XEP-xxxx: Stanza Forwarding

Abstract:This specification defines best practices for delivery of XMPP stanzas that are forwarded from one address to another.
Author:Peter Saint-Andre
Copyright:© 1999 - 2009 XMPP Standards Foundation. SEE LEGAL NOTICES.
Status:ProtoXEP
Type:Standards Track
Version:0.0.5
Last Updated:2009-04-10

WARNING: This document has not yet been accepted for consideration or approved in any official manner by the XMPP Standards Foundation, and this document must not be referred to as an XMPP Extension Protocol (XEP). If this document is accepted as a XEP by the XMPP Council, it will be published at <http://www.xmpp.org/extensions/> and announced on the <standards@xmpp.org> mailing list.


Table of Contents


1. Introduction
2. Requirements
3. Protocol
4. Determining Support
5. Security Considerations
6. IANA Considerations
7. Jabber Registrar Considerations
    7.1. Service Discovery Features
    7.2. SHIM Headers

Appendices
    A: Document Information
    B: Author Information
    C: Legal Notices
    D: Relation to XMPP
    E: Discussion Venue
    F: Requirements Conformance
    G: Notes
    H: Revision History


1. Introduction

The concept of communications forwarding is familiar from email and, before that, from postal mail: communications sent to one address are automatically re-directed to another address. Such forwarding can help make communications smoother when, for instance, people or applications move to new locations. In postal mail systems, such functionality is usually implemented by the entity responsible for delivery of communications within the locality of the original address (e.g., a local post office), as initiated by the person or organization that requires the change of address. The model is similar in electronic mail systems, often implemented by means of a .forward file.

This document specifies syntax and semantics for delivery of forwarding stanzas in XMPP systems. A companion document defines a method for setting up forwarding at a server.

2. Requirements

This proposal addresses the following requirements:

  1. Define syntax and semantics for stanza forwarding.
  2. Prevent infinite forwarding loops.

3. Protocol

Before stanzas can be forwarded, forwarding needs to be established from an old address to a new address. Methods for doing so are out of scope for this specification.

Once forwarding is established, the server MUST redirect all stanzas sent to the old address (including any resource thereof) to the new address.

Example 1. A sender communicates with a forwarded address

<message from='entity@example.org/resource' to='oldaccount@example.com'>
  <body>Hi!</body>
</message>
  

Before the server forwards the stanza, it MUST add a NumForwards Stanza Headers and Internet Metadata [1] header to the stanza (whose character data is the number "1") if there is no such header already included in the stanza, or if the stanza already includes such a header it MUST increment the value of the NumForwards header by 1 and include the revised NumForwards header in the stanza. (Inclusion and incrementing of the NumForwards header helps to prevent infinite forwarding loops; see the Security Considerations.)

In addition, the server MUST include 'oto' and 'ofrom' Extended Stanza Addressing [2] addresses so that the final recipient can determine the provenance of the stanza.

Example 2. Server forwards stanza

<message from='oldaccount@example.com' to='newaccount@example.net'>
  <body>Hi!</body>
  <headers xmlns='http://jabber.org/protocol/shim'>
    <header name='NumForwards'>1</header>
  </headers>
  <addresses xmlns='http://jabber.org/protocol/address'>
    <address type='oto' jid='oldaccount@example.com'/>
    <address type='ofrom' jid='entity@example.org/resource'/>
  </addresses>
</message>
  

Note: The 'oto' and 'ofrom' address types are not yet specified in the Extended Stanza Addressing specification; they will be added if this document advances to a status of Draft within the standards process of the XMPP Standards Foundation (XSF) [3].

4. Determining Support

If an entity supports the protocol specified herein, it MUST advertise that fact by returning a feature of "urn:xmpp:forwarding:1" in response to Service Discovery [4] information requests (see Protocol Namespaces regarding issuance of one or more permanent namespaces).

Example 3. Service discovery information request

<iq type='get'
    to='example.com'
    from='oldaccount@example.com'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
  

Example 4. Service discovery information response

<iq type='result'
    from='example.com'
    to='oldaccount@example.com'
    id='disco1'>
  <query xmlns='http://jabber.org/protocol/disco#info'>
    <feature var='http://jabber.org/protocol/forwarding'/>
  </query>
</iq>
  

In order for an application to determine whether an entity supports this protocol, where possible it SHOULD use the dynamic, presence-based profile of service discovery defined in Entity Capabilities [5]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.

5. Security Considerations

Deployment of stanza forwarding introduces the possibility of a denial of service attack if infinite loops occur; therefore, a server that implements stanza forwarding MUST also implement checking and incrementing of the NumForwards header. In particular, a server MUST be configured with a reasonable default limit for the maximum number of acceptable forwards (e.g., 10), which MAY be further configurable by the server administrator but which MUST NOT be removable (or changeable to an unreasonable value).

6. IANA Considerations

This specification requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].

7. Jabber Registrar Considerations

7.1 Service Discovery Features

The XMPP Registrar [7] shall include 'urn:xmpp:forwarding' in its registry of service discovery features.

7.2 SHIM Headers

The XMPP Registrar shall include the following entry in its registry of SHIM headers.

<header>
  <name>NumForwards</name>
  <desc>The number of times a stanza has been forwarded (must be a positive integer).</desc>
  <doc>XEP-xxxx</doc>
</header>
    

Appendices


Appendix A: Document Information

Series: XEP
Number: xxxx
Publisher: XMPP Standards Foundation
Status: ProtoXEP
Type: Standards Track
Version: 0.0.5
Last Updated: 2009-04-10
Approving Body: XMPP Council
Dependencies: XMPP Core
Supersedes: None
Superseded By: None
Short Name: forwarding


Appendix B: Author Information

Peter Saint-Andre

JabberID: stpeter@jabber.org
URI: https://stpeter.im/


Appendix C: Legal Notices

Copyright

This XMPP Extension Protocol is copyright © 1999 - 2009 by the XMPP Standards Foundation (XSF).

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. In no event shall the XMPP Standards Foundation or the authors of this Specification be liable for any claim, damages, or other liability, whether in an action of contract, tort, or otherwise, arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising out of the use or inability to use the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which may be found at <http://xmpp.org/extensions/ipr-policy.shtml> or obtained by writing to XSF, P.O. Box 1641, Denver, CO 80201 USA).

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 may 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

1. XEP-0131: Stanza Headers and Internet Metadata <http://xmpp.org/extensions/xep-0131.html>.

2. XEP-0033: Extended Stanza Addressing <http://xmpp.org/extensions/xep-0033.html>.

3. The XMPP Standards Foundation (XSF) is an independent, non-profit membership organization that develops open extensions to the IETF's Extensible Messaging and Presence Protocol (XMPP). For further information, see <http://xmpp.org/xsf/>.

4. XEP-0030: Service Discovery <http://xmpp.org/extensions/xep-0030.html>.

5. XEP-0115: Entity Capabilities <http://xmpp.org/extensions/xep-0115.html>.

6. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

7. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <http://xmpp.org/registrar/>.


Appendix H: Revision History

Version 0.0.5 (2009-04-10)

Changed service discovery feature to urn:xmpp:forwarding:0 in compliance with XMPP Registrar processes.

(psa)

Version 0.0.4 (2006-03-13)

Specified that from address of forwarded stanza must be JID of forwarding address (not server).

(psa)

Version 0.0.3 (2006-01-24)

Split forwarding semantics and forwarding request process into separate specifications; defined security considerations.

(psa)

Version 0.0.2 (2005-04-08)

Added confirmation protocol flow.

(psa)

Version 0.0.1 (2005-03-03)

First draft.

(psa)

END