XEP-0190: Best Practice for Closing Idle Streams

This document specifies a best practice for closing an XML stream that is perceived to be idle.

NOTICE: This Informational specification defines a best practice or protocol profile that has been approved by the XMPP Council and/or the XSF Board of Directors. Implementations are encouraged and the best practice or protocol profile is appropriate for deployment in production systems.

Document Information

Author Information

Carlo von Loesch

Email: lynX@jabber.getting.psyced.org
JabberID: lynX@ve.symlynX.com

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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.

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## 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. ##

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IPR Conformance

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Discussion Venue

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.

Conformance Terms

The following 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. Introduction
2. How to Close an Idle Stream
2.1. Handshake Stream Shutdown
2.2. Handshake Failure
3. Implementation Notes
4. Security Considerations
5. IANA Considerations
6. XMPP Registrar Considerations
Notes
Revision History

1. Introduction

Note: This document describes a protocol or best practice that is intended for incorporation into the specification that will supersede RFC 3920 [1] within the Internet Standards Process, i.e., rfc3920bis [2]. This document is provided only for the purpose of open community discussion of the potential modification and will be obsoleted as soon as the relevant RFC is published.

RFC 3920 describes several ways to terminate an XML stream, but does not always make a clear statement about which to use. This can lead to faulty implementations. In particular, closing a stream that has not been in use for a while is very often achieved using a connection-timeout error, then closing the socket. This can lead to loss of data. Therefore this document proposes a practice that will avoid such data loss.

Note: The recommendation described herein has been incorporated into rfc3920bis.

2. How to Close an Idle Stream

2.1 Handshake Stream Shutdown

As shown in the basic "session" example in the Simplified Stream Examples (4.8 of RFC 3920), it is a valid transaction to close the outgoing stream by sending

 </stream:stream>

then wait for the other entity to close its stream, like this:

 </stream:stream>

and shut down the underlying TCP connection.

This will ensure that, should the other entity have transmitted any data, it will arrive and be processed before the TCP connection is terminated.

Special care MUST be taken that under no circumstance further packets may be written to the socket after the stream was closed, until the other side shuts down the socket.

On the outgoing TCP connection, an implementation MAY do a read-only shutdown of the socket, as long as the other side will safely be able to send its stream termination token.

2.2 Handshake Failure

In case the other entity fails to close the stream within a reasonable time frame, the entity that started the handshake is entitled to terminate the TCP connection. Since the stream has already been closed, it is correct not to produce an error condition.

3. Implementation Notes

Existing implementations should be updated to use the 'Handshake Stream Shutdown' strategy when shutting down streams that are no longer needed. This strategy is fully backwards-compatible and does not introduce any known communication problems.

4. Security Considerations

5. IANA Considerations

6. XMPP Registrar Considerations

Notes

1. RFC 3920: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc3920>.

2. rfc3921bis: proposed revisions to Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/draft-saintandre-rfc3920bis>. (work in progress)

3. 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/>.

4. 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://www.xmpp.org/registrar/>.