Internet DRAFT - draft-moffitt-xmpp-over-websocket
draft-moffitt-xmpp-over-websocket
HyBi Working Group L. Stout, Ed.
Internet-Draft &yet
Intended status: Standards Track J. Moffitt
Expires: February 20, 2014 E. Cestari
cstar industries
August 19, 2013
An XMPP Sub-protocol for WebSocket
draft-moffitt-xmpp-over-websocket-04
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 February 20, 2014.
Copyright Notice
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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 . . . . . . . . . . . . . . . . . . . . . . 4
3.5. Closing the Connection . . . . . . . . . . . . . . . . . 5
3.6. Stanzas . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.7. Stream Restarts . . . . . . . . . . . . . . . . . . . . . 6
3.8. Pings and Keepalives . . . . . . . . . . . . . . . . . . 6
3.9. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . 6
3.10. Stream Management . . . . . . . . . . . . . . . . . . . . 7
4. Discovering Connection Method . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Informative References . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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. 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] 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.
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 the Extensible Messaging and Presence Protocol
(XMPP).
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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].
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.
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
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[WebSocket connection established]
C: <stream:stream xmlns:stream="http://etherx.jabber.org/streams"
xmlns="jabber:client"
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.
Unless noted in text, the word "message" will mean a WebSocket
message composed of text data frames.
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.
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.
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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 SHOULD close the
XMPP stream, if it has been established, by sending a message with
the closing </stream:stream> tag. The XMPP stream is considered
closed when a corresponding </stream:stream> tag is received from the
other party.
If a client closes the WebSocket connection without closing the XMPP
stream after having enabled stream management (see Section 3.10), the
server SHOULD keep the XMPP session alive for a period of time based
on server policy, as specified in [XEP-0198].
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]).
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.
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
| | | |
| | </stream:stream> | |
| |------------------------------------>| |
| | </stream:stream> | |
| |<------------------------------------| |
| | | |
| | (XMPP Stream Closed) | |
| +-------------------------------------+ |
| |
| WS CLOSE FRAME |
|------------------------------------------>|
| WS CLOSE FRAME |
|<------------------------------------------|
| |
| (Connection Closed) |
+-------------------------------------------+
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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 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 stream tag.
S: <success xmlns="urn:ietf:params:xml:ns:xmpp-sasl" />
[Streams implicitly closed]
C: <stream:stream xmlns:stream="http://etherx.jabber.org/streams"
xmlns="jabber:client"
to="example.com"
version="1.0">
3.8. Pings and Keepalives
XMPP servers send whitespace pings as keepalives between stanzas, 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
extension (or both) MAY be used to determine the state of the
connection.
3.9. Use of TLS
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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 Connection Method
The XMPP extension Discovering Alternate XMPP Connection Methods
[XEP-0156] provides a mechanism to discover the additional
information needed to connect to an XMPP server outside of the
procedure defined in in Section 3 of [RFC6120].
For the XMPP over Websocket connection type, the connection method
name "_xmpp-client-websocket" is used to specify a URI for the
server's WebSocket connection endpoint.
An example entry advertising that the URI "wss://example.com/xmpp" is
an XMPP over WebSocket endpoint, using a DNS TXT record as specified
in [XEP-0156]:
_xmppconnect IN TXT "_xmpp-client-websocket=wss://example.com/xmpp"
Implementation Note: A server is able to expose both BOSH [XEP-0206]
and WebSocket endpoints over the registered port 5280, using the URI
path and connection upgrade headers to determine which transport to
serve.
5. Security Considerations
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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 at the WebSocket or other appropriate layer.
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.
6. IANA Considerations
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: RFC XXXX
[[NOTE TO RFC EDITOR: Please change XXXX to the number assigned to
this document upon publication.]]
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.
[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.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
6455, December 2011.
[W3C.REC-xml-20081126]
Sperberg-McQueen, C., Yergeau, F., Paoli, J., Bray, T.,
and E. Maler, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
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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-0156]
Hildebrand, J. and P. Saint-Andre, "Discovering
Alternative XMPP Connection Methods", XSF XEP 0156, June
2007.
[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. and P. Saint-Andre, "XMPP Over BOSH", XSF XEP
0206, July 2010.
Authors' Addresses
Lance Stout (editor)
&yet
Email: lance@andyet.net
Jack Moffitt
Email: jack@metajack.im
Eric Cestari
cstar industries
Email: eric@cestari.info
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