RFC3921 Extensible Messaging and Presence Protocol (XMPP): InstantMessaging and Presence
3921 Extensible Messaging and Presence Protocol (XMPP): InstantMessaging and Presence. P. Saint-Andre, Ed.. October 2004. (Format: TXT=217527 bytes) (Status: PROPOSED STANDARD)
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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. Saint-Andre Standards Track [Page 1] 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 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 the3., , and 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]. Saint-Andre Standards Track [Page 2] RFC 3921 XMPP IM October 2004 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: o Exchange messages with other users o Exchange presence information with other users o Manage subscriptions to and from other users o Manage items in a contact list (in XMPP this is called a "roster") o Block communications to or from specific other users 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. [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. 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]. 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]. Saint-Andre Standards Track [Page 3] RFC 3921 XMPP IM October 2004 2. Syntax of XML Stanzas 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]. 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. 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: 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. 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. 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. 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 Saint-Andre Standards Track [Page 4] RFC 3921 XMPP IM October 2004 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). 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. 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. 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'). 2.1.2. Child Elements As described under extended namespaces (Section 2.4), a message stanza MAY contain any properly-namespaced 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 child; for details, see [XMPP-CORE]. Otherwise, the message stanza MAY contain any of the following child elements without an explicit namespace declaration: 1. 2.