Internet DRAFT - draft-hirano-httpbis-websocket-over-http2
draft-hirano-httpbis-websocket-over-http2
HTTPbis Working Group Y. Hirano
Internet-Draft Google, Inc.
Intended status: Standards Track August 12, 2014
Expires: February 13, 2015
WebSocket over HTTP/2
draft-hirano-httpbis-websocket-over-http2-01
Abstract
The WebSocket protocol enables two-way communication between a client
running untrusted code in a controlled environment to a remote host
that has opted-in to communications from that code. Since it
requires one TCP connection for every WebSocket connection, having
multiple WebSocket connections between the same client and the same
server is inefficient. On the other hand, HTTP/2 specifies a fast,
secure, multiplexed framing protocol. This document provides bi-
directional multiplexed communication by layering WebSocket on top of
HTTP/2.
Please send feedback to the ietf-http-wg@w3.org mailing list.
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-
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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 13, 2015.
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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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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Document Organization . . . . . . . . . . . . . . . . . . 3
2. Conformance Requirements and Terminology . . . . . . . . . . 3
3. Cross Protocol Negotiation . . . . . . . . . . . . . . . . . 4
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. server preference . . . . . . . . . . . . . . . . . . . . 4
3.3. WebSocket over HTTP/2 capability . . . . . . . . . . . . 4
3.4. secure connection . . . . . . . . . . . . . . . . . . . . 5
3.5. the server's preference . . . . . . . . . . . . . . . . . 6
4. Opening Handshake . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Handshake Request . . . . . . . . . . . . . . . . . . . . 6
4.2. Handshake Response . . . . . . . . . . . . . . . . . . . 7
4.2.1. The Alt-Svc header . . . . . . . . . . . . . . . . . 7
5. Data Framing . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Closing the Connection . . . . . . . . . . . . . . . . . . . 8
6.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 8
6.1.1. Close the WebSocket Connection . . . . . . . . . . . 8
6.1.2. Start the WebSocket Closing Handshake . . . . . . . . 8
6.1.3. The WebSocket Closing Handshake is Started . . . . . 8
6.1.4. The WebSocket Connection is Closed . . . . . . . . . 8
6.1.5. The WebSocket Connection Close Code . . . . . . . . . 8
6.1.6. The WebSocket Connection Close Reason . . . . . . . . 9
6.1.7. Fail the WebSocket Connection . . . . . . . . . . . . 9
6.2. Abnormal Closures . . . . . . . . . . . . . . . . . . . . 9
6.2.1. Client-Initiated Closure . . . . . . . . . . . . . . 9
6.2.2. Server-initiated closure . . . . . . . . . . . . . . 9
6.2.3. Recovering from Abnormal Closure . . . . . . . . . . 9
6.3. Normal Closure of Connections . . . . . . . . . . . . . . 9
6.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. Registration of New SETTINGS parameter . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
The WebSocket protocol was standardized to enable efficient
bidirectional messaging mainly for browsers. However, the core spec
in RFC 6455 left one problem about scalability unaddressed. That is
that one WebSocket connection uses one TCP connection. Use of
multiple WebSocket connections provides flexibility for web apps,
while using more TCP connections leads to more load to the end hosts
and also to network intermediaries.
For the HTTP/1.1, there has been effort to multiplex HTTP traffic
into one TCP connection called HTTP/2. The HTTP/2 defines a general
multiplexed transport on which not only HTTP but other messaging
application protocol may be layered onto. We can address the
scalability issue of WebSocket by using HTTP/2 framing's multiplexing
functionality.
In this document, we describe how to layer WebSocket semantics onto
HTTP/2 semantics by defining detailed mapping, replacement of
operations and events defined in RFC 6455.
1.1. Document Organization
WebSocket over HTTP/2 is a protocol that layers the WebSocket
protocol over an HTTP/2 stream rather than a TCP connection. This
document introduces some abstractions and overrides some definitions
in [RFC6455]. Definitions in [RFC6455] not overridden by this
document such as Error Handling or Extensions are still valid.
Section 3 describes how to choose the protocol to use between native
WebSocket and WebSocket over HTTP/2 for each server. Each of
Section 4, Section 5 and Section 6 overrides definitions and rules in
its counterpart in [RFC6455].
2. Conformance Requirements and Terminology
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].
Requirements phrased in the imperative as part of algorithms (such as
"strip any leading space characters" or "return false and abort these
steps") are to be interpreted with the meaning of the key word
("MUST", "SHOULD", "MAY", etc.) used in introducing the algorithm.
Conformance requirements phrased as algorithms or specific steps can
be implemented in any manner, so long as the end result is
equivalent. In particular, the algorithms defined in this
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specification are intended to be easy to understand and are not
intended to be performant.
Native WebSocket means the WebSocket specified in [RFC6455].
"Frame" has two meanings, WebSocket frame and HTTP/2 frame. When it
is obvious "WebSocket" and "HTTP/2" can be omitted. For example,
"DATA frame" means "HTTP/2 DATA frame" and "Close frame" means
"WebSocket Close frame".
3. Cross Protocol Negotiation
3.1. Overview
_This section is non-normative._.
To establish a WebSocket connection, a client needs to decide the
protocol to use. Roughly speaking, if a client knows the server's
preference the client will connect to the server with the protocol.
Otherwise, the client tries to connect to the server with the native
WebSocket.
3.2. server preference
The server can tell its preference between the WebSocket over HTTP/2
and the native WebSocket by the following means.
o Sending [ALT-SVC] information to the client
o Selecting an ALPN protocol
3.3. WebSocket over HTTP/2 capability
When two endpoints and all intermediaries between them understand
WebSocket over HTTP/2, we say the communication path consisting of
these nodes is capable of WebSocket over HTTP/2.
The client MUST send a SETTINGS frame containing
SETTINGS_WEBSOCKET_CAPABLE before it starts the first WebSocket
opening handshake on a HTTP/2 connection.
The client knows if the communication path towards the server is
capable of WebSocket over HTTP/2 when the handshake response is
received.
o If status code of the response is other than 501 (Not
Implemented), the communication path is capable of WebSocket over
HTTP/2.
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o If status code of the response is 501 (Not Implemented), the
communication path is not capable of WebSocket over HTTP/2.
When the server receives a handshake from a client, the server MUST
send the server's opening handshake.
If the server has never received a SETTINGS frame that contains
SETTINGS_WEBSOCKET_CAPABLE on the HTTP/2 connection, the server MUST
send a 501 (Not Implemented) status code.
Otherwise, the server MUST NOT send a 501 (Not Implemented) status
code.
The client MAY start an opening handshake with WebSocket over HTTP/2
without knowing if the communication path is capable of WebSocket
over HTTP/2. When the status code of the opening handshake handshake
from the server is 501 (Not Implemented), the client MAY start
another opening handshake with the native WebSocket. If it comes to
that, the connection failure MUST not be reported to the upper layer.
NOTE: The server may reset the stream. In such a case, the client
doesn't know if the communication path is capable of WebSocket over
HTTP/2.
The client MUST not start an opening handshake with WebSocket over
HTTP/2 when it knows that the communication path is not capable of
WebSocket over HTTP/2.
3.4. secure connection
If the client knows that the server prefers WebSocket over HTTP/2
more than the native WebSocket and there is an existing HTTP/2
connection, the client create an HTTP/2 stream on the HTTP/2
connection.
Otherwise, the client sets up a TLS connection. The client SHOULD
send one or two of the following application protocols as
ProtocolNameList as specified in [ALPN] in any order.
o "http/1.1" for the native WebSocket over TLS
o "h2ws" for secure WebSocket over HTTP/2.
If the server selects the "h2ws" protocol, the client SHOULD connect
to the server with WebSocket over HTTP/2 on the TLS connection. If
the server selects the "http/1.1" protocol or the server does not
support ALPN, the client SHOULD connect to the server with the native
WebSocket on the TLS connection. If the server returns
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"no_application_protocol" alert, the client MUST _Fail the WebSocket
connection_.
3.5. the server's preference
The client SHOULD keep track of the [ALT-SVC] information provided by
the server and use it as the server's preference.
Note that though a client uses the ALPN protocol when it sets up a
TLS connection, it SHOULD not use the information after that.
4. Opening Handshake
4.1. Handshake Request
The client initiates an opening handshake by sending a HEADERS frame.
The frame MUST NOT set the END_STREAM flag because WebSocket intends
to establish a bi-directional communication port and to send
arbitrary data after success in opening handshake. The HEADERS Name/
Value section will contain all of the following headers which are
associated with the WebSocket protocol [RFC6455] opening handshake.
Upgrade, Connection, Sec-WebSocket-Key, and Sec-WebSocket-Version
headers MUST NOT be included because we do not have to take care of
protocol upgrading or verification over HTTP. The following name/
value pairs MUST be present in every request:
":path": /resource name/ as used in the "Client Requirements"
section of the WebSocket protocol specification. (See [RFC6455])
":authority": /host:port/ (e.g. "www.example.com:1234") as used in
the "Client Requirements" section of the WebSocket protocol
specification. (See [RFC6455])
"websocket-version": the WebSocket protocol version of this
request. MUST be "WebSocket/13".
":scheme": the scheme portion of the URI. MUST be "ws" or "wss".
(See also /secure/ flag in [RFC6455])
"websocket-origin": /origin/ as used in the "Client Requirements"
section of the WebSocket protocol specification. (See [RFC6455])
In addition, the following OPTIONAL name/value pairs MAY be present:
"sec-websocket-protocol" - the Sec-WebSocket-Protocol header (See
[RFC6455])
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"sec-websocket-extensions" - the Sec-WebSocket-Extensions header
(See [RFC6455])
Also, other HTTP compatible header name/value pairs MAY be present.
4.2. Handshake Response
The server responds to a client request with a HEADERS frame. If the
server intends to allow the client connection, the HEADERS frame MUST
NOT set the END_STREAM flag and MUST have ":status" containing "101".
Any status code other than 101 indicates that the WebSocket handshake
has not completed and that the semantics of HTTP still apply. The
client MAY send some data to the server before receiving the
successful response. The server MUST ignore this data when opening
handshake fails. After sending successful response, the server can
send arbitrary data frames at any time. The response status line is
unfolded into name/value pairs like other WebSocket handshake headers
and MUST be present: ":status" - The WebSocket or fallback HTTP
response status code (e.g. "101" or "101 Switching Protocols". See
[RFC6455]). In addition, the following OPTIONAL name/value pairs MAY
be present:
"sec-websocket-protocol" - the Sec-WebSocket-Protocol header (See
[RFC6455])
"sec-websocket-extensions" - the Sec-WebSocket-Extensions header
(See [RFC6455])
Also, other HTTP compatible header name/value pairs MAY be present.
All header names MUST be lowercase. The successful server response
MUST have ":status" containing "101".
4.2.1. The Alt-Svc header
When the Alt-Svc header field is contained in the handshake response,
the client SHOULD use the advertised service if possible. Note that
the Alt-Svc header field takes effect even for the handshake response
whose status code is not 101.
If the client receives an opening handshake response having the Alt-
Svc header field and the client is able to work with the advertised
service, the client SHOULD send a Close frame with code 1006 and
reason like "Alternate Service: h2ws" and then close the WebSocket
connection as soon as possible. These transactions MUST be hidden
and MUST NOT be notified to upper layers like the JavaScript event
queue. Then, the client SHOULD connect to the advertised server with
the advertised protocol.
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5. Data Framing
TO BE WRITTEN
6. Closing the Connection
Some definitions in [RFC6455] are overridden in this section.
6.1. Definitions
6.1.1. Close the WebSocket Connection
To _Close the WebSocket Connection_, an endpoint closes the
underlying HTTP/2 stream. If the stream is already closed, the
endpoint MUST do nothing. Otherwise, the endpoint MUST send an
RST_STREAM frame with an appropriate error code.
6.1.2. Start the WebSocket Closing Handshake
To _Start the WebSocket Closing Handshake_ with a status code
(Section 6.4) /code/ and an optional close reason (Section 6.1.6)
/reason/, an endpoint MUST send a Close control frame, as described
in [RFC6455] whose status code is set to /code/ and whose close
reason is set to /reason/. The last HTTP/2 frame of the WebSocket
Close control frame MUST turn END_STREAM flag on.
6.1.3. The WebSocket Closing Handshake is Started
Same as Section 7.1.3 in [RFC6455].
6.1.4. The WebSocket Connection is Closed
When the underlying HTTP stream is closed, it is said that _The
WebSocket Connection is Closed_ and that the WebSocket connection is
in the CLOSED state. If the stream was closed after the WebSocket
closing handshake was completed, the WebSocket connection is said to
have been closed _cleanly_.
If the WebSocket connection could not be established, it is also said
that _The WebSocket Connection is Closed_, but not cleanly.
6.1.5. The WebSocket Connection Close Code
Same as Section 7.1.5 in [RFC6455].
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6.1.6. The WebSocket Connection Close Reason
Same as Section 7.1.6 in [RFC6455].
6.1.7. Fail the WebSocket Connection
Same as Section 7.1.7 in [RFC6455].
6.2. Abnormal Closures
6.2.1. Client-Initiated Closure
If at any point the underlying HTTP/2 stream is unexpectedly
terminated, the client MUST _Fail the WebSocket Connection_.
Except as indicated above or as specified by the application layer
(e.g. a script using the WebSocket API), clients SHOULD NOT close the
connection.
6.2.2. Server-initiated closure
Same as Section 7.2.2 in [RFC6455].
6.2.3. Recovering from Abnormal Closure
Same as Section 7.2.3 in [RFC6455].
6.3. Normal Closure of Connections
Same as Section 7.3 in [RFC6455].
6.4. Status Codes
Same as Section 7.4 in [RFC6455].
7. Security Considerations
[RFC6455] frame has the masking mechanism for two purposes.
o To prevent a misbehavior of transparent proxies.
o To prevent TLS side-channel attacks such as [BEAST].
These should be addressed at the HTTP/2 framing layer and WebSocket
over HTTP/2 has no masking mechanism.
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8. IANA Considerations
8.1. Registration of New SETTINGS parameter
This section describes a new SETTINGS parameter.
SETTINGS_WEBSOCKET_CAPABLE(0xxx): The Client uses this parameter to
declare that it wants to use WebSocket over HTTP/2. This parameter
must be sent before creating any WebSocket over HTTP/2 stream in an
HTTP/2 connection.
9. References
9.1. Normative References
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
6455, December 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[HTTP-2] Belshe, M., Peon, R., Thomson, M., and A. Melnikov,
"Hypertext Transfer Protocol version 2", August 2014.
[ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application Layer Protocol
Negotiation Extension", March 2014.
[ALT-SVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP
Alternative Services", July 2014.
9.2. Informative References
[BEAST] Duong, T. and J. Rizzo, "The BEAST attack", 2011.
Author's Address
Yutaka Hirano
Google, Inc.
Email: yhirano@google.com
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