HyBi Working Group J. Moffitt, Ed.
Internet-Draft
Intended status: Standards Track E. Cestari
Expires: December 27, 2012 ProcessOne
June 25, 2012
An XMPP Sub-protocol for WebSocket
draft-moffitt-xmpp-over-websocket-01
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
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 27, 2012.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. XMPP Sub-Protocol . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. XMPP Stream Setup . . . . . . . . . . . . . . . . . . . . 5
3.4. Stream Errors . . . . . . . . . . . . . . . . . . . . . . 6
3.5. Closing the Connection . . . . . . . . . . . . . . . . . . 6
3.6. Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.7. Stream Restarts . . . . . . . . . . . . . . . . . . . . . 6
3.8. Pings and Keepalives . . . . . . . . . . . . . . . . . . . 6
3.9. TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Informative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Applications using 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.
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] now exists to
solve these kinds of problems. The WebSocket protocol is a bi-
directional protocol that provides a simple message-based framing
layer over raw sockets and allows for more robust and efficient
communication in web applications.
This document defines a binding of the XMPP protocol over the
WebSocket protocol transport. It makes using XMPP within web
applications simpler and more efficient.
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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 whose top-level element name is message. In this
document, the word "message" will mean a WebSocket message, not an
XMPP message stanza (see Section 3.2).
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].
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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.
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.
Unless noted in text, the word "message" will mean a WebSocket
message containing a text data frame.
3.3. XMPP Stream Setup
The first message sent after the handshake is complete MUST be an
XMPP opening stream tag as defined in XMPP [RFC6120] or an XML text
declaration (see Section 4.3.1 of [W3C.REC-xml-20081126]) followed by
an XMPP opening stream tag. The stream tag MUST NOT be closed (i.e.
the closing </stream:stream> tag should not appear in the message) as
it is the start of the client's outgoing XML. The '<' character of
the tag or text declaration MUST be the first character of the text
payload.
The server MUST respond with a message containing an error (see
Section 3.4), its own opening stream tag, or an XML text declaration
followed by an opening stream tag.
Except in the case of certain stream errors (see Section 3.4), the
opening stream tag, <stream:stream>, MUST appear in a message by
itself.
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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 stream error
message MUST start with an opening stream tag (see Section 4.7.1 of
[RFC6120]) and end with a closing stream tag.
After the stream error and closing stream tag have been sent, the
server MUST close the connection as 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 MUST close the XMPP
stream if it has been established. To initiate the close, 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]).
Except in the case of certain stream errors (see Section 3.4), the
closing stream tag, </stream:stream>, MUST appear in a message by
itself.
3.6. Stanzas
Each XMPP stanza MUST be sent in its own message. A stanza MUST NOT
be split over multiple messages. All first level children of the
<stream:stream> element MUST be treated the same as stanzas (e.g.
<stream:features> and <stream:error>).
3.7. Stream Restarts
After successful SASL authentication, an XMPP stream must 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 must be opened.
The client MUST open a new stream as in Section 3.3 and MUST NOT send
a closing stream tag.
3.8. Pings and Keepalives
XMPP servers send whitespace pings as keepalives between stanzas, and
XMPP clients can do the same thing. These extra whitespace
characters are not significant in the protocol. Servers and clients
SHOULD use WebSocket ping messages instead for this purpose.
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The XMPP Ping extension [XEP-0199] allows entities to send and
respond to ping requests. A client sending a WebSocket ping is
equivalent to pinging the WebSocket server, which may also be the
XMPP server. When the XMPP server is not also the WebSocket server,
a WebSocket ping may be useful to check the health of the
intermediary server.
3.9. TLS
TLS cannot be used in The XMPP sub-protocol because the sub-protocol
does not allow for raw binary data to be sent. A server MUST NOT
advertise TLS as a stream feature (see Section 4.6 of [RFC6120]). A
client MUST ignore the TLS feature if it is advertised over
WebSocket.
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4. Examples
Examples will be added as soon as the WebSocket protocol
specification is more stable.
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5. IANA Considerations
If a registry is created for WebSocket sub-protocols, the xmpp sub-
protocol will be registered.
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6. Security Considerations
Since application level TLS cannot be used (see Section 3.9),
applications which need to protect the privacy of the XMPP traffic
need to do so a the WebSocket level or some other higher level.
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7. Informative 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.
[RFC6121] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Instant Messaging and Presence",
RFC 6121, March 2011.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, December 2011.
[W3C.REC-xml-20081126]
Sperberg-McQueen, C., Yergeau, F., Maler, E., Paoli, J.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>.
[XEP-0124]
Paterson, I., Smith, D., Saint-Andre, P., and J. Moffitt,
"Bidirectional-streams Over Synchronous HTTP (BOSH)", XSF
XEP 0124, July 2010.
[XEP-0199]
Saint-Andre, P., "XMPP Ping", XSF XEP 0199, June 2009.
[XEP-0206]
Paterson, I. and P. Saint-Andre, "XMPP Over BOSH", XSF
XEP 0206, July 2010.
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Authors' Addresses
Jack Moffitt (editor)
Email: jack@metajack.im
Eric Cestari
ProcessOne
Email: ecestari@process-one.com
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