From: http://www.ietf.org/internet-drafts/draft-ietf-xmpp-im-18.txt (ephemeral URL) Title: XMPP Instant Messaging IETF Network Working Group, Internet-Draft Reference: draft-ietf-xmpp-im-18 See also: http://xml.coverpages.org/xmpp.html Extensible Messaging and Presence Protocol (XMPP) ----------------------------------------------------------------------------------- Network Working Group P. Saint-Andre Internet-Draft J. Miller Expires: April 25, 2004 Jabber Software Foundation October 26, 2003 XMPP Instant Messaging draft-ietf-xmpp-im-18 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on April 25, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This memo describes extensions to and applications of the core features of the Extensible Messaging and Presence Protocol (XMPP Core [1]) that provide the basic instant messaging (IM) and presence functionality defined in RFC 2779 [2]. Saint-Andre & Miller Expires April 25, 2004 [Page 1] Internet-Draft XMPP Instant Messaging October 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 6 1.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 7 1.4 Discussion Venue . . . . . . . . . . . . . . . . . . . . . 7 1.5 Intellectual Property Notice . . . . . . . . . . . . . . . 7 2. Syntax of XML Stanzas . . . . . . . . . . . . . . . . . . 7 2.1 Message Syntax . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 Types of Message . . . . . . . . . . . . . . . . . . . . . 7 2.1.2 Child Elements . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Presence Syntax . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Types of Presence . . . . . . . . . . . . . . . . . . . . 10 2.2.2 Child Elements . . . . . . . . . . . . . . . . . . . . . . 11 2.3 IQ Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4 Extended Namespaces . . . . . . . . . . . . . . . . . . . 12 3. Session Establishment . . . . . . . . . . . . . . . . . . 13 4. Exchanging Messages . . . . . . . . . . . . . . . . . . . 16 4.1 Specifying an Intended Recipient . . . . . . . . . . . . . 16 4.2 Specifying a Message Type . . . . . . . . . . . . . . . . 17 4.3 Specifying a Message Body . . . . . . . . . . . . . . . . 17 4.4 Specifying a Message Subject . . . . . . . . . . . . . . . 17 4.5 Specifying a Conversation Thread . . . . . . . . . . . . . 18 5. Exchanging Presence Information . . . . . . . . . . . . . 19 5.1 Client and Server Presence Responsibilities . . . . . . . 19 5.2 Specifying Availability Status . . . . . . . . . . . . . . 22 5.3 Specifying Detailed Status Information . . . . . . . . . . 22 5.4 Specifying Presence Priority . . . . . . . . . . . . . . . 22 5.5 Presence Examples . . . . . . . . . . . . . . . . . . . . 22 6. Managing Subscriptions . . . . . . . . . . . . . . . . . . 26 6.1 Requesting a Subscription . . . . . . . . . . . . . . . . 26 6.2 Handling a Subscription Request . . . . . . . . . . . . . 27 6.3 Cancelling a Subscription from Another Entity . . . . . . 27 6.4 Unsubscribing from Another Entity's Presence . . . . . . . 27 7. Roster Management . . . . . . . . . . . . . . . . . . . . 28 7.1 Syntax and Semantics . . . . . . . . . . . . . . . . . . . 28 7.2 Business Rules . . . . . . . . . . . . . . . . . . . . . . 29 7.3 Retrieving One's Roster on Login . . . . . . . . . . . . . 29 7.4 Adding a Roster Item . . . . . . . . . . . . . . . . . . . 30 7.5 Updating a Roster Item . . . . . . . . . . . . . . . . . . 31 7.6 Deleting a Roster Item . . . . . . . . . . . . . . . . . . 31 8. Integration of Roster Items and Presence Subscriptions . . 32 8.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 32 8.2 User Subscribes to Contact . . . . . . . . . . . . . . . . 33 8.2.1 Alternate Flow: Contact Declines Subscription Request . . 37 8.3 Creating a Mutual Subscription . . . . . . . . . . . . . . 38 8.3.1 Alternate Flow: User Declines Subscription Request . . . . 41 Saint-Andre & Miller Expires April 25, 2004 [Page 2] Internet-Draft XMPP Instant Messaging October 2003 8.4 Unsubscribing . . . . . . . . . . . . . . . . . . . . . . 43 8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual . . 43 8.4.2 Case #2: Unsubscribing When Subscription is Mutual . . . . 45 8.5 Cancelling a Subscription . . . . . . . . . . . . . . . . 48 8.5.1 Case #1: Cancelling When Subscription is Not Mutual . . . 48 8.5.2 Case #2: Cancelling When Subscription is Mutual . . . . . 50 8.6 Removing a Roster Item and Cancelling All Subscriptions . 52 9. Subscription States . . . . . . . . . . . . . . . . . . . 54 9.1 Defined States . . . . . . . . . . . . . . . . . . . . . . 54 9.2 Server Handling of Outbound Presence, Categorized by Subscription State . . . . . . . . . . . . . . . . . . . . 55 9.2.1 Subscription State = None . . . . . . . . . . . . . . . . 55 9.2.2 Subscription State = None + Pending Out . . . . . . . . . 55 9.2.3 Subscription State = None + Pending In . . . . . . . . . . 56 9.2.4 Subscription State = None + Pending Out/In . . . . . . . . 56 9.2.5 Subscription State = To . . . . . . . . . . . . . . . . . 56 9.2.6 Subscription State = To + Pending In . . . . . . . . . . . 56 9.2.7 Subscription State = From . . . . . . . . . . . . . . . . 57 9.2.8 Subscription State = From + Pending Out . . . . . . . . . 57 9.2.9 Subscription State = Both . . . . . . . . . . . . . . . . 57 9.3 Server Handling of Outbound Presence, Categorized by Presence Type . . . . . . . . . . . . . . . . . . . . . . 57 9.3.1 Subscribe . . . . . . . . . . . . . . . . . . . . . . . . 58 9.3.2 Subscribed . . . . . . . . . . . . . . . . . . . . . . . . 58 9.3.3 Unsubscribe . . . . . . . . . . . . . . . . . . . . . . . 58 9.3.4 Unsubscribed . . . . . . . . . . . . . . . . . . . . . . . 59 9.4 Server Handling of Inbound Presence, Categorized by Subscription State . . . . . . . . . . . . . . . . . . . . 59 9.4.1 Subscription State = None . . . . . . . . . . . . . . . . 59 9.4.2 Subscription State = None + Pending Out . . . . . . . . . 60 9.4.3 Subscription State = None + Pending In . . . . . . . . . . 60 9.4.4 Subscription State = None + Pending Out/In . . . . . . . . 60 9.4.5 Subscription State = To . . . . . . . . . . . . . . . . . 60 9.4.6 Subscription State = To + Pending In . . . . . . . . . . . 61 9.4.7 Subscription State = From . . . . . . . . . . . . . . . . 61 9.4.8 Subscription State = From + Pending Out . . . . . . . . . 61 9.4.9 Subscription State = Both . . . . . . . . . . . . . . . . 61 9.5 Server Handling of Inbound Presence, Categorized by Presence Type . . . . . . . . . . . . . . . . . . . . . . 62 9.5.1 Subscribe . . . . . . . . . . . . . . . . . . . . . . . . 62 9.5.2 Subscribed . . . . . . . . . . . . . . . . . . . . . . . . 62 9.5.3 Unsubscribe . . . . . . . . . . . . . . . . . . . . . . . 62 9.5.4 Unsubscribed . . . . . . . . . . . . . . . . . . . . . . . 63 9.6 Server Delivery and Client Acknowledgement of Subscription State Change Notifications . . . . . . . . . 63 10. Blocking Communication . . . . . . . . . . . . . . . . . . 64 10.1 Syntax and Semantics . . . . . . . . . . . . . . . . . . . 65 10.2 Business Rules . . . . . . . . . . . . . . . . . . . . . . 67 Saint-Andre & Miller Expires April 25, 2004 [Page 3] Internet-Draft XMPP Instant Messaging October 2003 10.3 Retrieving One's Privacy Lists . . . . . . . . . . . . . . 68 10.4 Managing Active Lists . . . . . . . . . . . . . . . . . . 70 10.5 Managing the Default List . . . . . . . . . . . . . . . . 72 10.6 Editing a Privacy List . . . . . . . . . . . . . . . . . . 73 10.7 Adding a New Privacy List . . . . . . . . . . . . . . . . 73 10.8 Removing a Privacy List . . . . . . . . . . . . . . . . . 73 10.9 Blocking Messages . . . . . . . . . . . . . . . . . . . . 74 10.10 Blocking Inbound Presence Notifications . . . . . . . . . 76 10.11 Blocking Outbound Presence Notifications . . . . . . . . . 78 10.12 Blocking IQs . . . . . . . . . . . . . . . . . . . . . . . 79 10.13 Blocking All Communication . . . . . . . . . . . . . . . . 81 10.14 Blocked Entity Attempts to Communicate with User . . . . . 82 10.15 Higher-Level Heuristics . . . . . . . . . . . . . . . . . 83 11. IANA Considerations . . . . . . . . . . . . . . . . . . . 84 11.1 XML Namespace Name for Session Data . . . . . . . . . . . 84 12. Internationalization Considerations . . . . . . . . . . . 84 13. Security Considerations . . . . . . . . . . . . . . . . . 85 14. Server Rules for Handling XML Stanzas . . . . . . . . . . 85 15. Compliance Requirements . . . . . . . . . . . . . . . . . 87 15.1 Servers . . . . . . . . . . . . . . . . . . . . . . . . . 87 15.2 Clients . . . . . . . . . . . . . . . . . . . . . . . . . 87 Normative References . . . . . . . . . . . . . . . . . . . 88 Informative References . . . . . . . . . . . . . . . . . . 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . 89 A. vCards . . . . . . . . . . . . . . . . . . . . . . . . . . 89 B. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . 89 B.1 jabber:client . . . . . . . . . . . . . . . . . . . . . . 89 B.2 jabber:server . . . . . . . . . . . . . . . . . . . . . . 93 B.3 session . . . . . . . . . . . . . . . . . . . . . . . . . 97 B.4 jabber:iq:privacy . . . . . . . . . . . . . . . . . . . . 98 B.5 jabber:iq:roster . . . . . . . . . . . . . . . . . . . . . 100 C. Differences Between Jabber Instant Messaging and XMPP . . 101 C.1 Session Creation . . . . . . . . . . . . . . . . . . . . . 101 C.2 Privacy Rules . . . . . . . . . . . . . . . . . . . . . . 102 D. Revision History . . . . . . . . . . . . . . . . . . . . . 102 D.1 Changes from draft-ietf-xmpp-im-17 . . . . . . . . . . . . 102 D.2 Changes from draft-ietf-xmpp-im-16 . . . . . . . . . . . . 102 D.3 Changes from draft-ietf-xmpp-im-15 . . . . . . . . . . . . 103 D.4 Changes from draft-ietf-xmpp-im-14 . . . . . . . . . . . . 103 D.5 Changes from draft-ietf-xmpp-im-13 . . . . . . . . . . . . 103 D.6 Changes from draft-ietf-xmpp-im-12 . . . . . . . . . . . . 104 D.7 Changes from draft-ietf-xmpp-im-11 . . . . . . . . . . . . 104 D.8 Changes from draft-ietf-xmpp-im-10 . . . . . . . . . . . . 104 D.9 Changes from draft-ietf-xmpp-im-09 . . . . . . . . . . . . 105 D.10 Changes from draft-ietf-xmpp-im-08 . . . . . . . . . . . . 105 D.11 Changes from draft-ietf-xmpp-im-07 . . . . . . . . . . . . 105 D.12 Changes from draft-ietf-xmpp-im-06 . . . . . . . . . . . . 105 D.13 Changes from draft-ietf-xmpp-im-05 . . . . . . . . . . . . 105 Saint-Andre & Miller Expires April 25, 2004 [Page 4] Internet-Draft XMPP Instant Messaging October 2003 D.14 Changes from draft-ietf-xmpp-im-04 . . . . . . . . . . . . 106 D.15 Changes from draft-ietf-xmpp-im-03 . . . . . . . . . . . . 106 D.16 Changes from draft-ietf-xmpp-im-02 . . . . . . . . . . . . 106 D.17 Changes from draft-ietf-xmpp-im-01 . . . . . . . . . . . . 106 D.18 Changes from draft-ietf-xmpp-im-00 . . . . . . . . . . . . 107 D.19 Changes from draft-miller-xmpp-im-02 . . . . . . . . . . . 107 Intellectual Property and Copyright Statements . . . . . . 108 Saint-Andre & Miller Expires April 25, 2004 [Page 5] Internet-Draft XMPP Instant Messaging October 2003 1. Introduction 1.1 Overview The Extensible Messaging and Presence Protocol (XMPP) is a protocol for streaming XML [3] elements in order to exchange messages and presence information in close to real time. The core features of XMPP are defined in XMPP Core [1]. These features -- specifically XML streams, stream authentication and encryption, and the , , 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 [4]. 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 [2]. 1.2 Requirements For the purposes of this memo, the requirements of a basic instant messaging and presence application are defined by RFC 2779 [2]. At a high level, RFC 2779 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 RFC 2779, and the interested reader is directed to that document regarding the requirements addressed herein. Note: while XMPP-based instant messaging and presence meets the requirements of RFC 2779, it was not designed explicitly with RFC 2779 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 RFC 2779 [2]. Saint-Andre & Miller Expires April 25, 2004 [Page 6] Internet-Draft XMPP Instant Messaging October 2003 1.3 Terminology This memo inherits the terminology defined in XMPP Core [1]. 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 RFC 2119 [5]. 1.4 Discussion Venue The authors welcome discussion and comments related to the topics presented in this document. The preferred forum is the mailing list, for which archives and subscription information are available at . 1.5 Intellectual Property Notice This document is in full compliance with all provisions of Section 10 of RFC 2026. Parts of this specification use the term "jabber" for identifying namespaces and other protocol syntax. Jabber[tm] is a registered trademark of Jabber, Inc. Jabber, Inc. grants permission to the IETF for use of the Jabber trademark in association with this specification and its successors, if any. 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 [1]. 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 [1]. 2.1 Message Syntax Message stanzas in 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 errors. 2.1.1 Types of Message The 'type' attribute of a message stanza is RECOMMENDED; if included, Saint-Andre & Miller Expires April 25, 2004 [Page 7] Internet-Draft XMPP Instant Messaging October 2003 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 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 [1]). 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. A compliant client SHOULD present the message 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 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). 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. 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 NOT REQUIRED, 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'). Saint-Andre & Miller Expires April 25, 2004 [Page 8] Internet-Draft XMPP Instant Messaging October 2003 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 in 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 [1]. Otherwise, the message stanza MAY contain any of the following child elements without an explicit namespace declaration: 1. 2. 3. 2.1.2.1 Subject The element contains XML character data that specifies the topic of the message. The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the 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 element MUST NOT contain mixed content (as defined in Section 3.2.2 of the XML specification [3]). 2.1.2.2 Body The element contains XML character data that specifies the textual contents of the message; this child element is normally included but NOT REQUIRED. The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included but only if each instance possesses an 'xml:lang' attribute with a distinct language value. The element MUST NOT contain mixed content (as defined in Section 3.2.2 of the XML specification [3]). 2.1.2.3 Thread The element contains XML character data that specifies 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 element is generated by the sender and Saint-Andre & Miller Expires April 25, 2004 [Page 9] Internet-Draft XMPP Instant Messaging October 2003 that 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 element is OPTIONAL and is not used to identify individual messages, only conversations. A message stanza MUST NOT contain more than one element. The element MUST NOT possess any attributes. The value of the 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 element MUST NOT contain mixed content (as defined in Section 3.2.2 of the XML specification [3]). 2.2 Presence Syntax Presence stanzas are used in the 'jabber:client' or 'jabber:server' namespace to express an entity's current availability status (offline or online, along with various sub-states of the latter and optional user-defined descriptive text), and to communicate that status to other entities. Presence stanzas are also used to negotiate and manage subscriptions to the presence of other entities. 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: o unavailable -- Signals that the entity is no longer available for communication. o subscribe -- The sender wishes to subscribe to the recipient's presence. o subscribed -- The sender has allowed the recipient to receive their presence. o unsubscribe -- A notification that an entity is unsubscribing from another entity's presence. o unsubscribed -- The subscription request has been denied or a previously-granted subscription has been cancelled. Saint-Andre & Miller Expires April 25, 2004 [Page 10] Internet-Draft XMPP Instant Messaging October 2003 o probe -- A request for an entity's current presence; SHOULD be generated only by a server and SHOULD NOT be generated by a client. o error -- An error has occurred regarding processing or delivery of a previously-sent presence stanza. 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). 2.2.2 Child Elements As described under extended namespaces (Section 2.4), a presence stanza MAY contain any properly-namespaced child element. In accordance with the default namespace declaration, by default a presence stanza is in 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 child; for details, see XMPP Core [1]. If the presence stanza possesses no 'type' attribute, it MAY contain any of the following child elements (note that the child MAY be sent in a presence stanza of type "unavailable" or, for historical reasons, "subscribe"): 1. 2. 3. 2.2.2.1 Show The OPTIONAL element contains XML character data that specifies the particular availability status of an entity or specific resource. A presence stanza MUST NOT contain more than one element. The element MUST NOT possess any attributes. The XML character data contained in the element is not intended to be human-readable. If provided, the CDATA value MUST be one of the following (additional availability types could be defined through a properly-namespaced child element of the presence stanza): o away -- The entity or resource is temporarily away. o chat -- The entity or resource is actively interested in chatting. Saint-Andre & Miller Expires April 25, 2004 [Page 11] Internet-Draft XMPP Instant Messaging October 2003 o xa -- The entity or resource is away for an extended period (xa = "eXtended Away"). o dnd -- The entity or resource is busy (dnd = "Do Not Disturb"). If no element is provided, the entity is assumed to be online and available. 2.2.2.2 Status The OPTIONAL element contains a natural-language description of availability status. It is normally used in conjunction with the show element to provide a detailed description of an availability state (e.g., "In a meeting"). The element MUST NOT possess any attributes, with the exception of the 'xml:lang' attribute. Multiple instances of the element MAY be included but only if each instance possesses an 'xml:lang' attribute with a distinct language value. 2.2.2.3 Priority The OPTIONAL element contains XML character data that specifies the priority level of the connected resource. The value may be any integer between -128 and +127. A presence stanza MUST NOT contain more than one element. The element MUST NOT possess any attributes. If no priority is provided, a server SHOULD consider the priority to be zero. For information regarding the semantics of priority values in stanza routing within instant messaging and presence applications, refer to Server Rules for Handling XML Stanzas (Section 14). 2.3 IQ Syntax IQ stanzas provide a structured request-response mechanism. The basic semantics of that mechanism are defined in XMPP Core [1], whereas the specific semantics required to complete particular use cases are defined in all cases by an extended namespace (Section 2.4) (note that the 'jabber:client' and 'jabber:server' namespaces do not define any children of IQ stanzas). This memo defines two such extended namespaces, one for Roster Management (Section 7) and the other for Blocking Communication (Section 10); however, an IQ stanza MAY contain structured information qualified by any extended namespace. 2.4 Extended Namespaces While the three XML stanza kinds defined in the "jabber:client" or "jabber:server" namespace (along with their attributes and child elements) provide a basic level of functionality for messaging and Saint-Andre & Miller Expires April 25, 2004 [Page 12] Internet-Draft XMPP Instant Messaging October 2003 presence, XMPP uses XML namespaces to extend the stanzas for the purpose of providing additional functionality. Thus a message or presence MAY contain one or more optional child elements containing content that extends the meaning of the message (e.g., an XHTML-formatted version of the message body), and an IQ stanza MAY contain one such child element. This child element MAY have any name and MUST possess an 'xmlns' namespace declaration (other than "jabber:client", "jabber:server", or "http://etherx.jabber.org/ streams") that defines all data contained within the child element. Support for any given extended namespace is OPTIONAL on the part of any implementation (aside from the extended namespaces defined herein). If an entity does not understand such a namespace, the entity's expected behavior depends on whether the entity is (1) the recipient or (2) an entity that is routing the stanza to the recipient: Recipient: If a recipient receives a stanza that contains a child element it does not understand, it SHOULD ignore that specific XML data, i.e., it SHOULD not process it or present it to a user or associated application (if any). In particular: * If an entity receives a message or presence stanza that contains XML data qualified by a namespace it does not understand, the portion of the stanza that is in the unknown namespace SHOULD be ignored. * If an entity receives a message stanza whose only child element is qualified by a namespace it does not understand, it MUST ignore the entire stanza. * If an entity receives an IQ stanza of type "get" or "set" containing a child element qualified by a namespace it does not understand, the entity SHOULD return an IQ stanza of type "error" with an error condition of . Router: If a routing entity (usually a server) handles a stanza that contains a child element it does not understand, it SHOULD ignore the associated XML data by passing it on untouched to the recipient. 3. Session Establishment Most instant messaging and presence applications based on XMPP are implemented via a client-server architecture that requires a client to establish a session on a server in order to engage in the expected instant messaging and presence activities. However, there are several Saint-Andre & Miller Expires April 25, 2004 [Page 13] Internet-Draft XMPP Instant Messaging October 2003 pre-conditions that MUST be met before a client can establish an instant messaging and presence session. These are: 1. Stream Authentication -- a client MUST complete stream authentication as documented in XMPP Core [1] before attempting to establish a session or send any XML stanzas. 2. Resource Binding -- after completing stream authentication, a client MUST bind a resource to the stream so that the client's address is of the form . If a server supports sessions, it MUST include a element qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace in the stream features it advertises to a client after the completion of stream authentication as defined in XMPP Core [1]: Server advertises session establishment feature to client: Upon being so informed that session establishment is required (and after completing resource binding), the client SHOULD establish a session by sending to the server an IQ stanza of type "set" containing an empty child element qualified by the 'urn:ietf:params:xml:ns:xmpp-session' namespace: Step 1: Client requests session with server: Step 2: Server informs client that session has been created: Several error conditions are possible. For example, the server may encounter an internal condition that prevents it from creating the session, the username or authorization identity may lack permissions to create a session, or there may already be an active session associated with a resource of the same name. If the server encounters an internal condition that prevents it from creating the session, it MUST return an error. Step 2 (alt): Server responds with error (internal server error): If the username or resource is not allowed to create a session, the server MUST return an error (e.g., forbidden). Step 2 (alt): Server responds with error (username or resource not allowed to create session): If there is already an active session of the same name, the server MUST either (1) terminate the active session and allow the newly-requested session, or (2) disallow the newly-requested session and maintain the existing session. Which of these the server does is up to the implementation, although it is RECOMMENDED to implement case #1. In case #1, the server SHOULD send a stream error to the active session; in case #2, the server SHOULD send a stanza error to the newly-requested session. Step 2 (alt): Server informs active session of resource conflict (case #1): Saint-Andre & Miller Expires April 25, 2004 [Page 15] Internet-Draft XMPP Instant Messaging October 2003 Step 2 (alt): Server informs newly-requested session of resource conflict (case #2): After establishing a session, a client SHOULD send initial presence and request its roster as described below, although these actions are NOT REQUIRED. Note: before allowing the creation of instant messaging and presence sessions, a server MAY require prior account provisioning. Possible methods for account provisioning include account creation by a server administrator as well as in-band account registration using the 'jabber:iq:register' namespace; the latter method is documented by the Jabber Software Foundation [7] at but is out of scope for this memo. 4. Exchanging Messages Exchanging messages is a basic use of XMPP and is brought about when a user generates a message stanza that is addressed to another entity. As defined under Server Rules for Handling XML Stanzas (Section 14), the sender's server is responsible for delivering the message to the intended recipient (if the recipient is on the same server) or for routing the message to the recipient's server (if the recipient is on a different server). For information regarding the syntax of message stanzas as well as their defined attributes and child elements, refer to Message Syntax (Section 2.1). 4.1 Specifying an Intended Recipient An instant messaging client SHOULD specify an intended recipient for a message by providing the JID of an entity other than the sender in the 'to' attribute of the stanza. If the message is being sent in reply to a message previously received from an address of the form (e.g., within the context of a chat Saint-Andre & Miller Expires April 25, 2004 [Page 16] Internet-Draft XMPP Instant Messaging October 2003 session), the value of the 'to' address SHOULD be the full JID () rather than merely unless the sender has knowledge (via presence) that the intended recipient's resource is no longer available. If the message is being sent outside the context of any existing chat session or received message, the value of the 'to' address SHOULD be of the form rather than . 4.2 Specifying a Message Type As noted, it is RECOMMENDED for a message stanza to possess a 'type' attribute whose value captures the conversational context (if any) of the message (see Type (Section 2.1.1)). The following example shows a valid value of the 'type' attribute: Example: A message of a defined type: Wherefore art thou, Romeo? 4.3 Specifying a Message Body A message stanza MAY (and often will) contain a child element whose XML character data specifies the primary meaning of the message (see Body (Section 2.1.2.2)). Example: A message with a body: Wherefore art thou, Romeo? PročeŽ jsi ty, Romeo? 4.4 Specifying a Message Subject A message stanza MAY contain one or more child elements Saint-Andre & Miller Expires April 25, 2004 [Page 17] Internet-Draft XMPP Instant Messaging October 2003 specifying the topic of the message (see Subject (Section 2.1.2.1)). Example: A message with a subject: I implore you! Úpěnlivě prosim! Wherefore art thou, Romeo? PročeŽ jsi ty, Romeo? 4.5 Specifying a Conversation Thread A message stanza MAY contain a child element specifying the conversation thread in which the message is situated, for the purpose of tracking the conversation (see Thread (Section 2.1.2.3)). Example: A threaded conversation: Art thou not Romeo, and a Montague? e0ffe42b28561960c6b12b944a092794b9683a38 Neither, fair saint, if either thee dislike. e0ffe42b28561960c6b12b944a092794b9683a38 How cam'st thou hither, tell me, and wherefore? e0ffe42b28561960c6b12b944a092794b9683a38 Saint-Andre & Miller Expires April 25, 2004 [Page 18] Internet-Draft XMPP Instant Messaging October 2003 5. Exchanging Presence Information Exchanging presence information is made relatively straightforward within XMPP by using presence stanzas. However, we see here a contrast to the handling of messages: although a client MAY send directed presence information to another entity, normally presence information is sent from a client to its server (with no 'to' address) and then broadcasted by the server to any entities that are subscribed to the presence of the sending entity. (Note: in the terminology of RFC 2778 [8], we can say that the only watchers in XMPP are subscribers.) For information regarding the syntax of presence stanzas as well as their defined attributes and child elements, refer to XMPP Core [1]. 5.1 Client and Server Presence Responsibilities After establishing a session, a client SHOULD (but is NOT REQUIRED to) send initial presence to the server in order to signal its availability for communications. As defined herein, the initial presence stanza (1) MUST possess no 'to' address (signalling that it is meant to be handled by the server on behalf of the client) and (2) MUST possess no 'type' attribute (signalling the user's availability). Upon receiving initial presence from a client, the user's server MUST do the following: 1. Send presence probes (i.e., presence stanzas whose 'type' attribute is set to a value of "probe") from the full JID () of the user to the bare JID () of any contacts to which the user is subscribed in order to determine if they are available; such contacts are those which are present in the user's roster with the 'subscription' attribute set to a value of "to" or "both". 2. Broadcast initial presence from the full JID () of the user to the bare JID () of any contacts that are subscribed to the user's presence; such contacts are those which are present in the user's roster with the 'subscription' attribute set to a value of "from" or "both". Upon receiving a presence probe from the user, the contact's server MUST send to the user the last known availability information (i.e., the full XML of the last presence stanza) provided by each of the contact's active sessions (if there exist no active sessions, the server SHOULD NOT reply to the presence probe). The contact's server MUST send this information subject to domain-specific access rules, Saint-Andre & Miller Expires April 25, 2004 [Page 19] Internet-Draft XMPP Instant Messaging October 2003 and only if the user is in the contact's roster with a subscription state of "from" or "both" and the contact has not blocked outbound presence notifications to the user's bare or full JID (as defined under Blocking Outbound Presence Notifications (Section 10.11)). (Note: if a server receives a presence probe from a subdomain of the server's hostname or another such trusted service, it MAY provide presence information about the user to that entity.) Upon receiving initial presence from the user, the contact's server MUST deliver the user's presence stanza to the full JIDs () associated with all of the contact's active sessions, 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 probe from the contact). After sending initial presence, the user MAY update its presence information for broadcasting at any time during its active session by sending a presence stanza with no 'to' address and either no 'type' attribute or a 'type' attribute with a value of "unavailable". (Note: a user's client SHOULD NOT send a presence update to broadcast information that changes independently of the user's presence and availability.) If the presence stanza lacks a 'type' attribute (i.e., expresses availability), the user's server MUST broadcast the full XML of that presence stanza to all contacts (1) that are in the user's roster with a subscription type of "from" or "both", (2) to whom the user has not blocked outbound presence, and (3) from whom the server has not received a presence error during the user's session. If the presence stanza has a 'type' attribute set to a value of "unavailable", the user's server MUST broadcast the full XML of that presence stanza to all contacts meeting the three conditions just mentioned, as well as to any entities to which the user has sent directed available presence during the user's session (if the user has not yet sent directed unavailable presence to that entity). A user MAY send directed presence to another entity (i.e., a presence stanza with a 'to' attribute whose value is the JID of the other entity and with either no 'type' attribute or a 'type' attribute whose value is "unavailable"). There are three possible cases: 1. If the user sends directed presence to a contact that is in the Saint-Andre & Miller Expires April 25, 2004 [Page 20] Internet-Draft XMPP Instant Messaging October 2003 user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending unavailable presence broadcast, the user's server MUST route or deliver the full XML of that presence stanza (subject to privacy rules) but SHOULD NOT otherwise modify the contact's status regarding presence broadcast (i.e., it SHOULD include the contact's JID in any subsequent presence broadcasts initiated by the user). 2. If the user sends directed presence to an entity that is not in the user's roster with a subscription type of "from" or "both" after having sent initial presence and before sending unavailable presence broadcast, the user's server MUST route or deliver the full XML of that presence stanza to the entity but MUST NOT modify the contact's status regarding available presence broadcast (i.e., it MUST NOT include the entity's JID in any subsequent broadcasts of available presence initiated by the user); however, if the connected resource from which the user sent the directed presence become unavailable, the user's server MUST broadcast that unavailable presence to the entity (if the user has not yet sent directed unavailable presence to that entity). 3. If the user sends directed presence without first sending initial presence or after having sent unavailable presence broadcast, the user's server MUST treat the entities to which the user sends directed presence in the same way that it treats the entities listed in case 2 above. Before ending its session with a server, a client SHOULD gracefully become unavailable by sending a final presence stanza that possesses no 'to' attribute and that possesses a 'type' attribute whose value is "unavailable" (optionally, the final presence stanza MAY contain one or more elements specifying the reason why the user is no longer available). However, the user's server MUST NOT depend on receiving final presence from an available resource, since the resource may become unavailable unexpectedly. If the user's server detects that one of the user's resources has become unavailable for any reason (either gracefully or ungracefully), it MUST broadcast unavailable presence to all contacts (1) that are in the user's roster with a subscription type of "from" or "both", (2) to whom the user has not blocked outbound presence, and (3) from whom the server has not received a presence error during the user's session; the user's server MUST also send that unavailable presence stanza to any entities to which the user has sent directed presence during the user's session for that resource (if the user has not yet sent directed unavailable presence to that entity). Any presence stanza with no 'type' attribute and no 'to' attribute that is sent after sending directed unavailable presence or broadcasted unavailable Saint-Andre & Miller Expires April 25, 2004 [Page 21] Internet-Draft XMPP Instant Messaging October 2003 presence MUST be broadcasted by the server to all subscribers. 5.2 Specifying Availability Status A client MAY provide further information about its availability status by using the element (see Show (Section 2.2.2.1)). Example: Availability status: dnd 5.3 Specifying Detailed Status Information In conjunction with the element, a client MAY provide detailed status information by using the element (see Status (Section 2.2.2.2)). Example: Detailed status information: dnd Wooing Juliet Ja dvořím Juliet 5.4 Specifying Presence Priority A client MAY provide a priority for its resource by using the element (see Priority (Section 2.2.2.3)). Example: Presence priority: dnd Wooing Juliet Ja dvořím Juliet 1 5.5 Presence Examples The examples in this section illustrate the presence-related protocols described above. The user is romeo@example.net, he has Saint-Andre & Miller Expires April 25, 2004 [Page 22] Internet-Draft XMPP Instant Messaging October 2003 authorized a resource "orchard", and he has the following individuals in his roster: o juliet@example.com (subscription="both" and she has two active sessions, one whose resource is "chamber" and another whose resource is "balcony") o benvolio@example.org (subscription="to") o mercutio@example.org (subscription="from") Example 1: User sends initial presence: Example 2: User's server sends presence probes to contacts with subscription="to" and subscription="both" on behalf of the user's connected resource: Example 3: User's server sends initial presence to contacts with subscription="from" and subscription="both" on behalf of the user's connected resource: Example 4: Contacts' server replies to presence probe on behalf of all of the contact's available resources: Saint-Andre & Miller Expires April 25, 2004 [Page 23] Internet-Draft XMPP Instant Messaging October 2003 away be right back 0 1 dnd gallivanting Example 5: Contact's server delivers user's initial presence to all of the contact's available resources or returns error to user: Example 6: User sends directed presence to another user not in his roster: dnd courting Juliet Saint-Andre & Miller Expires April 25, 2004 [Page 24] Internet-Draft XMPP Instant Messaging October 2003 0 Example 7: User sends updated available presence information for broadcasting: away I shall return! 1 Example 8: Updated presence information is delivered only to one contact (not those from whom an error was received or to whom the user sent directed presence): away I shall return! 1 away I shall return! 1 Example 9: One of the contact's resources sends final presence: Example 10: Contact's server sends unavailable presence information to user: Example 11: User sends final presence: Saint-Andre & Miller Expires April 25, 2004 [Page 25] Internet-Draft XMPP Instant Messaging October 2003 gone home Example 12: Unavailable presence information is delivered to contact's one remaining resource as well as to the person to whom the user sent directed presence: gone home gone home 6. Managing Subscriptions In order to protect the privacy of instant messaging users and any other entities, presence and availability information is disclosed only to other entities that the user has approved. When a user has agreed that another entity may view its presence, the entity is said to have a subscription to the user's presence information. A subscription lasts across sessions; indeed, it lasts until the subscriber unsubscribes or the subscribee cancels the previously-granted subscription. Subscriptions are managed within XMPP by sending presence stanzas containing specially-defined attributes. Note: there are important interactions between subscriptions and rosters; these are defined under Integration of Roster Items and Presence Subscriptions (Section 8), and the reader must refer to that section for a complete understanding of presence subscriptions. 6.1 Requesting a Subscription A request to subscribe to another entity's presence is made by sending a presence stanza of type "subscribe". Example: Sending a subscription request: Saint-Andre & Miller Expires April 25, 2004 [Page 26] Internet-Draft XMPP Instant Messaging October 2003 If the subscription request is being sent to another instant messaging user, the JID supplied in the 'to' attribute SHOULD be of the form rather than . A user's server MUST NOT automatically approve subscription requests on the user's behalf. All subscription requests MUST be directed to the user's client. If there is no available resource associated with the user when the subscription request is received by the server, the user's server MUST store the subscription request offline for delivery when the user next becomes available. (Note: if a resource has authorized a session but has not provided initial presence, the server SHOULD NOT consider it to be available and therefore SHOULD NOT send subscription requests to it.) 6.2 Handling a Subscription Request When a client receives a subscription request from another entity, it MUST either approve the request by sending a presence stanza of type "subscribed" or refuse the request by sending a presence stanza of type "unsubscribed". Example: Approving a subscription request: Example: Refusing a presence subscription request: 6.3 Cancelling a Subscription from Another Entity If a user would like to cancel a previously-granted subscription request, it sends a presence stanza of type "unsubscribed". Example: Cancelling a previously granted subscription request: 6.4 Unsubscribing from Another Entity's Presence If a user would like to unsubscribe from the presence of another entity, it sends a presence stanza of type "unsubscribe". Saint-Andre & Miller Expires April 25, 2004 [Page 27] Internet-Draft XMPP Instant Messaging October 2003 Example: Unsubscribing from an entity's presence: 7. Roster Management In XMPP, one's contact list is called a roster, which consists of any number of specific roster items, each roster item being identified by a unique JID (usually of the form ). A user's roster is stored by the user's server on the user's behalf so that the user may access roster information from any available resource. Note: there are important interactions between rosters and subscriptions; these are defined under Integration of Roster Items and Presence Subscriptions (Section 8), and the reader must refer to that section for a complete understanding of roster management. 7.1 Syntax and Semantics Rosters are managed using IQ stanzas, specifically by means of a child element qualified by the 'jabber:iq:roster' namespace. The element MAY contain one or more children, each describing a unique roster item or "contact". The "key" or unique identifier for each roster item is a JID, encapsulated in the required 'jid' attribute of the element. The value of the 'jid' attribute SHOULD be of the form , especially if the item is associated with another (human) instant messaging user. The state of the presence subscription in relation to a roster item is captured in the 'subscription' attribute of the element. Allowable values for this attribute are: o "none" -- the user does not have a subscription to the contact, and the contact does not have a subscription to the user o "to" -- the user has a subscription to the contact, but the contact does not have a subscription to the user o "from" -- the contact has a subscription to the user, but the user does not have a subscription to the contact o "both" -- both the user and the contact have subscriptions to each other Each element MAY contain a 'name' attribute, which sets the Saint-Andre & Miller Expires April 25, 2004 [Page 28] Internet-Draft XMPP Instant Messaging October 2003 "nickname" to be associated with the JID, as determined by the user (not the contact). The value of the 'name' attribute is opaque. Each element MAY contain one or more child elements, for use in collecting roster items into various categories. The CDATA text of the element is opaque. 7.2 Business Rules A server MUST ignore any 'to' address on a roster "set", and MUST treat any roster "set" as applying to the sender. For added safety, a client SHOULD check the "from" address of a roster "push" to ensure that it is from a trusted source; specifically, the stanza SHOULD have no 'from' attribute (i.e., implicitly from the server) or the JID contained in the 'from' attribute SHOULD match the user's bare JID or full JID; otherwise, the client SHOULD ignore the roster "push". 7.3 Retrieving One's Roster on Login Upon connecting to the server, a client SHOULD request the roster (however, because receiving the roster may not be desirable for all resources, e.g., a connection with limited bandwidth, the client's request for the roster is NOT REQUIRED). If an available resource does not request the roster during a session, the server SHOULD NOT send it presence subscriptions and associated roster updates. Example: Client requests current roster from server: Example: Client receives roster from the server: Friends Friends Friends 7.4 Adding a Roster Item At any time, a user MAY add an item to his or her roster. Example: Client adds a new item: Servants The server MUST update the roster information in persistent storage, and also push the change out to all of the user's available resources that have requested the roster. This "roster push" consists of an IQ set from the server to the client and enables all available resources to remain in sync with the server-based roster information. Example: Server (1) pushes the updated roster information to all available resources and (2) replies with an IQ result to the sending resource: Servants Saint-Andre & Miller Expires April 25, 2004 [Page 30] Internet-Draft XMPP Instant Messaging October 2003 Servants Example: Connected resources reply with an IQ result to the server: 7.5 Updating a Roster Item Updating an existing roster item (e.g., changing the group) is done in the same way as adding a new roster item, i.e., by sending the roster item in an IQ set to the server. Example: User updates roster item (added group): Friends Lovers As with adding a roster item, when updating a roster item the server MUST update the roster information in persistent storage, and also initiate a roster push to all of the user's available resources that have requested the roster. 7.6 Deleting a Roster Item At any time, a user MAY delete an item from its roster by doing an IQ set and making sure that the value of the 'subscription' attribute is "remove" (a compliant server MUST ignore any other values of the 'subscription' attribute when received from a client). Saint-Andre & Miller Expires April 25, 2004 [Page 31] Internet-Draft XMPP Instant Messaging October 2003 Example: Client removes an item: As with adding a roster item, when deleting a roster item the server MUST update the roster information in persistent storage, initiate a roster push to all of the user's available resources that have requested the roster (with the 'subscription' attribute set to a value of "remove"), and send an IQ result to the initiating resource. For further information about the implications of this command, see Removing a Roster Item and Cancelling All Subscriptions (Section 8.6). 8. Integration of Roster Items and Presence Subscriptions 8.1 Overview Some level of integration between roster items and presence subscriptions is normally expected by an instant messaging user regarding the user's subscriptions to and from other contacts. This section describes the level of integration that MUST be supported within XMPP instant messaging applications. There are four primary subscription states: o None -- Neither the user nor the contact is subscribed to the other's presence o To -- The user is subscribed to the contact's presence but there is no subscription from the contact to the user o From -- There is a subscription from the contact to the user, but the user has not subscribed to the contact's presence o Both -- Both the user and the contact are subscribed to each other's presence (i.e., the union of 'from' and 'to') Each of these states is reflected in the roster of both the user and the contact, thus resulting in durable subscription states. Narrative explanations of how these subscription states interact with roster items in order to complete certain defined use cases are provided in the following sub-sections. Full details regarding server and client handling of all subscription states (including pending states between Saint-Andre & Miller Expires April 25, 2004 [Page 32] Internet-Draft XMPP Instant Messaging October 2003 the primary states listed above) is provided in Subscription States (Section 9). If a connected resource does not both send initial presence and request the roster, the server SHOULD NOT send it presence subscription requests or roster pushes. The 'from' and 'to' addresses are OPTIONAL in roster pushes; if included, their values SHOULD be the full JID of the resource for that session. A client MUST acknowledge each roster push with an IQ stanza of type "result" (for the sake of brevity, these stanzas are not shown in the following examples but are required by XMPP Core [1]). 8.2 User Subscribes to Contact The process by which a user subscribes to a contact, including the interaction between roster items and subscription states, is defined below. 1. In preparation for being able to render the contact in the user's client interface and for the server to keep track of the subscription, the user's client SHOULD perform a "roster set" for the new roster item. This request consists of an IQ stanza of type='set' containing a element in the 'jabber:iq:roster' namespace, which in turn contains an element that defines the new roster item; the element MUST possess a 'jid' attribute, MAY possess a 'name' attribute, MUST NOT possess a 'subscription' attribute, and MAY contain one or more child elements: MyBuddies 2. As a result, the user's server (1) MUST initiate a roster push for the new roster item to all available resources associated with this user that have requested the roster, setting the 'subscription' attribute to a value of "none"; and (2) MUST reply with an IQ stanza of type='result': Saint-Andre & Miller Expires April 25, 2004 [Page 33] Internet-Draft XMPP Instant Messaging October 2003 MyBuddies 3. If the user wants to request a subscription to the contact's presence, the user's client MUST send a presence stanza of type='subscribe' to the contact: 4. As a result, the user's server MUST initiate a second roster push to all of the user's available resources that have requested the roster, setting the contact to the pending sub-state of the 'none' subscription state; this pending sub-state is denoted by the inclusion of the ask='subscribe' attribute in the roster item: MyBuddies Note: if the user did not create a roster item before sending the subscription request, the server MUST now create one on behalf of the user and send a roster push to all of the user's available resources that have requested the roster, absent the 'name' attribute and the child. 5. The user's server MUST also stamp the presence stanza of type "subscribe" with the user's bare JID (i.e., ) as the 'from' address. If the contact is served by a different host than the user, the user's server MUST route the presence stanza to the contact's server for delivery to the contact (this case is Saint-Andre & Miller Expires April 25, 2004 [Page 34] Internet-Draft XMPP Instant Messaging October 2003 assumed throughout; however, if the contact is served by the same host, then the server can simply deliver the presence stanza directly): 6. Upon receiving the presence stanza of type "subscribe" addressed to the contact, the contact's server must determine if there is at least one active session in which the contact has sent available presence and has requested the roster. If so, it MUST deliver the subscription request to the contact (if not, the contact's server MUST store the subscription request offline for delivery when this condition is next met). No matter when the subscription request is delivered, the contact must decide whether or not to approve it (subject to configured preferences, the contact's client MAY approve or refuse the subscription request without presenting it to the contact). Here we assume the "happy path" that the contact approves the subscription request (the alternate flow of declining the subscription request is defined in Section 8.2.1). In this case, the contact's client (1) SHOULD perform a roster set specifying the desired nickname and group for the user (if any); and (2) MUST send a presence stanza of type "subscribed" to the user in order to approve the subscription request. SomeGroup 7. As a result, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, containing a roster item for the user with the subscription state set to 'from'; (2) MUST route the presence stanza of type "subscribed" to the user; and (3) MUST send available presence from all of the contact's available resources to the user: Saint-Andre & Miller Expires April 25, 2004 [Page 35] Internet-Draft XMPP Instant Messaging October 2003 SomeGroup 8. Upon receiving the presence stanza of type "subscribed" addressed to the user, the user's server MUST first verify that the contact is in the user's roster with either of the following states: (a) subscription='none' and ask='subscribe' or (b) subscription='from' and ask='subscribe'. If the contact is not in the user's roster with either of those states, the user's server MUST silently ignore the presence stanza of type "subscribed" (i.e., it MUST NOT route it to the user, modify the user's roster, or generate a roster push to the user's available resources). If the contact is in the user's roster with either of those states, the user's server (1) MUST deliver the presence stanza of type "subscribed" from the contact to the user; (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 "to"; and (3) MUST deliver the available presence stanza received from each of the contact's available resources to each of the user's available resources: MyBuddies 9. Upon receiving the presence stanza of type "subscribed", the user SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "subscribe" to the contact or "denying" it by sending a presence stanza of type "unsubscribe" 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 9.6). From the perspective of the user, there now exists a subscription to the contact; from the perspective of the contact, there now exists a subscription from the user. (Note: If at this point the user sends another subscription request to the contact, the user's server MUST silently ignore that request.) 8.2.1 Alternate Flow: Contact Declines Subscription Request The above activity flow represents the "happy path" related to the user's subscription request to the contact. The main alternate flow occurs if the contact refuses the user's subscription request. 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): 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 () of the contact: Saint-Andre & Miller Expires April 25, 2004 [Page 37] Internet-Draft XMPP Instant Messaging October 2003 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: MyBuddies 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 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 9.6). As a result of this activity, the contact is now in the user's roster with a subscription state of "none", whereas the user is not in the contact's roster at all. 8.3 Creating a Mutual Subscription The user and contact can build on the foregoing to create a mutual subscription (i.e., a subscription of type "both"). The process is defined below. 1. If the contact wants to create a mutual subscription, the contact MUST send a subscription request to the user (subject to configured preferences, the contact's client MAY send this automatically): Saint-Andre & Miller Expires April 25, 2004 [Page 38] Internet-Draft XMPP Instant Messaging October 2003 2. As a result, the contact's server (1) MUST initiate a roster push to all available resources associated with the contact that have requested the roster, with the user still in the 'from' subscription state but with a pending 'to' subscription denoted by the inclusion of the ask='subscribe' attribute in the roster item; and (2) MUST route the presence stanza of type "subscribe" to the user, first stamping the 'from' address as the bare JID () of the contact: SomeGroup 3. Upon receiving the presence stanza of type "subscribe" addressed to the user, the user's server must determine if there is at least one active session in which the user has sent available presence and has requested the roster. If so, the user's server MUST deliver the subscription request to the user (if not, it MUST store the subscription request offline for delivery when this condition is next met). No matter when the subscription request is delivered, the user must then decide whether or not to approve it (subject to configured preferences, the user's client MAY approve or refuse the subscription request without presenting it to the user). Here we assume the "happy path" that the user approves the subscription request (the alternate flow of declining the subscription request is defined in Section 8.3.1). In this case, the user's client MUST send a presence stanza of type "subscribed" to the contact in order to approve the subscription request. Saint-Andre & Miller Expires April 25, 2004 [Page 39] Internet-Draft XMPP Instant Messaging October 2003 4. As a result, the user's server (1) MUST initiate a roster push to all of the user's available resources that have requested the roster, containing a roster item for the contact with the 'subscription' attribute set to a value of "both"; (2) MUST route the presence stanza of type "subscribed" to the contact, first stamping the 'from' address as the bare JID () of the user; and (3) MUST send available presence from each of the user's available resources to the contact: MyBuddies 5. Upon receiving the presence stanza of type "subscribed" addressed to the contact, the contact's server MUST first verify that the user is in the contact's roster with either of the following states: (a) subscription='none' and ask='subscribe' or (b) subscription='from' and ask='subscribe'. If the user is not in the contact's roster with either of those states, the contact's server MUST silently ignore the presence stanza of type "subscribed" (i.e., it MUST NOT route it to the contact, modify the contact's roster, or generate a roster push to the contact's available resources). If the user is in the contact's roster with either of those states, the contact's server (1) MUST deliver the presence stanza of type "subscribed" from the user to the contact; (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 "both"; and (3) MUST deliver the available presence stanza received from each of the user's available resources to each of the contact's available resources: Saint-Andre & Miller Expires April 25, 2004 [Page 40] Internet-Draft XMPP Instant Messaging October 2003 SomeGroup 6. Upon receiving the presence stanza of type "subscribed", the contact SHOULD acknowledge receipt of that subscription state notification through either "affirming" it by sending a presence stanza of type "subscribe" to the user or "denying" it by sending a presence stanza of type "unsubscribe" 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 9.6). The user and the contact now have a mutual subscription to each other's presence -- i.e., the subscription is of type "both". The user's server MUST now send the user's current presence information to the contact. (Note: If at this point the user sends a subscription request to the contact or the contact sends a subscription request to the user, the sending user's server MUST silently ignore that request and not route it to the intended recipient.) 8.3.1 Alternate Flow: User Declines Subscription Request The above activity flow represents the "happy path" related to the contact's subscription request to the user. The main alternate flow occurs if the user refuses the contact's subscription request. 1. If the user wants to refuse the request, the user's client MUST send a presence stanza of type "unsubscribed" to the contact (instead of the presence stanza of type "subscribed" sent in Step Saint-Andre & Miller Expires April 25, 2004 [Page 41] Internet-Draft XMPP Instant Messaging October 2003 3 of Section 8.3): 2. 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 () of the user: 3. 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: SomeGroup 4. 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 9.6). Saint-Andre & Miller Expires April 25, 2004 [Page 42] Internet-Draft XMPP Instant Messaging October 2003 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". 8.4 Unsubscribing At any time after subscribing to a contact's presence, a user MAY unsubscribe. While the XML that the user sends to make this happen is the same in all instances, the subsequent subscription state is different depending on the subscription state obtaining when the unsubscribe "command" is sent. Both possible scenarios are defined below. 8.4.1 Case #1: Unsubscribing When Subscription is Not Mutual In the first case, the user has a subscription to the contact but the contact does not have a subscription to the user (i.e., the subscription is not yet mutual). 1. If the user wants to unsubscribe from the contact's presence, the user MUST send a presence stanza of type "unsubscribe" to the contact: 2. As a result, the user's server (1) MUST send 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 (2) MUST route the presence stanza of type "unsubscribe" to the contact, first stamping the 'from' address as the bare JID () of the user: MyBuddies 3. 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 offline, 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: SomeGroup 4. 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 9.6). 5. The contact's server then (1) MUST send a presence stanza of type "unsubscribed" to the user; and (2) SHOULD send unavailable presence from the contact to the user: Saint-Andre & Miller Expires April 25, 2004 [Page 44] Internet-Draft XMPP Instant Messaging October 2003 6. When the user's server receives a presence stanza of type "unsubscribed" and/or unavailable presence, it MUST deliver them to the user: 7. 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 9.6). 8.4.2 Case #2: Unsubscribing When Subscription is Mutual In the second case, the user has a subscription to the contact and the contact also has a subscription to the user (i.e., the subscription is mutual). 1. If the user wants to unsubscribe from the contact's presence, the user MUST send a presence stanza of type "unsubscribe" to the contact: 2. As a result, the user's server (1) MUST send 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"; and (2) MUST route the presence stanza of type "unsubscribe" to the contact, first stamping the 'from' address as the bare JID Saint-Andre & Miller Expires April 25, 2004 [Page 45] Internet-Draft XMPP Instant Messaging October 2003 () of the user: MyBuddies 3. 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 "to" (if the contact is offline, 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: SomeGroup 4. 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 Saint-Andre & Miller Expires April 25, 2004 [Page 46] Internet-Draft XMPP Instant Messaging October 2003 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 9.6). 5. The contact's server then (1) MUST send a presence stanza of type "unsubscribed" to the user; and (2) SHOULD send unavailable presence from the contact to the user: 6. When the user's server receives a presence stanza of type "unsubscribed" and/or unavailable presence, it MUST deliver them to the user: 7. 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 9.6). 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. In order to both completely cancel a mutual Saint-Andre & Miller Expires April 25, 2004 [Page 47] Internet-Draft XMPP Instant Messaging October 2003 subscription and fully remove the roster item from the user's roster, the user SHOULD update the roster item with subscription='remove' as defined under Removing a Roster Item and Cancelling All Subscriptions (Section 8.6). 8.5 Cancelling a Subscription At any time after approving a subscription request from a user, a contact MAY cancel that subscription. While the XML that the contact sends to make this happen is the same in all instances, the subsequent subscription state is different depending on the subscription state obtaining when the cancellation was sent. Both possible scenarios are defined below. 8.5.1 Case #1: Cancelling When Subscription is Not Mutual In the first case, the user has a subscription to the contact but the contact does not have a subscription to the user (i.e., the subscription is not yet mutual). 1. If the contact wants to cancel the user's subscription, the contact MUST send a presence stanza of type "unsubscribed" to the user: 2. As a result, the contact's server (1) MUST send a roster push to all of the contact's available resources that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "none"; (2) MUST route the presence stanza of type "unsubscribed" to the user, first stamping the 'from' address as the bare JID () of the contact; and (3) SHOULD send unavailable presence from the contact to the user: SomeGroup 3. 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 "none" (if the user is offline, the user's server MUST modify the roster item and send that modified item the next time the user requests the roster); (2) MUST deliver the "unsubscribed" state change notification to the user; and (3) MUST deliver the unavailable presence to the user: MyBuddies 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 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 Saint-Andre & Miller Expires April 25, 2004 [Page 49] Internet-Draft XMPP Instant Messaging October 2003 of the subscription state change to the user (see Section 9.6). 8.5.2 Case #2: Cancelling When Subscription is Mutual In the second case, the user has a subscription to the contact and the contact also has a subscription to the user (i.e., the subscription is mutual). 1. If the contact wants to cancel the user's subscription, the contact MUST send a presence stanza of type "unsubscribed" to the user: 2. As a result, the contact's server (1) MUST send a roster push to all of the contact's available resources that have requested the roster, containing an updated roster item for the user with the 'subscription' attribute set to a value of "to"; (2) MUST route the presence stanza of type "unsubscribed" to the user, first stamping the 'from' address as the bare JID () of the contact; and (3) SHOULD send unavailable presence from the contact to the user: SomeGroup 3. 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 Saint-Andre & Miller Expires April 25, 2004 [Page 50] Internet-Draft XMPP Instant Messaging October 2003 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 offline, 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 the user; and (3) MUST deliver the unavailable presence to the user: MyBuddies 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 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 9.6). 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. In order to both completely cancel a mutual subscription and fully remove the roster item from the contact's roster, the contact should update the roster item with subscription='remove' as defined under Removing a Roster Item and Cancelling All Subscriptions (Section 8.6). Saint-Andre & Miller Expires April 25, 2004 [Page 51] Internet-Draft XMPP Instant Messaging October 2003 8.6 Removing a Roster Item and Cancelling All Subscriptions Because there may be many steps involved in completely removing a roster item and cancelling subscriptions in both directions, the roster management protocol includes a "shortcut" method for doing so. The process may be initiated no matter what the current subscription state is by sending a roster set containing an item for the contact with the 'subscription' attribute set to a value of "remove": When the user removes a contact from his or her roster by setting the 'subscription' attribute to a value of "remove", the user's server (1) MUST automatically cancel any existing presence subscription between the user and the contact (both 'to' and 'from' as appropriate); (2) MUST remove the roster item from the user's roster and inform all of the user's available resources of the roster item removal; (3) MUST inform the resource that initiated the removal of success; and (4) SHOULD send unavailable presence to the contact: Upon receiving the presence stanza of type "unsubscribe", 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 "to" (if the contact is offline, 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 also deliver the "unsubscribe" state change notification to the contact: SomeGroup Upon receiving the presence stanza of type "unsubscribed", 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 offline, 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 also deliver the "unsubscribe" state change notification to the contact: SomeGroup Saint-Andre & Miller Expires April 25, 2004 [Page 53] Internet-Draft XMPP Instant Messaging October 2003 Upon receiving the presence stanza of type "unavailable" addressed to the contact, the contact's server MUST deliver the unavailable presence to the user: Note that when the user removes the contact from the user's roster, the end state of the contact's roster is that the user is still in the contact's roster with a subscription state of "none"; in order to completely remove the roster item for the user, the contact needs to also send a roster removal request. 9. Subscription States This section provides detailed information about subscription states. 9.1 Defined States There are nine possible subscription states, which are described here from the user's perspective: 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 responded 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 responded yet 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 responded yet, and user has sent contact a subscription request but contact has not responded yet 5. "To" = user is subscribed to contact (one-way) Saint-Andre & Miller Expires April 25, 2004 [Page 54] Internet-Draft XMPP Instant Messaging October 2003 6. "To + Pending In" = user is subscribed to contact, and contact has send user a subscription request but user has not responded 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 responded yet 9. "Both" = user and contact are subscribed to each other (two-way) 9.2 Server Handling of Outbound Presence, Categorized by Subscription State This section defines how a server MUST handle an outbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed" (i.e., route it to the intended recipient and/or make a change to the subscription state), categorized by the current subscription state. The general rule is that a server MUST route the stanza to the intended recipient if it would change the subscription state, and MUST NOT route the stanza if it would not change the subscription state. Detailed definitions are contained in the following sections. Naturally, if the stanza changes the subscription state, the server MUST change the subscription state in addition to routing the subscription state. 9.2.1 Subscription State = None +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | yes | "None + Pending Out" | | subscribed | no | no state change | | unsubscribe | no | no state change | | unsubscribed | no | no state change | +-------------------------------------------------------+ 9.2.2 Subscription State = None + Pending Out +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "None" | Saint-Andre & Miller Expires April 25, 2004 [Page 55] Internet-Draft XMPP Instant Messaging October 2003 | unsubscribed | no | no state change | +-------------------------------------------------------+ 9.2.3 Subscription State = None + Pending In +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | yes | "None + Pending Out/In" | | subscribed | yes | "From" | | unsubscribe | no | no state change | | unsubscribed | yes | "None" | +-------------------------------------------------------+ 9.2.4 Subscription State = None + Pending Out/In +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | no | no state change | | subscribed | yes | "From + Pending Out" | | unsubscribe | yes | "None + Pending In" | | unsubscribed | yes | "None + Pending Out" | +-------------------------------------------------------+ 9.2.5 Subscription State = To +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "None" | | unsubscribed | no | no state change | +-------------------------------------------------------+ 9.2.6 Subscription State = To + Pending In +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | no | no state change | | subscribed | yes | "Both" | | unsubscribe | yes | "None + Pending In" | Saint-Andre & Miller Expires April 25, 2004 [Page 56] Internet-Draft XMPP Instant Messaging October 2003 | unsubscribed | yes | "To" | +-------------------------------------------------------+ 9.2.7 Subscription State = From +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | yes | "From + Pending Out" | | subscribed | no | no state change | | unsubscribe | no | no state change | | unsubscribed | yes | "None" | +-------------------------------------------------------+ 9.2.8 Subscription State = From + Pending Out +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "From" | | unsubscribed | yes | "None + Pending Out" | +-------------------------------------------------------+ 9.2.9 Subscription State = Both +-------------------------------------------------------+ | STANZA TYPE | ROUTE? | NEW STATE | +-------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "From" | | unsubscribed | yes | "To" | +-------------------------------------------------------+ 9.3 Server Handling of Outbound Presence, Categorized by Presence Type This section defines how a server MUST handle an outbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed" (i.e., route it to the intended recipient and/or make a change to the subscription state), categorized by presence type. Saint-Andre & Miller Expires April 25, 2004 [Page 57] Internet-Draft XMPP Instant Messaging October 2003 9.3.1 Subscribe +----------------------------------------------------------------+ | EXISTING STATE | ROUTE? | NEW STATE | +----------------------------------------------------------------+ | "None" | yes | "None + Pending Out" | | "None + Pending Out" | no | no state change | | "None + Pending In" | yes | "None + Pending Out/In" | | "None + Pending Out/In" | no | no state change | | "To" | no | no state change | | "To + Pending In" | no | no state change | | "From" | yes | "From + Pending Out" | | "From + Pending Out" | no | no state change | | "Both" | no | no state change | +----------------------------------------------------------------+ 9.3.2 Subscribed +----------------------------------------------------------------+ | EXISTING STATE | ROUTE? | NEW STATE | +----------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | no | no state change | | "None + Pending In" | yes | "From" | | "None + Pending Out/In" | yes | "From + Pending Out" | | "To" | no | no state change | | "To + Pending In" | yes | "Both" | | "From" | no | no state change | | "From + Pending Out" | no | no state change | | "Both" | no | no state change | +----------------------------------------------------------------+ 9.3.3 Unsubscribe +----------------------------------------------------------------+ | EXISTING STATE | ROUTE? | NEW STATE | +----------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | yes | "None" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | yes | "None + Pending In" | | "To" | yes | "None" | | "To + Pending In" | yes | "None + Pending In" | | "From" | no | no state change | | "From + Pending Out" | yes | "From" | | "Both" | yes | "From" | Saint-Andre & Miller Expires April 25, 2004 [Page 58] Internet-Draft XMPP Instant Messaging October 2003 +----------------------------------------------------------------+ Note: When a user sends an outbound presence stanza of type "unsubscribe" that results in a subscription state change, the contact's server SHOULD auto-reply by sending a presence stanza of type "unsubscribed" to the user on behalf of the contact and MUST deliver that presence stanza to the contact. 9.3.4 Unsubscribed +----------------------------------------------------------------+ | EXISTING STATE | ROUTE? | NEW STATE | +----------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | no | no state change | | "None + Pending In" | yes | "None" | | "None + Pending Out/In" | yes | "None + Pending Out" | | "To" | no | no state change | | "To + Pending In" | yes | "To" | | "From" | yes | "None" | | "From + Pending Out" | yes | "None + Pending Out" | | "Both" | yes | "To" | +----------------------------------------------------------------+ 9.4 Server Handling of Inbound Presence, Categorized by Subscription State This section defines how a server MUST handle an inbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed" (i.e., deliver it to the intended recipient and/or make a change to the subscription state), categorized by subscription state. (Note: some of the presence stanza types should never be received as inbound stanzas, since the sender's server MUST NOT route them to the intended recipient; however, these stanza types are included for the sake of completeness.) 9.4.1 Subscription State = None +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | yes | "None + Pending In" | | subscribed | no | no state change | | unsubscribe | no | no state change | | unsubscribed | no | no state change | +--------------------------------------------------------+ Saint-Andre & Miller Expires April 25, 2004 [Page 59] Internet-Draft XMPP Instant Messaging October 2003 9.4.2 Subscription State = None + Pending Out +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | yes | "None + Pending Out/In" | | subscribed | yes | "To" | | unsubscribe | no | no state change | | unsubscribed | yes | "None" | +--------------------------------------------------------+ 9.4.3 Subscription State = None + Pending In +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "None" | | unsubscribed | no | no state change | +--------------------------------------------------------+ 9.4.4 Subscription State = None + Pending Out/In +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | no | no state change | | subscribed | yes | "To + Pending In" | | unsubscribe | yes | "None + Pending Out" | | unsubscribed | yes | "None + Pending In" | +--------------------------------------------------------+ 9.4.5 Subscription State = To +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | yes | "To + Pending In" | | subscribed | no | no state change | | unsubscribe | no | no state change | | unsubscribed | yes | "None" | +--------------------------------------------------------+ Saint-Andre & Miller Expires April 25, 2004 [Page 60] Internet-Draft XMPP Instant Messaging October 2003 9.4.6 Subscription State = To + Pending In +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "To" | | unsubscribed | yes | "None + Pending In" | +--------------------------------------------------------+ 9.4.7 Subscription State = From +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "None" | | unsubscribed | no | no state change | +--------------------------------------------------------+ 9.4.8 Subscription State = From + Pending Out +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | no | no state change | | subscribed | yes | "Both" | | unsubscribe | yes | "None + Pending Out" | | unsubscribed | yes | "From" | +--------------------------------------------------------+ 9.4.9 Subscription State = Both +--------------------------------------------------------+ | STANZA TYPE | DELIVER? | NEW STATE | +--------------------------------------------------------+ | subscribe | no | no state change | | subscribed | no | no state change | | unsubscribe | yes | "To" | | unsubscribed | yes | "From" | +--------------------------------------------------------+ Saint-Andre & Miller Expires April 25, 2004 [Page 61] Internet-Draft XMPP Instant Messaging October 2003 9.5 Server Handling of Inbound Presence, Categorized by Presence Type This section defines how a server MUST handle an inbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed" (i.e., deliver it to the intended recipient and/or make a change to the subscription state), categorized by presence type. 9.5.1 Subscribe +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | yes | "None + Pending In" | | "None + Pending Out" | yes | "None + Pending Out/In" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | no | no state change | | "To" | yes | "To + Pending In" | | "To + Pending In" | no | no state change | | "From" | no | no state change | | "From + Pending Out" | no | no state change | | "Both" | no | no state change | +------------------------------------------------------------------+ 9.5.2 Subscribed +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | yes | "To" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | yes | "To + Pending In" | | "To" | no | no state change | | "To + Pending In" | no | no state change | | "From" | no | no state change | | "From + Pending Out" | yes | "Both" | | "Both" | no | no state change | +------------------------------------------------------------------+ 9.5.3 Unsubscribe +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | no | no state change | Saint-Andre & Miller Expires April 25, 2004 [Page 62] Internet-Draft XMPP Instant Messaging October 2003 | "None + Pending Out" | no | no state change | | "None + Pending In" | yes | "None" | | "None + Pending Out/In" | yes | "None + Pending Out" | | "To" | no | no state change | | "To + Pending In" | yes | "To" | | "From" | yes | "None" | | "From + Pending Out" | yes | "None + Pending Out | | "Both" | yes | "To" | +------------------------------------------------------------------+ 9.5.4 Unsubscribed +------------------------------------------------------------------+ | EXISTING STATE | DELIVER? | NEW STATE | +------------------------------------------------------------------+ | "None" | no | no state change | | "None + Pending Out" | yes | "None" | | "None + Pending In" | no | no state change | | "None + Pending Out/In" | yes | "None + Pending In" | | "To" | yes | "None" | | "To + Pending In" | yes | "None + Pending In" | | "From" | no | no state change | | "From + Pending Out" | yes | "From" | | "Both" | yes | "From" | +------------------------------------------------------------------+ 9.6 Server Delivery and Client Acknowledgement of Subscription State Change Notifications When a server receives an inbound presence stanza of type "subscribe", "subscribed", "unsubscribe", or "unsubscribed" that consists of a subscription state change notification, in addition to sending the appropriate roster push (or updated roster when the roster is next requested), it MUST deliver the notification to the intended recipient at least once. A server MAY require the recipient to acknowledge receipt of the all state change notifications (and MUST require acknowledgement in the case of subscription requests, i.e., presence stanzas of type "subscribe"). In order to require acknowledgement, a server SHOULD send the notification to the recipient each time the recipient logs in, until the recipient acknowledges receipt of the notification by "affirming" or "denying" the notification, as shown in the following table: +--------------------------------------------------+ | NOTIFICATION | ACCEPT | DENY | +--------------------------------------------------+ Saint-Andre & Miller Expires April 25, 2004 [Page 63] Internet-Draft XMPP Instant Messaging October 2003 | subscribe | subscribed | unsubscribed | | subscribed | subscribe | unsubscribe | | unsubscribe | unsubscribed | subscribed | | unsubscribed | unsubscribe | subscribe | +--------------------------------------------------+ Obviously, given the foregoing subscription state charts, some of the acknowledgement stanzas will be routed to the contact and result in subscription state changes, while others will not. However, any such stanzas MUST result in the server's no longer sending the subscription state notification to the user. Because a user's server MUST automatically generate outbound presence stanzas of type "unsubscribe" and "unsubscribed" upon receiving a roster set with the 'subscription' attribute set to a value of "remove" (see Removing a Roster Item and Cancelling All Subscriptions (Section 8.6)) the server MUST treat a roster remove request as equivalent to sending those presence stanzas for purposes of determining whether to continue sending subscription state change notifications of type "subscribe" or "subscribed" to the user. 10. Blocking Communication Most instant messaging systems have found it necessary to implement some method for users to block communications from particular other users (this is also required by sections 5.1.5, 5.1.15, 5.3.2, and 5.4.10 of RFC 2779 [2]). In XMPP this is done using the 'jabber:iq:privacy' namespace by managing one's privacy lists. Server-side privacy lists enable successful completion of the following use cases: o Retrieving one's privacy lists. o Adding, removing, and editing one's privacy lists. o Setting, changing, or declining active lists. o Setting, changing, or declining the default list (i.e., the list that is active by default). o Allowing or blocking messages based on JID, group, or subscription type (or globally). o Allowing or blocking inbound presence notifications based on JID, group, or subscription type (or globally). o Allowing or blocking outbound presence notifications based on JID, Saint-Andre & Miller Expires April 25, 2004 [Page 64] Internet-Draft XMPP Instant Messaging October 2003 group, or subscription type (or globally). o Allowing or blocking IQs based on JID, group, or subscription type (or globally). o Allowing or blocking all communications based on JID, group, or subscription type (or globally). Note: presence notifications do not include presence subscriptions, only presence information that is broadcasted to entities that are subscribed to a user's presence information. Thus this includes presence stanzas with no 'type' attribute or of type='unavailable' only. 10.1 Syntax and Semantics A user MAY define one or more privacy lists, which are stored by the user's server. Each element contains one or more rules in the form of elements, and each element uses attributes to define a privacy rule type, a specific value to which the rules applies, the relevant action, and the place of the item in the processing order. The syntax is as follows: [] [] [] [] If the type is "jid", then the 'value' attribute MUST contain a valid Jabber ID. JIDs are matched in the following order: , then , then , then . If the value is , then any connected resource for that user@domain matches. If the value is , then only that resource matches. If the value is , then any user@domain Saint-Andre & Miller Expires April 25, 2004 [Page 65] Internet-Draft XMPP Instant Messaging October 2003 (or subdomain) matches. If the type is "group", then the 'value' attribute SHOULD contain the name of a group in the user's roster. (If a client attempts to update, create, or delete a list item with a group that is not in the user's roster, the server SHOULD return to the client an stanza error.) If the type is "subscription", then the 'value' attribute MUST be one of "both", "to", "from", or "none" as defined under Roster Syntax and Semantics (Section 7.1). If no 'type' attribute is included, the rule provides the "fall-through" case. The 'action' attribute MUST be included and its value MUST be either "accept" or "deny". The 'order' attribute MUST be included and its value MUST be a non-negative integer that is unique among all items in the list. (If a client attempts to create or update a list with non-unique order values, the server MUST return to the client a stanza error.) The element MAY contain one or more child elements that enable an entity to specify more granular control over which kinds of stanzas are to be blocked (i.e., rather than blocking all stanzas). The allowable child elements are: o -- blocks incoming message stanzas o -- blocks incoming IQ stanzas o -- blocks incoming presence notifications o -- blocks outgoing presence notifications Within the 'jabber:iq:privacy' namespace, the child of a client-generated IQ stanza of type "set" MUST NOT include more than one child element (i.e., the stanza must contain only one element, one element, or one element); if a client violates this rule, the server MUST return to the client a stanza error. When a client adds or updates a privacy list, the element SHOULD contain at least one child element; when a client removes a privacy list, the element SHOULD contain no child element. Saint-Andre & Miller Expires April 25, 2004 [Page 66] Internet-Draft XMPP Instant Messaging October 2003 When a client updates a privacy list, it must include all of the desired items (i.e., not a "delta"). 10.2 Business Rules 1. If there is an active list set for a session, it affects only the session for which it is activated, and only for the duration of the session. The server MUST apply the active list only and MUST NOT apply the default list. 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. 4. Privacy lists MUST be the first rule applied by a server, superseding (1) the routing and delivery rules specified in Server Rules for Handling XML Stanzas (Section 14), 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 . 6. As soon as a stanza is matched against a privacy list, the server SHOULD appropriately handle the stanza and cease processing. 7. If no fall-through item is provided in a list, the fall-through action is assumed to be "accept". 8. 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). 9. 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 Saint-Andre & Miller Expires April 25, 2004 [Page 67] Internet-Draft XMPP Instant Messaging October 2003 that list currently applies). 10.3 Retrieving One's Privacy Lists Example: Client requests names of privacy lists from server: Example: Server sends names of privacy lists to client, preceded by active list and default list: Example: Client requests a privacy list from server: Example: Server sends a privacy list to client: Example: Client requests another privacy list from server: Saint-Andre & Miller Expires April 25, 2004 [Page 68] Internet-Draft XMPP Instant Messaging October 2003 Example: Server sends another privacy list to client: Example: Client requests yet another privacy list from server: Example: Server sends yet another privacy list to client: Saint-Andre & Miller Expires April 25, 2004 [Page 69] Internet-Draft XMPP Instant Messaging October 2003 In this example, the user has three lists: (1) 'public', which allows communications from everyone except one specific entity (this is the default list); (2) 'private', which allows communications only with contacts who have a bidirectional subscription with the user (this is the active list); and (3) 'special', which allows communications only with three specific entities. If the user attempts to retrieve a list but a list by that name does not exist, the server MUST return an stanza error to the user: Example: Client attempts to retrieve non-existent list: The user is allowed to retrieve only one list at a time. If the user attempts to retrieve more than one list in the same request, the server MUST return a stanza error to the user: Example: Client attempts to retrieve more than one list: 10.4 Managing Active Lists In order to set or change the active list currently being applied by the server, the user MUST send an IQ stanza of type "set" with a Saint-Andre & Miller Expires April 25, 2004 [Page 70] Internet-Draft XMPP Instant Messaging October 2003 element qualified by the 'jabber:iq:privacy' namespace that contains an empty child element possessing a 'name' attribute whose value is set to the desired list name. Example: Client requests change of active list: The server MUST activate and apply the requested list before sending the result back to the client. Example: Server acknowledges success of active list change: If the user attempts to set an active list but a list by that name does not exist, the server MUST return an stanza error to the user: Example: Client attempts to set a non-existent list as active: In order to decline the use of any active list, the user MUST send an empty element with no name. Example: Client declines the use of active lists: Saint-Andre & Miller Expires April 25, 2004 [Page 71] Internet-Draft XMPP Instant Messaging October 2003 10.5 Managing the Default List In order to change its default list, the user MUST send an IQ stanza of type "set" with a element qualified by the 'jabber:iq:privacy' namespace that contains an empty child element possessing a 'name' attribute whose value is set to the desired list name. Example: Client requests change of default list: Example: Server acknowledges success of default list change: If the user attempts to set a default list but a list by that name does not exist, the server MUST return an stanza error to the user: Example: Client attempts to set a non-existent list as default: In order to decline the use of a default list (i.e., to use the domain's stanza routing rules at all times), the user MUST send an empty element with no name. Example: Client declines the use of the default list: Saint-Andre & Miller Expires April 25, 2004 [Page 72] Internet-Draft XMPP Instant Messaging October 2003 10.6 Editing a Privacy List In order to edit a privacy list, the user MUST send an IQ stanza of type "set" with a element qualified by the 'jabber:iq:privacy' namespace that contains one child element possessing a 'name' attribute whose value is set to the list name the user would like to edit. The element MUST contain one or more elements, which specify the user's desired changes to the list by including all elements in the list (not the "delta"). Example: Client edits a privacy list: Example: Server acknowledges success of list edit: Note: The value of the 'order' attribute for any given item is not fixed. Thus in the foregoing example if the user would like to add 4 items between the "tybalt@example.com" item and the "paris@example.org" item, the user's client MUST renumber the relevant items before submitting the list to the server. 10.7 Adding a New Privacy List The same protocol used to edit an existing list is used to create a new list. If the list name matches that of an existing list, the request to add a new list will overwrite the old one. 10.8 Removing a Privacy List In order to remove a privacy list, the user MUST send an IQ stanza of type "set" with a element qualified by the Saint-Andre & Miller Expires April 25, 2004 [Page 73] Internet-Draft XMPP Instant Messaging October 2003 'jabber:iq:privacy' namespace that contains one empty child element possessing a 'name' attribute whose value is set to the list name the user would like to remove. Example: Client removes a privacy list: Example: Server acknowledges success of list removal: If a user attempts to remove an active list or the default list, the server MUST return a stanza error to the user. The user MUST first set another list to active or default before removing it. If the user attempts to remove a list but a list by that name does not exist, the server MUST return an stanza error to the user: If the user attempts to remove more than one list in the same request, the server MUST return a stanza error to the user. 10.9 Blocking Messages Server-side privacy lists enable a user to block incoming messages from other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Example: User blocks based on JID: Saint-Andre & Miller Expires April 25, 2004 [Page 74] Internet-Draft XMPP Instant Messaging October 2003 As a result of creating and applying the foregoing list, the user will not receive messages from the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not receive messages from any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not receive messages from any users with the specified subscription type. Example: User blocks globally: Saint-Andre & Miller Expires April 25, 2004 [Page 75] Internet-Draft XMPP Instant Messaging October 2003 As a result of creating and applying the foregoing list, the user will not receive messages from any other users. 10.10 Blocking Inbound Presence Notifications Server-side privacy lists enable a user to block incoming presence notifications from other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Note: presence notifications do not include presence subscriptions, only presence information that is broadcasted to the user because the user previously subscribed to a contact's presence information. Thus this includes presence stanzas with no 'type' attribute or of type='unavailable' only. Example: User blocks based on JID: As a result of creating and applying the foregoing list, the user will not receive presence notifications from the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not receive presence notifications from any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not receive presence notifications from any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive presence notifications from any other users. Saint-Andre & Miller Expires April 25, 2004 [Page 77] Internet-Draft XMPP Instant Messaging October 2003 10.11 Blocking Outbound Presence Notifications Server-side privacy lists enable a user to block outgoing presence notifications to other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Note: presence notifications do not include presence subscriptions, only presence information that is broadcasted to contacts because those contacts previously subscribed to the user's presence information. Thus this includes presence stanzas with no 'type' attribute or of type='unavailable' only. Example: User blocks based on JID: As a result of creating and applying the foregoing list, the user will not send presence notifications to the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user Saint-Andre & Miller Expires April 25, 2004 [Page 78] Internet-Draft XMPP Instant Messaging October 2003 will not send presence notifications to any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not send presence notifications to any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not send presence notifications to any other users. 10.12 Blocking IQs Server-side privacy lists enable a user to block incoming IQ stanzas from other users based on the other user's JID, roster group, or subscription status (or globally). The following examples illustrate the protocol. Example: User blocks based on JID: Saint-Andre & Miller Expires April 25, 2004 [Page 79] Internet-Draft XMPP Instant Messaging October 2003 As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from the user with the specified JID. Example: User blocks based on roster group: As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from any users in the specified roster group. Example: User blocks based on subscription type: Saint-Andre & Miller Expires April 25, 2004 [Page 80] Internet-Draft XMPP Instant Messaging October 2003 As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive IQ stanzas from any other users. 10.13 Blocking All Communication Server-side privacy lists enable a user to block all stanzas from and to other users based on the other user's JID, roster group, or subscription status (or globally). Note that this includes subscription-related presence stanzas, which are excluded by Blocking Inbound Presence Notifications (Section 10.10). The following examples illustrate the protocol. Example: User blocks based on JID: As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, the user with the specified JID. Example: User blocks based on roster group: Saint-Andre & Miller Expires April 25, 2004 [Page 81] Internet-Draft XMPP Instant Messaging October 2003 As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, any users in the specified roster group. Example: User blocks based on subscription type: As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, any users with the specified subscription type. Example: User blocks globally: As a result of creating and applying the foregoing list, the user will not receive any communications from, nor send any stanzas to, any other users. 10.14 Blocked Entity Attempts to Communicate with User If a blocked entity attempts to send message or presence stanzas to Saint-Andre & Miller Expires April 25, 2004 [Page 82] Internet-Draft XMPP Instant Messaging October 2003 the user, the user's server SHOULD silently drop the stanza and MUST NOT return an error to the sending entity. If a blocked entity attempts to send an IQ stanza of type "get" or "set" to the user, the user's server MUST return to the sending entity a stanza error, since this is the standard error code sent from a client that does not understand the namespace of an IQ get or set. IQ stanzas of other types SHOULD be silently dropped by the server. Example: Blocked entity attempts to send IQ get: Example: Server returns error to blocked entity: 10.15 Higher-Level Heuristics When building a representation of a higher-level privacy heuristic, a client SHOULD use the simplest possible representation. For example, the heuristic "block all communications with any user not in my roster" could be constructed in any of the following ways: o allow communications from all JIDs in my roster (i.e., listing each JID as a separate list item), but block communications with everyone else o allow communications from any user who is in one of the groups that make up my roster (i.e., listing each group as a separate list item), but block communications from everyone else Saint-Andre & Miller Expires April 25, 2004 [Page 83] Internet-Draft XMPP Instant Messaging October 2003 o allow communications from any user with whom I have a subscription of 'both' or 'to' or 'from' (i.e., listing each subscription value separately), but block communications from everyone else o block communications from anyone whose subscription state is 'none' The final representation is the simplest and SHOULD be used; here is the XML that would be sent in this case: 11. IANA Considerations For a number of related IANA considerations, refer to the relevant section of XMPP Core [1]. 11.1 XML Namespace Name for Session Data A URN sub-namespace for session-related data in the Extensible Messaging and Presence Protocol (XMPP) is defined as follows. URI: urn:ietf:params:xml:ns:xmpp-session Specification: [RFCXXXX] Description: This is the XML namespace name for session-related data in the Extensible Messaging and Presence Protocol (XMPP) as defined by [RFCXXXX]. Registrant Contact: IETF, XMPP Working Group, 12. Internationalization Considerations For internationalization considerations, refer to the relevant section of XMPP Core [1]. Saint-Andre & Miller Expires April 25, 2004 [Page 84] Internet-Draft XMPP Instant Messaging October 2003 13. Security Considerations Core security considerations for XMPP are defined in the relevant section of XMPP Core [1]. Additional considerations that apply only to instant messaging and presence applications of XMPP are defined in several places within this memo; specifically: o When a server processes a stanza of any kind whose intended recipient is a user associated with one of the server's hostnames, the server MUST first apply any privacy rules (Section 10) that are in force (see Server Rules for Handling XML Stanzas (Section 14)). o When a server processes an inbound presence stanza of type "probe" whose intended recipient is a user associated with one of the server's hostnames, the server MUST NOT reveal the user's presence information if the sender is a user who is not authorized to receive that information as determined by presence subscriptions (see Client and Server Presence Responsibilities (Section 5.1)). o When a server processes an outbound presence stanza with no type or of type "unavailable", it MUST follow the rules defined under Client and Server Presence Responsibilities (Section 5.1) in order to ensure that such presence information is not broadcasted to entities that are not authorized to know such information. 14. Server Rules for Handling XML Stanzas Basic routing and delivery rules for servers are defined in XMPP Core [1]. This section defines additional rules for XMPP-compliant instant messaging and presence servers. If the hostname of the domain identifier portion of the JID contained in the 'to' attribute of a stanza matches the hostname of the server itself and the JID contained in the 'to' attribute is of the form or , the server MUST first apply any privacy rules (Section 10) that are in force. If privacy rules allow the stanza, it SHOULD be routed or delivered to the intended recipient of the stanza as represented by the JID contained in the 'to' attribute. The following additional rules apply to instant messaging and presence applications, over and above those defined in XMPP Core [1]: 1. If the JID is of the form and an available resource matches the full JID, the recipient's server MUST Saint-Andre & Miller Expires April 25, 2004 [Page 85] Internet-Draft XMPP Instant Messaging October 2003 deliver the stanza to that resource. 2. If the JID is of the form and no available resources match the full JID, the recipient's server (a) SHOULD silently ignore the stanza (i.e., neither deliver it nor return an error) if it is a presence stanza, (b) MUST return a stanza error to the sender if it is an IQ stanza, and (c) MUST treat the stanza as if it were addressed to if it is a message stanza. 3. If the JID is of the form and there is at least one available resource available for the user, the recipient's server MUST follow these rules: 1. 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 element, the server SHOULD consider it to have provided a value of zero). If two 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 values) to choose between them. However, the server MUST NOT deliver the stanza to an available resource with a negative priority. 2. For presence stanzas other than those of type "probe", the server MUST deliver the stanza to all available resources, except that the server MUST NOT deliver the stanza to an available resource that provided a negative value for the element; for presence probes, the server SHOULD reply based on the rules defined in Client and Server Presence Responsibilities (Section 5.1). 3. 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 stanza error. 4. If the JID is of the form and there are no available resources associated with the user, how the stanza is handled depends on the stanza type: 1. For presence stanzas of type "subscribe", the server MUST maintain a record of the stanza and deliver it when the user next becomes available, as specified under Client and Server Saint-Andre & Miller Expires April 25, 2004 [Page 86] Internet-Draft XMPP Instant Messaging October 2003 Presence Responsibilities (Section 5.1). 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. However, if offline message storage is not enabled, the server MUST return to the sender a stanza error. (Note: offline message storage is not defined in XMPP since it strictly is 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 stanza error. 15. Compliance Requirements This section summarizes the specific aspects of the Extensible Messaging and Presence Protocol that MUST be supported by instant messaging servers and clients in order to be considered compliant implementations. All such applications MUST comply with the requirements specified in XMPP Core [1]. The text in this section specifies additional compliance requirements for instant messaging servers and clients; note well that the requirements described here supplement but do not supersede the core requirements. 15.1 Servers In addition to core server compliance requirements, an instant messaging and presence server MUST additionally support the following IM-related protocols: o All server-related instant messaging syntax and semantics defined in this document, including presence broadcast on behalf of clients, presence subscriptions, roster storage and manipulation, privacy rules, and IM-specific routing and delivery rules 15.2 Clients In addition to core client compliance requirements, an instant Saint-Andre & Miller Expires April 25, 2004 [Page 87] Internet-Draft XMPP Instant Messaging October 2003 messaging client MUST additionally support the following IM-related protocols: o Generation and handling of the IM-specific semantics of XML stanzas as defined by the XML schemas, including the 'type' attribute of message and presence stanzas as well as their child elements o All client-related instant messaging syntax and semantics defined in this document, including presence subscriptions, roster management, and privacy rules o End-to-end object encryption as defined in XMPP e2e [6] Normative References [1] Saint-Andre, P. and J. Miller, "XMPP Core", draft-ietf-xmpp-core-19 (work in progress), October 2003. [2] Day, M., Aggarwal, S. and J. Vincent, "Instant Messaging / Presence Protocol Requirements", RFC 2779, February 2000. [3] Bray, T., Paoli, J., Sperberg-McQueen, C. and E. Maler, "Extensible Markup Language (XML) 1.0 (2nd ed)", W3C REC-xml, October 2000, . [4] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C REC-xml-names, January 1999, . [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [6] Saint-Andre, P., "End-to-End Object Encryption in XMPP", draft-ietf-xmpp-e2e-05 (work in progress), August 2003. Informative References [7] Jabber Software Foundation, "Jabber Software Foundation", . [8] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [9] Dawson, F. and T. Howes, "vCard MIME Directory Profile", RFC 2426, September 1998. Saint-Andre & Miller Expires April 25, 2004 [Page 88] Internet-Draft XMPP Instant Messaging October 2003 Authors' Addresses Peter Saint-Andre Jabber Software Foundation EMail: stpeter@jabber.org Jeremie Miller Jabber Software Foundation EMail: jeremie@jabber.org Appendix A. vCards Sections 3.1.3 and 4.1.4 of RFC 2779 [2] require that it be possible to retrieve out-of-band contact information for other users (e.g., telephone number or email address). An XML representation of the vCard specification defined in RFC 2426 [9] is in common use within the Jabber community to provide such information but is out of scope for XMPP (documentation of this protocol is contained in "JEP-0054: vcard-temp", published by the Jabber Software Foundation [7]). Appendix B. XML Schemas The following XML schemas are descriptive, not normative. For schemas defining the core features of XMPP, refer to XMPP Core [1]. B.1 jabber:client Saint-Andre & Miller Expires April 25, 2004 [Page 89] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 90] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 91] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 92] Internet-Draft XMPP Instant Messaging October 2003 B.2 jabber:server Saint-Andre & Miller Expires April 25, 2004 [Page 93] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 94] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 95] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 96] Internet-Draft XMPP Instant Messaging October 2003 B.3 session Saint-Andre & Miller Expires April 25, 2004 [Page 97] Internet-Draft XMPP Instant Messaging October 2003 B.4 jabber:iq:privacy Saint-Andre & Miller Expires April 25, 2004 [Page 98] Internet-Draft XMPP Instant Messaging October 2003 Saint-Andre & Miller Expires April 25, 2004 [Page 99] Internet-Draft XMPP Instant Messaging October 2003 B.5 jabber:iq:roster Saint-Andre & Miller Expires April 25, 2004 [Page 100] Internet-Draft XMPP Instant Messaging October 2003 Appendix C. Differences Between Jabber Instant Messaging and XMPP This section is non-normative. XMPP has been adapted from the protocols originally developed in the Jabber open-source community, which can be thought of as "XMPP 0.9". Because there exists a large installed base of Jabber implementations and deployments, it may be helpful to specify the key differences between Jabber and XMPP in order to expedite and encourage upgrades of those implementations and deployments to XMPP. This section summarizes the differences that relate specifically to instant messaging and presence applications, while the corresponding section of XMPP Core [1] summarizes the differences that relate to all XMPP applications. C.1 Session Creation The client-to-server authentication protocol developed in the Jabber community assumes that every client is an IM client and therefore Saint-Andre & Miller Expires April 25, 2004 [Page 101] Internet-Draft XMPP Instant Messaging October 2003 initiates an IM session upon successful authentication and resource binding, which are performed simultaneously (documention of this protocol is contained in "JEP-0078: Non-SASL Authentication", published by the Jabber Software Foundation [7]). XMPP maintains a stricter separation between core functionality and IM functionality; therefore, an IM session is not created until the client specifically requests one using the protocol defined under Session Establishment (Section 3). C.2 Privacy Rules The Jabber community began to define a protocol for communications blocking (privacy rules) in late 2001, but that effort was deprecated once the XMPP Working Group was formed. Therefore the protocol defined under Blocking Communication (Section 10) is the only such protocol defined for use in the Jabber community. Appendix D. Revision History Note to RFC Editor: please remove this entire appendix, and the corresponding entries in the table of contents, prior to publication. D.1 Changes from draft-ietf-xmpp-im-17 o Added missing server handling rules for cases. o Further clarified privacy rules syntax by describing child elements of . o Clarified several points related to session establishment. o Checked all references. o Completed a thorough proofreading and consistency check of the entire text. D.2 Changes from draft-ietf-xmpp-im-16 o Added sentence to make explicit that blocking all communication includes subscription-related presence stanzas. o Added clause to make explicit that privacy rules must be applied before handling of subscription-related presence stanzas and corresponding generation of roster pushes. o Added syntax and semantics section for the 'jabber:iq:roster' Saint-Andre & Miller Expires April 25, 2004 [Page 102] Internet-Draft XMPP Instant Messaging October 2003 namespace. o Removed content about 'jabber:iq:last' namespace. o Added several internal references from the security considerations section to other sections of this document. o Moved most delivery handling rules from XMPP IM to XMPP Core. o Moved detailed stanza syntax descriptions from XMPP Core to XMPP IM. o Moved stanza schemas from XMPP Core to XMPP IM. D.3 Changes from draft-ietf-xmpp-im-15 o Specified stream error to be sent to active session if there is a conflict regarding session creation. o Fixed several more typographical errors in the privacy rules examples. o Corrected an error regarding server handling of IQ stanzas sent to bare JIDs. o Added section on compliance requirements for instant messaging server and client implementations. o Added non-normative section on differences between Jabber usage and XMPP specifications. D.4 Changes from draft-ietf-xmpp-im-14 o Added subscription state charts. o Fixed several typographical errors in the privacy rules examples. o Changed datatype of 'order' attribute in privacy rules from nonNegativeInteger to unsignedInt. D.5 Changes from draft-ietf-xmpp-im-13 o Made one small change to privacy list syntax rules. Saint-Andre & Miller Expires April 25, 2004 [Page 103] Internet-Draft XMPP Instant Messaging October 2003 D.6 Changes from draft-ietf-xmpp-im-12 o Clarified meaning of the default message type as well as handling of unknown or unsupported types. o Made several small editorial changes. D.7 Changes from draft-ietf-xmpp-im-11 o Further clarified subscription syntax and semantics. o Further clarified presence responsibilities for clients and servers. o Added 'xml:lang' example to presence status. o Added subsection on presence priority. o Defined server handling of unsolicited presence stanzas of type "subscribed". o Specified default resource priority if not provided. o Corrected several errors in the schemas. o Added privacy list business rule regarding roster changes. o Removed the 'jabber:iq:privacy:error' namespace (not necessary). o Documented message type='normal'. o Made numerous small editorial changes throughout. D.8 Changes from draft-ietf-xmpp-im-10 o Clarified presence responsibilities for servers and clients. o Clarified the routing and delivery rules for servers. o Made the 'xml:lang' examples more complete. o Corrected several errors in the unsubscribe workflow. o Made small editorial changes in several sections. Saint-Andre & Miller Expires April 25, 2004 [Page 104] Internet-Draft XMPP Instant Messaging October 2003 D.9 Changes from draft-ietf-xmpp-im-09 o Clarified rules regarding allowable JID types in rosters. o Further clarified the semantics and routing implications of presence priorities. o Removed several obsolete subsections. D.10 Changes from draft-ietf-xmpp-im-08 o Removed authorization content (now addressed in XMPP Core). o Added protocol for initiating an IM session, including schema and IANA registration template. o Corrected <*-condition/> elements to be . o Made small editorial changes to address RFC Editor requirements. D.11 Changes from draft-ietf-xmpp-im-07 o Added several error cases for resource authorization and updated relevant schema. D.12 Changes from draft-ietf-xmpp-im-06 o Specified that IQ result stanzas are required in response to roster pushes. o Changed stanza error namespace names to conform to the format defined in "The IETF XML Registry" as specified in XMPP Core. o Removed note to RFC Editor regarding provisional namespace names. D.13 Changes from draft-ietf-xmpp-im-05 o Removed use of ask='unsubscribe' per list discussion. o Clarified handling of resource conflict during authorization. o Added schemas for jabber:iq:auth, jabber:iq:auth:error, and jabber:iq:privacy:error. Saint-Andre & Miller Expires April 25, 2004 [Page 105] Internet-Draft XMPP Instant Messaging October 2003 o Corrected several small protocol errors in the examples. o Clarified semantics of message types. D.14 Changes from draft-ietf-xmpp-im-04 o Specified sending of unavailable presence after unsubscribe and subscription-cancellation actions. o Further specified syntax and business rules for privacy lists. o Brought error codes into line with definitions in draft-ietf-xmpp-core. o Added note to RFC Editor regarding provisional namespace names. o Removed vCard content and DTD, instead pointing to JSF documentation. D.15 Changes from draft-ietf-xmpp-im-03 o Fixed order processing on privacy rules per list discussion. o Made numerous small editorial changes. D.16 Changes from draft-ietf-xmpp-im-02 o Added a great deal more detail to the narrative regarding server-side privacy rules as well as the interaction between rosters and subscriptions. o Removed DTDs in favor of schemas (with the exception of vCard XML). o Removed non-normative documentation of authentication using jabber:iq:auth and of in-band registration using jabber:iq:register, since these are maintained by the Jabber Software Foundation and are not part of the XMPP specification. D.17 Changes from draft-ietf-xmpp-im-01 o Made numerous small editorial changes. Saint-Andre & Miller Expires April 25, 2004 [Page 106] Internet-Draft XMPP Instant Messaging October 2003 D.18 Changes from draft-ietf-xmpp-im-00 o Moved registration and authentication via jabber:iq:auth to non-normative appendices. o Changed initial presence stanza from MUST be empty to SHOULD be empty. o Specified that user or clients should not send presence stanzas of type='probe'. o Specified the algorithm for digest passwords. D.19 Changes from draft-miller-xmpp-im-02 o Added information about the 'jabber:iq:last' protocol to meet the requirement defined in section 3.2.4 of RFC 2779. o Added information about the 'jabber:iq:privacy' protocol to meet the requirement defined in section 2.3.5 of RFC 2779. o Added information about the vCard XML protocol to meet the requirement defined in sections 3.1.3 and 4.1.4 of RFC 2779. o Changed the material describing authentication (but not resource authorization) with 'jabber:iq:auth' to non-normative. o Noted that the only watchers are subscribers. o Nomenclature changes: (1) from "chunks" to "stanzas"; (2) from "host" to "server"; (3) from "node" to "client" or "user" (as appropriate). 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