HYBI Working Group G. Montenegro, Ed.
Internet-Draft Microsoft Corporation
Intended status: Informational M. Stachowiak, Ed.
Expires: February 24, 2011 Apple
August 23, 2010
HyBi WebSocket Requirements and Features
draft-ietf-hybi-websocket-requirements-01
Abstract
This document considers the requirements and resulting features
needed for the design of the WebSocket Protocol. The goal of the
document is to provide a stable base for protocol design and related
discussion.
Requirements Language
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 RFC 2119 [RFC2119].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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 February 24, 2011.
Copyright Notice
Copyright (c) 2010 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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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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. WebSocket Requirements . . . . . . . . . . . . . . . . . . . . 4
3.1. WebSocket Client Requirements . . . . . . . . . . . . . . . 5
3.2. WebSocket Server Requirements . . . . . . . . . . . . . . . 6
3.3. WebSocket Proxies Requirements . . . . . . . . . . . . . . 6
3.4. WebSocket Security Requirements . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
HTTP [RFC2616] is a client/server protocol, where the HTTP servers
store the data and provide it when it is requested by clients. When
used to retrieve data from an HTTP server, the client sends HTTP
requests to the server, and the server returns the requested data in
HTTP responses. So the client has to poll continuously the server in
order to receive new data.
Recently, techniques that enable bidirectional communication over
HTTP have become more pervasive. Those techniques reduce the need to
poll continuously the server thanks to the usage of HTTP hanging
requests and multiple connections between the client and the server
[I-D.ietf-hybi-design-space].
The goal of HyBi is to provide an efficient and clean two-way
communication channel between client and server.
The communication channel will:
o Allow each side to, independently from the other, send data when
it is willing and ready to do so.
o Rely on a single TCP connection for traffic in both directions.
o Reduce the high overhead produced by HTTP headers in each request/
response.
The goal of this work is to provide the set of requirements the
WebSocket Protocol MUST meet.
In the following sections we list and analyse the requirements from
the perspective of clients and servers.
2. Terminology
This document uses the following HyBi-related terms:
connection: A transport layer virtual circuit established between a
client and a server for the purpose of communication.
frame: The basic unit of WebSocket communication, consisting of a
structured sequence of octets matching the syntax defined in the
actual protocol and transmitted on the established communication
channel.
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message: user message: a block of related data with identified
boundaries. A message may comprise multiple frames.
origin server: The server on which a given resource resides or is to
be created.
WebSocket handshake: The process (and associated capability
negotiation) that sets up the WebSocket communication channel.
WebSocket communication channel: After the WebSocket handshake is
complete, the resultant bi-directional communication path between
client and server over the transport (e.g., TCP, or SSL over TCP).
WebSocket sub-protocol: The negotiated sub-protocol for use on a
WebSocket communication channel that dictates framing, encoding,
etc.
3. WebSocket Requirements
The following requirements for the WebSocket Protocol have been
identified both in the HyBi wg input document
[I-D.ietf-hybi-thewebsocketprotocol] and in the HyBi mailing list
dicussion.
REQ. 1: The WebSocket Protocol MUST run directly on top of the
transport protocol (over which the communication was running up to
and including the WebSocket handshake).
REQ. 2: The WebSocket Protocol MUST be able to handle (send and
receive) messages on the transport protocol (over which the
communication was running up to and including the WebSocket
handshake).
Reason: transfer data as message obviates the need for the receiver
to parse/handle partial content.
REQ. 3: The protocol MUST support the ability to fragment a message
into frames of a given length.
REQ. 4: It MUST be possible to send a message when the total size is
either unknown or exceeds a fixed buffer size.
Reason: This will allow dynamic messages to be constructed and sent
without the need to buffer the entire message.
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REQ. 5: Textual data MUST be encoded as UTF-8.
REQ. 6: The protocol MUST support and clearly distinguish between
textual and binary data types (e.g. binary) via a common framing
with explicit length indication.
REQ. 7: The WebSocket protocol MUST allow HTTP and WebSocket
connections to be served from the same port. Consideration MUST
be given:
* to provide WebSocket services via modules that plug in to
existing web infrastructure.
* to making it possible and practical to implement standalone
implementations of the protocol without requiring a fully
conforming HTTP implementation.
Reason: Some server developers would like to integrate WebSocket
support into existing HTTP servers. In addition, the default HTTP
and HTTPS ports are ofter favoured for traffic that has to go through
a firewall, so service providers will likely want to be able to use
WebSocket over ports 80 and 443, even when running a Web server on
the same host. However there could be scenarios where it is not
opportune or possible to setup a proxy on the same HTTP server.
REQ. 8: If using an HTTP Upgrade exchange in the WebSocket
handshake, the protocol MUST be HTTP compatible up to and
including the Upgrade exchange.
REQ. 9: The protocol SHOULD make it possible and practical to reuse
existing HTTP components where appropriate.
Reason: Reusing existing well-debugged software decreases the number
of implementation errors as well as the possibility to introduce
security holes, and increases development speed, especially when the
WebSocket server is implemented as modules that plug in to existing
popular Web servers.
3.1. WebSocket Client Requirements
REQ. 10: The WebSocket Client MUST be able to set up a communication
channel with a WebSocket Server using a well-defined handshake.
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REQ. 11: The WebSocket Protocol MUST provide for graceful close of
an active WebSocket connection on request from the user
Application.
Reason: a clean shutdown signals that the other endpoint has
definitely received all the messages sent prior to the close, so
there is no protocol uncertainty about what has been processed and
what can be retried on another connection.
REQ. 12: WebSocket Protocol MUST also allow ungraceful close, either
on request from the user application or as a result of a detected
error condition.
REQ. 13: The WebSocket Client MUST be able to request the server,
during the handshake, to use a specific WebSocket sub-protocol.
REQ. 14: The WebSocket Client MUST have the ability to send and
clearly distinguish between arbitrary text or binary content to
the server on the established communication channel.
3.2. WebSocket Server Requirements
REQ. 15: The WebSocket Server that accepts to set up a communication
channel with a WebSocket Client MUST use a well-defined handshake.
REQ. 16: The WebSocket Server MUST have the ability to send and
clearly distinguish between arbitrary text or binary content to
the client on the established communication channel.
3.3. WebSocket Proxies Requirements
Todo
REQ. 17: The WebSocket protocol MUST work over existing proxies to
the same extent as HTTP or HTTPS already does.
Reason: This is in line with Req on HTTP compliance.
3.4. WebSocket Security Requirements
REQ. 18: The WebSocket Protocol MUST use the Origin-based security
model commonly used by Web browsers to restrict which Web pages
can contact a WebSocket sever when the WebSocket protocol is used
from a Web page.
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REQ. 19: When used directly (not from a Web page), the WebSocket
Protocol MUST use a security model equivalent to that of direct
HTTP or HTTPS usage.
REQ. 20: WebSocket should be designed to be robust against cross-
protocol attacks. The protocol design should consider and
mitigate the risk presented by WebSocket clients to existing
servers (including HTTP servers). It should also consider and
mitigate the risk to WebSocket servers presented by clients for
other protocols (including HTTP).
Reason: As the WebSocket protocol is expected to be often used in
browsers, a careful design is necessary to mitigate the chances for
hostile JavaScript to use WebSocket for a cross-protocol attack
against vanilla HTTP resources or non-HTTP servers. More the design
should prevent the possibility for cross-site XMLHttpRequest (using
CORS or XDomainRequest) to be used for a cross-protocol attack
against WebSocket resources, potentially violating integrity (though
not confidentiality).
4. Security Considerations
5. IANA Considerations
This requirements document does not mandate any immediate IANA
actions. However, such IANA considerations may arise from future
HyBi specification documents which try to meet the requirements given
here.
6. Acknowledgments
The initial requirements were created by Salvatore Loreto. Thanks to
Greg Wilkins for fulfilling previous editing duties.
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.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
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Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[I-D.ietf-hybi-thewebsocketprotocol]
Hickson, I., "The WebSocket protocol",
draft-ietf-hybi-thewebsocketprotocol-00 (work in
progress), May 2010.
7.2. Informative References
[I-D.ietf-hybi-design-space]
Moffitt, J., Loreto, S., Saint-Andre, P., and S. Salsano,
"Design Space for Bidirectional Protocols",
draft-ietf-hybi-design-space-00 (work in progress),
June 2010.
Appendix A. Change Log (to be removed by RFC Editor before publication)
From version -00 to version -01:
o Modified definition of a Message to reflect recent consensus that
it may comprise multiple frames.
o Added definitions for WebSocket handshake, WebSocket communication
channel and WebSocket sub-protocol.
o Updated references to official IETF documents, moved "design-
space" to informational.
o Added a new requirement to support the ability to fragment a
message into frames of a given length
o Reworded Req 5 to reflect recent consensus on "binary+data" as
well as common framing with explicit length indication
o Reworded Req 7 to reflect recent consensus (declared in
Maastricht) on "HTTP compliance"
o Reworded Req 12 and 13 into a single Req on the client being able
to send text or binary content. Elided mention of "discrete
blocks" as the structure of messages is captured elsewhere.
o Reworded Req 15 and 16 into a single Req on the server being able
to send text or binary content. Elided mention of "discrete
blocks" as the structure of messages is captured elsewhere.
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o Added a requirement in the proxies requirements section along the
lines of the HTTP compliance requirement, per consensus declared
in Maastricht.
o Modified security requirement when used from outside a browser to
avoid wording in terms of a security model equivalent to that of
browser-based usage.
o Various editorial changes.
Authors' Addresses
Gabriel Montenegro (editor)
Microsoft Corporation
One Microsoft Way
Redmond 98052
USA
Email: gabriel.montenegro@microsoft.com
Maciej Stachowiak (editor)
Apple
Email: mjs@apple.com
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