xmpp 之Jabber RFC3921 [草稿]

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Network Working Group                                P. Saint-Andre, Ed.
Request for Comments: 3921                    Jabber Software Foundation
Category: Standards Track                                   October 2004


          Extensible Messaging and Presence Protocol (XMPP):
                     Instant Messaging and Presence

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 (2004).

Abstract

   This memo describes extensions to and applications of the core
   features of the Extensible Messaging and Presence Protocol (XMPP)
   that provide the basic instant messaging (IM) and presence
   functionality defined in RFC 2779.



Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.   Syntax of XML Stanzas  . . . . . . . . . . . . . . . . . . .   4
   3.   Session Establishment  . . . . . . . . . . . . . . . . . . .  10
   4.   Exchanging Messages  . . . . . . . . . . . . . . . . . . . .  13
   5.   Exchanging Presence Information  . . . . . . . . . . . . . .  16
   6.   Managing Subscriptions . . . . . . . . . . . . . . . . . . .  26
   7.   Roster Management  . . . . . . . . . . . . . . . . . . . . .  27
   8.   Integration of Roster Items and Presence Subscriptions . . .  32
   9.   Subscription States  . . . . . . . . . . . . . . . . . . . .  56
   10.  Blocking Communication . . . . . . . . . . . . . . . . . . .  62
   11.  Server Rules for Handling XML Stanzas  . . . . . . . . . . .  85
   12.  IM and Presence Compliance Requirements  . . . . . . . . . .  88
   13.  Internationalization Considerations  . . . . . . . . . . . .  89
   14.  Security Considerations  . . . . . . . . . . . . . . . . . .  89
   15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  90
   16.  References . . . . . . . . . . . . . . . . . . . . . . . . .  91
   A.   vCards . . . . . . . . . . . . . . . . . . . . . . . . . . .  93
   B.   XML Schemas. . . . . . . . . . . . . . . . . . . . . . . . .  93
   C.   Differences Between Jabber IM/Presence Protocols and XMPP. . 105
   Contributors . . . . . . . . . . . . . . . . . . . . . . . . . .  106
   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .  106
   Author's Address. . . . . . . . . . . . . . . . . . . . . . . . . 106
   Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 107

1.  Introduction

1.1.  Overview

   The Extensible Messaging and Presence Protocol (XMPP) is a protocol
   for streaming XML [XML] elements in order to exchange messages and
   presence information in close to real time.  The core features of
   XMPP are defined in Extensible Messaging and Presence Protocol
   (XMPP): Core [XMPP-CORE].  These features -- mainly XML streams, use
   of TLS and SASL, and the <message/>, <presence/>, and <iq/> children
   of the stream root -- provide the building blocks for many types of
   near-real-time applications, which may be layered on top of the core
   by sending application-specific data qualified by particular XML
   namespaces [XML-NAMES].  This memo describes extensions to and
   applications of the core features of XMPP that provide the basic
   functionality expected of an instant messaging (IM) and presence
   application as defined in RFC 2779 [IMP-REQS].

   XMPP是一种通过将XML elements流化以达到近乎实时地传递消息(message)和在线信息
   (presence information)的协议。XMPP的核心功能在(XMPP): Core [XMPP-CORE]中定义。
   这些功能——主要包括XML的流化，TLS和SASL的使用，以及像<message/>,<presence/>以及
   <iq/>这样的流的子元素——提供给我们一些素材，使我们能创建很多"半实时(near-real-time)"
   的应用程序，而这些半实时的应用程序或许会位于应用程序的核心层之上，专门负责发送由程序专用的
   XML数据。这份memo讲述的是怎样扩展和使用XMPP的核心功能，而XMPP的核心协议仅涵盖了由RFC 
   2779[IMP-REQS]定义的，基本的IM和presence application 所应该提供的功能。 




1.2.  Requirements

   For the purposes of this memo, the requirements of a basic instant
   messaging and presence application are defined by [IMP-REQS], which
   at a high level stipulates that a user must be able to complete the
   following use cases:
   
   作为本文档的基础，基本的IM和"在线应用程序presence application"的要求
   刊载在[IMP-REQS]里面。这份文档在大体上规定了用户必须能完成如下的功能。

   o  Exchange messages with other users
      与其它用户交换消息
   o  Exchange presence information with other users
      与其它用户交换在线信息
   o  Manage subscriptions to and from other users
      管理和限制自己或他人的在线信息的发布
   o  Manage items in a contact list (in XMPP this is called a "roster")
      管理通讯录里的资料(XMPP称之为roster)
   o  Block communications to or from specific other users
      切断与他人的通讯

   Detailed definitions of these functionality areas are contained in
   [IMP-REQS], and the interested reader is directed to that document
   regarding the requirements addressed herein.

   这些功能的详细定义刊载在[IMP-REQS]里，感兴趣的读者可以自己去看。

   [IMP-REQS] also stipulates that presence services must be separable
   from instant messaging services; i.e., it must be possible to use the
   protocol to provide a presence service, an instant messaging service,
   or both.  Although the text of this memo assumes that implementations
   and deployments will want to offer a unified instant messaging and
   presence service, there is no requirement that a service must offer
   both a presence service and an instant messaging service, and the
   protocol makes it possible to offer separate and distinct services
   for presence and for instant messaging.

   [IMP-REQS]同时还规定，在线信息的服务必须与及时信息的服务相分离。比方说，
   协议必须允许你只使用在线信息，或及时信息服务，当然也可以两个都用。虽然
   我们认为真正实现的时候，在线信息和及时信息服务肯定是合二为一的，但是它
   也没有强求你一定必须同时提供在线信息合及时信息服务。这个协议完全允许你
   提供单独的在线信息或及时信息服务。

   Note: While XMPP-based instant messaging and presence meets the
   requirements of [IMP-REQS], it was not designed explicitly with that
   specification in mind, since the base protocol evolved through an
   open development process within the Jabber open-source community
   before RFC 2779 was written.  Note also that although protocols
   addressing many other functionality areas have been defined in the
   Jabber community, such protocols are not included in this memo
   because they are not required by [IMP-REQS].

   注意：虽然基于XMPP的及时信息和在线服务符合[IMP-REQS]的要求，但它并
   不是刻意去实现的，因为Jabber开源社区早在RFC 2779发布之前就已经促成了
   基本的协议。同时还要指出的是，虽然Jabber社区还为协议设计了很多别的方面
   的功能，但由于[IMP-REQS]并没有要求，因此我们这里也就不涉及了。

1.3.  Terminology

   This memo inherits the terminology defined in [XMPP-CORE].

   The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
   "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14, RFC 2119 [TERMS].




2.  Syntax of XML Stanzas

    XML Stanzas的语法

   The basic semantics and common attributes of XML stanzas qualified by
   the 'jabber:client' and 'jabber:server' namespaces are defined in
   [XMPP-CORE].  However, these namespaces also define various child
   elements, as well as values for the common 'type' attribute, that are
   specific to instant messaging and presence applications.  Thus,
   before addressing particular "use cases" for such applications, we
   here further describe the syntax of XML stanzas, thereby
   supplementing the discussion in [XMPP-CORE].

   XML stanzas都归在'jabber:client'和'jabber:server'名字空间之下，其基本语义
   和常用属性由[XMPP-CORE]定义。除了常用的'type'属性的值之外，这两个名字空间
   还定义了很多专供及时信息或在线信息服务的child elements。因此在描述此类应用
   程序的“use case”之前，我们先探讨一下XML stanzas的语法，也借此补充一下
   [XMPP-CORE]。

2.1.  Message Syntax
      
   Message stanzas qualified by the 'jabber:client' or 'jabber:server'
   namespace are used to "push" information to another entity.  Common
   uses in instant messaging applications include single messages,
   messages sent in the context of a chat conversation, messages sent in
   the context of a multi-user chat room, headlines and other alerts,
   and errors.

   归在'jabber:client'或'jabber:server'名字空间之下的Message stanzas是用来
   向另一个entity"推"信息用的。在IM应用程序里，这种stanzas常用被用于发送“单条
   消息(single message)”，在chat环境下发送消息，在多用户的chat room的环境下
   发送消息，以及发送headline，警告和错误消息。

2.1.1.  Types of Message

   The 'type' attribute of a message stanza is RECOMMENDED; if included,
   it specifies the conversational context of the message, thus
   providing a hint regarding presentation (e.g., in a GUI).  If
   included, the 'type' attribute MUST have one of the following values:

   message stanza的'type'属性是RECOMMENDED的；如果有，它表示这个消息是在怎样
   的交谈环境下发出的，因此它也暗示了该怎样显示这条消息(比方说在GUI环境下)。
   'type'属性如果有必须(MUST)是下面值里的一个。

   o  chat -- The message is sent in the context of a one-to-one chat
      conversation.  A compliant client SHOULD present the message in an
      interface enabling one-to-one chat between the two parties,
      including an appropriate conversation history.
      
      chat -- 消息是在一对一的chat谈话中发出的。客户端应当(SHOULD)在一个
      能让用户进行一对一谈话的界面里提示这条消息，包括交谈的记录。

   o  error -- An error has occurred related to a previous message sent
      by the sender (for details regarding stanza error syntax, refer to
      [XMPP-CORE]).  A compliant client SHOULD present an appropriate
      interface informing the sender of the nature of the error.
      
      error -- 表示先前发送的消息发生了错误(关于stanza的错误的语法，
      请参阅[XMPP-CORE])。客户端应当(SHOULD)能告诉发送发错误的性质。

   o  groupchat -- The message is sent in the context of a multi-user
      chat environment (similar to that of [IRC]).  A compliant client
      SHOULD present the message in an interface enabling many-to-many
      chat between the parties, including a roster of parties in the
      chatroom and an appropriate conversation history.  Full definition
      of XMPP-based groupchat protocols is out of scope for this memo.

      groupchat -- 这条消息是在多用户交谈环境下发出的(类似[IRC])。客户端
      应当(SHOULD)在能允许用户进行多对多谈话的界面里显示这条消息，这其中
      应该包括chat room的参与者的roster(名单)，以及适当的谈话记录。基于XMPP
      的群组交谈协议超出了本文档的范围。

   o  headline -- The message is probably generated by an automated
      service that delivers or broadcasts content (news, sports, market
      information, RSS feeds, etc.).  No reply to the message is
      expected, and a compliant client SHOULD present the message in an
      interface that appropriately differentiates the message from
      standalone messages, chat sessions, or groupchat sessions (e.g.,
      by not providing the recipient with the ability to reply).
      
      headline -- 这条消息或许是由某个后台服务生成并发送或广播的(新闻，体育，
      市场信息，RSS服务等到)。它不需要用户的回应。客户端应当(SHOULD)在
      一个合适的界面下提示这条消息以将其与"standalone message"，"chat session"
      和"groupchat session"相区分(比方说用户只能看不能reply)。

   o  normal -- The message is a single message that is sent outside the
      context of a one-to-one conversation or groupchat, and to which it
      is expected that the recipient will reply.  A compliant client
      SHOULD present the message in an interface enabling the recipient
      to reply, but without a conversation history.

      normal -- 这是一个single message，既不是一对一的交谈，也不是群组交谈，
      而且允许接受方回应。客户端应当(SHOULD)在一个能让用户reply的界面里显示
      这条消息，但是不要有谈话记录。

   An IM application SHOULD support all of the foregoing message types;
   if an application receives a message with no 'type' attribute or the
   application does not understand the value of the 'type' attribute
   provided, it MUST consider the message to be of type "normal" (i.e.,
   "normal" is the default).  The "error" type MUST be generated only in
   response to an error related to a message received from another
   entity.
    
   IM application应当支持所有上述message type，如果它收到了一个没有'type'属性的message
   或者它看不懂这个'type'属性，那它必须(MUST)将其认做是"normal"的message(也就是说，
   "normal"是默认的属性)。"error"只限于(MUST)用来回应与对方发出的message相关的错误。

   Although the 'type' attribute is OPTIONAL, it is considered polite to
   mirror the type in any replies to a message; furthermore, some
   specialized applications (e.g., a multi-user chat service) MAY at
   their discretion enforce the use of a particular message type (e.g.,
   type='groupchat').
   
   虽然'type'属性是OPTIONAL的，但是最好在回应信息里面附上相同的'type'信息；此外有些专用程序
   (比方说多用户的chat service)可以(MAY)根据他们自己的需要，强制使用特定的message type
   (比方说type='groupchat')。

2.1.2.  Child Elements

   As described under extended namespaces (Section 2.4), a message
   stanza MAY contain any properly-namespaced child element.

   正如我们将在"扩展名字空间"(Section2.4)所讲的，message stanza可以(MAY)包含任意的
   "属于适当的名字空间"的child element。

   In accordance with the default namespace declaration, by default a
   message stanza is qualified by the 'jabber:client' or 'jabber:server'
   namespace, which defines certain allowable children of message
   stanzas.  If the message stanza is of type "error", it MUST include
   an <error/> child; for details, see [XMPP-CORE].  Otherwise, the
   message stanza MAY contain any of the following child elements
   without an explicit namespace declaration:
   
   为了与默认的名字空间的声明相一致，默认情况下，message stanza被归到'jabber:client'或
   'jabber:server'名字空间下。这两个名字空间定义了一些被认可的message stanza的child。
   'error'类型的message stanza必须(MUST)包含<error/> child；具体细节请看[XMPP-CORE]。
   除此之外，message stanza可以(MAY)不经声明就使用下列的child elements。

   1.  <subject/>
   2.  <body/>
   3.  <thread/>

2.1.2.1.  Subject

   The <subject/> element contains human-readable XML character data
   that specifies the topic of the message.  The <subject/> element MUST
   NOT possess any attributes, with the exception of the 'xml:lang'
   attribute.  Multiple instances of the <subject/> element MAY be
   included for the purpose of providing alternate versions of the same
   subject, but only if each instance possesses an 'xml:lang' attribute
   with a distinct language value.  The <subject/> element MUST NOT
   contain mixed content (as defined in Section 3.2.2 of [XML]).

   <subject/> element包含human-readable的，表示message的标题的XML字符数据。
   <subject/>绝对不能(MUST NOT)包含除'xml:lang'之外的任何属性。为了能提供同一个
   subject的多个版本，一个message里面可以(MAY)包含多个<body/> element。但这仅限于
   每个<body/>都包含'xml:lang'属性，并且其language值都不相同的情形。<subject/>
   绝对不能(MUST NOT)包含mixed content(见Section 3.2.2)


2.1.2.2.  Body

   The <body/> element contains human-readable XML character data that
   specifies the textual contents of the message; this child element is
   normally included but is OPTIONAL.  The <body/> element MUST NOT
   possess any attributes, with the exception of the 'xml:lang'
   attribute.  Multiple instances of the <body/> element MAY be included
   but only if each instance possesses an 'xml:lang' attribute with a
   distinct language value.  The <body/> element MUST NOT contain mixed
   content (as defined in Section 3.2.2 of [XML]).

   <body/> element包含human-readable的，用来表示消息的正文内容的XML字符数据；通常
   message都会包含这个child，但它是可选的(OPTIONAL)。<body/> element绝对不能(MUST NOT)
   包含除'xml:lang'之外的任何属性。一个message里面可以(MAY)包含多个<subject/> element。
   但这仅限于每个<subject/>都包含'xml:lang'属性，并且其language值都不相同的情形。
   <body/>绝对不能(MUST NOT)包含mixed content(见Section 3.2.2)

2.1.2.3.  Thread

   The <thread/> element contains non-human-readable XML character data
   specifying an identifier that is used for tracking a conversation
   thread (sometimes referred to as an "instant messaging session")
   between two entities.  The value of the <thread/> element is
   generated by the sender and SHOULD be copied back in any replies.  If
   used, it MUST be unique to that conversation thread within the stream
   and MUST be consistent throughout that conversation (a client that
   receives a message from the same full JID but with a different thread
   ID MUST assume that the message in question exists outside the
   context of the existing conversation thread).  The use of the
   <thread/> element is OPTIONAL and is not used to identify individual
   messages, only conversations.  A message stanza MUST NOT contain more
   than one <thread/> element.  The <thread/> element MUST NOT possess
   any attributes.  The value of the <thread/> element MUST be treated
   as opaque by entities; no semantic meaning may be derived from it,
   and only exact comparisons may be made against it.  The <thread/>
   element MUST NOT contain mixed content (as defined in Section 3.2.2
   of [XML]).

   <thread/> element包含非human-readable的XML字符数据。它是一个用于表示两个entity
   之间的conversion thread的(有时也被称作"instance messaging session")标识符。
   <thread/> element的值由sender生成，而且每次回复的时候必须(SHOULD)包含在内。如果
   用到了它，那么它必须(MUST)与stream里的conversation thread一一对应，而且整个谈话期间
   必须保持一致(如果client端收到了同一个JID发出的，但是thread ID不同的message，必须(MUST)
   认定这个消息与当前的conversation thread无关。)<thread/> element是OPTIONAL的，
   且不用于标识单个message，它是用来标识conversation的。一个message stanza MUST NOT
   包含二个或二个以上的<thread/> element。<thread> element MUST NOT包含任何属性。
   对entities来说<thread/>的值必须(MUST)是不透明的；不能用它来获取任何语义信息，而且只能
   对它进行精确地比较。<thread/> MUST NOT包含mixed content(Section 3.2.2)

2.2.  Presence Syntax

   Presence stanzas are used qualified by the 'jabber:client' or
   'jabber:server' namespace to express an entity's current network
   availability (offline or online, along with various sub-states of the
   latter and optional user-defined descriptive text), and to notify
   other entities of that availability.  Presence stanzas are also used
   to negotiate and manage subscriptions to the presence of other
   entities.

   Presence stanza属于'jabber:client'或'jabber:server'名字空间，它们是用来表示
   entity的当前网络可得性(offline还是online，此外后者还有很多sub-state和可选的用户
   自定义的叙述性文字)，并且将其通知给其它entities的。Persence stanzas也被用于协商
   和管理订阅其它entities的presence信息。

2.2.1.  Types of Presence

   The 'type' attribute of a presence stanza is OPTIONAL.  A presence
   stanza that does not possess a 'type' attribute is used to signal to
   the server that the sender is online and available for communication.
   If included, the 'type' attribute specifies a lack of availability, a
   request to manage a subscription to another entity's presence, a
   request for another entity's current presence, or an error related to
   a previously-sent presence stanza.  If included, the 'type' attribute
   MUST have one of the following values:

   presence stanza的'type'属性是OPTIONAL的。不带'type'属性的presence stanza
   是用来通知服务器sender已经上线，并且available for communication。如果有，那么这个
   'type'或者用来表示可得性方面的限制，或者用来管理订阅其它用户的presence信息，或者用于
   查询其它用户的当前可得性，或者是先前发送的presence stanza出了错。如果有，'type'属性
   MUST是下列值中的一个:

   o  unavailable -- Signals that the entity is no longer available for
      communication.
      
      unavailable -- 表示entity不再available for communication了

   o  subscribe -- The sender wishes to subscribe to the recipient's
      presence.
      
      subscribe -- sender希望能订阅recipent的presence信息

   o  subscribed -- The sender has allowed the recipient to receive
      their presence.
      
      subscribed -- 发送方同意让接受方订阅自己的在线信息

   o  unsubscribe -- The sender is unsubscribing from another entity's
      presence.
      
      unsubscribe -- 发送方取消订阅另一方的在线信息

   o  unsubscribed -- The subscription request has been denied or a
      previously-granted subscription has been cancelled.

      unsubscribed -- 订阅请求被拒绝或者先前授予的订阅权限被撤销了

   o  probe -- A request for an entity's current presence; SHOULD be
      generated only by a server on behalf of a user.

      probe -- 请求entity的当前在线信息；只有(SHOULD)server才能代表用户去生成此类信息。

   o  error -- An error has occurred regarding processing or delivery of
      a previously-sent presence stanza.

      error -- 先前发送的presence stanza在处理或投送过程中出现了错误。

   For detailed information regarding presence semantics and the
   subscription model used in the context of XMPP-based instant
   messaging and presence applications, refer to Exchanging Presence
   Information (Section 5) and Managing Subscriptions (Section 6).

   要想详细了解相关信息，请参阅Section 5 Exchanging Presence Information
   和Section 6 Managing Subscriptions。

2.2.2.  Child Elements

   As described under extended namespaces (Section 2.4), a presence
   stanza MAY contain any properly-namespaced child element.

   就像Section 2.4的扩展名字空间所说的，presence stanza 可以包含任何
   properly-namespaced的child element。

   In accordance with the default namespace declaration, by default a
   presence stanza is qualified by the 'jabber:client' or
   'jabber:server' namespace, which defines certain allowable children
   of presence stanzas.  If the presence stanza is of type "error", it
   MUST include an <error/> child; for details, see [XMPP-CORE].  If the
   presence stanza possesses no 'type' attribute, it MAY contain any of
   the following child elements (note that the <status/> child MAY be
   sent in a presence stanza of type "unavailable" or, for historical
   reasons, "subscribe"):

   为了与默认的名字空间的声明保持一致，默认的presence stanza被归在'jabber:client'
   或'jabber:server'名字空间之下，这两个名字空间还定义了一些被认可的presence stanza
   的children。如果presence stanza是'error'类型的，那么它MUST包含<error/>；细节请看
   [XMPP-CORE]。如果presence stanza没有'type'属性，那么它MAY包含下列child element
   (注意，<status/> child可以随'unavailable' type的presence stanza或，出于历史原因，
   'subscribe' type的presence stanza发出。)

   1.  <show/>
   2.  <status/>
   3.  <priority/>

Network Working Group P. Saint-Andre, Ed. Request for Comments: 3921 Jabber Software Foundation Category: Standards Track October 2004

(XMPP): Instant Messaging and Presence

Extensible Messaging and Presence Protocol

Status of this Memo

Abstract

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RFC 3921 XMPP IM October 2004

Table of Contents

  1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
  2. Syntax of XML Stanzas . . . . . . . . . . . . . . . . . . . . . . . 4
  3. Session Establishment . . . . . . . . . . . . . . . . . . . . . . . 10
  4. Exchanging Messages . . . . . . . . . . . . . . . . . . . .. . . . 13
  5. Exchanging Presence Information . . . . . . . . . . . . . . . 16
  6. Managing Subscriptions . . . . . . . . . . . . . . . . . . . . . . . 26
  7. Roster Management . . . . . . . . . . . . . . . . . . . . . . . . . 27
  8. Integration of Roster Items and Presence Subscriptions . . . 32
  9. Subscription States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
  10. Blocking Communication . . . . . . . . . . . . . . . . . . . 62
  11. Server Rules for Handling XML Stanzas . . . . . . . . . . . 85
  12. IM and Presence Compliance Requirements . . . . . . . . . . 88
  13. Internationalization Considerations . . . . . . . . . . . . 89
  14. Security Considerations . . . . . . . . . . . . . . . . . . 89
  15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 90
  16. References . . . . . . . . . . . . . . . . . . . . . . . . . 91
  17. vCards . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 B. XML Schemas. . . . . . . . . . . . . . . . . . . . . . . . . 93 C. Differences Between Jabber IM/Presence Protocols and XMPP. . 105 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 106 Author's Address. . . . . . . . . . . . . . . . . . . . . . . . . 106 Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 107

1. Introduction

1.1. Overview

XMPP是一种将XML elements流化以达到近乎实时地传递消息(message)和在线信息(presence information)的协议。XMPP的核心功能在(XMPP): Core [XMPP-CORE]中定义。这些功能——主要包括XML的流化，TLS和SASL的使用，以及像<message/>,<presence/>以及<iq/>这样的流的子元素——提供给我们一些素材，使我们能创建很多"半实时(near-real-time)"的应用程序，而这些半实时的应用程序或许会位于应用程序的核心层之上，专门负责发送由程序专用的XML数据。这份memo讲述的是怎样扩展和使用XMPP的核心功能，而XMPP的核心协议仅涵盖了由RFC 2779 [IMP-REQS]定义的，基本的IM和presence application 所应该提供的功能。

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1.2. Requirements

1.3. Terminology

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2. Syntax of XML Stanzas

2.1. Message Syntax

2.1.1. Types of Message

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2.1.2. Child Elements

2.1.2.1. Subject

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2.1.2.2. Body

2.1.2.3. Thread

2.2. Presence Syntax

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2.2.1. Types of Presence

==== 2.2.2. Child Elements ====

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2.2.2.1. Show

2.2.2.2. Status

2.2.2.3. Priority

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2.3. IQ Syntax

2.4. Extended Namespaces

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3. Session Establishment

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4. Exchanging Messages

4.1. Specifying an Intended Recipient

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4.2. Specifying a Message Type

4.3. Specifying a Message Body

4.4. Specifying a Message Subject

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4.5. Specifying a Conversation Thread

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5. Exchanging Presence Information

5.1. Client and Server Presence Responsibilities

5.1.1. Initial Presence

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  1. Broadcast initial presence from the full JID (e.g.,

    • <[email protected]/resource>) of the user to all contacts that are subscribed to the user's presence information; such contacts are those for which a JID is present in the user's roster with the 'subscription' attribute set to a value of "from" or "both". (Note: The user's server MUST NOT broadcast initial presence to contacts to which the user is blocking outbound presence notifications, as described under Blocking Outbound Presence Notifications (Section 10.11).)

    In addition, the user's server MUST broadcast initial presence from the user's new available resource to any of the user's existing available resources (if any). Upon receiving initial presence from the user, the contact's server MUST deliver the user's presence stanza to the full JIDs

    (<[email protected]/resource>) associated with all of the contact's available resources, but only if the user is in the contact's roster with a subscription state of "to" or "both" and the contact has not blocked inbound presence notifications from the user's bare or full JID (as defined under Blocking Inbound Presence Notifications (Section 10.10)). If the user's server receives a presence stanza of type "error" in response to the initial presence that it sent to a contact on behalf of the user, it SHOULD NOT send further presence updates to that contact (until and unless it receives a presence stanza from the contact).

5.1.2. Presence Broadcast

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5.1.3. Presence Probes

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  1. Else, if the contact has at least one available resource, the
    • server MUST reply to the presence probe by sending to the user the full XML of the last presence stanza with no 'to' attribute received by the server from each of the contact's available resources (again, subject to privacy lists in force for each session).

5.1.4. Directed Presence

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5.1.5. Unavailable Presence

5.1.6. Presence Subscriptions

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5.2. Specifying Availability Status

5.3. Specifying Detailed Status Information

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5.4. Specifying Presence Priority

=== 5.5. Presence Examples ===

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6. Managing Subscriptions

6.1. Requesting a Subscription

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6.2. Handling a Subscription Request

6.3. Cancelling a Subscription from Another Entity

6.4. Unsubscribing from Another Entity's Presence

7. Roster Management

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7.1. Syntax and Semantics

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7.2. Business Rules

=== 7.3. Retrieving One's Roster on Login ===

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7.4. Adding a Roster Item

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7.5. Updating a Roster Item

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7.6. Deleting a Roster Item

8. Integration of Roster Items and Presence Subscriptions

8.1. Overview

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8.2. User Subscribes to Contact

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8.2.1. Alternate Flow: Contact Declines Subscription Request

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  1. If the contact wants to refuse the request, the contact's client
    • MUST send a presence stanza of type "unsubscribed" to the user (instead of the presence stanza of type "subscribed" sent in Step 6 of Section 8.2):

    <presence to='[email protected]' type='unsubscribed'/>

  2. As a result, the contact's server MUST route the presence stanza
    • of type "unsubscribed" to the user, first stamping the 'from'

      address as the bare JID (<[email protected]>) of the contact:

    <presence

    Note: If the contact's server previously added the user to the contact's roster for tracking purposes, it MUST remove the relevant item at this time.
  3. Upon receiving the presence stanza of type "unsubscribed"
    • addressed to the user, the user's server (1) MUST deliver that presence stanza to the user and (2) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "none" and with no 'ask' attribute:

    <presence

    <iq type='set'>

    </iq>

  4. Upon receiving the presence stanza of type "unsubscribed", the
    • user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by

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8.3. Creating a Mutual Subscription

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8.3.1. Alternate Flow: User Declines Subscription Request

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  1. As a result, the user's server MUST route the presence stanza of
    • type "unsubscribed" to the contact, first stamping the 'from'

      address as the bare JID (<[email protected]>) of the user:

    <presence

  2. Upon receiving the presence stanza of type "unsubscribed"
    • addressed to the contact, the contact's server (1) MUST deliver that presence stanza to the contact; and (2) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "from" and with no 'ask' attribute:

    <presence

    <iq type='set'>

    </iq>

  3. Upon receiving the presence stanza of type "unsubscribed", the
    • contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the user or "denying" it by sending a presence stanza of type "subscribe" to the user; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the contact's server know that it MUST no longer send notification of the subscription state change to the contact (see Section 9.4).
    As a result of this activity, there has been no change in the subscription state; i.e., the contact is in the user's roster with a subscription state of "to" and the user is in the contact's roster with a subscription state of "from".

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8.4. Unsubscribing

8.4.1. Case #1: Unsubscribing When Subscription is Not Mutual

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  1. Upon receiving the presence stanza of type "unsubscribe"
    • addressed to the contact, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "none" (if the contact is unavailable or has not requested the roster, the contact's server MUST modify the roster item and send that modified item the next time the contact requests the roster); and (2) MUST deliver the "unsubscribe" state change notification to the contact:

    <iq type='set'>

    </iq>

    <presence

  2. Upon receiving the presence stanza of type "unsubscribe", the
    • contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribed" to the user or "denying" it by sending a presence stanza of type "subscribed" to the user; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the contact's server know that it MUST no longer send notification of the subscription state change to the contact (see Section 9.4).
  3. The contact's server then (1) MUST send a presence stanza of type
    • "unsubscribed" to the user; and (2) SHOULD send unavailable presence from all of the contact's available resources to the user:

    <presence

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8.4.2. Case #2: Unsubscribing When Subscription is Mutual

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  1. The contact's server then (1) MUST send a presence stanza of type
    • "unsubscribed" to the user; and (2) SHOULD send unavailable presence from all of the contact's available resources to the user:

    <presence

    <presence

  2. When the user's server receives the presence stanzas of type
    • "unsubscribed" and "unavailable", it MUST deliver them to the user:

    <presence

    <presence

  3. Upon receiving the presence stanza of type "unsubscribed", the
    • user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4).
    Note: Obviously this does not result in removal of the roster item from the user's roster, and the contact still has a subscription to the user's presence information. In order to both completely cancel

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8.5. Cancelling a Subscription

8.5.1. Case #1: Cancelling When Subscription is Not Mutual

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8.5.2. Case #2: Cancelling When Subscription is Mutual

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  1. Upon receiving the presence stanza of type "unsubscribed"
    • addressed to the user, the user's server (1) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing an updated roster item for the contact with the 'subscription' attribute set to a value of "from" (if the user is unavailable or has not requested the roster, the user's server MUST modify the roster item and send that modified item the next time the user requests the roster); and (2) MUST deliver the "unsubscribed" state change notification to all of the user's available resources; and (3) MUST deliver the unavailable presence to all of the user's available resources:

    <iq type='set'>

    </iq>

    <presence

    <presence

  2. Upon receiving the presence stanza of type "unsubscribed", the
    • user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "unsubscribe" to the contact or "denying" it by sending a presence stanza of type "subscribe" to the contact; this step does not necessarily affect the subscription state (see Subscription States (Section 9) for details), but instead lets the user's server know that it MUST no longer send notification of the subscription state change to the user (see Section 9.4).
    Note: Obviously this does not result in removal of the roster item from the contact's roster, and the contact still has a subscription to the user's presence information. In order to both completely cancel a mutual subscription and fully remove the roster item from

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8.6. Removing a Roster Item and Cancelling All Subscriptions

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9. Subscription States

9.1. Defined States

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  1. "None" = contact and user are not subscribed to each other, and
    • neither has requested a subscription from the other
  2. "None + Pending Out" = contact and user are not subscribed to
    • each other, and user has sent contact a subscription request but contact has not replied yet
  3. "None + Pending In" = contact and user are not subscribed to each
    • other, and contact has sent user a subscription request but user has not replied yet (note: contact's server SHOULD NOT push or deliver roster items in this state, but instead SHOULD wait until contact has approved subscription request from user)
  4. "None + Pending Out/In" = contact and user are not subscribed to
    • each other, contact has sent user a subscription request but user has not replied yet, and user has sent contact a subscription request but contact has not replied yet
  5. "To" = user is subscribed to contact (one-way)
  6. "To + Pending In" = user is subscribed to contact, and contact
    • has sent user a subscription request but user has not replied yet
  7. "From" = contact is subscribed to user (one-way)
  8. "From + Pending Out" = contact is subscribed to user, and user
    • has sent contact a subscription request but contact has not replied yet
  9. "Both" = user and contact are subscribed to each other (two-way)

9.2. Server Handling of Outbound Presence Subscription Stanzas

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9.3. Server Handling of Inbound Presence Subscription Stanzas

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9.4. Server Delivery and Client Acknowledgement of Subscription Requests and State Change Notifications

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10. Blocking Communication

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10.1. Syntax and Semantics

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10.2. Business Rules

  1. If there is an active list set for a session, it affects only the
    • session(s) for which it is activated, and only for the duration of the session(s); the server MUST apply the active list only and MUST NOT apply the default list (i.e., there is no "layering" of lists).
  2. The default list applies to the user as a whole, and is processed
    • if there is no active list set for the target session/resource to which a stanza is addressed, or if there are no current sessions for the user.
  3. If there is no active list set for a session (or there are no
    • current sessions for the user), and there is no default list, then all stanzas SHOULD BE accepted or appropriately processed by the server on behalf of the user in accordance with the Server Rules for Handling XML Stanzas (Section 11).
  4. Privacy lists MUST be the first delivery rule applied by a
    • server, superseding (1) the routing and delivery rules specified in Server Rules for Handling XML Stanzas (Section 11), and (2) the handling of subscription-related presence stanzas (and corresponding generation of roster pushes) specified in Integration of Roster Items and Presence Subscriptions (Section 8).
  5. The order in which privacy list items are processed by the server
    • is important. List items MUST be processed in ascending order determined by the integer values of the 'order' attribute for

      each <item/>.

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  1. As soon as a stanza is matched against a privacy list rule, the
    • server MUST appropriately handle the stanza in accordance with the rule and cease processing.
  2. If no fall-through item is provided in a list, the fall-through
    • action is assumed to be "allow".
  3. If a user updates the definition for an active list, subsequent
    • processing based on that active list MUST use the updated definition (for all resources to which that active list currently applies).
  4. If a change to the subscription state or roster group of a roster
    • item defined in an active or default list occurs during a user's session, subsequent processing based on that list MUST take into account the changed state or group (for all resources to which that list currently applies).
  5. When the definition for a rule is modified, the server MUST send
    • an IQ stanza of type "set" to all connected resources, containing

      a <query/> element with only one <list/> child element, where the 'name' attribute is set to the name of the modified privacy list. These "privacy list pushes" adhere to the same semantics as the "roster pushes" used in roster management, except that only the list name itself (not the full list definition or the "delta") is pushed to the connected resources. It is up to the receiving resource to determine whether to retrieve the modified list definition, although a connected resource SHOULD do so if the list currently applies to it.

  6. When a resource attempts to remove a list or specify a new
    • default list while that list applies to a connected resource other than the sending resource, the server MUST return a

      <conflict/> error to the sending resource and MUST NOT make the requested change.

10.3. Retrieving One's Privacy Lists

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10.4. Managing Active Lists

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10.5. Managing the Default List

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10.6. Editing a Privacy List

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10.7. Adding a New Privacy List

10.8. Removing a Privacy List

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10.9. Blocking Messages

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10.10. Blocking Inbound Presence Notifications

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10.11. Blocking Outbound Presence Notifications

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10.12. Blocking IQ Stanzas

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10.13. Blocking All Communication

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10.14. Blocked Entity Attempts to Communicate with User

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10.15. Higher-Level Heuristics

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11. Server Rules for Handling XML Stanzas

11.1. Inbound Stanzas

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  1. Else if the JID is of the form <user@domain> and there is at

    • least one available resource available for the user, the recipient's server MUST follow these rules:
    • For message stanzas, the server SHOULD deliver the stanza to
      • the highest-priority available resource (if the resource did

        not provide a value for the <priority/> element, the server SHOULD consider it to have provided a value of zero). If two or more available resources have the same priority, the server MAY use some other rule (e.g., most recent connect time, most recent activity time, or highest availability as determined by some hierarchy of <show/> values) to choose between them or MAY deliver the message to all such resources. However, the server MUST NOT deliver the stanza to an available resource with a negative priority; if the only available resource has a negative priority, the server SHOULD handle the message as if there were no available resources (defined below). In addition, the server MUST NOT rewrite the 'to' attribute (i.e., it MUST leave it as <user@domain> rather than change it to <user@domain/ resource>).

    • For presence stanzas other than those of type "probe", the
      • server MUST deliver the stanza to all available resources; for presence probes, the server SHOULD reply based on the rules defined in Presence Probes (Section 5.1.3). In addition, the server MUST NOT rewrite the 'to' attribute

        (i.e., it MUST leave it as <user@domain> rather than change it to <user@domain/resource>).

    • For IQ stanzas, the server itself MUST reply on behalf of the
      • user with either an IQ result or an IQ error, and MUST NOT deliver the IQ stanza to any of the available resources. Specifically, if the semantics of the qualifying namespace define a reply that the server can provide, the server MUST reply to the stanza on behalf of the user; if not, the server

        MUST reply with a <service-unavailable/> stanza error.

  2. Else if the JID is of the form <user@domain> and there are no

    • available resources associated with the user, how the stanza is handled depends on the stanza type:

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  1. For presence stanzas of type "subscribe", "subscribed",
    • "unsubscribe", and "unsubscribed", the server MUST maintain a record of the stanza and deliver the stanza at least once (i.e., when the user next creates an available resource); in addition, the server MUST continue to deliver presence stanzas of type "subscribe" until the user either approves or denies the subscription request (see also Presence Subscriptions (Section 5.1.6)).
  2. For all other presence stanzas, the server SHOULD silently
    • ignore the stanza by not storing it for later delivery or replying to it on behalf of the user.
  3. For message stanzas, the server MAY choose to store the
    • stanza on behalf of the user and deliver it when the user next becomes available, or forward the message to the user via some other means (e.g., to the user's email account). However, if offline message storage or message forwarding is not enabled, the server MUST return to the sender a

      <service-unavailable/> stanza error. (Note: Offline message storage and message forwarding are not defined in XMPP, since they are strictly a matter of implementation and service provisioning.)

  4. For IQ stanzas, the server itself MUST reply on behalf of the
    • user with either an IQ result or an IQ error. Specifically, if the semantics of the qualifying namespace define a reply that the server can provide, the server MUST reply to the stanza on behalf of the user; if not, the server MUST reply

      with a <service-unavailable/> stanza error.

11.2. Outbound Stanzas

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  1. First attempt to resolve the foreign hostname using an [SRV]
    • Service of "xmpp-server" and Proto of "tcp", resulting in resource records such as "_xmpp-server._tcp.example.com.", as specified in [XMPP-CORE].
  2. If the "xmpp-server" address record resolution fails, attempt to
    • resolve the "_im" or "_pres" [SRV] Service as specified in

      [IMP-SRV], using the "_im" Service for <message/> stanzas and the "_pres" Service for <presence/> stanzas (it is up to the implementation how to handle <iq/> stanzas). This will result in one or more resolutions of the form "_im.<proto>.example.com." or "_pres.<proto>.example.com.", where "<proto>" would be a label registered in the Instant Messaging SRV Protocol Label registry or the Presence SRV Protocol Label registry: either "_xmpp" for an XMPP-aware domain or some other IANA-registered label (e.g., "_simple") for a non-XMPP-aware domain.

  3. If both SRV address record resolutions fail, attempt to perform a
    • normal IPv4/IPv6 address record resolution to determine the IP address using the "xmpp-server" port of 5269 registered with the IANA, as specified in [XMPP-CORE].
    Administrators of server deployments are strongly encouraged to keep the _im._xmpp, _pres._xmpp, and _xmpp._tcp SRV records properly synchronized, since different implementations might perform the "_im" and "_pres" lookups before the "xmpp-server" lookup.

12. IM and Presence Compliance Requirements

12.1. Servers

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12.2. Clients

13. Internationalization Considerations

14. Security Considerations

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15. IANA Considerations

15.1. XML Namespace Name for Session Data

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15.2. Instant Messaging SRV Protocol Label Registration

15.3. Presence SRV Protocol Label Registration

16. References

16.1. Normative References

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16.2. Informative References

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Appendix A. vCards

Appendix B. XML Schemas

B.1 jabber:client

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B.2 jabber:server

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B.3 session

B.4 jabber:iq:privacy

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B.5 jabber:iq:roster

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Appendix C. Differences Between Jabber IM/Presence Protocols and XMPP

C.1 Session Establishment

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C.2 Privacy Lists

Contributors

Acknowledgements

Author's Address

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Intellectual Property

Acknowledgement

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