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rfc:rfc2244

Network Working Group C. Newman Request for Comments: 2244 Innosoft Category: Standards Track J. G. Myers

                                                              Netscape
                                                         November 1997
         ACAP -- Application Configuration Access Protocol

Status of this Memo

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

Copyright Notice

 Copyright (C) The Internet Society 1997.  All Rights Reserved.

Abstract

 The Application Configuration Access Protocol (ACAP) is designed to
 support remote storage and access of program option, configuration
 and preference information.  The data store model is designed to
 allow a client relatively simple access to interesting data, to allow
 new information to be easily added without server re-configuration,
 and to promote the use of both standardized data and custom or
 proprietary data.  Key features include "inheritance" which can be
 used to manage default values for configuration settings and access
 control lists which allow interesting personal information to be
 shared and group information to be restricted.

Newman & Myers Standards Track [Page i] RFC 2244 ACAP November 1997

                         Table of Contents

Status of this Memo ……………………………………….. i Copyright Notice ………………………………………….. i Abstract …………………………………………………. i ACAP Protocol Specification ………………………………… 1 1. Introduction ……………………………………… 1 1.1. Conventions Used in this Document …………………… 1 1.2. ACAP Data Model …………………………………… 1 1.3. ACAP Design Goals …………………………………. 1 1.4. Validation ……………………………………….. 2 1.5. Definitions ………………………………………. 2 1.6. ACAP Command Overview ……………………………… 4 2. Protocol Framework ………………………………… 4 2.1. Link Level ……………………………………….. 4 2.2. Commands and Responses …………………………….. 4 2.2.1. Client Protocol Sender and Server Protocol Receiver …… 4 2.2.2. Server Protocol Sender and Client Protocol Receiver …… 5 2.3. Server States …………………………………….. 6 2.3.1. Non-Authenticated State ……………………………. 6 2.3.2. Authenticated State ……………………………….. 6 2.3.3. Logout State ……………………………………… 6 2.4. Operational Considerations …………………………. 7 2.4.1. Untagged Status Updates ……………………………. 7 2.4.2. Response when No Command in Progress ………………… 7 2.4.3. Auto-logout Timer …………………………………. 7 2.4.4. Multiple Commands in Progress ………………………. 8 2.5. Server Command Continuation Request …………………. 8 2.6. Data Formats ……………………………………… 8 2.6.1. Atom …………………………………………….. 9 2.6.2. Number …………………………………………… 9 2.6.3. String …………………………………………… 9 2.6.3.1. 8-bit and Binary Strings …………………………… 10 2.6.4. Parenthesized List ………………………………… 10 2.6.5. NIL ……………………………………………… 10 3. Protocol Elements …………………………………. 10 3.1. Entries and Attributes …………………………….. 10 3.1.1. Predefined Attributes ……………………………… 11 3.1.2. Attribute Metadata ………………………………… 12 3.2. ACAP URL scheme …………………………………… 13 3.2.1. ACAP URL User Name and Authentication Mechanism ………. 13 3.2.2. Relative ACAP URLs ………………………………… 14 3.3. Contexts …………………………………………. 14

Newman & Myers Standards Track [Page ii] RFC 2244 ACAP November 1997

3.4. Comparators ………………………………………. 15 3.5. Access Control Lists (ACLs) ………………………… 17 3.6. Server Response Codes ……………………………… 18 4. Namespace Conventions ……………………………… 21 4.1. Dataset Namespace …………………………………. 21 4.2. Attribute Namespace ……………………………….. 21 4.3. Formal Syntax for Dataset and Attribute Namespace …….. 22 5. Dataset Management ………………………………… 23 5.1. Dataset Inheritance ……………………………….. 23 5.2. Dataset Attributes ………………………………… 24 5.3. Dataset Creation ………………………………….. 25 5.4. Dataset Class Capabilities …………………………. 25 5.5. Dataset Quotas ……………………………………. 26 6. Command and Response Specifications …………………. 26 6.1. Initial Connection ………………………………… 26 6.1.1. ACAP Untagged Response …………………………….. 26 6.2. Any State ………………………………………… 27 6.2.1. NOOP Command ……………………………………… 27 6.2.2. LANG Command ……………………………………… 28 6.2.3. LANG Intermediate Response …………………………. 28 6.2.4. LOGOUT Command ……………………………………. 29 6.2.5. OK Response ………………………………………. 29 6.2.6. NO Response ………………………………………. 29 6.2.7. BAD Response ……………………………………… 30 6.2.8. BYE Untagged Response ……………………………… 30 6.2.9. ALERT Untagged Response ……………………………. 31 6.3. Non-Authenticated State ……………………………. 31 6.3.1. AUTHENTICATE Command ………………………………. 31 6.4. Searching ………………………………………… 33 6.4.1. SEARCH Command ……………………………………. 33 6.4.2. ENTRY Intermediate Response ………………………… 37 6.4.3. MODTIME Intermediate Response ………………………. 38 6.4.4. REFER Intermediate Response ………………………… 38 6.4.5. Search Examples …………………………………… 38 6.5. Contexts …………………………………………. 39 6.5.1. FREECONTEXT Command ……………………………….. 39 6.5.2. UPDATECONTEXT Command ……………………………… 40 6.5.3. ADDTO Untagged Response ……………………………. 40 6.5.4. REMOVEFROM Untagged Response ……………………….. 41 6.5.5. CHANGE Untagged Response …………………………… 41 6.5.6. MODTIME Untagged Response ………………………….. 42 6.6. Dataset modification ………………………………. 42 6.6.1. STORE Command …………………………………….. 42 6.6.2. DELETEDSINCE Command ………………………………. 45 6.6.3. DELETED Intermediate Response ………………………. 45 6.7. Access Control List Commands ……………………….. 45 6.7.1. SETACL Command ……………………………………. 46 6.7.2. DELETEACL Command …………………………………. 46

Newman & Myers Standards Track [Page iii] RFC 2244 ACAP November 1997

6.7.3. MYRIGHTS Command ………………………………….. 47 6.7.4. MYRIGHTS Intermediate Response ……………………… 47 6.7.5. LISTRIGHTS Command ………………………………… 47 6.7.6. LISTRIGHTS Intermediate Response ……………………. 48 6.8. Quotas …………………………………………… 48 6.8.1. GETQUOTA Command ………………………………….. 48 6.8.3. QUOTA Untagged Response ……………………………. 49 6.9. Extensions ……………………………………….. 49 7. Registration Procedures ……………………………. 49 7.1. ACAP Capabilities …………………………………. 50 7.2. ACAP Response Codes ……………………………….. 50 7.3. Dataset Classes …………………………………… 51 7.4. Vendor Subtree ……………………………………. 51 8. Formal Syntax …………………………………….. 52 9. Multi-lingual Considerations ……………………….. 61 10. Security Considerations ……………………………. 62 11. Acknowledgments …………………………………… 63 12. Authors' Addresses ………………………………… 63 Appendices ……………………………………………….. 64 A. References ……………………………………….. 64 B. ACAP Keyword Index ………………………………… 66 C. Full Copyright Statement

Newman & Myers Standards Track [Page iv] RFC 2244 ACAP November 1997

ACAP Protocol Specification

1. Introduction

1.1. Conventions Used in this Document

 In examples, "C:" and "S:" indicate lines sent by the client and
 server respectively.  If such lines are wrapped without a new "C:" or
 "S:" label, then the wrapping is for editorial clarity and is not
 part of the command.
 The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT",
 and "MAY" in this document are to be interpreted as described in "Key
 words for use in RFCs to Indicate Requirement Levels" [KEYWORDS].

1.2. ACAP Data Model

 An ACAP server exports a hierarchical tree of entries.  Each level of
 the tree is called a dataset, and each dataset is made up of a list
 of entries.  Each entry has a unique name and may contain any number
 of named attributes.  Each attribute within an entry may be single
 valued or multi-valued and may have associated metadata to assist
 access and interpretation of the value.
 The rules with which a client interprets the data within a portion of
 ACAP's tree of entries are called a dataset class.

1.3. ACAP Design Goals

 ACAP's primary purpose is to allow users access to their
 configuration data from multiple network-connected computers.  Users
 can then sit down in front of any network-connected computer, run any
 ACAP-enabled application and have access to their own configuration
 data.  Because it is hoped that many applications will become ACAP-
 enabled, client simplicity was preferred to server or protocol
 simplicity whenever reasonable.
 ACAP is designed to be easily manageable.  For this reason, it
 includes "inheritance" which allows one dataset to inherit default
 attributes from another dataset.  In addition, access control lists
 are included to permit delegation of management and quotas are
 included to control storage.  Finally, an ACAP server which is
 conformant to this base specification should be able to support most
 dataset classes defined in the future without requiring a server
 reconfiguration or upgrade.

Newman & Myers Standards Track [Page 1] RFC 2244 ACAP November 1997

 ACAP is designed to operate well with a client that only has
 intermittent access to an ACAP server.  For this reason, each entry
 has a server maintained modification time so that the client may
 detect changes.  In addition, the client may ask the server for a
 list of entries which have been removed since it last accessed the
 server.
 ACAP presumes that a dataset may be potentially large and/or the
 client's network connection may be slow, and thus offers server
 sorting, selective fetching and change notification for entries
 within a dataset.
 As required for most Internet protocols, security, scalability and
 internationalization were important design goals.
 Given these design goals, an attempt was made to keep ACAP as simple
 as possible.  It is a traditional Internet text based protocol which
 massively simplifies protocol debugging.  It was designed based on
 the successful IMAP [IMAP4] protocol framework, with a few
 refinements.

1.4. Validation

 By default, any value may be stored in any attribute for which the
 user has appropriate permission and quota.  This rule is necessary to
 allow the addition of new simple dataset classes without
 reconfiguring or upgrading the server.
 In some cases, such as when the value has special meaning to the
 server, it is useful to have the server enforce validation by
 returning the INVALID response code to a STORE command. These cases
 MUST be explicitly identified in the dataset class specification
 which SHOULD include specific fixed rules for validation.  Since a
 given ACAP server may be unaware of any particular dataset class
 specification, clients MUST NOT depend on the presence of enforced
 validation on the server.

1.5. Definitions

 access control list (ACL)
      A set of identifier, rights pairs associated with an object.  An
      ACL is used to determine which operations a user is permitted to
      perform on that object.  See section 3.5.
 attribute
      A named value within an entry.  See section 3.1.

Newman & Myers Standards Track [Page 2] RFC 2244 ACAP November 1997

 comparator
      A named function which can be used to perform one or more of
      three comparison operations: ordering, equality and substring
      matching.  See section 3.4.
 context
      An ordered subset of entries in a dataset, created by a SEARCH
      command with a MAKECONTEXT modifier.  See section 3.3.
 dataset
      One level of hierarchy in ACAP's tree of entries.
 dataset class specification
      The rules which allow a client to interpret the data within a
      portion of ACAP's tree of entries.
 entry
      A set of attributes with a unique entry name.  See section 3.1.
 metadata
      Information describing an attribute, its value and any access
      controls associated with that attribute.  See section 3.1.2.
 NIL  This represents the non-existence of a particular data item.
 NUL  A control character encoded as 0 in US-ASCII [US-ASCII].
 octet
      An 8-bit value.  On most modern computer systems, an octet is
      one byte.
 SASL Simple Authentication and Security Layer [SASL].
 UTC  Universal Coordinated Time as maintained by the Bureau
      International des Poids et Mesures (BIPM).
 UTF-8
      An 8-bit transformation format of the Universal Character Set
      [UTF8].  Note that an incompatible change was made to the coded
      character set referenced by [UTF8], so for the purpose of this
      document, UTF-8 refers to the UTF-8 encoding as defined by
      version 2.0 of Unicode [UNICODE-2], or ISO 10646 [ISO-10646]
      including amendments one through seven.

Newman & Myers Standards Track [Page 3] RFC 2244 ACAP November 1997

1.6. ACAP Command Overview

 The AUTHENTICATE, NOOP, LANG and LOGOUT commands provide basic
 protocol services.  The SEARCH command is used to select, sort, fetch
 and monitor changes to attribute values and metadata.  The
 UPDATECONTEXT and FREECONTEXT commands are also used to assist in
 monitoring changes in attribute values and metadata.  The STORE
 command is used to add, modify and delete entries and attributes.
 The DELETEDSINCE command is used to assist a client in
 re-synchronizing a cache with the server.  The GETQUOTA, SETACL,
 DELETEACL, LISTRIGHTS and MYRIGHTS commands are used to examine
 storage quotas and examine or modify access permissions.

2. Protocol Framework

2.1. Link Level

 The ACAP protocol assumes a reliable data stream such as provided by
 TCP.  When TCP is used, an ACAP server listens on port 674.

2.2. Commands and Responses

 An ACAP session consists of the establishment of a client/server
 connection, an initial greeting from the server, and client/server
 interactions.  These client/server interactions consist of a client
 command, server data, and a server completion result.
 ACAP is a text-based line-oriented protocol.  In general,
 interactions transmitted by clients and servers are in the form of
 lines; that is, sequences of characters that end with a CRLF.  The
 protocol receiver of an ACAP client or server is either reading a
 line, or is reading a sequence of octets with a known count (a
 literal) followed by a line.  Both clients and servers must be
 capable of handling lines of arbitrary length.

2.2.1. Client Protocol Sender and Server Protocol Receiver

 The client command begins an operation.  Each client command is
 prefixed with a identifier (an alphanumeric string of no more than 32
 characters, e.g., A0001, A0002, etc.) called a "tag".  A different
 tag SHOULD be generated by the client for each command.
 There are two cases in which a line from the client does not
 represent a complete command.  In one case, a command argument is
 quoted with an octet count (see the description of literal in section
 2.6.3); in the other case, the command arguments require server

Newman & Myers Standards Track [Page 4] RFC 2244 ACAP November 1997

 feedback (see the AUTHENTICATE command).  In some of these cases, the
 server sends a command continuation request if it is ready for the
 next part of the command.  This response is prefixed with the token
 "+".
      Note: If, instead, the server detected an error in a
      command, it sends a BAD completion response with tag
      matching the command (as described below) to reject the
      command and prevent the client from sending any more of the
      command.
      It is also possible for the server to send a completion or
      intermediate response for some other command (if multiple
      commands are in progress), or untagged data.  In either
      case, the command continuation request is still pending;
      the client takes the appropriate action for the response,
      and reads another response from the server.
 The ACAP server reads a command line from the client, parses the
 command and its arguments, and transmits server data and a server
 command completion result.

2.2.2. Server Protocol Sender and Client Protocol Receiver

 Data transmitted by the server to the client come in four forms:
 command continuation requests, command completion results,
 intermediate responses, and untagged responses.
 A command continuation request is prefixed with the token "+".
 A command completion result indicates the success or failure of the
 operation.  It is tagged with the same tag as the client command
 which began the operation.  Thus, if more than one command is in
 progress, the tag in a server completion response identifies the
 command to which the response applies.  There are three possible
 server completion responses: OK (indicating success), NO (indicating
 failure), or BAD (indicating protocol error such as unrecognized
 command or command syntax error).
 An intermediate response returns data which can only be interpreted
 within the context of a command in progress.  It is tagged with the
 same tag as the client command which began the operation.  Thus, if
 more than one command is in progress, the tag in an intermediate
 response identifies the command to which the response applies.  A
 tagged response other than "OK", "NO", or "BAD" is an intermediate
 response.

Newman & Myers Standards Track [Page 5] RFC 2244 ACAP November 1997

 An untagged response returns data or status messages which may be
 interpreted outside the context of a command in progress.  It is
 prefixed with the token "*".  Untagged data may be sent as a result
 of a client command, or may be sent unilaterally by the server.
 There is no syntactic difference between untagged data that resulted
 from a specific command and untagged data that were sent
 unilaterally.
 The protocol receiver of an ACAP client reads a response line from
 the server.  It then takes action on the response based upon the
 first token of the response, which may be a tag, a "*", or a "+" as
 described above.
 A client MUST be prepared to accept any server response at all times.
 This includes untagged data that it may not have requested.
 This topic is discussed in greater detail in the Server Responses
 section.

2.3. Server States

 An ACAP server is in one of three states.  Most commands are valid in
 only certain states.  It is a protocol error for the client to
 attempt a command while the server is in an inappropriate state for
 that command.  In this case, a server will respond with a BAD command
 completion result.

2.3.1. Non-Authenticated State

 In non-authenticated state, the user must supply authentication
 credentials before most commands will be permitted.  This state is
 entered when a connection starts.

2.3.2. Authenticated State

 In authenticated state, the user is authenticated and most commands
 will be permitted.  This state is entered when acceptable
 authentication credentials have been provided.

2.3.3. Logout State

 In logout state, the session is being terminated, and the server will
 close the connection.  This state can be entered as a result of a
 client request or by unilateral server decision.

Newman & Myers Standards Track [Page 6] RFC 2244 ACAP November 1997

          +--------------------------------------+
          |initial connection and server greeting|
          +--------------------------------------+
                    || (1)                  || (2)
                    VV                      ||
          +-----------------+               ||
          |non-authenticated|               ||
          +-----------------+               ||
           || (4)      || (3)               ||
           ||          VV                   ||
           ||          +----------------+   ||
           ||          | authenticated  |   ||
           ||          +----------------+   ||
           ||            || (4)             ||
           VV            VV                 VV
          +--------------------------------------+
          |     logout and close connection      |
          +--------------------------------------+
       (1) connection (ACAP greeting)
       (2) rejected connection (BYE greeting)
       (3) successful AUTHENTICATE command
       (4) LOGOUT command, server shutdown, or connection closed

2.4. Operational Considerations

2.4.1. Untagged Status Updates

 At any time, a server can send data that the client did not request.

2.4.2. Response when No Command in Progress

 Server implementations are permitted to send an untagged response
 while there is no command in progress.  Server implementations that
 send such responses MUST deal with flow control considerations.
 Specifically, they must either (1) verify that the size of the data
 does not exceed the underlying transport's available window size, or
 (2) use non-blocking writes.

2.4.3. Auto-logout Timer

 If a server has an inactivity auto-logout timer, that timer MUST be
 of at least 30 minutes duration.  The receipt of ANY command from the
 client during that interval MUST suffice to reset the auto-logout
 timer.

Newman & Myers Standards Track [Page 7] RFC 2244 ACAP November 1997

2.4.4. Multiple Commands in Progress

 The client is not required to wait for the completion result of a
 command before sending another command, subject to flow control
 constraints on the underlying data stream.  Similarly, a server is
 not required to process a command to completion before beginning
 processing of the next command, unless an ambiguity would result
 because of a command that would affect the results of other commands.
 If there is such an ambiguity, the server executes commands to
 completion in the order given by the client.

2.5. Server Command Continuation Request

 The command continuation request is indicated by a "+" token instead
 of a tag.  This indicates that the server is ready to accept the
 continuation of a command from the client.
 This response is used in the AUTHENTICATE command to transmit server
 data to the client, and request additional client data.  This
 response is also used if an argument to any command is a
 synchronizing literal (see section 2.6.3).
 The client is not permitted to send the octets of a synchronizing
 literal unless the server indicates that it expects it.  This permits
 the server to process commands and reject errors on a line-by-line
 basis, assuming it checks for non-synchronizing literals at the end
 of each line.  The remainder of the command, including the CRLF that
 terminates a command, follows the octets of the literal.  If there
 are any additional command arguments the literal octets are followed
 by a space and those arguments.
 Example:    C: A099 FREECONTEXT {10}
             S: + "Ready for additional command text"
             C: FRED
             C: FOOB
             S: A099 OK "FREECONTEXT completed"
             C: A044 BLURDYBLOOP {102856}
             S: A044 BAD "No such command as 'BLURDYBLOOP'"

2.6. Data Formats

 ACAP uses textual commands and responses.  Data in ACAP can be in one
 of five forms: atom, number, string, parenthesized list or NIL.

Newman & Myers Standards Track [Page 8] RFC 2244 ACAP November 1997

2.6.1. Atom

 An atom consists of one to 1024 non-special characters.  It must
 begin with a letter.  Atoms are used for protocol keywords.

2.6.2. Number

 A number consists of one or more digit characters, and represents a
 numeric value.  Numbers are restricted to the range of an unsigned
 32-bit integer: 0 < number < 4,294,967,296.

2.6.3. String

 A string is in one of two forms: literal and quoted string.  The
 literal form is the general form of string.  The quoted string form
 is an alternative that avoids the overhead of processing a literal at
 the cost of restrictions of what may be in a quoted string.
 A literal is a sequence of zero or more octets (including CR and LF),
 prefix-quoted with an octet count in the form of an open brace ("{"),
 the number of octets, close brace ("}"), and CRLF.  In the case of
 literals transmitted from server to client, the CRLF is immediately
 followed by the octet data.
 There are two forms of literals transmitted from client to server.
 The form where the open brace ("{") and number of octets is
 immediately followed by a close brace ("}") and CRLF is called a
 synchronizing literal.  When sending a synchronizing literal, the
 client must wait to receive a command continuation request before
 sending the octet data (and the remainder of the command).  The other
 form of literal, the non-synchronizing literal, is used to transmit a
 string from client to server without waiting for a command
 continuation request.  The non-synchronizing literal differs from the
 synchronizing literal by having a plus ("+") between the number of
 octets and the close brace ("}") and by having the octet data
 immediately following the CRLF.
 A quoted string is a sequence of zero to 1024 octets excluding NUL,
 CR and LF, with double quote (<">) characters at each end.
 The empty string is represented as "" (a quoted string with zero
 characters between double quotes), as {0} followed by CRLF (a
 synchronizing literal with an octet count of 0), or as {0+} followed
 by a CRLF (a non-synchronizing literal with an octet count of 0).
      Note: Even if the octet count is 0, a client transmitting a
      synchronizing literal must wait to receive a command
      continuation request.

Newman & Myers Standards Track [Page 9] RFC 2244 ACAP November 1997

2.6.3.1. 8-bit and Binary Strings

 Most strings in ACAP are restricted to UTF-8 characters and may not
 contain NUL octets.  Attribute values MAY contain any octets
 including NUL.

2.6.4. Parenthesized List

 Data structures are represented as a "parenthesized list"; a sequence
 of data items, delimited by space, and bounded at each end by
 parentheses.  A parenthesized list can contain other parenthesized
 lists, using multiple levels of parentheses to indicate nesting.
 The empty list is represented as () -- a parenthesized list with no
 members.

2.6.5. NIL

 The special atom "NIL" represents the non-existence of a particular
 data item that is represented as a string or parenthesized list, as
 distinct from the empty string "" or the empty parenthesized list ().

3. Protocol Elements

 This section defines data formats and other protocol elements used
 throughout the ACAP protocol.

3.1. Entries and Attributes

 Within a dataset, each entry name is made up of zero or more UTF-8
 characters other than slash ("/").  A slash separated list of
 entries, one at each level of the hierarchy, forms the full path to
 an entry.
 Each entry is made up of a set of attributes.  Each attribute has a
 hierarchical name in UTF-8, with each component of the name separated
 by a period (".").
 The value of an attribute is either single or multi-valued.  A single
 value is NIL (has no value), or a string of zero or more octets.  A
 multi-value is a list of zero or more strings, each of zero or more
 octets.
 Attribute names are not permitted to contain asterisk ("*") or
 percent ("%") and MUST be valid UTF-8 strings which do not contain
 NUL.  Invalid attribute names result in a BAD response.  Entry names

Newman & Myers Standards Track [Page 10] RFC 2244 ACAP November 1997

 are not permitted to begin with "." or contain slash ("/") and MUST
 be valid UTF-8 strings which do not contain NUL.  Invalid entry names
 in the entry field of a command result in a BAD response.
 Use of non-visible UTF-8 characters in attribute and entry names is
 discouraged.

3.1.1. Predefined Attributes

 Attribute names which do not contain a dot (".") are reserved for
 standardized attributes which have meaning in any dataset.  The
 following attributes are defined by the ACAP protocol.
 entry
      Contains the name of the entry.  MUST be single valued.
      Attempts to use illegal or multi-valued values for the entry
      attribute are protocol errors and MUST result in a BAD
      completion response.  This is a special case.
 modtime
      Contains the date and time any read-write metadata in the entry
      was last modified.  This value MUST be in UTC, MUST be
      automatically updated by the server.
      The value consists of 14 or more US-ASCII digits.  The first
      four indicate the year, the next two indicate the month, the
      next two indicate the day of month, the next two indicate the
      hour (0 - 23), the next two indicate the minute, and the next
      two indicate the second.  Any further digits indicate fractions
      of a second.
      The time, particularly fractions of a second, need not be
      accurate.  It is REQUIRED, however, that any two entries in a
      dataset changed by successive modifications have strictly
      ascending modtime values.  In addition, each STORE command
      within a dataset (including simultaneous stores from different
      connections) MUST use different modtime values.
      This attribute has enforced validation, so any attempt to STORE
      a value in this attribute MAY result in a NO response with an
      INVALID response code.
 subdataset
      If this attribute is set, it indicates the existence of a sub-
      dataset of this entry.

Newman & Myers Standards Track [Page 11] RFC 2244 ACAP November 1997

      The value consists of a list of relative ACAP URLs (see section
      3.2) which may be used to locate the sub-dataset.  The base URL
      is the full path to the entry followed by a slash ("/").  The
      value "." indicates a subdataset is located directly under this
      one.  Multiple values indicate replicated copies of the
      subdataset.
      For example, if the dataset "/folder/site/" has an entry
      "public-folder" with a subdataset attribute of ".", then there
      exists a dataset "/folder/site/public-folder/".  If the value of
      the subdataset attribute was instead
      "//other.acap.domain//folder/site/public-folder/", that would
      indicate the dataset is actually located on a different ACAP
      server.
      A dataset can be created by storing a "subdataset" attribute
      including ".", and a sub-hierarchy of datasets is deleted by
      storing a NIL value to the "subdataset" attribute on the entry
      in the parent dataset.
      This attribute has enforced syntax validation.  Specifically, if
      an attempt is made to STORE a non-list value (other than NIL),
      an empty list, or one of the values does not follow the URL
      syntax rules [BASIC-URL, REL-URL], then this will result in a NO
      response with an INVALID response code.

3.1.2. Attribute Metadata

 Each attribute is made up of metadata items which describe that
 attribute, its value and any associated access controls.  Metadata
 items may be either read-only, in which case the client is never
 permitted to modify the item, or read-write, in which case the client
 may modify the item if the access control list (ACL) permits.
 The following metadata items are defined in this specification:
 acl    The access control list for the attribute, if one exists.  If
        the attribute does not have an ACL, NIL is returned.
        Read-write.  See section 3.5 for the contents of an ACL.
 attribute
        The attribute name.  Read-only.
 myrights
        The set of rights that the client has to the attribute.
        Read-only.  See section 3.5 for the possible rights.

Newman & Myers Standards Track [Page 12] RFC 2244 ACAP November 1997

 size   This is the length of the value.  In the case of a
        multi-value, this is a list of lengths for each of the values.
        Read-only.
 value  The value.  For a multi-value, this is a list of single
        values.  Read-write.
 Additional items of metadata may be defined in extensions to this
 protocol.  Servers MUST respond to unrecognized metadata by returning
 a BAD command completion result.

3.2. ACAP URL scheme

 ACAP URLs are used within the ACAP protocol for the "subdataset"
 attribute, referrals and inheritance.  They provide a convenient
 syntax for referring to other ACAP datasets.  The ACAP URL follows
 the common Internet scheme syntax as defined in [BASIC-URL] except
 that plaintext passwords are not permitted.  If :<port> is omitted,
 the port defaults to 674.
 An ACAP URL has the following general form:
 url-acap  = "acap://" url-server "/" url-enc-entry [url-filter]
             [url-extension]
 The <url-server> element includes the hostname, and optional user
 name, authentication mechanism and port number.  The <url-enc-entry>
 element contains the name of an entry path encoded according to the
 rules in [BASIC-URL].
 The <url-filter> element is an optional list of interesting attribute
 names.  If omitted, the URL refers to all attributes of the named
 entry.  The <url-extension> element is reserved for extensions to
 this URL scheme.
 Note that unsafe or reserved characters such as " " or "?" MUST be
 hex encoded as described in the URL specification [BASIC-URL].  Hex
 encoded octets are interpreted according to UTF-8 [UTF8].

3.2.1. ACAP URL User Name and Authentication Mechanism

 A user name and/or authentication mechanism may be supplied.  They
 are used in the "AUTHENTICATE" command after making the connection to
 the ACAP server.  If no user name or authentication mechanism is
 supplied, then the SASL ANONYMOUS [SASL-ANON] mechanism is used by
 default.  If an authentication mechanism is supplied without a user

Newman & Myers Standards Track [Page 13] RFC 2244 ACAP November 1997

 name, then one SHOULD be obtained from the specified mechanism or
 requested from the user as appropriate.  If a user name is supplied
 without an authentication mechanism then ";AUTH=*" is assumed.
 The ";AUTH=" authentication parameter is interpreted as described in
 the IMAP URL Scheme [IMAP-URL].
 Note that if unsafe or reserved characters such as " " or ";" are
 present in the user name or authentication mechanism, they MUST be
 encoded as described in the URL specification [BASIC-URL].

3.2.2. Relative ACAP URLs

 Because ACAP uses "/" as the hierarchy separator for dataset paths,
 it works well with the relative URL rules defined in the relative URL
 specification [REL-URL].
 The <aauth> grammar element is considered part of the user name for
 purposes of resolving relative ACAP URLs.
 The base URL for a relative URL stored in an attribute's value is
 formed by taking the path to the dataset containing that attribute,
 appending a "/" followed by the entry name of the entry containing
 that attribute followed by "/".

3.3. Contexts

 A context is subset of entries in a dataset or datasets, created by a
 SEARCH command with a MAKECONTEXT modifier.  Context names are
 client-generated strings and must not start with the slash ('/')
 character.
 When a client creates a context, it may request automatic
 notification of changes.  A client may also request enumeration of
 entries within a context.  Enumeration simplifies the implementation
 of a "virtual scrollbar" by the client.
 A context exists only within the ACAP session in which it was
 created.  When the connection is closed, all contexts associated with
 that connection are automatically discarded.  A server is required to
 support at least 100 active contexts within a session.  If the server
 supports a larger limit it must advertise it in a CONTEXTLIMIT
 capability.

Newman & Myers Standards Track [Page 14] RFC 2244 ACAP November 1997

3.4. Comparators

 A comparator is a named function which takes two input values and can
 be used to perform one or more of four comparison operations:
 ordering, equality, prefix and substring matching.
 The ordering operation is used both for the SORT search modifier and
 the COMPARE and COMPARESTRICT search keys.  Ordering comparators can
 determine the ordinal precedence of any two values.  When used for
 ordering, a comparator's name can be prefixed with "+" or "-" to
 indicate that the ordering should be normal order or reversed order
 respectively.  If no prefix is included, "+" is assumed.
 For the purpose of ordering, a comparator may designate certain
 values as having an undefined ordinal precedence.  Such values always
 collate with equal value after all other values regardless of whether
 normal or reversed ordering is used.  Unless the comparator
 definition specifies otherwise, multi-values and NIL values have an
 undefined ordinal precedence.
 The equality operation is used for the EQUAL search modifier, and
 simply determines if the two values are considered equal under the
 comparator function.  When comparing a single value to a multi-value,
 the two are considered equal if any one of the multiple values is
 equal to the single value.
 The prefix match operation is used for the PREFIX search modifier,
 and simply determines if the search value is a prefix of the item
 being searched.  In the case of prefix search on a multi-value, the
 match is successful if the value is a prefix of any one of the
 multiple values.
 The substring match operation is used for the SUBSTRING search
 modifier, and simply determines if search value is a substring of the
 item being searched.  In the case of substring search on a multi-
 value, the match is successful if the value is a substring of any one
 of the multiple values.
 Rules for naming and registering comparators will be defined in a
 future specification.  Servers MUST respond to unknown or improperly
 used comparators with a BAD command completion result.

Newman & Myers Standards Track [Page 15] RFC 2244 ACAP November 1997

 The following comparators are defined by this standard and MUST be
 implemented:
    i;octet
         Operations: Ordering, Equality, Prefix match, Substring match
         For collation, the i;octet comparator interprets the value of
         an attribute as a series of unsigned octets with ordinal
         values from 0 to 255.  When ordering two strings, each octet
         pair is compared in sequence until the octets are unequal or
         the end of the string is reached.  When collating two strings
         where the shorter is a prefix of the longer, the shorter
         string is interpreted as having a smaller ordinal value.  The
         "i;octet" or "+i;octet" forms collate smaller ordinal values
         earlier, and the "-i;octet" form collates larger ordinal
         values earlier.
         For the equality function, two strings are equal if they are
         the same length and contain the same octets in the same
         order.  NIL is equal only to itself.
         For non-binary, non-nil single values, i;octet ordering is
         equivalent to the ANSI C [ISO-C] strcmp() function applied to
         C string representations of the values.  For non-binary,
         non-nil single values, i;octet substring match is equivalent
         to the ANSI C strstr() function applied to the C string
         representations of the values.
    i;ascii-casemap
         Operations: Ordering, Equality, Prefix match, Substring match
         The i;ascii-casemap comparator first applies a mapping to the
         attribute values which translates all US-ASCII letters to
         uppercase (octet values 0x61 to 0x7A are translated to octet
         values 0x41 to 0x5A respectively), then applies the i;octet
         comparator as described above.  With this function the values
         "hello" and "HELLO" have the same ordinal value and are
         considered equal.
    i;ascii-numeric
         Operations: Ordering, Equality
         The i;ascii-numeric comparator interprets strings as decimal
         positive integers represented as US-ASCII digits.  All values
         which do not begin with a US-ASCII digit are considered equal
         with an ordinal value higher than all non-NIL single-valued

Newman & Myers Standards Track [Page 16] RFC 2244 ACAP November 1997

         attributes.  Otherwise, all US-ASCII digits (octet values
         0x30 to 0x39) are interpreted starting from the beginning of
         the string to the first non-digit or the end of the string.

3.5. Access Control Lists (ACLs)

 An access control list is a set of identifier, rights pairs used to
 restrict access to a given dataset, attribute or attribute within an
 entry.  An ACL is represented by a multi-value with each value
 containing an identifier followed by a tab character followed by the
 rights.  The syntax is defined by the "acl" rule in the formal syntax
 in section 8.
 Identifier is a UTF-8 string.  The identifier "anyone" is reserved to
 refer to the universal identity (all authentications, including
 anonymous).  All user name strings accepted by the AUTHENTICATE
 command to authenticate to the ACAP server are reserved as
 identifiers for the corresponding user.  Identifiers starting with a
 slash ("/") character are reserved for authorization groups which
 will be defined in a future specification.  Identifiers MAY be
 prefixed with a dash ("-") to indicate a revocation of rights.  All
 other identifiers have implementation-defined meanings.
 Rights is a string listing a (possibly empty) set of alphanumeric
 characters, each character listing a set of operations which is being
 controlled.  Letters are reserved for "standard" rights, listed
 below.  The set of standard rights may only be extended by a
 standards-track or IESG approved experimental RFC.  Digits are
 reserved for implementation or site defined rights.  The currently
 defined standard rights are:
 x - search (use EQUAL search key with i;octet comparator)
 r - read (access with SEARCH command)
 w - write (modify with STORE command)
 i - insert (perform STORE on a previously NIL value)
 a - administer (perform SETACL or STORE on ACL attribute/metadata)
 An implementation may force rights to always or never be granted.  In
 particular, implementations are expected to grant implicit read and
 administer rights to a user's personal dataset storage in order to
 avoid denial of service problems.  Rights are never tied, unlike the
 IMAP ACL extension [IMAP-ACL].
 It is possible for multiple identifiers in an access control list to
 apply to a given user (or other authentication identity).  For
 example, an ACL may include rights to be granted to the identifier
 matching the user, one or more implementation-defined identifiers

Newman & Myers Standards Track [Page 17] RFC 2244 ACAP November 1997

 matching groups which include the user, and/or the identifier
 "anyone".  These rights are combined by taking the union of all
 positive rights which apply to a given user and subtracting the union
 of all negative rights which apply to that user.  A client MAY avoid
 this calculation by using the MYRIGHTS command and metadata items.
 Each attribute of each entry of a dataset may potentially have an
 ACL.  If an attribute in an entry does not have an ACL, then access
 is controlled by a default ACL for that attribute in the dataset, if
 it exists.  If there is no default ACL for that attribute in the
 dataset, access is controlled by a default ACL for that dataset.  The
 default ACL for a dataset must exist.
 In order to perform any access or manipulation on an entry in a
 dataset, the client must have 'r' rights on the "entry" attribute of
 the entry.  Implementations should take care not to reveal via error
 messages the existence of an entry for which the client does not have
 'r' rights.  A client does not need access to the "subdataset"
 attribute of the parent dataset in order to access the contents of a
 dataset.
 Many of the ACL commands and responses include an "acl object"
 parameter, for specifying what the ACL applies to.  This is a
 parenthesized list.  The list contains just the dataset name when
 referring to the default ACL for a dataset.  The list contains a
 dataset name and an attribute name when referring to the default ACL
 for an attribute in a dataset.  The list contains a dataset name, an
 attribute name, and an entry name when referring to the ACL for an
 attribute of an entry of a dataset.

3.6. Server Response Codes

 An OK, NO, BAD, ALERT or BYE response from the server MAY contain a
 response code to describe the event in a more detailed machine
 parsable fashion.  A response code consists of data inside
 parentheses in the form of an atom, possibly followed by a space and
 arguments.  Response codes are defined when there is a specific
 action that a client can take based upon the additional information.
 In order to support future extension, the response code is
 represented as a slash-separated hierarchy with each level of
 hierarchy representing increasing detail about the error.  Clients
 MUST tolerate additional hierarchical response code detail which they
 don't understand.
 The currently defined response codes are:

Newman & Myers Standards Track [Page 18] RFC 2244 ACAP November 1997

    AUTH-TOO-WEAK
         This response code is returned on a tagged NO result from an
         AUTHENTICATE command.  It indicates that site security policy
         forbids the use of the requested mechanism for the specified
         authentication identity.
    ENCRYPT-NEEDED
         This response code is returned on a tagged NO result from an
         AUTHENTICATE command.  It indicates that site security policy
         requires the use of a strong encryption mechanism for the
         specified authentication identity and mechanism.
    INVALID
         This response code indicates that a STORE command included
         data which the server implementation does not permit.  It
         MUST NOT be used unless the dataset class specification for
         the attribute in question explicitly permits enforced server
         validation.  The argument is the attribute which was invalid.
    MODIFIED
         This response code indicates that a conditional store failed
         because the modtime on the entry is later than the modtime
         specified with the STORE command UNCHANGEDSINCE modifier.
         The argument is the entry which had been modified.
    NOEXIST
         This response code indicates that a search or NOCREATE store
         failed because a specified dataset did not exist.  The
         argument is the dataset which does not exist.
    PERMISSION
         A command failed due to insufficient permission based on the
         access control list or implicit rights.  The argument is the
         acl-object which caused the permission failure.
    QUOTA
         A STORE or SETACL command which would have increased the size
         of the dataset failed due to insufficient quota.
    REFER
         This response code may be returned in a tagged NO response to
         any command that takes a dataset name as a parameter.  It has
         one or more arguments with the syntax of relative URLs.  It
         is a referral, indicating that the command should be retried
         using one of the relative URLs.

Newman & Myers Standards Track [Page 19] RFC 2244 ACAP November 1997

    SASL This response code can occur in the tagged OK response to a
         successful AUTHENTICATE command and includes the optional
         final server response data from the server as specified by
         SASL [SASL].
    TOOMANY
         This response code may be returned in a tagged OK response to
         a SEARCH command which includes the LIMIT modifier.  The
         argument returns the total number of matching entries.
    TOOOLD
         The modtime specified in the DELETEDSINCE command is too old,
         so deletedsince information is no longer available.
    TRANSITION-NEEDED
         This response code occurs on a NO response to an AUTHENTICATE
         command.  It indicates that the user name is valid, but the
         entry in the authentication database needs to be updated in
         order to permit authentication with the specified mechanism.
         This can happen if a user has an entry in a system
         authentication database such as Unix /etc/passwd, but does
         not have credentials suitable for use by the specified
         mechanism.
    TRYLATER
         A command failed due to a temporary server failure.  The
         client MAY continue using local information and try the
         command later.
    TRYFREECONTEXT
         This response code may be returned in a tagged NO response to
         a SEARCH command which includes the MAKECONTEXT modifier.  It
         indicates that a new context may not be created due to the
         server's limit on the number of existing contexts.
    WAYTOOMANY
         This response code may be returned in a tagged NO response to
         a SEARCH command which includes a HARDLIMIT search modifier.
         It indicates that the SEARCH would have returned more entries
         than the HARDLIMIT permitted.
    Additional response codes MUST be registered with IANA according
    to the proceedures in section 7.2.  Client implementations MUST
    tolerate response codes that they do not recognize.

Newman & Myers Standards Track [Page 20] RFC 2244 ACAP November 1997

4. Namespace Conventions

4.1. Dataset Namespace

 The dataset namespace is a slash-separated hierarchy.  The first
 component of the dataset namespace is a dataset class.  Dataset
 classes MUST have a vendor prefix (vendor.<vendor/product>) or be
 specified in a standards track or IESG approved experimental RFC.
 See section 7.3 for the registration template.
 The second component of the dataset name is "site", "group", "host",
 or "user" referring to server-wide data, administrative group data,
 per-host data and per-user data respectively.
 For "group", "host", and "user" areas, the third component of the
 path is the group name, the fully qualified host domain name, or the
 user name.  A path of the form "/<dataset-class>/~/" is a convenient
 abbreviation for "/<dataset-class>/user/<current-user>/".
 Dataset names which begin with "/byowner/" are reserved as an
 alternate view of the namespace.  This provides a way to see all the
 dataset classes which a particular owner uses.  For example,
 "/byowner/~/<dataset-class>/" is an alternate name for
 "/<dataset-class>/~/".  Byowner provides a way to view a list of
 dataset classes owned by a given user; this is done using the dataset
 "/byowner/user/<current-user>/" with the NOINHERIT SEARCH modifier.
 The dataset "/" may be used to find all dataset classes visible to
 the current user.  A dataset of the form "/<dataset-class>/user/" may
 be used to find all users which have made a dataset or entry of that
 class visible to the current user.
 The formal syntax for a dataset name is defined by the "dataset-name"
 rule in section 4.3.

4.2. Attribute Namespace

 Attribute names which do not contain a dot (".") are reserved for
 standardized attributes which have meaning in any dataset.  In order
 to simplify client implementations, the attribute namespace is
 intended to be unique across all datasets.  To achieve this,
 attribute names are prefixed with the dataset class name followed by
 a dot (".").  Attributes which affect management of the dataset are
 prefixed with "dataset.".  In addition, a subtree of the "vendor."
 attribute namespace may be registered with IANA according to the
 rules in section 7.4.  ACAP implementors are encouraged to help
 define interoperable dataset classes specifications rather than using
 the private attribute namespace.

Newman & Myers Standards Track [Page 21] RFC 2244 ACAP November 1997

 Some users or sites may wish to add their own private attributes to
 certain dataset classes.  In order to enable this, the "user.<user-
 name>." and "site." subtrees of the attribute namespace are reserved
 for user-specific and site-specific attributes respectively and will
 not be standardized.  Such attributes are not interoperable so are
 discouraged in favor of defining standard attributes.  A future
 extension is expected to permit discovery of syntax for user or
 site-specific attributes.  Clients wishing to support display of user
 or site-specific attributes should display the value of any non-NIL
 single-valued "user.<user-name>." or "site."  attribute which has
 valid UTF-8 syntax.
 The formal syntax for an attribute name is defined by the
 "attribute-name" rule in the next section.

4.3. Formal Syntax for Dataset and Attribute Namespace

 The naming conventions for datasets and attributes are defined by the
 following ABNF.   Note that this grammar is not part of the ACAP
 protocol syntax in section 8, as dataset names and attribute names
 are encoded as strings within the ACAP protocol.
 attribute-dacl  = "dataset.acl" *("." name-component)
 attribute-dset  = dataset-std 1*("." name-component)
                   ;; MUST be defined in a dataset class specification
 attribute-name  = attribute-std / attr-site / attr-user / vendor-name
 attribute-std   = "entry" / "subdataset" / "modtime" /
                   "dataset.inherit" / attribute-dacl / attribute-dset
 attr-site       = "site" 1*("." name-component)
 attr-user       = "user." name-component 1*("." name-component)
 byowner         = "/byowner/" owner "/"
                   [dataset-class "/" dataset-sub]
 dataset-class   = dataset-std / vendor-name
 dataset-normal  = "/" [dataset-class "/"
                   (owner-prefix / dataset-tail)]
 dataset-name    = byowner / dataset-normal

Newman & Myers Standards Track [Page 22] RFC 2244 ACAP November 1997

 dataset-std     = name-component
                   ;; MUST be registered with IANA and the spec MUST
                   ;; be published as a standards track or
                   ;; IESG-approved experimental RFC
 dataset-sub     = *(dname-component "/")
                   ;; The rules for this portion of the namespace may
                   ;; be further restricted by the dataset class
                   ;; specification.
 dataset-tail    = owner "/" dataset-sub
 dname-component = 1*UTF8-CHAR
                   ;; MUST NOT begin with "." or contain "/"
 name-component  = 1*UTF8-CHAR
                   ;; MUST NOT contain ".", "/", "%", or "*"
 owner           = "site" / owner-host / owner-group /
                   owner-user / "~"
 owner-group     = "group/" dname-component
 owner-host      = "host/" dname-component
 owner-prefix    = "group/" / "host/" / "user/"
 owner-user      = "user/" dname-component
 vendor-name     = vendor-token *("." name-component)
 vendor-token    = "vendor." name-component
                   ;; MUST be registered with IANA

5. Dataset Management

 The entry with an empty name ("") in the dataset is used to hold
 management information for the dataset as a whole.

5.1. Dataset Inheritance

 It is possible for one dataset to inherit data from another.  The
 dataset from which the data is inherited is called the base dataset.
 Data in the base dataset appears in the inheriting dataset, except
 when overridden by a STORE to the inheriting dataset.

Newman & Myers Standards Track [Page 23] RFC 2244 ACAP November 1997

 The base dataset is usually a system-wide or group-wide set of
 defaults.  A system-wide dataset usually has one inheriting dataset
 per user, allowing each user to add to or modify the defaults as
 appropriate.
 An entry which exists in both the inheriting and base dataset
 inherits a modtime equal to the greater of the two modtimes.  An
 attribute in such an entry is inherited from the base dataset if it
 was never modified by a STORE command in the inheriting dataset or if
 DEFAULT was stored to that attribute.  This permits default entries
 to be amended rather than replaced in the inheriting dataset.
 The "subdataset" attribute is not directly inherited.  If the base
 dataset includes a "subdataset" attribute and the inheriting dataset
 does not, then the "subdataset" attribute will inherit a virtual
 value of a list containing a ".".  The subdataset at that node is
 said to be a "virtual" dataset as it is simply a virtual copy of the
 appropriate base dataset with all "subdataset" attributes changed to
 a list containing a ".".  A virtual dataset is not visible if
 NOINHERIT is specified on the SEARCH command.
 Servers MUST support at least two levels of inheritance.  This
 permits a user's dataset such as "/options/user/fred/common" to
 inherit from a group dataset such as "/options/group/dinosaur
 operators/common" which in turn inherits from a server-wide dataset
 such as "/options/site/common".

5.2. Dataset Attributes

 The following attributes apply to management of the dataset when
 stored in the "" entry of a dataset.  These attributes are not
 inherited.
 dataset.acl
      This holds the default access control list for the dataset.
      This attribute is validated, so an invalid access control list
      in a STORE command will result in a NO response with an INVALID
      response code.
 dataset.acl.<attribute>
      This holds the default access control list for an attribute
      within the dataset.  This attribute is validated, so an invalid
      access control list in a STORE command will result in a NO
      response with an INVALID response code.
 dataset.inherit
      This holds the name of a dataset from which to inherit according
      to the rules in the previous section.  This attribute MAY refer

Newman & Myers Standards Track [Page 24] RFC 2244 ACAP November 1997

      to a non-existent dataset, in which case nothing is inherited.
      This attribute is validated, so illegal dataset syntax or an
      attempt to store a multi-value will result in a NO response with
      an INVALID response code.

5.3. Dataset Creation

 When a dataset is first created (by storing a "." in the subdataset
 attribute or storing an entry in a previously non-existent dataset),
 the dataset attributes are initialized with the values from the
 parent dataset in the "/byowner/" hierarchy.  In the case of the
 "dataset.inherit" attribute, the appropriate hierarchy component is
 added.  For example, given the following entry (note that \t refers
 to the US-ASCII horizontal tab character):
 entry path        "/byowner/user/joe/"
 dataset.acl       ("joe\txrwia" "fred\txr")
 dataset.inherit   "/byowner/site"
 If a new dataset class "/byowner/user/joe/new" is created, it will
 have the following dataset attributes:
 entry path        "/byowner/user/joe/new/"
 dataset.acl       ("joe\txrwia" "fred\txr")
 dataset.inherit   "/byowner/site/new"
 Note that the dataset "/byowner/user/joe/new/" is equivalent to
 "/new/user/joe/".

5.4. Dataset Class Capabilities

 Certain dataset classes or dataset class features may only be useful
 if there is an active updating client or integrated server support
 for the feature.  The dataset class "capability" is reserved to allow
 clients or servers to advertise such features.  The "entry" attribute
 within this dataset class is the name of the dataset class whose
 features are being described.  The attributes are prefixed with
 "capability.<dataset-class>." and are defined by the appropriate
 dataset class specification.
 Since it is possible for an unprivileged user to run an active client
 for himself, a per-user capability dataset is useful.  The dataset
 "/capability/~/" holds information about all features available to
 the user (via inheritance), and the dataset "/capability/site/" holds
 information about all features supported by the site.

Newman & Myers Standards Track [Page 25] RFC 2244 ACAP November 1997

5.5. Dataset Quotas

 Management and scope of quotas is implementation dependent.  Clients
 can check the applicable quota limit and usage (in bytes) with the
 GETQUOTA command.  Servers can notify the client of a low quota
 situation with the QUOTA untagged response.

6. Command and Response Specifications

 ACAP commands and responses are described in this section.  Commands
 are organized first by the state in which the command is permitted,
 then by a general category of command type.
 Command arguments, identified by "Arguments:" in the command
 descriptions below, are described by function, not by syntax.  The
 precise syntax of command arguments is described in the Formal Syntax
 section.
 Some commands cause specific server data to be returned; these are
 identified by "Data:" in the command descriptions below.  See the
 response descriptions in the Responses section for information on
 these responses, and the Formal Syntax section for the precise syntax
 of these responses.  It is possible for server data to be transmitted
 as a result of any command; thus, commands that do not specifically
 require server data specify "no specific data for this command"
 instead of "none".
 The "Result:" in the command description refers to the possible
 tagged status responses to a command, and any special interpretation
 of these status responses.

6.1. Initial Connection

 Upon session startup, the server sends one of two untagged responses:
 ACAP or BYE.  The untagged BYE response is described in section
 6.2.8.

6.1.1. ACAP Untagged Response

 Data:       capability list
    The untagged ACAP response indicates the session is ready to
    accept commands and contains a space-separated listing of
    capabilities that the server supports.  Each capability is
    represented by a list containing the capability name optionally
    followed by capability specific string arguments.

Newman & Myers Standards Track [Page 26] RFC 2244 ACAP November 1997

    ACAP capability names MUST be registered with IANA according to
    the rules in section 7.1.
    Client implementations SHOULD NOT require any capability name
    beyond those defined in this specification, and MUST tolerate any
    unknown capability names.  A client implementation MAY be
    configurable to require SASL mechanisms other than CRAM-MD5
    [CRAM-MD5] for site security policy reasons.
    The following initial capabilities are defined:
    CONTEXTLIMIT
          The CONTEXTLIMIT capability has one argument which is a
          number describing the maximum number of contexts the server
          supports per connection.  The number 0 indicates the server
          has no limit, otherwise this number MUST be greater than
          100.
    IMPLEMENTATION
          The IMPLEMENTATION capability has one argument which is a
          string describing the server implementation.  ACAP clients
          MUST NOT alter their behavior based on this value.  It is
          intended primarily for debugging purposes.
    SASL  The SASL capability includes a list of the authentication
          mechanisms supported by the server.  See section 6.3.1.
 Example:    S: * ACAP (IMPLEMENTATION "ACME v3.5")
                       (SASL "CRAM-MD5") (CONTEXTLIMIT "200")

6.2. Any State

 The following commands and responses are valid in any state.

6.2.1. NOOP Command

 Arguments:  none
 Data:       no specific data for this command (but see below)
 Result:     OK - noop completed
             BAD - command unknown or arguments invalid
    The NOOP command always succeeds.  It does nothing.  It can be
    used to reset any inactivity auto-logout timer on the server.
 Example:    C: a002 NOOP

Newman & Myers Standards Track [Page 27] RFC 2244 ACAP November 1997

             S: a002 OK "NOOP completed"

6.2.2. LANG Command

 Arguments:  list of language preferences
 Data:       intermediate response: LANG
 Result:     OK - lang completed
             NO - no matching language available
             BAD - command unknown or arguments invalid
    One or more arguments are supplied to indicate the client's
    preferred languages [LANG-TAGS] for error messages.  The server
    will match each client preference in order against its internal
    table of available error string languages.  For a client
    preference to match a server language, the client's language tag
    MUST be a prefix of the server's tag and match up to a "-" or the
    end of string.  If a match is found, the server returns an
    intermediate LANG response and an OK response.  The LANG response
    indicates the actual language selected and appropriate comparators
    for use with the languages listed in the LANG command.
    If no LANG command is issued, all error text strings MUST be in
    the registered language "i-default" [CHARSET-LANG-POLICY],
    intended for an international audience.
 Example:    C: A003 LANG "fr-ca" "fr" "en-ca" "en-uk"
             S: A003 LANG "fr-ca" "i;octet" "i;ascii-numeric"
                     "i;ascii-casemap" "en;primary" "fr;primary"
             S: A003 OK "Bonjour"

6.2.3. LANG Intermediate Response

 Data:       language for error responses
             appropriate comparators
    The LANG response indicates the language which will be used for
    error responses and the comparators which are appropriate for the
    languages listed in the LANG command.  The comparators SHOULD be
    in approximate order from most efficient (usually "i;octet") to
    most appropriate for human text in the preferred language.

Newman & Myers Standards Track [Page 28] RFC 2244 ACAP November 1997

6.2.4. LOGOUT Command

 Arguments:  none
 Data:       mandatory untagged response: BYE
 Result:     OK - logout completed
             BAD - command unknown or arguments invalid
    The LOGOUT command informs the server that the client is done with
    the session.  The server must send a BYE untagged response before
    the (tagged) OK response, and then close the network connection.
 Example:    C: A023 LOGOUT
             S: * BYE "ACAP Server logging out"
             S: A023 OK "LOGOUT completed"
             (Server and client then close the connection)

6.2.5. OK Response

 Data:       optional response code
             human-readable text
    The OK response indicates an information message from the server.
    When tagged, it indicates successful completion of the associated
    command.  The human-readable text may be presented to the user as
    an information message.  The untagged form indicates an
    information-only message; the nature of the information MAY be
    indicated by a response code.
 Example:    S: * OK "Master ACAP server is back up"

6.2.6. NO Response

 Data:       optional response code
             human-readable text
    The NO response indicates an operational error message from the
    server.  When tagged, it indicates unsuccessful completion of the
    associated command.  The untagged form indicates a warning; the
    command may still complete successfully.  The human-readable text
    describes the condition.
 Example:    C: A010 SEARCH "/addressbook/" DEPTH 3 RETURN ("*")
                     EQUAL "entry" "+i;octet" "bozo"
             S: * NO "Master ACAP server is down, your data may

Newman & Myers Standards Track [Page 29] RFC 2244 ACAP November 1997

                      be out of date."
             S: A010 OK "search done"
                ...
             C: A222 STORE ("/folder/site/comp.mail.misc"
                            "folder.creation-time" "19951206103412")
             S: A222 NO (PERMISSION ("/folder/site/")) "Permission
             denied"

6.2.7. BAD Response

 Data:       optional response code
             human-readable text
    The BAD response indicates an error message from the server.  When
    tagged, it reports a protocol-level error in the client's command;
    the tag indicates the command that caused the error.  The untagged
    form indicates a protocol-level error for which the associated
    command can not be determined; it may also indicate an internal
    server failure.  The human-readable text describes the condition.
 Example:    C: ...empty line...
             S: * BAD "Empty command line"
             C: A443 BLURDYBLOOP
             S: A443 BAD "Unknown command"
             C: A444 NOOP Hello
             S: A444 BAD "invalid arguments"

6.2.8. BYE Untagged Response

 Data:       optional response code
             human-readable text
    The untagged BYE response indicates that the server is about to
    close the connection.  The human-readable text may be displayed to
    the user in a status report by the client.  The BYE response may
    be sent as part of a normal logout sequence, or as a panic
    shutdown announcement by the server.  It is also used by some
    server implementations as an announcement of an inactivity auto-
    logout.
    This response is also used as one of two possible greetings at
    session startup.  It indicates that the server is not willing to
    accept a session from this client.
 Example:    S: * BYE "Auto-logout; idle for too long"

Newman & Myers Standards Track [Page 30] RFC 2244 ACAP November 1997

6.2.9. ALERT Untagged Response

 Data:       optional response code
             human-readable text
    The human-readable text contains a special human generated alert
    message that MUST be presented to the user in a fashion that calls
    the user's attention to the message.  This is intended to be used
    for vital messages from the server administrator to the user, such
    as a warning that the server will soon be shut down for
    maintenance.
 Example:    S: * ALERT "This ACAP server will be shut down in
                         10 minutes for system maintenance."

6.3. Non-Authenticated State

 In non-authenticated state, the AUTHENTICATE command establishes
 authentication and enters authenticated state.  The AUTHENTICATE
 command provides a general mechanism for a variety of authentication
 techniques.
 Server implementations may allow non-authenticated access to certain
 information by supporting the SASL ANONYMOUS [SASL-ANON] mechanism.
 Once authenticated (including as anonymous), it is not possible to
 re-enter non-authenticated state.
 Only the any-state commands (NOOP, LANG and LOGOUT) and the
 AUTHENTICATE command are valid in non-authenticated state.

6.3.1. AUTHENTICATE Command

 Arguments:  SASL mechanism name
             optional initial response
 Data:       continuation data may be requested
 Result:     OK - authenticate completed, now in authenticated state
             NO - authenticate failure: unsupported authentication
                  mechanism, credentials rejected
             BAD - command unknown or arguments invalid,
                  authentication exchange cancelled

Newman & Myers Standards Track [Page 31] RFC 2244 ACAP November 1997

    The AUTHENTICATE command indicates a SASL [SASL] authentication
    mechanism to the server.  If the server supports the requested
    authentication mechanism, it performs an authentication protocol
    exchange to authenticate and identify the user.  Optionally, it
    also negotiates a security layer for subsequent protocol
    interactions.  If the requested authentication mechanism is not
    supported, the server rejects the AUTHENTICATE command by sending
    a tagged NO response.
    The authentication protocol exchange consists of a series of
    server challenges and client answers that are specific to the
    authentication mechanism.  A server challenge consists of a
    command continuation request with the "+" token followed by a
    string.  The client answer consists of a line consisting of a
    string.  If the client wishes to cancel an authentication
    exchange, it should issue a line with a single unquoted "*".  If
    the server receives such an answer, it must reject the
    AUTHENTICATE command by sending a tagged BAD response.
    The optional initial-response argument to the AUTHENTICATE command
    is used to save a round trip when using authentication mechanisms
    that are defined to send no data in the initial challenge.  When
    the initial-response argument is used with such a mechanism, the
    initial empty challenge is not sent to the client and the server
    uses the data in the initial-response argument as if it were sent
    in response to the empty challenge.  If the initial-response
    argument to the AUTHENTICATE command is used with a mechanism that
    sends data in the initial challenge, the server rejects the
    AUTHENTICATE command by sending a tagged NO response.
    The service name specified by this protocol's profile of SASL is
    "acap".
    If a security layer is negotiated through the SASL authentication
    exchange, it takes effect immediately following the CRLF that
    concludes the authentication exchange for the client, and the CRLF
    of the tagged OK response for the server.
    All ACAP implementations MUST implement the CRAM-MD5 SASL
    mechanism [CRAM-MD5], although they MAY offer a configuration
    option to disable it if site security policy dictates.  The
    example below is the same example described in the CRAM-MD5
    specification.
    If an AUTHENTICATE command fails with a NO response, the client
    may try another authentication mechanism by issuing another
    AUTHENTICATE command.  In other words, the client may request
    authentication types in decreasing order of preference.

Newman & Myers Standards Track [Page 32] RFC 2244 ACAP November 1997

 Example:    S: * ACAP (IMPLEMENTATION "Blorfysoft v3.5")
                       (SASL "CRAM-MD5" "KERBEROS_V4")
             C: A001 AUTHENTICATE "CRAM-MD5"
             S: + "<1896.697170952@postoffice.reston.mci.net>"
             C: "tim b913a602c7eda7a495b4e6e7334d3890"
             S: A001 OK "CRAM-MD5 authentication successful"

6.4. Searching

 This section describes the SEARCH command, for retrieving data from
 datasets.

6.4.1. SEARCH Command

 Arguments:  dataset or context name
             optional list of modifiers
             search criteria
 Data:       intermediate responses: ENTRY, MODTIME, REFER
             untagged responses: ADDTO, REMOVEFROM, CHANGE, MODTIME
 Result:     OK - search completed
             NO - search failure: can't perform search
             BAD - command unknown or arguments invalid
    The SEARCH command identifies a subset of entries in a dataset and
    returns information on that subset to the client.  Inherited
    entries and attributes are included in the search unless the
    NOINHERIT search modifier is included or the user does not have
    permission to read the attributes in the base dataset.
    The first argument to SEARCH identifies what is to be searched.
    If the string begins with a slash ("/"), it is the name of a
    dataset to be searched, otherwise it is a name of a context that
    was created by a SEARCH command given previously in the session.
    A successful SEARCH command MAY result in intermediate ENTRY
    responses and MUST result in a MODTIME intermediate response.
    Following that are zero or more modifiers to the search.  Each
    modifier may be specified at most once.  The defined modifiers
    are:

Newman & Myers Standards Track [Page 33] RFC 2244 ACAP November 1997

    DEPTH number
         The SEARCH command will traverse the dataset tree up to the
         specified depth.  ENTRY responses will include the full path
         to the entry.  A value of "0" indicates that the search
         should traverse the entire tree.  A value of "1" is the
         default and indicates only the specified dataset should be
         searched.  If a dataset is traversed which is not located on
         the current server, then a REFER intermediate response is
         returned for that subtree and the search continues.
    HARDLIMIT number
         If the SEARCH command would result in more than number
         entries, the SEARCH fails with a NO completion result with a
         WAYTOOMANY response code.
    LIMIT number number
         Limits the number of intermediate ENTRY responses that the
         search may generate.  The first numeric argument specifies
         the limit, the second number specifies the number of entries
         to return if the number of matches exceeds the limit.  If the
         limit is exceeded, the SEARCH command still succeeds,
         returning the total number of matches in a TOOMANY response
         code in the tagged OK response.
    MAKECONTEXT [ENUMERATE] [NOTIFY] context
         Causes the SEARCH command to create a context with the name
         given in the argument to refer to the matching entries.  If
         the SEARCH is successful, the context name may then be given
         as an argument to subsequent SEARCH commands to search the
         set of matching entries.  If a context with the specified
         name already exists, it is first freed.  If a new context may
         not be created due to the server's limit on the number of
         existing contexts, the command fails, returning a
         TRYFREECONTEXT response code in the NO completion response.
         The optional "ENUMERATE" and "NOTIFY" arguments may be
         included to request enumeration of the context (for virtual
         scroll bars) or change notifications for the context.  If
         "NOTIFY" is not requested, the context represents a snapshot
         of the entries at the time the SEARCH was issued.
         ENUMERATE requests that the contents of the context be
         ordered according to the SORT modifier and that sequential
         numbers, starting with one, be assigned to the entries in the
         context.  This permits the RANGE modifier to be used to fetch
         portions of the ordered context.

Newman & Myers Standards Track [Page 34] RFC 2244 ACAP November 1997

         NOTIFY requests that the server send untagged ADDTO,
         REMOVEFROM, CHANGE, and MODTIME responses while the context
         created by this SEARCH command exists.  The server MAY issue
         untagged ADDTO, REMOVEFROM, CHANGE and MODTIME notifications
         for a context at any time between the issuing of the SEARCH
         command with MAKECONTEXT NOTIFY and the completion of a
         FREECONTEXT command for the context.  Notifications are only
         issued for changes which occur after the server receives the
         SEARCH command which created the context.  After issuing a
         sequence of ADDTO, REMOVEFROM or CHANGE notifications, the
         server MUST issue an untagged MODTIME notification indicating
         that the client has all updates to the entries in the context
         up to and including the given modtime value.  Servers are
         permitted a reasonable delay to batch change notifications
         before sending them to the client.
         The position arguments of the ADDTO, REMOVEFROM and CHANGE
         notifications are 0 if ENUMERATE is not requested.
    NOINHERIT
         This causes the SEARCH command to operate without
         inheritance.  It can be used to tell which values are
         explicit overrides.  If MAKECONTEXT is also specified, the
         created context is also not affected by inheritance.
    RETURN (metadata...)
         Specifies what is to be returned in intermediate ENTRY
         responses.  If this modifier is not specified, no
         intermediate ENTRY responses are returned.
         Inside the parentheses is an optional list of attributes,
         each optionally followed by a parenthesized list of metadata.
         If the parenthesized list of metadata is not specified, it
         defaults to "(value)".
         An attribute name with a trailing "*" requests all attributes
         with that prefix.  A "*" by itself requests all attributes.
         If the parenthesized list of metadata is not specified for an
         attribute with a trailing "*", it defaults to "(attribute
         value)".  Results matching such an attribute pattern are
         grouped in parentheses.
         Following the last intermediate ENTRY response, the server
         returns a single intermediate MODTIME response.

Newman & Myers Standards Track [Page 35] RFC 2244 ACAP November 1997

    SORT (attribute comparator ...)
         Specifies the order in which any resulting ENTRY replies are
         to be returned to the client.  The SORT modifier takes as an
         argument a parenthesized list of one or more
         attribute/comparator pairs.  Attribute lists the attribute to
         sort on, comparator specifies the name of the collation rule
         to apply to the values of the attribute.  Successive
         attribute/comparator pairs are used to order two entries only
         when all preceding pairs indicate the two entries collate the
         same.
         If the SORT modifier is used in conjunction with the
         MAKECONTEXT modifier, the SORT modifier specifies the
         ordering of entries in the created context.
         If no SORT modifier is specified, or none of the
         attribute/comparator pairs indicates an order for the two
         entries, the server uses the order of the entries that exists
         in the context or dataset being searched.
    Following the modifiers is the search criteria.  Searching
    criteria consist of one or more search keys.  Search keys may be
    combined using the AND, and OR search keys.  For example, the
    criteria (the newline is for readability and not part of the
    criteria):
        AND COMPARE "modtime" "+i;octet" "19951206103400"
            COMPARE "modtime" "-i;octet" "19960112000000"
    refers to all entries modified between 10:34 December 6 1995 and
    midnight January 12, 1996 UTC.
    The currently defined search keys are as follows.
    ALL  This matches all entries.
    AND search-key1 search-key2
         Entries that match both search keys.
    COMPARE attribute comparator value
         Entries for which the value of the specified attribute
         collates using the specified comparator the same or later
         than the specified value.
    COMPARESTRICT attribute comparator value
         Entries for which the specified attribute collates using the
         specified comparator later than the specified value.

Newman & Myers Standards Track [Page 36] RFC 2244 ACAP November 1997

    EQUAL attribute comparator value
         Entries for which the value of the attribute is equal to the
         specified value using the specified comparator.
    NOT search-key
         Entries that do not match the specified search key.
    OR search-key1 search-key2
         Entries that match either search key.
    PREFIX attribute comparator value
         Entries which begin with the specified value using the
         specified comparator.  If the specified comparator doesn't
         support substring matching, a BAD response is returned.
    RANGE start end time
         Entries which are within the specified range of the
         enumerated context's ordering.  The lowest-ordered entry in
         the context is assigned number one, the next lowest entry is
         assigned number two, and so on.  The numeric arguments
         specify the lowest and highest numbers to match. The time
         specifies that the client has processed notifications for the
         context up to the specified time.  If the context has been
         modified since then, the server MUST either return a NO with
         a MODIFIED response code, or return the results that the
         SEARCH would have returned if none of the changes since that
         time had been made.
         RANGE is only permitted on enumerated contexts.  If RANGE is
         used with a dataset or non-enumerated context, the server
         MUST return a BAD response.
    SUBSTRING attribute comparator value
         Entries which contain the specified value, using the
         specified comparator.  If the specified comparator doesn't
         support substring matching, a BAD response is returned.

6.4.2. ENTRY Intermediate Response

 Data:       entry name
             entry data
    The ENTRY intermediate response occurs as a result of a SEARCH or
    STORE command. This is the means by which dataset entries are
    returned to the client.

Newman & Myers Standards Track [Page 37] RFC 2244 ACAP November 1997

    The ENTRY response begins with the entry name, if a SEARCH command
    without the DEPTH modifier was issued, or the entry path in other
    cases.  This is followed by a set of zero or more items, one for
    each metadata item in the RETURN search modifier.  Results
    matching an attribute pattern or returning multiple metadata items
    are grouped in parentheses.

6.4.3. MODTIME Intermediate Response

 Data:       modtime value
    The MODTIME intermediate response occurs as a result of a SEARCH
    command.  It indicates that the just created context or the
    previously returned ENTRY responses include all updates to the
    returned entries up to and including the modtime value in the
    argument.

6.4.4. REFER Intermediate Response

 Data:       dataset path
             relative ACAP URLs
    The REFER intermediate response occurs as a result of a
    multi-level SEARCH where one of the levels is located on a
    different server.  The response indicates the dataset which is not
    located on the current server and one or more relative ACAP URLs
    for where that dataset may be found.

6.4.5. Search Examples

 Here are some SEARCH command exchanges between the client and server:
 C: A046 SEARCH "/addressbook/" DEPTH 3 RETURN ("addressbook.Alias"
         "addressbook.Email" "addressbook.List") OR NOT EQUAL
         "addressbook.Email" "i;octet" NIL NOT EQUAL
         "addressbook.List" "i;octet" NIL
 S: A046 ENTRY "/addressbook/user/joe/A0345" "fred"
         "fred@stone.org" NIL
 S: A046 ENTRY "/addressbook/user/fred/A0537" "joe" "joe@stone.org"
         NIL
 S: A046 ENTRY "/addressbook/group/Dinosaur Operators/A423"
         "saurians" NIL "1"
 S: A046 MODTIME "19970728105252"
 S: A046 OK "SEARCH completed"
 C: A047 SEARCH "/addressbook/user/fred/" RETURN ("*") EQUAL "entry"
         "i;octet" "A0345"
 S: A047 ENTRY "A0345" (("modtime" "19970728102226")

Newman & Myers Standards Track [Page 38] RFC 2244 ACAP November 1997

         ("addressbook.Alias" "fred") ("addressbook.Email"
         "fred@stone.org") ("addressbook.CommonName"
         "Fred Flintstone") ("addressbook.Surname" "Flintstone")
         ("addressbook.GivenName" "Fred"))
 S: A047 MODTIME "19970728105258"
 S: A047 OK "SEARCH completed"
 C: A048 SEARCH "/options/~/vendor.example/" RETURN
         ("option.value"("size" "value" "myrights"))
         SORT ("entry" "i;octet") COMPARE "modtime" "i;octet"
         "19970727123225"
 S: A048 ENTRY "blurdybloop" (5 "ghoti" "rwia")
 S: A048 ENTRY "buckybits" (2 "10" "rwia")
 S: A048 ENTRY "windowSize" (7 "100x100" "rwia")
 S: A048 MODTIME "19970728105304"
 S: A048 OK "SEARCH completed"
 C: A049 SEARCH "/addressbook/~/public" RETURN ("addressbook.Alias"
         "addressbook.Email") MAKECONTEXT ENUMERATE "blob" LIMIT 100 1
         SORT ("addressbook.Alias" "i;octet") NOT EQUAL
         "addressbook.Email" NIL
 S: A049 ENTRY "A437" "aaguy" "aaguy@stone.org"
 S: A049 MODTIME "19970728105308"
 S: A049 OK (TOOMANY 347) "Context 'blob' created"
 C: A050 SEARCH "blob" RANGE 2 2 "19970728105308" ALL
 S: A050 ENTRY "A238" "abguy" "abguy@stone.org"
 S: A050 MODTIME "19970728105310"
 S: A050 OK "SEARCH Completed"

6.5. Contexts

 The following commands use contexts created by a SEARCH command with
 a MAKECONTEXT modifier.

6.5.1. FREECONTEXT Command

 Arguments:  context name
 Data:       no specific data for this command
 Result:     OK - freecontext completed
             NO - freecontext failure: no such context
             BAD - command unknown or arguments invalid

Newman & Myers Standards Track [Page 39] RFC 2244 ACAP November 1997

    The FREECONTEXT command causes the server to free all state
    associated with the named context.  The context may no longer be
    searched and the server will no longer issue any untagged
    responses for the context.  The context is no longer counted
    against the server's limit on the number of contexts.
 Example:    C: A683 FREECONTEXT "blurdybloop"
             S: A683 OK "Freecontext completed"

6.5.2. UPDATECONTEXT Command

 Arguments:  list of context names
 Data:       untagged responses: ADDTO REMOVEFROM CHANGE MODTIME
 Result:     OK - Updatecontext completed: all updates completed
             NO - Updatecontext failed: no such context
                                        not a notify context
             BAD - command unknown or arguments invalid
    The UPDATECONTEXT command causes the server to ensure that the
    client is notified of all changes known to the server for the
    contexts listed as arguments up to the current time.  The contexts
    listed in the arguments must have been previously given to a
    successful SEARCH command with a MAKECONTEXT NOTIFY modifier.  A
    MODTIME untagged response MUST be returned if any read-write
    metadata in the context changed since the last MODTIME for that
    context.  This includes metadata which is not listed in the RETURN
    modifier for the context.
    While a server may issue untagged ADDTO, REMOVEFROM, CHANGE, and
    MODTIME at any time, the UPDATECONTEXT command is used to "prod"
    the server to send any notifications it has not sent yet.
    The UPDATECONTEXT command SHOULD NOT be used to poll for updates.
 Example:    C: Z4S9 UPDATECONTEXT "blurdybloop" "blarfl"
             S: Z4S9 OK "client has been notified of all changes"

6.5.3. ADDTO Untagged Response

 Data:       context name
             entry name
             position
             metadata list

Newman & Myers Standards Track [Page 40] RFC 2244 ACAP November 1997

    The untagged ADDTO response informs the client that an entry has
    been added to a context.  The response includes the position
    number of the added entry (the first entry in the context is
    numbered 1) and those metadata contained in the entry which match
    the RETURN statement when the context was created.
    For enumerated contexts, the ADDTO response implicitly adds one to
    the position of all members of the context which had position
    numbers that were greater than or equal to the ADDTO position
    number.  For non-enumerated contexts, the position field is always
    0.
 Example:    S: * ADDTO "blurdybloop" "fred" 15
                  ("addressbook.Email" "fred@stone.org")

6.5.4. REMOVEFROM Untagged Response

 Data:       context name
             entry name
             old position
    The untagged REMOVEFROM response informs the client that an entry
    has been removed from a context.  The response includes the
    position number that the removed entry used to have (the first
    entry in the context is numbered 1).
    For enumerated contexts, the REMOVEFROM response implicitly
    subtracts one from the position numbers of all members of the
    context which had position numbers greater than the REMOVEFROM
    position number.  For non-enumerated contexts, the position field
    is always 0.
 Example:    S: * REMOVEFROM "blurdybloop" "fred" 15

6.5.5. CHANGE Untagged Response

 Data:       context name
             entry name
             old position
             new position
             metadata list
    The untagged CHANGE response informs the client that an entry in a
    context has either changed position in the context or has changed
    the values of one or more of the attributes specified in the
    RETURN modifier when the context was created.

Newman & Myers Standards Track [Page 41] RFC 2244 ACAP November 1997

    The response includes the previous and current position numbers of
    the entry (which are 0 if ENUMERATE was not specified on the
    context) and the attribute metadata requested in the RETURN
    modifier when the context was created.
    For enumerated contexts, the CHANGE response implicitly changes
    the position numbers of all entries which had position numbers
    between the old and new position.  If old position is less than
    new position, than one is subtracted from all entries which had
    position numbers in that range.  Otherwise one is added to all
    entries which had position numbers in that range.  If the old
    position and new position are the same, then no implicit position
    renumbering occurs.
    CHANGE responses are not issued for entries which have changed
    position implicitly due to another ADDTO, REMOVEFROM or CHANGE
    response.
 Example:    S: * CHANGE "blurdybloop" "fred" 15 10
                  ("addressbook.Email" "fred@stone.org")

6.5.6. MODTIME Untagged Response

 Data:       context name
             modtime value
    The untagged MODTIME response informs the client that it has
    received all updates to entries in the context which have modtime
    values less than or equal to the modtime value in the argument.
 Example:    S: * MODTIME mycontext "19970320162338"

6.6. Dataset modification

 The following commands and responses handle modification of datasets.

Newman & Myers Standards Track [Page 42] RFC 2244 ACAP November 1997

6.6.1. STORE Command

 Arguments:  entry store list
 Data:       intermediate responses: ENTRY
 Result:     OK - store completed
             NO - store failure: can't store that name
                  UNCHANGEDSINCE specified and entry changed
             BAD - command unknown or arguments invalid
                   invalid UTF-8 syntax in attribute name
    Creates, modifies, or deletes the named entries in the named
    datasets.  The values of metadata not specified in the command are
    not changed.  Setting the "value" metadata of an attribute to NIL
    removes that attribute from the entry.  Setting the "value" of the
    "entry" attribute to NIL removes that entry from the dataset and
    cancels inheritance for the entire entry.  Setting the "value" of
    the "entry" attribute to DEFAULT removes that entry from the
    inheriting dataset and reverts the entry and its attributes to
    inherited values, if any.  Changing the value of the "entry"
    attribute renames the entry.
    Storing DEFAULT to the "value" metadata of an attribute is
    equivalent to storing NIL, except that inheritance is enabled for
    that attribute.  If a non-NIL value is inherited then an ENTRY
    intermediate response is generated to notify the client of the
    this change.  The ENTRY response includes the entry-path and the
    attribute name and value metadata for each attribute which
    reverted to a non-NIL inherited setting.
    Storing NIL to the "value" metadata of an attribute MAY be treated
    equivalent to storing DEFAULT to that "value" if there is a NIL
    value in the base dataset.
    The STORE command is followed by one or more entry store lists.
    Each entry store list begins with an entry path followed by STORE
    modifiers, followed by zero or more attribute store items.  Each
    attribute store item is made up of the attribute name followed by
    NIL (to remove the attribute's value), DEFAULT (to revert the item
    to any inherited value), a single value (to set the attribute's
    single value), or a list of metadata items to modify.  The
    following STORE modifiers may be specified:

Newman & Myers Standards Track [Page 43] RFC 2244 ACAP November 1997

    NOCREATE
         By default, the server MUST create any datasets necessary to
         store the entry, including multiple hierarchy levels.  If
         NOCREATE is specified, the STORE command will fail with a
         NOEXIST error unless the parent dataset already exists.
    UNCHANGEDSINCE
         If the "modtime" of the entry is later than the
         unchangedsince time, then the store fails with a MODIFIED
         response code.  Use of UNCHANGEDSINCE with a time of
         "00000101000000" will always fail if the entry exists.
         Clients writing to a shared dataset are encouraged to use
         UNCHANGEDSINCE when modifying an existing entry.
    The server MUST either make all the changes specified in a single
    STORE command or make none of them.  If successful, the server
    MUST update the "modtime" attribute for every entry which was
    changed.
    It is illegal to list any metadata item within an attribute twice,
    any attribute within an entry twice or any entry path twice.  The
    server MUST return a BAD response if this happens.
    The server MAY re-order the strings in a multi-value on STORE and
    MAY remove duplicate strings.  However, SEARCH MUST return multi-
    values and the associated size list metadata in a consistant
    order.
 Example:    C: A342 STORE ("/addressbook/user/fred/ABC547"
                     "addressbook.TelephoneNumber" "555-1234"
                     "addressbook.CommonName" "Barney Rubble"
                     "addressbook.AlternateNames" ("value"
                     ("Barnacus Rubble" "Coco Puffs Thief"))
                     "addressbook.Email" NIL)
             S: A342 OK "Store completed"
             C: A343 STORE ("/addressbook/user/joe/ABD42"
                     UNCHANGEDSINCE "19970320162338"
                     "user.joe.hair-length" "10 inches")
             S: A343 NO (MODIFIED) "'ABD42' has been changed
                     by somebody else."
             C: A344 STORE ("/addressbook/group/Developers/ACD54"
                     "entry" NIL)
             S: A344 OK "Store completed"
             C: A345 STORE ("/option/~/common/SMTPserver"
                     "option.value" DEFAULT)
             S: A345 ENTRY "/option/~/common/SMTPserver"

Newman & Myers Standards Track [Page 44] RFC 2244 ACAP November 1997

                     "option.value" "smtp.server.do.main"
             S: A345 OK "Store completed"
             C: A347 STORE ("/addressbook/~/" "dataset.inherit"
                     "/addressbook/group/Developers")
             S: A347 OK "Store completed"

6.6.2. DELETEDSINCE Command

 Arguments:  dataset name
             time
 Data:       intermediate response: DELETED
 Result:     OK - DELETEDSINCE completed
             NO - DELETEDSINCE failure: can't read dataset
                  date too far in the past
             BAD - command unknown or arguments invalid
    The DELETEDSINCE command returns in intermediate DELETED replies
    the names of entries that have been deleted from the named dataset
    since the given time.
    Servers may impose a limit on the number or age of deleted entry
    names they keep track of.  If the server does not have information
    going back to the specified time, the command fails, returning a
    TOOOLD response code in the tagged NO response.
 Example:    C: Z4S9 DELETEDSINCE "/folder/site/" 19951205103412
             S: Z4S9 DELETED "blurdybloop"
             S: Z4S9 DELETED "anteaters"
             S: Z4S9 OK "DELETEDSINCE completed"
             C: Z4U3 DELETEDSINCE "/folder/site/" 19951009040854
             S: Z4U3 NO (TOOOLD) "Don't have that information"

6.6.3. DELETED Intermediate Response

 Data:       entry name
    The intermediate DELETED response occurs as a result of a
    DELETEDSINCE command. It returns an entry that has been deleted
    from the dataset specified in the DELETEDSINCE command.

6.7. Access Control List Commands

 The commands in this section are used to manage access control lists.

Newman & Myers Standards Track [Page 45] RFC 2244 ACAP November 1997

6.7.1. SETACL Command

 Arguments:  acl object
             authentication identifier
             access rights
 Data:       no specific data for this command
 Result:     OK - setacl completed
             NO - setacl failure: can't set acl
             BAD - command unknown or arguments invalid
    The SETACL command changes the access control list on the
    specified object so that the specified identifier is granted the
    permissions enumerated in rights.  If the object did not
    previously have an access control list, one is created.
 Example:    C: A123 SETACL ("/addressbook/~/public/") "anyone" "r"
             S: A123 OK "Setacl complete"
             C: A124 SETACL ("/folder/site/") "B1FF" "rwa"
             S: A124 NO (PERMISSION ("/folder/site/")) "'B1FF' not
                     permitted to modify access rights
                     for '/folder/site/'"

6.7.2. DELETEACL Command

 Arguments:  acl object
             optional authentication identifier
 Data:       no specific data for this command
 Result:     OK - deleteacl completed
             NO - deleteacl failure: can't delete acl
             BAD - command unknown or arguments invalid
    If given the optional identifier argument, the DELETEACL command
    removes any portion of the access control list on the specified
    object for the specified identifier.
    If not given the optional identifier argument, the DELETEACL
    command removes the ACL from the object entirely, causing access
    to be controlled by a higher-level default ACL.  This form of the
    DELETEACL command is not permitted on the default ACL for a
    dataset and servers MUST return a BAD.

Newman & Myers Standards Track [Page 46] RFC 2244 ACAP November 1997

 Example:    C: A223 DELETEACL ("/addressbook/~/public") "anyone"
             S: A223 OK "Deleteacl complete"
             C: A224 DELETEACL ("/folder/site")
             S: A224 BAD "Can't delete ACL from dataset"
             C: A225 DELETEACL ("/addressbook/user/fred"
                     "addressbook.Email" "barney")
             S: A225 OK "Deleteacl complete"

6.7.3. MYRIGHTS Command

 Arguments:  acl object
 Data:       intermediate responses: MYRIGHTS
 Result:     OK - myrights completed
             NO - myrights failure: can't get rights
             BAD - command unknown or arguments invalid
    The MYRIGHTS command returns the set of rights that the client has
    to the given dataset or dataset attribute.
 Example:    C: A003 MYRIGHTS ("/folder/site")
             S: A003 MYRIGHTS "r"
             S: A003 OK "Myrights complete"

6.7.4. MYRIGHTS Intermediate Response

 Data:       rights
    The MYRIGHTS response occurs as a result of a MYRIGHTS command.
    The argument is the set of rights that the client has for the
    object referred to in the MYRIGHTS command.

6.7.5. LISTRIGHTS Command

 Arguments:  acl object
             authentication identifier
 Data:       untagged responses: LISTRIGHTS
 Result:     OK - listrights completed
             NO - listrights failure: can't get rights list
             BAD - command unknown or arguments invalid

Newman & Myers Standards Track [Page 47] RFC 2244 ACAP November 1997

    The LISTRIGHTS command takes an object and an identifier and
    returns information about what rights the current user may revoke
    or grant to that identifier in the ACL for that object.
 Example:    C: a001 LISTRIGHTS ("/folder/~/") "smith"
             S: a001 LISTRIGHTS "xra" "w" "i"
             S: a001 OK Listrights completed
             C: a005 LISTRIGHTS ("/folder/site/archive/imap") "anyone"
             S: a005 LISTRIGHTS "" "x" "r" "w" "i"
             S: a005 OK Listrights completed

6.7.6. LISTRIGHTS Intermediate Response

 Data:       required rights
             list of optional rights
    The LISTRIGHTS response occurs as a result of a LISTRIGHTS
    command.  The first argument is a string containing the (possibly
    empty) set of rights the identifier will always be granted on the
    dataset or attribute.
    Following this are zero or more strings each containing a single
    right which the current user may revoke or grant to the identifier
    in the dataset or attribute.
    The same right MUST NOT be listed more than once in the LISTRIGHTS
    response.

6.8. Quotas

 The section defines the commands and responses relating to quotas.

6.8.1. GETQUOTA Command

 Arguments:  dataset
 Data:       untagged responses: QUOTA
 Result:     OK - Quota information returned
             NO - Quota failure: can't access resource limit
                                 no resource limit
             BAD - command unknown or arguments invalid

Newman & Myers Standards Track [Page 48] RFC 2244 ACAP November 1997

    The GETQUOTA command takes the name of a dataset, and returns in
    an untagged QUOTA response the name of the dataset, quota limit in
    bytes that applies to that dataset and the quota usage within that
    limit.  The scope of a quota limit is implementation dependent.
 Example:    C: A043 GETQUOTA "/option/user/fred/common"
             S: * QUOTA "/option/user/fred/common" 1048576 2475
             S: A043 OK "Getquota completed"

6.8.3. QUOTA Untagged Response

 Data:       dataset
             quota limit in bytes
             amount of quota limit used
             extension data
    The QUOTA untagged response is generated as a result of a GETQUOTA
    command or MAY be generated by the server in response to a SEARCH
    or STORE command to warn about high usage of a quota.  It includes
    the name of the applicable dataset, the quota limit in bytes, the
    quota usage and some optional extension data.  Clients MUST
    tolerate the extension data as its use is reserved for a future
    extension.

6.9. Extensions

 In order to simplify the process of extending the protocol, clients
 MUST tolerate unknown server responses which meet the syntax of
 response-extend.  In addition, clients MUST tolerate unknown server
 response codes which meet the syntax of resp-code-ext.  Availability
 of new commands MUST be announced via a capability on the initial
 greeting line and such commands SHOULD meet the syntax of
 command-extend.
 Servers MUST respond to unknown commands with a BAD command
 completion result.  Servers MUST skip over non-synchronizing literals
 contained in an unknown command.  This may be done by assuming the
 unknown command matches the command-extend syntax, or by reading a
 line at a time and checking for the non-synchronizing literal syntax
 at the end of the line.

7. Registration Procedures

 ACAP's usefulness comes from providing a structured storage model for
 all sorts of configuration data.  However, for its potential to be
 achieved, it is important that the Internet community strives for the
 following goals:

Newman & Myers Standards Track [Page 49] RFC 2244 ACAP November 1997

 (1) Standardization.  It is very important to standardize dataset
 classes.  The authors hope that ACAP achieves the success that SNMP
 has seen with the definition of numerous standards track MIBs.
 (2) Community Review.  In the absence of standardization, it is
 important to get community review on a proposal to improve its
 engineering quality.  Community review is strongly recommended prior
 to registration.  The ACAP implementors mailing list
 <ietf-acap@andrew.cmu.edu> should be used for this purpose.
 (3) Registration.  Registration serves a two-fold purpose.  First it
 prevents use of the same name for different purposes, and second it
 provides a one-stop list which can be used to locate existing
 extensions or dataset classes to prevent duplicate work.
 The following registration templates may be used to register ACAP
 protocol elements with the Internet Assigned Numbers Authority
 (IANA).

7.1. ACAP Capabilities

 New ACAP capabilities MUST be registered prior to use.  Careful
 consideration should be made before extending the protocol, as it can
 lead to complexity or interoperability problems.  Review of proposals
 on the acap implementors mailing list is strongly encouraged prior to
 registration.
 To: iana@iana.org
 Subject: Registration of ACAP capability
 Capability name:
 Capability keyword:
 Capability arguments:
 Published Specification(s):
 (Optional, but strongly encouraged)
 Person and email address to contact for further information:

7.2. ACAP Response Codes

 ACAP response codes are registered on a first come, first served
 basis.  Review of proposals on the acap implementors mailing list is
 strongly encouraged prior to registration.

Newman & Myers Standards Track [Page 50] RFC 2244 ACAP November 1997

 To: iana@iana.org
 Subject: Registration of ACAP response code
 Response Code:
 Arguments (use ABNF to specify syntax):
 Purpose:
 Published Specification(s):
 (Optional, but strongly encouraged)
 Person and email address to contact for further information:

7.3. Dataset Classes

 A dataset class provides a core set of attributes for use in a
 specified hierarchy.  It may also define rules for the dataset
 hierarchy underneath that class.  Dataset class specifications must
 be standards track or IESG approved experimental RFCs.
 To: iana@iana.org
 Subject: Registration of ACAP dataset class
 Dataset class name/attribute prefix:
 Purpose:
 Published Specification(s):
 (Standards track or IESG approved experimental RFC)
 Person and email address to contact for further information:

7.4. Vendor Subtree

 Vendors may reserve a portion of the ACAP namespace for private use.
 Dataset class names beginning with "vendor.<company/product name>."
 are reserved for use by that company or product.  In addition, all
 attribute names beginning with "vendor.<company/product name>." are
 reserved for use by that company or product once registered.
 Registration is on a first come, first served basis.  Whenever
 possible, private attributes and dataset classes should be avoided in
 favor of improving interoperable dataset class definitions.

Newman & Myers Standards Track [Page 51] RFC 2244 ACAP November 1997

 To: iana@iana.org
 Subject: Registration of ACAP vendor subtree
 Private Prefix: vendor.<company/product name>.
 Person and email address to contact for further information:
 (company names and addresses should be included when appropriate)

8. Formal Syntax

 The following syntax specification uses the augmented Backus-Naur
 Form (BNF) notation as specified in [ABNF].  This uses the ABNF core
 rules as specified in Appendix A of the ABNF specification [ABNF].
 Except as noted otherwise, all alphabetic characters are
 case-insensitive.  The use of upper or lower case characters to
 define token strings is for editorial clarity only.  Implementations
 MUST accept these strings in a case-insensitive fashion.
 The "initial-greeting" rule below defines the initial ACAP greeting
 from the server.  The "command" rule below defines the syntax for
 commands sent by the client.  The "response" rule below defines the
 syntax for responses sent by the server.
 ATOM-CHAR          = "!" / %x23-27 / %x2A-5B / %x5D-7A / %x7C-7E
                      ;; Any CHAR except ATOM-SPECIALS
 ATOM-SPECIALS      = "(" / ")" / "{" / SP / CTL / QUOTED-SPECIALS
 CHAR               = %x01-7F
 DIGIT-NZ           = %x31-39
                      ; non-zero digits ("1" - "9")
 QUOTED-CHAR        = SAFE-UTF8-CHAR / "\" QUOTED-SPECIALS
 QUOTED-SPECIALS    = <"> / "\"
 SAFE-CHAR          = %x01-09 / %x0B-0C / %x0E-21 /
                      %x23-5B / %x5D-7F
                      ;; any TEXT-CHAR except QUOTED-SPECIALS
 SAFE-UTF8-CHAR     = SAFE-CHAR / UTF8-2 / UTF8-3 / UTF8-4 /
                      UTF8-5 / UTF8-6
 TAG-CHAR           = %x21 / %x23-27 / %x2C-5B / %x5D-7A / %x7C-7E
                      ;; Any ATOM-CHAR except "*" or "+"

Newman & Myers Standards Track [Page 52] RFC 2244 ACAP November 1997

 TEXT-CHAR          = %x01-09 / %x0B-0C / %x0E-7F
                      ;; any CHAR except CR and LF
 TEXT-UTF8-CHAR     = SAFE-UTF8-CHAR / QUOTED-SPECIALS
 UTF8-1             = %x80-BF
 UTF8-2             = %xC0-DF UTF8-1
 UTF8-3             = %xE0-EF 2UTF8-1
 UTF8-4             = %xF0-F7 3UTF8-1
 UTF8-5             = %xF8-FB 4UTF8-1
 UTF8-6             = %xFC-FD 5UTF8-1
 UTF8-CHAR          = TEXT-UTF8-CHAR / CR / LF
 acl                = "(" [acl-identrights *(SP acl-identrights)] ")"
                      *(SPACE acl-identrights)] ")"
 acl-identifier     = string-utf8
                      ;; MUST NOT contain HTAB
 acl-identrights    = string-utf8
                      ;; The identifier followed by a HTAB,
                      ;; followed by the rights.
 acl-delobject      = "(" dataset SP attribute [SP entry-name] ")"
 acl-object         = "(" dataset [SP attribute [SP entry-name]] ")"
 acl-rights         = quoted
 atom               = ALPHA *1023ATOM-CHAR
 attribute          = string-utf8
                      ;; dot-separated attribute name
                      ;; MUST NOT contain "*" or "%"
 attribute-store    = attribute SP (value-nildef /
                      "(" 1*(metadata-write-q SP value-store) ")")
                      ;; MUST NOT include the same metadata twice
 auth-type          = <"> auth-type-name <">

Newman & Myers Standards Track [Page 53] RFC 2244 ACAP November 1997

 auth-type-name     = iana-token
                      ;; as defined in SASL [SASL]
 command            = tag SP (command-any / command-auth /
                      command-nonauth) CRLF
                      ;; Modal based on state
 command-authent    = "AUTHENTICATE" SP auth-type
                      [SP string] *(CRLF string)
 command-any        = "NOOP" / command-lang / "LOGOUT" /
                      command-extend
 command-auth       = command-delacl / command-dsince /
                      command-freectx / command-getquota /
                      command-lrights / command-myrights /
                      command-search / command-setacl /
                      command-store
                      ;; only valid in authenticated state
 command-delacl     = "DELETEACL" SP acl-delobject [SP acl-identifier]
 command-dsince     = "DELETEDSINCE" SP dataset SP time
 command-extend     = extend-token [SP extension-data]
 command-freectx    = "FREECONTEXT" SP context
 command-getquota   = "GETQUOTA" SP dataset
 command-lang       = "LANG" *(SP lang-tag)
 command-lrights    = "LISTRIGHTS" SP acl-object
 command-myrights   = "MYRIGHTS" SP acl-object
 command-nonauth    = command-authent
                      ;; only valid in non-authenticated state
 command-search     = "SEARCH" SP (dataset / context)
                      *(SP search-modifier) SP search-criteria
                      ;; MUST NOT include same search-modifier twice
 command-setacl     = "SETACL" SP acl-object SP acl-identifier
                      SP acl-rights
 command-store      = "STORE" SP store-entry-list

Newman & Myers Standards Track [Page 54] RFC 2244 ACAP November 1997

 comparator         = <"> comparator-name <">
 comparator-name    = ["+" / "-"] iana-token
 context            = string-utf8
                      ;; MUST NOT begin with slash ("/")
 dataset            = string-utf8
                      ;; slash-separated dataset name
                      ;; begins with slash
 entry              = entry-name / entry-path
 entry-name         = string-utf8
                      ;; entry name MUST NOT contain slash
                      ;; MUST NOT begin with "."
 entry-path         = string-utf8
                      ;; slash-separated path to entry
                      ;; begins with slash
 entry-relative     = string-utf8
                      ;; potentially relative path to entry
 extend-token       = atom
                      ;; MUST be defined by a standards track or
                      ;; IESG approved experimental protocol extension
 extension-data     = extension-item *(SP extension-item)
 extension-item     = extend-token / string / number /
                      "(" [extension-data] ")"
 iana-token         = atom
                      ;; MUST be registered with IANA
 initial-greeting   = "*" SP "ACAP" *(SP "(" init-capability ")") CRLF
 init-capability    = init-cap-context / init-cap-extend /
                      init-cap-implem / init-cap-sasl
 init-cap-context   = "CONTEXTLIMIT" SP string
 init-cap-extend    = iana-token [SP string-list]
 init-cap-implem    = "IMPLEMENTATION" SP string
 init-cap-sasl      = "SASL" SP string-list

Newman & Myers Standards Track [Page 55] RFC 2244 ACAP November 1997

 lang-tag           = <"> Language-Tag <">
                      ;; Language-Tag rule is defined in [LANG-TAGS]
 literal            = "{" number [ "+" ] "}" CRLF *OCTET
                      ;; The number represents the number of octets
                      ;; MUST be literal-utf8 except for values
 literal-utf8       = "{" number [ "+" ] "}" CRLF *UTF8-CHAR
                      ;; The number represents the number of octets
                      ;; not the number of characters
 metadata           = attribute [ "(" metadata-type-list ")" ]
                      ;; attribute MAY end in "*" as wildcard.
 metadata-list      = metadata *(SP metadata)
 metadata-type      = "attribute" / "myrights" / "size" /
                      "count" / metadata-write
 metadata-type-q    = <"> metadata-type <">
 metadata-type-list = metadata-type-q *(SP metadata-type-q)
 metadata-write     = "value" / "acl"
 metadata-write-q   = <"> metadata-write <">
 nil                = "NIL"
 number             = *DIGIT
                      ;; A 32-bit unsigned number.
                      ;; (0 <= n < 4,294,967,296)
 nz-number          = DIGIT-NZ *DIGIT
                      ;; A 32-bit unsigned non-zero number.
                      ;; (0 < n < 4,294,967,296)
 position           = number
                      ;; "0" if context is not enumerated
                      ;; otherwise this is non-zero
 quota-limit        = number
 quota-usage        = number
 quoted             = <"> *QUOTED-CHAR <">
                      ;; limited to 1024 octets between the <">s

Newman & Myers Standards Track [Page 56] RFC 2244 ACAP November 1997

 response           = response-addto / response-alert / response-bye /
                      response-change / response-cont /
                      response-deleted / response-done /
                      response-entry / response-extend /
                      response-listr / response-lang /
                      response-mtimei / response-mtimeu /
                      response-myright / response-quota /
                      response-refer / response-remove / response-stat
 response-addto     = "*" SP "ADDTO" SP context SP entry-name
                      SP position SP return-data-list
 response-alert     = "*" SP "ALERT" SP resp-body CRLF
                     ;; Client MUST display alert text to user
 response-bye       = "*" SP "BYE" SP resp-body CRLF
                     ;; Server will disconnect condition
 response-change    = "*" SP "CHANGE" SP context SP entry-name
                      SP position SP position SP return-data-list
 response-cont      = "+" SP string
 response-deleted   = tag SP "DELETED" SP entry-name
 response-done      = tag SP resp-cond-state CRLF
 response-entry     = tag SP "ENTRY" SP entry SP return-data-list
 response-extend    = (tag / "*") SP extend-token [SP extension-data]
 response-lang      = "*" SP "LANG" SP lang-tag 1*(SP comparator)
 response-listr     = tag SP "LISTRIGHTS" SP acl-rights
                      *(SP acl-rights)
 response-mtimei    = tag SP "MODTIME" SP time
 response-mtimeu    = "*" SP "MODTIME" SP context SP time
 response-myright   = tag SP "MYRIGHTS" SP acl-rights
 response-quota     = "*" SP "QUOTA" SP dataset SP quota-limit
                      SP quota-usage [SP extension-data]
 response-refer     = tag SP "REFER" SP dataset
                      1*(SP <"> url-relative <">)

Newman & Myers Standards Track [Page 57] RFC 2244 ACAP November 1997

 response-remove    = "*" SP "REMOVEFROM" SP context SP
                      entry-name SP position
 response-stat      = "*" SP resp-cond-state CRLF
 resp-body          = ["(" resp-code ")" SP] quoted
 resp-code          = "AUTH-TOO-WEAK" / "ENCRYPT-NEEDED" /
                      resp-code-inval / resp-code-mod /
                      resp-code-noexist / resp-code-perm / "QUOTA" /
                      resp-code-refer / resp-code-sasl /
                      resp-code-toomany / "TOOOLD" /
                      "TRANSITION-NEEDED" / "TRYFREECONTEXT" /
                      "TRYLATER" / "WAYTOOMANY" / resp-code-ext
 resp-code-ext      = iana-token [SP extension-data]
                      ;; unknown codes MUST be tolerated by the client
 resp-code-inval    = "INVALID" 1*(SP entry-path SP attribute)
 resp-code-mod      = "MODIFIED" SP entry-path
 resp-code-noexist  = "NOEXIST" SP dataset
 resp-code-perm     = "PERMISSION" SP acl-object
 resp-code-refer    = "REFER" 1*(SP <"> url-relative <">)
 resp-code-sasl     = "SASL" SP string
 resp-code-toomany  = "TOOMANY" SP nz-number
 resp-cond-state    = ("OK" / "NO" / "BAD") SP resp-body
                      ;; Status condition
 return-attr-list   = "(" return-metalist *(SP return-metalist) ")"
                      ;; occurs when "*" in RETURN pattern on SEARCH
 return-data        = return-metadata / return-metalist /
                      return-attr-list
 return-data-list   = return-data *(SP return-data)
 return-metalist    = "(" return-metadata *(SP return-metadata) ")"
                      ;; occurs when multiple metadata items requested
 return-metadata    = nil / string / value-list / acl

Newman & Myers Standards Track [Page 58] RFC 2244 ACAP November 1997

 searchkey-equal    = "EQUAL" SP attribute SP comparator SP value-nil
 searchkey-comp     = "COMPARE" SP attribute SP comparator SP value
 searchkey-prefix   = "PREFIX" SP attribute SP comparator SP value
 searchkey-range    = "RANGE" SP nz-number SP nz-number SP time
 searchkey-strict   = "COMPARESTRICT" SP attribute SP comparator
                      SP value
 searchkey-substr   = "SUBSTRING" SP attribute SP comparator SP value
 searchmod-depth    = "DEPTH" SP number
 searchmod-hard     = "HARDLIMIT" SP nz-number
 searchmod-limit    = "LIMIT" SP number SP number
 searchmod-make     = "MAKECONTEXT" [SP "ENUMERATE"]
                      [SP "NOTIFY"] SP context
 searchmod-ninh     = "NOINHERIT"
 searchmod-return   = "RETURN" SP "(" [metadata-list] ")"
 searchmod-sort     = "SORT" SP "(" sort-list ")"
 search-criteria    = "ALL" / searchkey-equal / searchkey-comp /
                      searchkey-strict / searchkey-range /
                      searchkey-prefix / searchkey-substr /
                      "NOT" SP search-criteria /
                      "OR" SP search-criteria SP search-criteria /
                      "AND" SP search-criteria SP search-criteria
 search-modifier    = searchmod-depth / searchmod-hard /
                      searchmod-limit / searchmod-make /
                      searchmod-ninh / searchmod-return /
                      searchmod-sort
 sort-list          = sort-item *(SP sort-item)
 sort-item          = attribute SP comparator
 store-entry        = "(" entry-path *(SP store-modifier)
                          *(SP attribute-store) ")"
                      ;; MUST NOT include same store-modifier twice
                      ;; MUST NOT include same attribute twice

Newman & Myers Standards Track [Page 59] RFC 2244 ACAP November 1997

 store-entry-list   = store-entry *(SP store-entry)
                      ;; MUST NOT include same entry twice
 store-modifier     = store-mod-unchang / store-mod-nocreate
 store-mod-nocreate = "NOCREATE"
 store-mod-unchang  = "UNCHANGEDSINCE" SP time
 string             = quoted / literal
 string-list        = string *(SP string)
 string-utf8        = quoted / literal-utf8
 tag                = 1*32TAG-CHAR
 time               = <"> time-year time-month time-day time-hour
                      time-minute time-second time-subsecond <">
                      ;; Timestamp in UTC
 time-day           = 2DIGIT ;; 01-31
 time-hour          = 2DIGIT ;; 00-23
 time-minute        = 2DIGIT ;; 00-59
 time-month         = 2DIGIT ;; 01-12
 time-second        = 2DIGIT ;; 00-60
 time-subsecond     = *DIGIT
 time-year          = 4DIGIT
 value              = string
 value-list         = "(" [value *(SP value)] ")"
 value-nil          = value / nil
 value-nildef       = value-nil / "DEFAULT"
 value-store        = value-nildef / value-list / acl
 url-acap           = "acap://" url-server "/" url-enc-entry
                      [url-filter] [url-extension]
                      ;; url-enc-entry interpreted relative to "/"

Newman & Myers Standards Track [Page 60] RFC 2244 ACAP November 1997

 url-attr-list      = url-enc-attr *("&" url-enc-attr)
 url-auth           = ";AUTH=" ("*" / url-enc-auth)
 url-achar          = uchar / "&" / "=" / "~"
                      ;; See RFC 1738 for definition of "uchar"
 url-char           = uchar / "=" / "~" / ":" / "@" / "/"
                      ;; See RFC 1738 for definition of "uchar"
 url-enc-attr       = 1*url-char
                      ;; encoded version of attribute name
 url-enc-auth       = 1*url-achar
                      ;; encoded version of auth-type-name above
 url-enc-entry      = 1*url-char
                      ;; encoded version of entry-relative above
 url-enc-user       = *url-achar
                      ;; encoded version of login userid
 url-extension      = *("?" 1*url-char)
 url-filter         = "?" url-attr-list
 url-relative       = url-acap / [url-enc-entry] [url-filter]
                      ;; url-enc-entry is relative to base URL
 url-server         = [url-enc-user [url-auth] "@"] hostport
                      ;; See RFC 1738 for definition of "hostport"

9. Multi-lingual Considerations

 The IAB charset workshop [IAB-CHARSET] came to a number of
 conclusions which influenced the design of ACAP.  The decision to use
 UTF-8 as the character encoding scheme was based on that work.  The
 LANG command to negotiate a language for error messages is also
 included.
 Section 3.4.5 of the IAB charset workshop report states that there
 should be a way to identify the natural language for human readable
 strings.  Several promising proposals have been made for use within
 ACAP, but no clear consensus on a single method is apparent at this
 stage.  The following rules are likely to permit the addition of
 multi-lingual support in the future:

Newman & Myers Standards Track [Page 61] RFC 2244 ACAP November 1997

 (1) A work in progress called Multi-Lingual String Format (MLSF)
 proposes a layer on top of UTF-8 which uses otherwise illegal UTF-8
 sequences to store language tags.  In order to permit its addition to
 a future version of this standard, client-side UTF-8 interpreters
 MUST be able to silently ignore illegal multi-byte UTF-8 characters,
 and treat illegal single-byte UTF-8 characters as end of string
 markers.  Servers, for the time being, MUST be able to silently
 accept illegal UTF-8 characters, except in attribute names and entry
 names.  Clients MUST NOT send illegal UTF-8 characters to the server
 unless a future standard changes this rule.
 (2) There is a proposal to add language tags to Unicode.  To support
 this, servers MUST be able to store UTF-8 characters of up to 20 bits
 of data.
 (3) The metadata item "language" is reserved for future use.

10. Security Considerations

 The AUTHENTICATE command uses SASL [SASL] to provide basic
 authentication, authorization, integrity and privacy services.  This
 is described in section 6.3.1.
 When the CRAM-MD5 mechanism is used, the security considerations for
 the CRAM-MD5 SASL mechanism [CRAM-MD5] apply.  The CRAM-MD5 mechanism
 is also susceptible to passive dictionary attacks.  This means that
 if an authentication session is recorded by a passive observer, that
 observer can try common passwords through the CRAM-MD5 mechanism and
 see if the results match.  This attack is reduced by using hard to
 guess passwords.  Sites are encouraged to educate users and have the
 password change service test candidate passwords against a
 dictionary.  ACAP implementations of CRAM-MD5 SHOULD permit passwords
 of at least 64 characters in length.
 ACAP protocol transactions are susceptible to passive observers or
 man in the middle attacks which alter the data, unless the optional
 encryption and integrity services of the AUTHENTICATE command are
 enabled, or an external security mechanism is used for protection.
 It may be useful to allow configuration of both clients and servers
 to refuse to transfer sensitive information in the absence of strong
 encryption.
 ACAP access control lists provide fine grained authorization for
 access to attributes.  A number of related security issues are
 described in section 3.5.
 ACAP URLs have the same security considerations as IMAP URLs
 [IMAP-URL].

Newman & Myers Standards Track [Page 62] RFC 2244 ACAP November 1997

 ACAP clients are encouraged to consider the security problems
 involved with a lab computer situation.  Specifically, a client cache
 of ACAP configuration information MUST NOT allow access by an
 unauthorized user.  One way to assure this is for an ACAP client to
 be able to completely flush any non-public cached configuration data
 when a user leaves.
 As laptop computers can be easily stolen and a cache of configuration
 data may contain sensitive information, a disconnected mode ACAP
 client may wish to encrypt and password protect cached configuration
 information.

11. Acknowledgments

 Many thanks to the follow people who have contributed to ACAP over
 the past four years: Wallace Colyer, Mark Crispin, Jack DeWinter, Rob
 Earhart, Ned Freed, Randy Gellens, Terry Gray, J. S. Greenfield,
 Steve Dorner, Steve Hole, Steve Hubert, Dave Roberts, Bart Schaefer,
 Matt Wall and other participants of the IETF ACAP working group.

12. Authors' Addresses

 Chris Newman
 Innosoft International, Inc.
 1050 Lakes Drive
 West Covina, CA 91790 USA
 Email: chris.newman@innosoft.com
 John Gardiner Myers
 Netscape Communications
 501 East Middlefield Road
 Mail Stop MV-029
 Mountain View, CA 94043
 Email: jgmyers@netscape.com

Newman & Myers Standards Track [Page 63] RFC 2244 ACAP November 1997

Appendices

A. References

 [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications:
 ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd,
 November 1997.
     <ftp://ds.internic.net/rfc/rfc2234.txt>
 [BASIC-URL] Berners-Lee, Masinter, McCahill, "Uniform Resource
 Locators (URL)", RFC 1738, CERN, Xerox Coproration, University of
 Minnesota, December 1994.
     <ftp://ds.internic.net/rfc/rfc1738.txt>
 [CHARSET-LANG-POLICY] Alvestrand, "IETF Policy on Character Sets and
 Languages", work in progress.
 [CRAM-MD5] Klensin, Catoe, Krumviede, "IMAP/POP AUTHorize Extension
 for Simple Challenge/Response", RFC 2195, MCI, September 1997.
     <ftp://ds.internic.net/rfc/rfc2195.txt>
 [IAB-CHARSET] Weider, Preston, Simonsen, Alvestrand, Atkinson,
 Crispin, Svanberg, "The Report of the IAB Character Set Workshop held
 29 February - 1 March, 1996", RFC 2130, April 1997.
     <ftp://ds.internic.net/rfc/rfc2130.txt>
 [IMAP4] Crispin, M., "Internet Message Access Protocol - Version
 4rev1", RFC 2060, University of Washington, December 1996.
     <ftp://ds.internic.net/rfc/rfc2060.txt>
 [IMAP-ACL] Myers, J., "IMAP4 ACL extension", RFC 2086, Carnegie
 Mellon, January 1997.
     <ftp://ds.internic.net/rfc/rfc2086.txt>
 [IMAP-URL] Newman, "IMAP URL Scheme", RFC 2192, Innosoft, July 1997.
     <ftp://ds.internic.net/rfc/rfc2192.txt>
 [ISO-10646] ISO/IEC 10646-1:1993(E) "Information Technology--
 Universal Multiple-octet Coded Character Set (UCS)." See also
 amendments 1 through 7, plus editorial corrections.

Newman & Myers Standards Track [Page 64] RFC 2244 ACAP November 1997

 [ISO-C] "Programming languages -- C", ISO/IEC 9899:1990,
 International Organization for Standardization.  This is effectively
 the same as ANSI C standard X3.159-1989.
 [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate
 Requirement Levels", RFC 2119, Harvard University, March 1997.
     <ftp://ds.internic.net/rfc/rfc2119.txt>
 [LANG-TAGS] Alvestrand, H., "Tags for the Identification of
 Languages", RFC 1766.
     <ftp://ds.internic.net/rfc/rfc1766.txt>
 [REL-URL] Fielding, "Relative Uniform Resource Locators", RFC 1808,
 UC Irvine, June 1995.
     <ftp://ds.internic.net/rfc/rfc1808.txt>
 [SASL] Myers, J., "Simple Authentication and Security Layer (SASL)",
 RFC 2222, Netscape Communications, October 1997.
     <ftp://ds.internic.net/rfc/rfc2222.txt>
 [SASL-ANON] Newman, C., "Anonymous SASL Mechanism", RFC 2245,
 November 1997.
 [UNICODE-2] The Unicode Consortium, "The Unicode Standard, Version
 2.0", Addison-Wesley, 1996. ISBN 0-201-48345-9.
 [US-ASCII] "USA Standard Code for Information Interchange," X3.4.
 American National Standards Institute: New York (1968).
 [UTF8] Yergeau, F. "UTF-8, a transformation format of Unicode and ISO
 10646", RFC 2044, Alis Technologies, October 1996.
     <ftp://ds.internic.net/rfc/rfc2044.txt>

Newman & Myers Standards Track [Page 65] RFC 2244 ACAP November 1997

B. ACAP Keyword Index

     ACAP (untagged response) ...................................   26
     ADDTO (untagged response) ..................................   40
     ALERT (untagged response) ..................................   31
     ALL (search keyword) .......................................   36
     AND (search keyword) .......................................   36
     AUTH-TOO-WEAK (response code) ..............................   19
     AUTHENTICATE (command) .....................................   31
     BAD (response) .............................................   30
     BYE (untagged response) ....................................   30
     CHANGE (untagged response) .................................   41
     COMPARE (search keyword) ...................................   36
     COMPARESTRICT (search keyword) .............................   36
     CONTEXTLIMIT (ACAP capability) .............................   27
     DELETEACL (command) ........................................   46
     DELETED (intermediate response) ............................   45
     DELETEDSINCE (command) .....................................   45
     DEPTH (search modifier) ....................................   34
     ENCRYPT-NEEDED (response code) .............................   19
     ENTRY (intermediate response) ..............................   37
     EQUAL (search keyword) .....................................   37
     FREECONTEXT (command) ......................................   39
     GETQUOTA (command) .........................................   48
     HARDLIMIT (search modifier) ................................   34
     IMPLEMENTATION (ACAP capability) ...........................   27
     INVALID (response code) ....................................   19
     LANG (command) .............................................   28
     LANG (intermediate response) ...............................   28
     LIMIT (search modifier) ....................................   34
     LISTRIGHTS (command) .......................................   47
     LISTRIGHTS (intermediate response) .........................   48
     LOGOUT (command) ...........................................   29
     MAKECONTEXT (search modifier) ..............................   34
     MODIFIED (response code) ...................................   19
     MODTIME (intermediate response) ............................   38
     MODTIME (untagged response) ................................   42
     MYRIGHTS (command) .........................................   47
     MYRIGHTS (intermediate response) ...........................   47
     NO (response) ..............................................   29
     NOCREATE (store modifier) ..................................   44
     NOEXIST (response code) ....................................   19
     NOINHERIT (search modifier) ................................   35
     NOOP (command) .............................................   27
     NOT (search keyword) .......................................   37
     OK (response) ..............................................   29
     OR (search keyword) ........................................   37
     PERMISSION (response code) .................................   19

Newman & Myers Standards Track [Page 66] RFC 2244 ACAP November 1997

     PREFIX (search keyword) ....................................   37
     QUOTA (response code) ......................................   19
     QUOTA (untagged response) ..................................   49
     RANGE (search keyword) .....................................   37
     REFER (intermediate response) ..............................   38
     REFER (response code) ......................................   19
     REMOVEFROM (untagged response) .............................   41
     RETURN (search modifier) ...................................   35
     SASL (ACAP capability) .....................................   27
     SASL (response code) .......................................   20
     SEARCH (command) ...........................................   33
     SETACL (command) ...........................................   46
     SORT (search modifier) .....................................   36
     STORE (command) ............................................   42
     SUBSTRING (search keyword) .................................   37
     TOOMANY (response code) ....................................   20
     TOOOLD (response code) .....................................   20
     TRANSITION-NEEDED (response code) ..........................   20
     TRYFREECONTEXT (response code) .............................   20
     TRYLATER (response code) ...................................   20
     UNCHANGEDSINCE (store modifier) ............................   44
     UPDATECONTEXT (command) ....................................   40
     WAYTOOMANY (response code) .................................   20
     acl (attribute metadata) ...................................   12
     anyone (ACL identifier) ....................................   17
     attribute (attribute metadata) .............................   12
     dataset.acl (dataset attribute) ............................   24
     dataset.acl.<attribute> (dataset attribute) ................   24
     dataset.inherit (dataset attribute) ........................   24
     entry (predefined attribute) ...............................   11
     i;ascii-casemap (comparator) ...............................   16
     i;ascii-numeric (comparator) ...............................   16
     i;octet (comparator) .......................................   16
     modtime (predefined attribute) .............................   11
     myrights (attribute metadata) ..............................   12
     size (attribute metadata) ..................................   13
     subdataset (predefined attribute) ..........................   11
     value (attribute metadata) .................................   13

Newman & Myers Standards Track [Page 67] RFC 2244 ACAP November 1997

C. Full Copyright Statement

 Copyright (C) The Internet Society 1997. All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implmentation may be prepared, copied, published and
 distributed, in whole or in part, without restriction of any kind,
 provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of developing
 Internet standards in which case the procedures for copyrights defined
 in the Internet Standards process must be followed, or as required to
 translate it into languages other than English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
 NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
 WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Newman & Myers Standards Track [Page 68]

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