-known/host-meta HTTP/1.1
    Host: example.com
    Accept: application/xrd+xml

Bierman, et al. Standards Track [Page 112] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 200 OK
    Content-Type: application/xrd+xml
    Content-Length: nnn
    <XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
        <Link rel='restconf' href='/restconf'/>
    </XRD>
 The client may then retrieve the top-level API resource, using the
 root resource "/restconf".
    GET /restconf HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "ietf-restconf:restconf" : {
        "data" : {},
        "operations" : {},
        "yang-library-version" : "2016-06-21"
      }
    }
 To request that the response content be encoded in XML, the "Accept"
 header can be used, as in this example request:
    GET /restconf HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml

Bierman, et al. Standards Track [Page 113] RFC 8040 RESTCONF January 2017

 The server will return the same conceptual data either way, which
 might be as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+xml
    <restconf xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
      <data/>
      <operations/>
      <yang-library-version>2016-06-21</yang-library-version>
    </restconf>

B.1.2. Retrieve the Server Module Information

 It is possible that the YANG library module will change over time.
 The client can retrieve the revision date of the "ietf-yang-library"
 module supported by the server from the API resource, as described in
 the previous section.
 In this example, the client is retrieving the module information from
 the server in JSON format:
    GET /restconf/data/ietf-yang-library:modules-state HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json

Bierman, et al. Standards Track [Page 114] RFC 8040 RESTCONF January 2017

 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Last-Modified: Thu, 26 Jan 2017 14:00:14 GMT
    Content-Type: application/yang-data+json
    {
      "ietf-yang-library:modules-state" : {
        "module-set-id" : "5479120c17a619545ea6aff7aa19838b036ebbd7",
        "module" : [
          {
            "name" : "foo",
            "revision" : "2012-01-02",
            "schema" : "https://example.com/modules/foo/2012-01-02",
            "namespace" : "http://example.com/ns/foo",
            "feature" : [ "feature1", "feature2" ],
            "deviation" : [
              {
                "name" : "foo-dev",
                "revision" : "2012-02-16"
              }
            ],
            "conformance-type" : "implement"
          },
          {
            "name" : "ietf-yang-library",
            "revision" : "2016-06-21",
            "schema" : "https://example.com/modules/\
              ietf-yang-library/2016-06-21",
            "namespace" :
              "urn:ietf:params:xml:ns:yang:ietf-yang-library",
            "conformance-type" : "implement"
          },
          {
            "name" : "foo-types",
            "revision" : "2012-01-05",
            "schema" :
              "https://example.com/modules/foo-types/2012-01-05",
            "namespace" : "http://example.com/ns/foo-types",
            "conformance-type" : "import"
          },

Bierman, et al. Standards Track [Page 115] RFC 8040 RESTCONF January 2017

          {
            "name" : "bar",
            "revision" : "2012-11-05",
            "schema" : "https://example.com/modules/bar/2012-11-05",
            "namespace" : "http://example.com/ns/bar",
            "feature" : [ "bar-ext" ],
            "conformance-type" : "implement",
            "submodule" : [
              {
                "name" : "bar-submod1",
                "revision" : "2012-11-05",
                "schema" :
                 "https://example.com/modules/bar-submod1/2012-11-05"
              },
              {
                "name" : "bar-submod2",
                "revision" : "2012-11-05",
                "schema" :
                 "https://example.com/modules/bar-submod2/2012-11-05"
              }
            ]
          }
        ]
      }
    }

Bierman, et al. Standards Track [Page 116] RFC 8040 RESTCONF January 2017

B.1.3. Retrieve the Server Capability Information

 In this example, the client is retrieving the capability information
 from the server in XML format, and the server supports all of the
 RESTCONF query parameters, plus one vendor parameter:
    GET /restconf/data/ietf-restconf-monitoring:restconf-state/\
        capabilities HTTP/1.1
    Host: example.com
    Accept: application/yang-data+xml
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Last-Modified: Thu, 26 Jan 2017 16:00:14 GMT
    Content-Type: application/yang-data+xml
    <capabilities
        xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
     <capability>\
      urn:ietf:params:restconf:capability:defaults:1.0?\
         basic-mode=explicit\
     </capability>
     <capability>\
      urn:ietf:params:restconf:capability:with-defaults:1.0\
     </capability>
     <capability>\
      urn:ietf:params:restconf:capability:depth:1.0\
     </capability>
     <capability>\
      urn:ietf:params:restconf:capability:fields:1.0\
     </capability>
     <capability>\
      urn:ietf:params:restconf:capability:filter:1.0\
     </capability>
     <capability>\
      urn:ietf:params:restconf:capability:start-time:1.0\
     </capability>
     <capability>\
      urn:ietf:params:restconf:capability:stop-time:1.0\
     </capability>
     <capability>\
      http://example.com/capabilities/myparam\
     </capability>
    </capabilities>

Bierman, et al. Standards Track [Page 117] RFC 8040 RESTCONF January 2017

B.2. Data Resource and Datastore Resource Examples

B.2.1. Create New Data Resources

 To create a new "artist" resource within the "library" resource, the
 client might send the following request:
    POST /restconf/data/example-jukebox:jukebox/library HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    {
      "example-jukebox:artist" : [
        {
          "name" : "Foo Fighters"
        }
      ]
    }
 If the resource is created, the server might respond as follows:
    HTTP/1.1 201 Created
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Location: https://example.com/restconf/data/\
        example-jukebox:jukebox/library/artist=Foo%20Fighters
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    ETag: "b3830f23a4c"

Bierman, et al. Standards Track [Page 118] RFC 8040 RESTCONF January 2017

 To create a new "album" resource for this artist within the "jukebox"
 resource, the client might send the following request:
    POST /restconf/data/example-jukebox:jukebox/\
        library/artist=Foo%20Fighters HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <album xmlns="http://example.com/ns/example-jukebox">
      <name>Wasting Light</name>
      <year>2011</year>
    </album>
 If the resource is created, the server might respond as follows:
    HTTP/1.1 201 Created
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Location: https://example.com/restconf/data/\
        example-jukebox:jukebox/library/artist=Foo%20Fighters/\
        album=Wasting%20Light
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    ETag: "b8389233a4c"

B.2.2. Detect Datastore Resource Entity-Tag Change

 In this example, the server just supports the datastore last-changed
 timestamp.  Assume that the client has cached the "Last-Modified"
 header from the response to the previous request.  This value is used
 as in the "If-Unmodified-Since" header in the following request to
 patch an "album" list entry with a key value of "Wasting Light".
 Only the "genre" field is being updated.
    PATCH /restconf/data/example-jukebox:jukebox/\
        library/artist=Foo%20Fighters/album=Wasting%20Light/\
        genre HTTP/1.1
    Host: example.com
    If-Unmodified-Since: Thu, 26 Jan 2017 20:56:30 GMT
    Content-Type: application/yang-data+json
    { "example-jukebox:genre" : "example-jukebox:alternative" }

Bierman, et al. Standards Track [Page 119] RFC 8040 RESTCONF January 2017

 In this example, the datastore resource has changed since the time
 specified in the "If-Unmodified-Since" header.  The server might
 respond as follows:
    HTTP/1.1 412 Precondition Failed
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Last-Modified: Thu, 26 Jan 2017 19:41:00 GMT
    ETag: "b34aed893a4c"

Bierman, et al. Standards Track [Page 120] RFC 8040 RESTCONF January 2017

B.2.3. Edit a Datastore Resource

 In this example, assume that there is a top-level data resource named
 "system" from the example-system module, and this container has a
 child leaf called "enable-jukebox-streaming":
    container system {
      leaf enable-jukebox-streaming {
        type boolean;
      }
    }
 In this example, PATCH is used by the client to modify two top-level
 resources at once, in order to enable jukebox streaming and add an
 "album" sub-resource to each of two "artist" resources:
    PATCH /restconf/data HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <data xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
      <system xmlns="http://example.com/ns/example-system">
        <enable-jukebox-streaming>true</enable-jukebox-streaming>
      </system>
      <jukebox xmlns="http://example.com/ns/example-jukebox">
        <library>
          <artist>
            <name>Foo Fighters</name>
            <album>
              <name>One by One</name>
              <year>2012</year>
            </album>
          </artist>
          <artist>
            <name>Nick Cave and the Bad Seeds</name>
            <album>
              <name>Tender Prey</name>
              <year>1988</year>
            </album>
          </artist>
        </library>
      </jukebox>
    </data>

Bierman, et al. Standards Track [Page 121] RFC 8040 RESTCONF January 2017

B.2.4. Replace a Datastore Resource

 In this example, the entire configuration datastore contents are
 being replaced.  Any child nodes not present in the <data> element
 but present in the server will be deleted.
    PUT /restconf/data HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <data xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
      <jukebox xmlns="http://example.com/ns/example-jukebox">
        <library>
          <artist>
            <name>Foo Fighters</name>
            <album>
              <name>One by One</name>
              <year>2012</year>
            </album>
          </artist>
          <artist>
            <name>Nick Cave and the Bad Seeds</name>
            <album>
              <name>Tender Prey</name>
              <year>1988</year>
            </album>
          </artist>
        </library>
      </jukebox>
    </data>

B.2.5. Edit a Data Resource

 In this example, the client modifies one data node by adding an
 "album" sub-resource by sending a PATCH for the data resource:
    PATCH /restconf/data/example-jukebox:jukebox/library/\
       artist=Nick%20Cave%20and%20the%20Bad%20Seeds HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+xml
    <artist xmlns="http://example.com/ns/example-jukebox">
      <name>Nick Cave and the Bad Seeds</name>
      <album>
        <name>The Good Son</name>
        <year>1990</year>
      </album>
    </artist>

Bierman, et al. Standards Track [Page 122] RFC 8040 RESTCONF January 2017

B.3. Query Parameter Examples

B.3.1. "content" Parameter

 The "content" parameter is used to select the types of data child
 resources (configuration and/or non-configuration) that are returned
 by the server for a GET method request.
 In this example, a simple YANG list is used that has configuration
 and non-configuration child resources.
   container events {
     list event {
       key name;
       leaf name { type string; }
       leaf description { type string; }
       leaf event-count {
         type uint32;
         config false;
       }
     }
   }

Bierman, et al. Standards Track [Page 123] RFC 8040 RESTCONF January 2017

 Example 1: content=all
 To retrieve all of the child resources, the "content" parameter is
 set to "all", or omitted, since this is the default value.  The
 client might send the following:
    GET /restconf/data/example-events:events?\
        content=all HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+json
    {
      "example-events:events" : {
        "event" : [
          {
            "name" : "interface-up",
            "description" : "Interface up notification count",
            "event-count" : 42
          },
          {
            "name" : "interface-down",
            "description" : "Interface down notification count",
            "event-count" : 4
          }
        ]
      }
    }

Bierman, et al. Standards Track [Page 124] RFC 8040 RESTCONF January 2017

 Example 2: content=config
 To retrieve only the configuration child resources, the "content"
 parameter is set to "config".  Note that the "ETag" and
 "Last-Modified" headers are only returned if the "content" parameter
 value is "config".
    GET /restconf/data/example-events:events?\
        content=config HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Last-Modified: Thu, 26 Jan 2017 16:45:20 GMT
    ETag: "eeeada438af"
    Cache-Control: no-cache
    Content-Type: application/yang-data+json
    {
      "example-events:events" : {
        "event" : [
          {
            "name" : "interface-up",
            "description" : "Interface up notification count"
          },
          {
            "name" : "interface-down",
            "description" : "Interface down notification count"
          }
        ]
      }
    }

Bierman, et al. Standards Track [Page 125] RFC 8040 RESTCONF January 2017

 Example 3: content=nonconfig
 To retrieve only the non-configuration child resources, the "content"
 parameter is set to "nonconfig".  Note that configuration ancestors
 (if any) and list key leafs (if any) are also returned.  The client
 might send the following:
    GET /restconf/data/example-events:events?\
       content=nonconfig HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+json
    {
      "example-events:events" : {
        "event" : [
          {
            "name" : "interface-up",
            "event-count" : 42
          },
          {
            "name" : "interface-down",
            "event-count" : 4
          }
        ]
      }
    }

B.3.2. "depth" Parameter

 The "depth" parameter is used to limit the number of levels of child
 resources that are returned by the server for a GET method request.
 The "depth" parameter starts counting levels at the level of the
 target resource that is specified, so that a depth level of "1"
 includes just the target resource level itself.  A depth level of "2"
 includes the target resource level and its child nodes.

Bierman, et al. Standards Track [Page 126] RFC 8040 RESTCONF January 2017

 This example shows how different values of the "depth" parameter
 would affect the reply content for the retrieval of the top-level
 "jukebox" data resource.
 Example 1: depth=unbounded
 To retrieve all of the child resources, the "depth" parameter is not
 present or is set to the default value "unbounded".
    GET /restconf/data/example-jukebox:jukebox?\
        depth=unbounded HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+json
    {
      "example-jukebox:jukebox" : {
        "library" : {
          "artist" : [
            {
              "name" : "Foo Fighters",
              "album" : [
                {
                  "name" : "Wasting Light",
                  "genre" : "example-jukebox:alternative",
                  "year" : 2011,
                  "song" : [
                    {
                      "name" : "Wasting Light",
                      "location" :
                        "/media/foo/a7/wasting-light.mp3",
                      "format" : "MP3",
                      "length" : 286
                    },

Bierman, et al. Standards Track [Page 127] RFC 8040 RESTCONF January 2017

                    {
                      "name" : "Rope",
                      "location" : "/media/foo/a7/rope.mp3",
                      "format" : "MP3",
                      "length" : 259
                    }
                  ]
                }
              ]
            }
          ]
        },
        "playlist" : [
          {
            "name" : "Foo-One",
            "description" : "example playlist 1",
            "song" : [
              {
                "index" : 1,
                "id" : "/example-jukebox:jukebox/library\
                   /artist[name='Foo Fighters']\
                   /album[name='Wasting Light']\
                   /song[name='Rope']"
              },
              {
                "index" : 2,
                "id" : "/example-jukebox:jukebox/library\
                   /artist[name='Foo Fighters']\
                   /album[name='Wasting Light']\
                   /song[name='Bridge Burning']"
              }
            ]
          }
        ],
        "player" : {
          "gap" : 0.5
        }
      }
    }

Bierman, et al. Standards Track [Page 128] RFC 8040 RESTCONF January 2017

 Example 2: depth=1
 To determine if one or more resource instances exist for a given
 target resource, the value "1" is used.
    GET /restconf/data/example-jukebox:jukebox?depth=1 HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+json
    {
      "example-jukebox:jukebox" : {}
    }

Bierman, et al. Standards Track [Page 129] RFC 8040 RESTCONF January 2017

 Example 3: depth=3
 To limit the depth level to the target resource plus two child
 resource layers, the value "3" is used.
    GET /restconf/data/example-jukebox:jukebox?depth=3 HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Cache-Control: no-cache
    Content-Type: application/yang-data+json
    {
      "example-jukebox:jukebox" : {
        "library" : {
          "artist" : {}
        },
        "playlist" : [
          {
            "name" : "Foo-One",
            "description" : "example playlist 1",
            "song" : {}
          }
        ],
        "player" : {
          "gap" : 0.5
        }
      }
    }

B.3.3. "fields" Parameter

 In this example, the client is retrieving the datastore resource in
 JSON format, but retrieving only the "modules-state/module" list, and
 only the "name" and "revision" nodes from each list entry.  Note that
 the top node returned by the server matches the target resource node
 (which is "data" in this example).  The "module-set-id" leaf is not
 returned because it is not selected in the fields expression.

Bierman, et al. Standards Track [Page 130] RFC 8040 RESTCONF January 2017

    GET /restconf/data?fields=ietf-yang-library:modules-state/\
        module(name;revision) HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "ietf-restconf:data" : {
        "ietf-yang-library:modules-state" : {
          "module" : [
            {
              "name" : "example-jukebox",
              "revision" : "2016-08-15"
            },
            {
              "name" : "ietf-inet-types",
              "revision" : "2013-07-15"
            },
            {
              "name" : "ietf-restconf-monitoring",
              "revision" : "2017-01-26"
            },
            {
              "name" : "ietf-yang-library",
              "revision" : "2016-06-21"
            },
            {
              "name" : "ietf-yang-types",
              "revision" : "2013-07-15"
            }
          ]
        }
      }
    }

Bierman, et al. Standards Track [Page 131] RFC 8040 RESTCONF January 2017

B.3.4. "insert" Parameter

 In this example, a new first song entry in the "Foo-One" playlist is
 being created.
 Request from client:
    POST /restconf/data/example-jukebox:jukebox/\
        playlist=Foo-One?insert=first HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    {
      "example-jukebox:song" : [
         {
           "index" : 1,
           "id" : "/example-jukebox:jukebox/library\
              /artist[name='Foo Fighters']\
              /album[name='Wasting Light']\
              /song[name='Rope']"
         }
       ]
    }
 Response from server:
    HTTP/1.1 201 Created
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    Location: https://example.com/restconf/data/\
        example-jukebox:jukebox/playlist=Foo-One/song=1
    ETag: "eeeada438af"

Bierman, et al. Standards Track [Page 132] RFC 8040 RESTCONF January 2017

B.3.5. "point" Parameter

 In this example, the client is inserting a new song entry in the
 "Foo-One" playlist after the first song.
 Request from client:
    POST /restconf/data/example-jukebox:jukebox/\
        playlist=Foo-One?insert=after&point=\
        %2Fexample-jukebox%3Ajukebox\
        %2Fplaylist%3DFoo-One%2Fsong%3D1 HTTP/1.1
    Host: example.com
    Content-Type: application/yang-data+json
    {
      "example-jukebox:song" : [
         {
           "index" : 2,
           "id" : "/example-jukebox:jukebox/library\
              /artist[name='Foo Fighters']\
              /album[name='Wasting Light']\
              /song[name='Bridge Burning']"
         }
       ]
    }
 Response from server:
    HTTP/1.1 201 Created
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT
    Location: https://example.com/restconf/data/\
        example-jukebox:jukebox/playlist=Foo-One/song=2
    ETag: "abcada438af"

Bierman, et al. Standards Track [Page 133] RFC 8040 RESTCONF January 2017

B.3.6. "filter" Parameter

 The following URIs show some examples of notification filter
 specifications:
    // filter = /event/event-class='fault'
    GET /streams/NETCONF?filter=%2Fevent%2Fevent-class%3D'fault'
    // filter = /event/severity<=4
    GET /streams/NETCONF?filter=%2Fevent%2Fseverity%3C%3D4
    // filter = /linkUp|/linkDown
    GET /streams/SNMP?filter=%2FlinkUp%7C%2FlinkDown
    // filter = /*/reporting-entity/card!='Ethernet0'
    GET /streams/NETCONF?\
       filter=%2F*%2Freporting-entity%2Fcard%21%3D'Ethernet0'
    // filter = /*/email-addr[contains(.,'company.com')]
    GET /streams/critical-syslog?\
       filter=%2F*%2Femail-addr[contains(.%2C'company.com')]
    // Note: The module name is used as the prefix.
    // filter = (/example-mod:event1/name='joe' and
    //           /example-mod:event1/status='online')
    GET /streams/NETCONF?\
      filter=(%2Fexample-mod%3Aevent1%2Fname%3D'joe'%20and\
              %20%2Fexample-mod%3Aevent1%2Fstatus%3D'online')
    // To get notifications from just two modules (e.g., m1 + m2)
    // filter=(/m1:* or /m2:*)
    GET /streams/NETCONF?filter=(%2Fm1%3A*%20or%20%2Fm2%3A*)

B.3.7. "start-time" Parameter

 The following URI shows an example of the "start-time" query
 parameter:
    // start-time = 2014-10-25T10:02:00Z
    GET /streams/NETCONF?start-time=2014-10-25T10%3A02%3A00Z

Bierman, et al. Standards Track [Page 134] RFC 8040 RESTCONF January 2017

B.3.8. "stop-time" Parameter

 The following URI shows an example of the "stop-time" query
 parameter:
    // start-time = 2014-10-25T10:02:00Z
    // stop-time = 2014-10-25T12:31:00Z
    GET /mystreams/NETCONF?start-time=2014-10-25T10%3A02%3A00Z\
       &stop-time=2014-10-25T12%3A31%3A00Z

B.3.9. "with-defaults" Parameter

 Assume that the server implements the module "example" defined in
 Appendix A.1 of [RFC6243], and assume that the server's datastore is
 as defined in Appendix A.2 of [RFC6243].
 If the server's "basic-mode" parameter in the "defaults" protocol
 capability URI (Section 9.1.2) is "trim", the following request for
 interface "eth1" might be as follows:
 Without query parameter:
    GET /restconf/data/example:interfaces/interface=eth1 HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "example:interface" : [
        {
          "name" : "eth1",
          "status" : "up"
        }
      ]
    }
 Note that the "mtu" leaf is missing because it is set to the default
 "1500", and the server's default-handling "basic-mode" parameter is
 "trim".

Bierman, et al. Standards Track [Page 135] RFC 8040 RESTCONF January 2017

 With query parameter:
    GET /restconf/data/example:interfaces/interface=eth1\
        ?with-defaults=report-all HTTP/1.1
    Host: example.com
    Accept: application/yang-data+json
 The server might respond as follows:
    HTTP/1.1 200 OK
    Date: Thu, 26 Jan 2017 20:56:30 GMT
    Server: example-server
    Content-Type: application/yang-data+json
    {
      "example:interface" : [
        {
          "name" : "eth1",
          "mtu" : 1500,
          "status" : "up"
        }
      ]
    }
 Note that the server returns the "mtu" leaf because the "report-all"
 mode was requested with the "with-defaults" query parameter.

Bierman, et al. Standards Track [Page 136] RFC 8040 RESTCONF January 2017

Acknowledgements

 The authors would like to thank the following people for their
 contributions to this document: Ladislav Lhotka, Juergen
 Schoenwaelder, Rex Fernando, Robert Wilton, and Jonathan Hansford.
 The authors would like to thank the following people for their
 excellent technical reviews of this document: Mehmet Ersue, Mahesh
 Jethanandani, Qin Wu, Joe Clarke, Bert Wijnen, Ladislav Lhotka,
 Rodney Cummings, Frank Xialiang, Tom Petch, Robert Sparks, Balint
 Uveges, Randy Presuhn, Sue Hares, Mark Nottingham, Benoit Claise,
 Dale Worley, and Lionel Morand.
 Contributions to this material by Andy Bierman are based upon work
 supported by the United States Army, Space & Terrestrial
 Communications Directorate (S&TCD) under Contract
 No. W15P7T-13-C-A616.  Any opinions, findings, and conclusions or
 recommendations expressed in this material are those of the author(s)
 and do not necessarily reflect the views of the S&TCD.

Authors' Addresses

 Andy Bierman
 YumaWorks
 Email: andy@yumaworks.com
 Martin Bjorklund
 Tail-f Systems
 Email: mbj@tail-f.com
 Kent Watsen
 Juniper Networks
 Email: kwatsen@juniper.net

Bierman, et al. Standards Track [Page 137]

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