XEP-0184: Message Receipts

NOTICE: The protocol defined herein is a Draft Standard of the XMPP Standards Foundation. Implementations are encouraged and the protocol is appropriate for deployment in production systems, but some changes to the protocol are possible before it becomes a Final Standard.

Table of Contents

1. Introduction

While Advanced Message Processing [1] provides message acknowledgements at the server level, it does not extend that model all the way to the client. [2] However, sometimes client-level acknowledgements are needed, for example to provide "receipts". This document defines a mechanism for XMPP message receipts, which are functionally equivalent to the "delivered" or "displayed" event in Message Events [3], which this specification in part obsoletes. [4]

Note: This extension is functionally equivalent to an Advanced Message Processing rule of "receipt" but uses a dedicated namespace to simplify processing by end user clients and intermediate routers.

2. Requirements

This document addresses the following requirements:

1. Enable a sender to request notification that an XMPP message stanza has been received.
2. Enable a recipient to provide message receipts if desired.

3. What This Protocol Provides

This document defines a protocol that enables a sender to ask the recipient to return a receipt for a message. Although the return of a message receipt lets the sender know that the message has been delivered, there are many reasons why the sender might not receive a receipt immediately or at all, including but not limited to the following:

• The sender addressed the message to the recipient's bare JID <localpart@domain.tld> and therefore does not know if the recipient even supports message receipts.
• The sender has not bothered to determine whether the recipient supports message receipts.
• The recipient (or the particular intended resource to which the sender addressed the message) does not in fact support message receipts.
• The intended resource supports message receipts but the recipient's server delivers the message to another resource that does not support message receipts.
• The recipient's client receives the message but experiences a malfunction before generating a receipt.
• The recipient returns a receipt but the receipt is lost on the way back from the recipient to the sender (e.g., because of connectivity issues or software failures at any hop).
• The recipient simply does not wish to return a receipt for the sent message.

Because of these significant limitations, this protocol does not provide complete or even partial reliability or guaranteed delivery. Therefore, the sender SHOULD NOT impute any meaning to the lack of a receipt unless it has established with the recipient that receipt requests will be honored; however, methods for doing so are out of scope for this specification and it is NOT RECOMMENDED to take any particular action (such as resending a message) without such methods. [5]

4. When to Request Receipts

A sender could request receipts on any non-error message (chat, groupchat, headline, or normal) no matter if the recipient's address is a bare JID <localpart@domain.tld> or a full JID <localpart@domain.tld/resource>. Whether it is appropriate or advisable to do so it another question. This section provides recommendations about when and when not to request receipts, and what results to expect in each scenario.

5. Determining Support

If an entity supports message receipts, it MUST report that by including a Service Discovery [7] feature of "urn:xmpp:receipts" in response to disco#info requests:

Example 1. Initial Service Discovery information request

<iq from='northumberland@shakespeare.lit/westminster'
    id='disco1'
    to='kingrichard@royalty.england.lit/throne'
    type='get'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  

Example 2. Service Discovery information response

<iq from='kingrichard@royalty.england.lit/throne'
    id='disco1'
    to='northumberland@shakespeare.lit/westminster'
    type='result'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='urn:xmpp:receipts'/>
  </query>
</iq>
  

Support can also be determined via Entity Capabilities [8] a.k.a. "caps".

6. Protocol Format

In order to make it possible for senders to request and for recipients to generate message receipts, we define a dedicated protocol extension qualified by the 'urn:xmpp:receipts' namespace.

There are two allowable elements in this namespace:

• <request/> -- included by a sending entity that wishes to know if the message has been received.
• <received/> -- included by a receiving entity that wishes to inform the sending entity that the message has been received.

Specifically, the receiving entity shall return a <received/> notice if it has received and processed the message. The term "processed" is understood to include presentation to a human user if appropriate or any other application-specific client-side processing, including generation of an error response if the application determines that the message contents cannot be handled.

The following is an example of a message that includes a request for return receipt.

Example 3. A message with receipt requested

<message
    from='northumberland@shakespeare.lit/westminster'
    id='richard2-4.1.247'
    to='kingrichard@royalty.england.lit/throne'>
  <body>My lord, dispatch; read o'er these articles.</body>
  <request xmlns='urn:xmpp:receipts'/>
</message>
  

Note: A sender MUST include an 'id' attribute on every message that requests a receipt, so that the sender can properly track the receipt.

The recipient shall generate a receipt if and only if it supports the protocol defined herein and it is configured to return receipts, either globally or for this recipient (otherwise it MUST NOT return a receipt and SHOULD NOT return an error).

Example 4. A message receipt

<message
    from='kingrichard@royalty.england.lit/throne'
    id='bi29sg183b4v'
    to='northumberland@shakespeare.lit/westminster'>
  <received xmlns='urn:xmpp:receipts' id='richard2-4.1.247'/>
</message>
  

The <received/> element SHOULD be the only child of the <message/> stanza and SHOULD include an 'id' attribute that echoes the 'id' attribute of the sent message.

7. Security Considerations

It is possible for a recipient to leak its presence when returning message receipts; therefore, a recipient SHOULD NOT return message receipts to senders who are not otherwise authorized to view its presence.

8. IANA Considerations

No interaction with the Internet Assigned Numbers Authority (IANA) [9] is necessary as a result of this document.

9. XMPP Registrar Considerations

10. XML Schema

<?xml version='1.0' encoding='UTF-8'?>

<xs:schema
    xmlns:xs='http://www.w3.org/2001/XMLSchema'
    targetNamespace='urn:xmpp:receipts'
    xmlns='urn:xmpp:receipts'
    elementFormDefault='qualified'>

  <xs:annotation>
    <xs:documentation>
      The protocol documented by this schema is defined in
      XEP-0184: http://xmpp.org/extensions/xep-0184.html
    </xs:documentation>
  </xs:annotation>

  <xs:element name='received'>
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base='xs:empty'>
          <xs:attribute name='id' type='xs:string' use='optional'/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

  <xs:element name='request' type='empty'/>

  <xs:simpleType name='empty'>
    <xs:restriction base='xs:string'>
      <xs:enumeration value=''/>
    </xs:restriction>
  </xs:simpleType>

</xs:schema>
  

11. Acknowledgements

Thanks to Joe Kemp, Kevin Smith, Remko Tronçon, and Matthew Wild for their input.

Appendices

Appendix A: Document Information

Series: XEP
Number: 0184
Publisher: XMPP Standards Foundation
Status: Draft
Type: Standards Track
Version: 1.1
Last Updated: 2010-03-31
Approving Body: XMPP Council
Dependencies: XMPP Core
Supersedes: XEP-0022 (in part)
Superseded By: None
Short Name: receipts
Schema: <http://xmpp.org/schemas/receipts.xsd>
Source Control: HTML  RSS
This document in other formats: XML  PDF

Appendix B: Author Information

Appendix C: Legal Notices

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 3920) and XMPP IM (RFC 3921) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.

Errata can be sent to <editor@xmpp.org>.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

Appendix G: Notes

Appendix H: Revision History

Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/

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