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.
This proposal addresses the following requirements:
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.
<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 (XEP-0131) [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 (XEP-0033) [2] addresses so that the final recipient can determine the provenance of the 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].
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 (XEP-0030) [4] information requests (see Protocol Namespaces regarding issuance of one or more permanent namespaces).
<iq type='get'
to='example.com'
from='oldaccount@example.com'
id='disco1'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<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 (XEP-0115) [5]. However, if an application has not received entity capabilities information from an entity, it SHOULD use explicit service discovery instead.
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).
This specification requires no interaction with the Internet Assigned Numbers Authority (IANA) [6].
The XMPP Registrar [7] shall include 'urn:xmpp:forwarding' in its registry of service discovery features.
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>
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) 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.
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 <https://xmpp.org/community/> for a complete list.
Errata can be sent to <editor@xmpp.org>.
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".
1. XEP-0131: Stanza Headers and Internet Metadata <https://xmpp.org/extensions/xep-0131.html>.
2. XEP-0033: Extended Stanza Addressing <https://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 <https://xmpp.org/about/xmpp-standards-foundation>.
4. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
5. XEP-0115: Entity Capabilities <https://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 <https://xmpp.org/registrar/>.
Note: Older versions of this specification might be available at https://xmpp.org/extensions/attic/
Changed service discovery feature to urn:xmpp:forwarding:0 in compliance with XMPP Registrar processes.
Specified that from address of forwarded stanza must be JID of forwarding address (not server).
Split forwarding semantics and forwarding request process into separate specifications; defined security considerations.
Added confirmation protocol flow.
First draft.
@report{saint-andre2005forwarding,
title = {Stanza Forwarding},
author = {Saint-Andre, Peter},
type = {XEP},
number = {xxxx},
version = {0.0.5},
institution = {XMPP Standards Foundation},
url = {https://xmpp.org/extensions/xep-xxxx.html},
date = {2005-03-03/2009-04-10},
}END