XMPP Working Group L. Stout, Ed.
Internet-Draft &yet
Intended status: Standards Track J. Moffitt
Expires: December 8, 2014 Mozilla
E. Cestari
cstar industries
June 6, 2014
An XMPP Sub-protocol for WebSocket
draft-ietf-xmpp-websocket-07
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
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 8, 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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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. WebSocket Messages . . . . . . . . . . . . . . . . . . . 4
3.3. XMPP Framing . . . . . . . . . . . . . . . . . . . . . . 4
3.3.1. Framed XML Stream . . . . . . . . . . . . . . . . . . 4
3.3.2. Framed Stream Namespace . . . . . . . . . . . . . . . 5
3.3.3. Stream Frames . . . . . . . . . . . . . . . . . . . . 5
3.4. Stream Initiation . . . . . . . . . . . . . . . . . . . . 6
3.5. Stream Errors . . . . . . . . . . . . . . . . . . . . . . 6
3.6. Closing the Connection . . . . . . . . . . . . . . . . . 7
3.6.1. see-other-uri . . . . . . . . . . . . . . . . . . . . 8
3.7. Stream Restarts . . . . . . . . . . . . . . . . . . . . . 8
3.8. Pings and Keepalives . . . . . . . . . . . . . . . . . . 8
3.9. Use of TLS . . . . . . . . . . . . . . . . . . . . . . . 9
3.10. Stream Management . . . . . . . . . . . . . . . . . . . . 9
4. Discovering the WebSocket Connection Method . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5.1. WebSocket Subprotocol Name . . . . . . . . . . . . . . . 10
5.2. URN Sub-Namespace . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6.1. Intermediary Services . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. XML Schema . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
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
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these kinds of problems and is a bidirectional protocol that provides
a simple message-based framing layer over raw sockets, allowing 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 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", "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
value |xmpp| in the list of protocols for the |Sec-WebSocket-
Protocol| header. 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" />
S: <open xmlns="urn:ietf:params:xml:ns:xmpp-framing"
from="example.com"
id="++TR84Sm6A3hnt3Q065SnAbbk3Y="
xml:lang="en"
version="1.0" />
3.2. WebSocket Messages
Data frame messages in the XMPP sub-protocol MUST be of the text type
and contain UTF-8 encoded data.
3.3. XMPP Framing
The WebSocket XMPP sub-protocol deviates from the standard method of
constructing and using XML streams as defined in [RFC6120] by
adopting the message framing provided by WebSocket to delineate the
stream open and close headers, stanzas, and other top-level stream
elements.
3.3.1. Framed XML Stream
The start of a framed XML stream is marked by the use of an opening
"stream header" which is an <open/> element with the appropriate
attributes and namespace declarations (see Section 3.3.2). The
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attributes of the <open/> element are the same as those of the
<stream/> element defined defined for the 'http://etherx.jabber.org/
streams' namespace in [RFC6120] and with the same semantics and
restrictions.
The end of a framed XML stream is denoted by the closing "stream
header" which is a <close/> element with its associated attributes
and namespace declarations (see Section 3.3.2).
The introduction of the <open/> and <close/> elements is motivated by
the parsable XML document framing restriction in Section 3.3.3. As a
consequence, note that a framed XML stream does not provided a
wrapping <stream:stream/> element encompassing the entirety of the
XML stream, as in [RFC6120].
3.3.2. Framed Stream Namespace
The XML stream "headers" (the <open/> and <close/> elements) MUST be
qualified by the namespace 'urn:ietf:params:xml:ns:xmpp-framing' (the
"framed stream namespace"). If this rule is violated, the entity
that receives the offending stream header MUST close the stream with
an error, which MUST be <invalid-namespace> (see Section 4.9.3.10 of
[RFC6120]).
3.3.3. Stream Frames
The individual frames of a framed XML stream have a one-to-one
correspondence with WebSocket messages, and MUST be parsable as
standalone XML documents, complete with all relevant namespace and
language declarations. The inclusion of XML declarations, however,
is NOT RECOMMENDED as WebSocket messages are already mandated to be
UTF-8 encoded and therefore would only add a constant size overhead
to each message.
The first character of each frame MUST be a '<' character.
Every XMPP stanza or other XML element (including the stream open and
close headers) sent directly over the XML stream MUST be sent in its
own frame.
Example of a WebSocket message that contains an independently
parsable XML document:
<message xmlns="jabber:client" xml:lang="en">
<body>Every WebSocket message is parsable by itself.</body>
</message>
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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 prefix MUST be declared or use an unprefixed form:
<stream:features xmlns:stream="http://etherx.jabber.org/streams">
<bind xmlns="urn:ietf:params:xml:ns:xmpp-bind"/>
</stream:features>
-- OR --
<error xmlns="http://etherx.jabber.org/streams">
<host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
</error>
3.4. Stream Initiation
The first message sent after the WebSocket opening handshake MUST be
from the initiating entity, and MUST be an <open/> element qualified
by the "urn:ietf:params:xml:ns:xmpp-framing" namespace and with the
same attributes mandated for the <stream> opening tag as described in
Section 4.7 of [RFC6120].
The receiving entity MUST respond with either an <open /> element
(whose attributes match those described in Section 4.7 of [RFC6120])
or a <close /> element (see Section 3.6.1).
An example of a successful stream initiation exchange:
C: <open xmlns="urn:ietf:params:xml:ns:xmpp-framing"
to="example.com"
version="1.0" />
S: <open xmlns="urn:ietf:params:xml:ns:xmpp-framing"
from="example.com"
id="++TR84Sm6A3hnt3Q065SnAbbk3Y="
xml:lang="en"
version="1.0" />
Clients MUST NOT multiplex XMPP streams over the same WebSocket.
3.5. 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
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error in a second WebSocket message frame. The server MUST then
close the connection as specified in Section 3.6.
3.6. Closing the Connection
The closing process for the XMPP sub-protocol mirrors that of the
XMPP TCP binding as defined in Section 4.4 of [RFC6120], except that
a <close/> element is used instead of the ending </stream:stream>
tag.
Either the server or the client may close the connection at any time.
Before closing the connection, the closing party is expected to first
close the XMPP stream (if one has been opened) 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, and
the XMPP session is ended.
To then close the WebSocket connection, the closing party MUST
initiate the WebSocket closing handshake (see Section 7.1.2 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 the WebSocket connection is closed or broken without the XMPP
stream having been closed first, then the XMPP stream is considered
implicitly closed and the XMPP session ended; however, if the use of
stream management resumption was negotiated (see [XEP-0198]), the
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server SHOULD consider the XMPP session still alive for a period of
time based on server policy as specified in [XEP-0198].
3.6.1. see-other-uri
If the server wishes at any point 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 connection endpoint (which MAY be for
a different transport method, such as BOSH (see [XEP-0124] and
[XEP-0206]).
Clients MUST NOT accept suggested endpoints with a lower security
context (e.g. moving from a "wss://" endpoint to a "ws://" or "http:/
/" 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" />
3.7. Stream Restarts
Whenever a stream restart is mandated, both the server and client
streams are implicitly closed and new streams MUST be opened, using
the same process as in Section 3.4. The client MUST send a new
stream <open/> element and MUST NOT send a closing <close/> element.
An example of restarting the stream after successful SASL
negotiation:
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
Traditionally, XMPP servers and clients often send "whitespace
keepalives" (see Section 4.6.1 of [RFC6120]) between stanzas to
maintain an XML stream. However, for the XMPP sub-protocol, each
message is required to start with a '<' character, and as such
whitespace keepalives MUST NOT be used.
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As alternatives, the XMPP Ping extension [XEP-0199] and the XMPP
Stream Management extension [XEP-0198] provide pinging mechanisms.
The use of either of these extensions (or both) MAY be used to
determine the state of the connection.
Clients and servers MAY also use WebSocket ping control frames for
this purpose, but note that some environments, such as browsers, do
not provide access for generating or monitoring ping control frames.
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,
when TLS is used, it MUST be enabled 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.
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<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>
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>
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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"
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.
6.1. Intermediary Services
If the XMPP over WebSocket endpoint is provided as an intermediary
service between a backend XMPP service and the client, then it SHOULD
encrypt its connection to the backend XMPP service using any
available and appropriate technologies, such as TLS and StartTLS.
If data privacy is desired, a client SHOULD encrypt its messages
using an application specific end-to-end encryption technology, as
there is no way for the client to ensure that the XMPP over WebSocket
service is using an encryped connection to the backend XMPP service.
Methods for doing so are beyond the scope of this specification.
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.
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[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.
[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.
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[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>
<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'/>
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<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>
Authors' Addresses
Lance Stout (editor)
&yet
Email: lance@andyet.net
Jack Moffitt
Mozilla
Email: jack@metajack.im
Eric Cestari
cstar industries
Email: eric@cstar.io
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