XMPP Working Group L. Stout, Ed.
Internet-Draft &yet
Intended status: Standards Track J. Moffitt
Expires: September 15, 2014 Mozilla
E. Cestari
cstar industries
March 14, 2014
An XMPP Sub-protocol for WebSocket
draft-ietf-xmpp-websocket-02
Abstract
This document defines a binding for the XMPP protocol over a
WebSocket transport layer. A WebSocket binding for XMPP provides
higher performance than the current HTTP binding for XMPP.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 15, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. XMPP Sub-Protocol . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. XMPP Stream Setup . . . . . . . . . . . . . . . . . . . . 4
3.4. Stream Errors . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Closing the Connection . . . . . . . . . . . . . . . . . 5
3.5.1. see-other-uri . . . . . . . . . . . . . . . . . . . . 6
3.6. Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.7. Stream Restarts . . . . . . . . . . . . . . . . . . . . . 7
3.8. Pings and Keepalives . . . . . . . . . . . . . . . . . . 7
3.9. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . 8
3.10. Stream Management . . . . . . . . . . . . . . . . . . . . 8
4. Discovering the WebSocket Connection Method . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
5.1. WebSocket Subprotocol Name . . . . . . . . . . . . . . . 9
5.2. URN Sub-Namespace . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. XML Schema . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Applications using the Extensible Messaging and Presence Protocol
(XMPP) (see [RFC6120] and [RFC6121]) on the Web currently make use of
BOSH (see [XEP-0124] and [XEP-0206]), an XMPP binding to HTTP. BOSH
is based on the HTTP long polling technique, and it suffers from high
transport overhead compared to XMPP's native binding to TCP. In
addition, there are a number of other known issues with long polling
[RFC6202], which have an impact on BOSH-based systems.
It would be much better in most circumstances to avoid tunneling XMPP
over HTTP long polled connections and instead use the XMPP protocol
directly. However, the APIs and sandbox that browsers have provided
do not allow this. The WebSocket protocol [RFC6455] exists to solve
these kinds of problems. The WebSocket protocol is a bidirectional
protocol that provides a simple message-based framing layer over raw
sockets and allows for more robust and efficient communication in web
applications.
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The WebSocket protocol enables two-way communication between a client
and a server, effectively emulating TCP at the application layer and
therefore overcoming many of the problems with existing long-polling
techniques for bidirectional HTTP. This document defines a WebSocket
sub-protocol for XMPP.
2. Terminology
The basic unit of framing in the WebSocket protocol is called a
message. In XMPP, the basic unit is the stanza, which is a subset of
the first-level children of each document in an XMPP stream (see
Section 9 of [RFC6120]). XMPP also has a concept of messages, which
are stanzas with a top-level element of <message/>. In this
document, the word "message" will mean a WebSocket message, not an
XMPP message stanza, unless otherwise noted.
The 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 [RFC2119].
3. XMPP Sub-Protocol
3.1. Handshake
The XMPP sub-protocol is used to transport XMPP over a WebSocket
connection. The client and server agree to this protocol during the
WebSocket handshake (see Section 1.3 of [RFC6455]).
During the WebSocket handshake, the client MUST include the |Sec-
WebSocket-Protocol| header in its handshake, and the value |xmpp|
MUST be included in the list of protocols. The reply from the server
MUST also contain |xmpp| in its own |Sec-WebSocket-Protocol| header
in order for an XMPP sub-protocol connection to be established.
Once the handshake is complete, WebSocket messages sent or received
will conform to the protocol defined in the rest of this document.
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C: GET /xmpp-websocket HTTP/1.1
Host: example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Origin: http://example.com
...
Sec-WebSocket-Protocol: xmpp
Sec-WebSocket-Version: 13
S: HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
...
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Protocol: xmpp
[WebSocket connection established]
C: <open xmlns="urn:ietf:params:xml:ns:xmpp-framing"
to="example.com"
version="1.0" />
3.2. Messages
Data frame messages in the XMPP sub-protocol MUST be of the text type
and contain UTF-8 encoded data. The close control frame's contents
are specified in Section 3.5. Control frames other than close are
not restricted.
3.3. XMPP Stream Setup
The first message sent after the handshake is complete MUST be an
<open/> element qualified by the "urn:ietf:params:xml:ns:xmpp-
framing" namespace. The 'from', 'id', 'to', and 'version' attributes
of this element mirror those of the XMPP opening stream tag as
defined for the 'http://etherx.jabber.org/streams' namespace in XMPP
[RFC6120]. The '<' character of the open tag MUST be the first
character of the text payload.
The server MUST respond with an <open /> element, or a <close />
element (see Section 3.5.1).
Clients MUST NOT attempt to multiplex XMPP streams for multiple JIDs
over the same WebSocket.
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3.4. Stream Errors
Stream level errors in XMPP are terminal. Should such an error
occur, the server MUST send the stream error as a complete element in
a message to the client.
If the error occurs during the opening of a stream, the server MUST
send the initial open element response, followed by the stream level
error in a second WebSocket message frame. The server MUST then
close the connection as specified in Section 3.5.
3.5. Closing the Connection
Either the server or the client may close the connection at any time.
Before closing the connection, the closing party SHOULD close the
XMPP stream, if it has been established, by sending a message with
the <close/> element, qualified by the "urn:ietf:params:xml:ns:xmpp-
framing" namespace. The stream is considered closed when a
corresponding <close/> element is received from the other party.
To initiate closing the WebSocket connection, the closing party MUST
send a normal WebSocket close message with an empty body. The
connection is considered closed when a matching close message is
received (see Section 1.4 of [RFC6455]).
An example of ending an XMPP over WebSocket session by first closing
the XMPP stream layer and then the WebSocket connection layer:
Client (XMPP WSS) Server
| | | |
| | <close xmlns="urn:ietf:params:xml:ns:xmpp-framing /> | |
| |------------------------------------------------------------>| |
| | <close xmlns="urn:ietf:params:xml:ns:xmpp-framing" /> | |
| |<------------------------------------------------------------| |
| | | |
| | (XMPP Stream Closed) | |
| +-------------------------------------------------------------+ |
| |
| WS CLOSE FRAME |
|------------------------------------------------------------------>|
| WS CLOSE FRAME |
|<------------------------------------------------------------------|
| |
| (Connection Closed) |
+-------------------------------------------------------------------+
If a client closes the WebSocket connection without closing the XMPP
stream after having enabled stream management (see Section 3.10), the
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server SHOULD keep the XMPP session alive for a period of time based
on server policy, as specified in [XEP-0198]. If the client has not
negotiated the use of [XEP-0198], there is no distinction between a
stream that was closed as described above and a simple disconnection;
the stream is then considered implicitly closed and the XMPP session
ended.
3.5.1. see-other-uri
If the server (or a connection mananger intermediary) wishes to
instruct the client to move to a different WebSocket endpoint (e.g.
for load balancing purposes), the server MAY send a <close/> element
and set the "see-other-uri" attribute to the URI of the new WebSocket
endpoint.
Clients MUST NOT accept suggested endpoints with a lower security
context (e.g. moving from a "wss://" endpoint to a "ws://" endpoint).
An example of the server closing a stream and instructing the client
to connect at a different WebSocket endpoint:
S: <close xmlns="urn:ietf:params:xml:ns:xmpp-framing"
see-other-uri="wss://otherendpoint.example/xmpp-bind" />
3.6. Stanzas
Every XMPP stanza or other XML element sent directly over the XMPP
stream (e.g. <features xmlns="http://etherx.jabber.org/streams"/>)
MUST be sent in its own message. As such, every WebSocket text
message that is received MUST be a complete and parsable XML
fragment, with all relevant xmlns and xml:lang declarations
specified.
As it is already mandated that the content of each message is UTF-8
encoded, XML text declarations SHOULD NOT be included in messages.
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Examples of WebSocket messages that contain independently parsable
XML fragments (note that for stream features and errors, there is no
parent context element providing the "stream" namespace prefix as in
[RFC6120], and thus the stream namespace MUST be declared):
<features xmlns="http://etherx.jabber.org/streams">
<bind xmlns="urn:ietf:params:xml:ns:xmpp-bind"/>
</features>
<error xmlns="http://etherx.jabber.org/streams">
<host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</error>
<message xmlns="jabber:client" xml:lang="en">
<body>Every WebSocket message is parsable by itself.</body>
</message>
3.7. Stream Restarts
After successful SASL authentication, an XMPP stream needs to be
restarted. In these cases, as soon as the message is sent (or
received) containing the success indication, both the server and
client streams are implicitly closed, and new streams need to be
opened. The client MUST open a new stream as in Section 3.3 and MUST
NOT send a closing <close/> element.
S: <success xmlns="urn:ietf:params:xml:ns:xmpp-sasl" />
[Streams implicitly closed]
C: <open xmlns="urn:ietf:params:xml:ns:xmpp-framing"
to="example.com"
version="1.0" />
3.8. Pings and Keepalives
XMPP servers often send "whitespace keepalives" (see Section 4.6.1 of
[RFC6120]) between stanzas to maintain an XML stream, and XMPP
clients can do the same as these extra whitespace characters are not
significant in the protocol. Servers and clients SHOULD use
WebSocket ping control frames instead for this purpose.
In some cases, the WebSocket connection might be served by an
intermediary connection manager and not the XMPP server. In these
situations, the use of WebSocket ping messages are insufficient to
test that the XMPP stream is still alive. Both the XMPP Ping
extension [XEP-0199] and the XMPP Stream Management extension
[XEP-0198] provide mechanisms to ping the XMPP server, and either
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extension (or both) MAY be used to determine the state of the
connection.
3.9. Use of TLS
TLS cannot be used at the XMPP sub-protocol layer because the sub-
protocol does not allow for raw binary data to be sent. Instead,
enabling TLS SHOULD be done at the WebSocket layer using secure
WebSocket connections via the |wss| URI scheme. (See Section 10.6 of
[RFC6455].)
Because TLS is to be provided outside of the XMPP sub-protocol layer,
a server MUST NOT advertise TLS as a stream feature (see Section 4.6
of [RFC6120]), and a client MUST ignore any advertised TLS stream
feature, when using the XMPP sub-protocol.
3.10. Stream Management
In order to alleviate the problems of temporary disconnections, the
XMPP Stream Management extension [XEP-0198] MAY be used to confirm
when stanzas have been received by the server.
In particular, the use of session resumption in [XEP-0198] MAY be
used to allow for recreating the same stream session state after a
temporary network unavailability or after navigating to a new URL in
a browser.
4. Discovering the WebSocket Connection Method
Section 3 of [RFC6120] defines a procedure for connecting to an XMPP
server, including ways to discover the TCP/IP address and port of the
server. When using the WebSocket binding as specified in this
document (instead of the TCP binding as specified in [RFC6120]), a
client needs an alternative way to discover information about the
server's connection methods, since web browsers and other WebSocket-
capable software applications typically cannot obtain such
information from the Domain Name System.
The alternative lookup process uses Web Host Metadata [RFC6415] and
Web Linking [RFC5988], where the link relation type is "urn:xmpp:alt-
connections:websocket" as described in Discovering Alternate XMPP
Connection Methods [XEP-0156]. An example follows.
<XRD xmlns='http://docs.oasis-open.org/ns/xri/xrd-1.0'>
<Link rel="urn:xmpp:alt-connections:websocket"
href="wss://webcm.example.net:443/ws" />
</XRD>
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Servers MAY expose discovery information using host-meta documents,
and clients MAY use such information to determine the WebSocket
endpoint for a server.
Use of web-host metadata MAY be used to establish trust between the
XMPP server domain and the WebSocket endpoint, particularly in multi-
tenant situations where the same WebSocket endpoint is serving
multiple XMPP domains.
5. IANA Considerations
5.1. WebSocket Subprotocol Name
This specification requests IANA to register the WebSocket XMPP sub-
protocol under the "WebSocket Subprotocol Name" Registry with the
following data:
Subprotocol Identifier: xmpp
Subprotocol Common Name: WebSocket Transport for the Extensible
Messaging and Presence Protocol (XMPP)
Subprotocol Definition: this document
5.2. URN Sub-Namespace
A URN sub-namespace for framing of Extensible Messaging and Presence
Protocol (XMPP) streams is defined as follows.
URI: urn:ietf:params:xml:ns:xmpp-framing
Specification: this document
Description: This is the XML namespace name for framing of
Extensible Messaging and Presence Protocol (XMPP) streams as
defined by RFC XXXX.
Registrant Contact: IESG <iesg@ietf.org>
6. Security Considerations
Since application level TLS cannot be used (see Section 3.9),
applications need to protect the privacy of XMPP traffic at the
WebSocket or other appropriate layer.
Browser based applications are not able to inspect and verify at the
application layer the certificate used for the WebSocket connection
to ensure that it corresponds to the domain specified as the "to"
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address of the XMPP stream. For hosts whose domain matches the
origin for the WebSocket connection, that check is already performed
by the browser. However, in situations where the domain of the XMPP
server might not match the origin for the WebSocket endpoint
(especially multi-tenant hosting situations), the web host metadata
method (see [RFC6415] and [XEP-0156]) MAY be used to delegate trust
from the XMPP server domain to the WebSocket origin.
When presented with a new WebSocket endpoint via the "see-other-uri"
attribute of a <close/> element, clients MUST NOT accept the
suggestion if the security context of the new endpoint is lower than
the current one in order to prevent downgrade attacks from a "wss://"
endpoint to "ws://".
The Security Considerations for both WebSocket (see Section 10 of
[RFC6455] and XMPP (see Section 13 of [RFC6120]) apply to the
WebSocket XMPP sub-protocol.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
6455, December 2011.
7.2. Informative References
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6121] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence", RFC
6121, March 2011.
[RFC6202] Loreto, S., Saint-Andre, P., Salsano, S., and G. Wilkins,
"Known Issues and Best Practices for the Use of Long
Polling and Streaming in Bidirectional HTTP", RFC 6202,
April 2011.
[RFC6415] Hammer-Lahav, E. and B. Cook, "Web Host Metadata", RFC
6415, October 2011.
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[XEP-0124]
Paterson, I., Smith, D., Saint-Andre, P., Moffitt, J., and
L. Stout, "Bidirectional-streams Over Synchronous HTTP
(BOSH)", XSF XEP 0124, November 2013.
[XEP-0156]
Hildebrand, J., Saint-Andre, P., and L. Stout,
"Discovering Alternative XMPP Connection Methods", XSF XEP
0156, January 2014.
[XEP-0198]
Karneges, J., Saint-Andre, P., Hildebrand, J., Forno, F.,
Cridland, D., and M. Wild, "Stream Management", XSF XEP
0198, June 2011.
[XEP-0199]
Saint-Andre, P., "XMPP Ping", XSF XEP 0199, June 2009.
[XEP-0206]
Paterson, I., Saint-Andre, P., and L. Stout, "XMPP Over
BOSH", XSF XEP 0206, November 2013.
[XML-SCHEMA]
Thompson, H., Maloney, M., Mendelsohn, N., and D. Beech,
"XML Schema Part 1: Structures Second Edition", World Wide
Web Consortium Recommendation REC-xmlschema-1-20041028,
October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.
Appendix A. XML Schema
The following schema formally defines the 'urn:ietf:params:xml:ns
:xmpp-framing' namespace used in this document, in conformance with
W3C XML Schema [XML-SCHEMA]. Because validation of XML streams and
stanzas is optional, this schema is not normative and is provided for
descriptive purposes only.
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:ietf:params:xml:ns:xmpp-framing'
xmlns='urn:ietf:params:xml:ns:xmpp-framing'
elementFormDefault='unqualified'>
<xs:element name='open'>
<xs:complexType>
<xs:simpleContent>
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<xs:extension base='empty'>
<xs:attribute name='from' type='xs:string'
use='optional'/>
<xs:attribute name='id' type='xs:string'
use='optional'/>
<xs:attribute name='to' type='xs:string'
use='optional'/>
<xs:attribute name='version' type='xs:decimal'
use='optional'/>
<xs:attribute ref='xml:lang'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:element name='close'>
<xs:complexType>
<xs:simpleContent>
<xs:extension base='empty'>
<xs:attribute name='from' type='xs:string'
use='optional'/>
<xs:attribute name='id' type='xs:string'
use='optional'/>
<xs:attribute name='see-other-uri' type='xs:anyURI'
use='optional'/>
<xs:attribute name='to' type='xs:string'
use='optional'/>
<xs:attribute name='version' type='xs:decimal'
use='optional'/>
<xs:attribute ref='xml:lang'
use='optional'/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
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Authors' Addresses
Lance Stout (editor)
&yet
Email: lance@andyet.net
Jack Moffitt
Mozilla
Email: jack@metajack.im
Eric Cestari
cstar industries
Email: eric@cestari.info
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