[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: (draft-hixie-thewebsocketprotocol)
00 01 02 03 04 05 06 07 08 09 10 11
12 13 14 15 16 17 RFC 6455
HyBi Working Group I. Fette
Internet-Draft Google, Inc.
Intended status: Standards Track A. Melnikov
Expires: March 3, 2012 Isode Ltd
August 31, 2011
The WebSocket protocol
draft-ietf-hybi-thewebsocketprotocol-13
Abstract
The WebSocket protocol enables two-way communication between a client
running untrusted code running in a controlled environment to a
remote host that has opted-in to communications from that code. The
security model used for this is the Origin-based security model
commonly used by Web browsers. The protocol consists of an opening
handshake followed by basic message framing, layered over TCP. The
goal of this technology is to provide a mechanism for browser-based
applications that need two-way communication with servers that does
not rely on opening multiple HTTP connections (e.g. using
XMLHttpRequest or <iframe>s and long polling).
Please send feedback to the hybi@ietf.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-
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 March 3, 2012.
Copyright Notice
Copyright (c) 2011 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
Fette & Melnikov Expires March 3, 2012 [Page 1]
Internet-Draft The WebSocket protocol August 2011
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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Protocol Overview . . . . . . . . . . . . . . . . . . . . 5
1.3. Opening Handshake . . . . . . . . . . . . . . . . . . . . 7
1.4. Closing Handshake . . . . . . . . . . . . . . . . . . . . 9
1.5. Design Philosophy . . . . . . . . . . . . . . . . . . . . 10
1.6. Security Model . . . . . . . . . . . . . . . . . . . . . . 11
1.7. Relationship to TCP and HTTP . . . . . . . . . . . . . . . 12
1.8. Establishing a Connection . . . . . . . . . . . . . . . . 12
1.9. Subprotocols Using the WebSocket protocol . . . . . . . . 12
2. Conformance Requirements . . . . . . . . . . . . . . . . . . . 14
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 14
3. WebSocket URIs . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Opening Handshake . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Client Requirements . . . . . . . . . . . . . . . . . . . 17
4.2. Server-side Requirements . . . . . . . . . . . . . . . . . 22
4.2.1. Reading the Client's Opening Handshake . . . . . . . . 23
4.2.2. Sending the Server's Opening Handshake . . . . . . . . 24
4.3. Collected ABNF for new header fields used in handshake . . 27
5. Data Framing . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.2. Base Framing Protocol . . . . . . . . . . . . . . . . . . 29
5.3. Client-to-Server Masking . . . . . . . . . . . . . . . . . 33
5.4. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 34
5.5. Control Frames . . . . . . . . . . . . . . . . . . . . . . 36
5.5.1. Close . . . . . . . . . . . . . . . . . . . . . . . . 36
5.5.2. Ping . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.5.3. Pong . . . . . . . . . . . . . . . . . . . . . . . . . 37
5.6. Data Frames . . . . . . . . . . . . . . . . . . . . . . . 38
5.7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 38
5.8. Extensibility . . . . . . . . . . . . . . . . . . . . . . 39
6. Sending and Receiving Data . . . . . . . . . . . . . . . . . . 40
6.1. Sending Data . . . . . . . . . . . . . . . . . . . . . . . 40
6.2. Receiving Data . . . . . . . . . . . . . . . . . . . . . . 40
7. Closing the connection . . . . . . . . . . . . . . . . . . . . 42
7.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 42
Fette & Melnikov Expires March 3, 2012 [Page 2]
Internet-Draft The WebSocket protocol August 2011
7.1.1. Close the WebSocket Connection . . . . . . . . . . . . 42
7.1.2. Start the WebSocket Closing Handshake . . . . . . . . 42
7.1.3. The WebSocket Closing Handshake is Started . . . . . . 42
7.1.4. The WebSocket Connection is Closed . . . . . . . . . . 43
7.1.5. The WebSocket Connection Close Code . . . . . . . . . 43
7.1.6. The WebSocket Connection Close Reason . . . . . . . . 43
7.1.7. Fail the WebSocket Connection . . . . . . . . . . . . 44
7.2. Abnormal Closures . . . . . . . . . . . . . . . . . . . . 44
7.2.1. Client-Initiated Closure . . . . . . . . . . . . . . . 44
7.2.2. Server-Initiated Closure . . . . . . . . . . . . . . . 45
7.2.3. Recovering From Abnormal Closure . . . . . . . . . . . 45
7.3. Normal Closure of Connections . . . . . . . . . . . . . . 45
7.4. Status Codes . . . . . . . . . . . . . . . . . . . . . . . 45
7.4.1. Defined Status Codes . . . . . . . . . . . . . . . . . 46
7.4.2. Reserved Status Code Ranges . . . . . . . . . . . . . 47
8. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 49
8.1. Handling Errors in UTF-8 Encoded Data . . . . . . . . . . 49
9. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9.1. Negotiating Extensions . . . . . . . . . . . . . . . . . . 50
9.2. Known Extensions . . . . . . . . . . . . . . . . . . . . . 51
10. Security Considerations . . . . . . . . . . . . . . . . . . . 52
10.1. Non-Browser Clients . . . . . . . . . . . . . . . . . . . 52
10.2. Origin Considerations . . . . . . . . . . . . . . . . . . 52
10.3. Attacks On Infrastructure (Masking) . . . . . . . . . . . 53
10.4. Implementation-Specific Limits . . . . . . . . . . . . . . 54
10.5. WebSocket client authentication . . . . . . . . . . . . . 54
10.6. Connection confidentiality and integrity . . . . . . . . . 55
10.7. Handling of invalid data . . . . . . . . . . . . . . . . . 55
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 56
11.1. Registration of new URI Schemes . . . . . . . . . . . . . 56
11.1.1. Registration of "ws" Scheme . . . . . . . . . . . . . 56
11.1.2. Registration of "wss" Scheme . . . . . . . . . . . . . 57
11.2. Registration of the "WebSocket" HTTP Upgrade Keyword . . . 58
11.3. Registration of new HTTP Header Fields . . . . . . . . . . 58
11.3.1. Sec-WebSocket-Key . . . . . . . . . . . . . . . . . . 58
11.3.2. Sec-WebSocket-Extensions . . . . . . . . . . . . . . . 59
11.3.3. Sec-WebSocket-Accept . . . . . . . . . . . . . . . . . 60
11.3.4. Sec-WebSocket-Protocol . . . . . . . . . . . . . . . . 60
11.3.5. Sec-WebSocket-Version . . . . . . . . . . . . . . . . 61
11.4. WebSocket Extension Name Registry . . . . . . . . . . . . 62
11.5. WebSocket Subprotocol Name Registry . . . . . . . . . . . 62
11.6. WebSocket Version Number Registry . . . . . . . . . . . . 63
11.7. WebSocket Close Code Number Registry . . . . . . . . . . . 64
11.8. WebSocket Opcode Registry . . . . . . . . . . . . . . . . 66
11.9. WebSocket Framing Header Bits Registry . . . . . . . . . . 67
12. Using the WebSocket protocol from Other Specifications . . . . 68
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 69
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Fette & Melnikov Expires March 3, 2012 [Page 3]
Internet-Draft The WebSocket protocol August 2011
14.1. Normative References . . . . . . . . . . . . . . . . . . . 70
14.2. Informative References . . . . . . . . . . . . . . . . . . 71
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 73
Fette & Melnikov Expires March 3, 2012 [Page 4]
Internet-Draft The WebSocket protocol August 2011
1. Introduction
1.1. Background
_This section is non-normative._
Historically, creating Web applications that need bidirectional
communication between a client and a server (e.g., instant messaging
and gaming applications) has required an abuse of HTTP to poll the
server for updates while sending upstream notifications as distinct
HTTP calls.[RFC6202]
This results in a variety of problems:
o The server is forced to use a number of different underlying TCP
connections for each client: one for sending information to the
client, and a new one for each incoming message.
o The wire protocol has a high overhead, with each client-to-server
message having an HTTP header.
o The client-side script is forced to maintain a mapping from the
outgoing connections to the incoming connection to track replies.
A simpler solution would be to use a single TCP connection for
traffic in both directions. This is what the WebSocket protocol
provides. Combined with the WebSocket API, it provides an
alternative to HTTP polling for two-way communication from a Web page
to a remote server. [WSAPI]
The same technique can be used for a variety of Web applications:
games, stock tickers, multiuser applications with simultaneous
editing, user interfaces exposing server-side services in real time,
etc.
1.2. Protocol Overview
_This section is non-normative._
The protocol has two parts: a handshake, and then the data transfer.
The handshake from the client looks as follows:
Fette & Melnikov Expires March 3, 2012 [Page 5]
Internet-Draft The WebSocket protocol August 2011
GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Origin: http://example.com
Sec-WebSocket-Protocol: chat, superchat
Sec-WebSocket-Version: 13
The handshake from the server looks as follows:
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Protocol: chat
The leading line from the client follows the Request-Line format.
The leading line from the server follows the Status-Line format. The
Request-Line and Status-Line productions are defined in [RFC2616].
After the leading line in both cases come an unordered set of header
fields. The meaning of these header fields is specified in Section 4
of this document. Additional header fields may also be present, such
as cookies [RFC6265]. The format and parsing of headers is as
defined in [RFC2616].
Once the client and server have both sent their handshakes, and if
the handshake was successful, then the data transfer part starts.
This is a two-way communication channel where each side can,
independently from the other, send data at will.
Clients and servers, after a successful handshake, transfer data back
and forth in conceptual units referred to in this specification as
"messages". On the wire a message is composed of one or more frames.
The WebSocket message does not necessarily correspond to a particular
network layer framing, as a fragmented message may be coalesced or
split by an intermediary.
A frame has an associated type. Each frame belonging to the same
message contain the same type of data. Broadly speaking, there are
types for textual data, which is interpreted as UTF-8 [RFC3629] text,
binary data (whose interpretation is left up to the application), and
control frames, which are not intended to carry data for the
application, but instead for protocol-level signaling, such as to
signal that the connection should be closed. This version of the
protocol defines six frame types and leaves ten reserved for future
Fette & Melnikov Expires March 3, 2012 [Page 6]
Internet-Draft The WebSocket protocol August 2011
use.
1.3. Opening Handshake
_This section is non-normative._
The opening handshake is intended to be compatible with HTTP-based
server-side software and intermediaries, so that a single port can be
used by both HTTP clients talking to that server and WebSocket
clients talking to that server. To this end, the WebSocket client's
handshake is an HTTP Upgrade request:
GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Origin: http://example.com
Sec-WebSocket-Protocol: chat, superchat
Sec-WebSocket-Version: 13
In compliance with [RFC2616], header fields in the handshake may be
sent by the client in any order, so the order in which different
header fields are received is not significant.
The "Request-URI" of the GET method [RFC2616] is used to identify the
endpoint of the WebSocket connection, both to allow multiple domains
to be served from one IP address and to allow multiple WebSocket
endpoints to be served by a single server.
The client includes the hostname in the Host header field of its
handshake as per [RFC2616], so that both the client and the server
can verify that they agree on which host is in use.
Additional header fields are used to select options in the WebSocket
protocol. Typical options available in this version are the
subprotocol selector (|Sec-WebSocket-Protocol|), list of extensions
support by the client (|Sec-WebSocket-Extensions|), |Origin| header
field, etc. The |Sec-WebSocket-Protocol| request-header field can be
used to indicate what subprotocols (application-level protocols
layered over the WebSocket protocol) are acceptable to the client.
The server selects one or none of the acceptable protocols and echoes
that value in its handshake to indicate that it has selected that
protocol.
Sec-WebSocket-Protocol: chat
The |Origin| header field [I-D.ietf-websec-origin] is used to protect
Fette & Melnikov Expires March 3, 2012 [Page 7]
Internet-Draft The WebSocket protocol August 2011
against unauthorized cross-origin use of a WebSocket server by
scripts using the |WebSocket| API in a Web browser. The server is
informed of the script origin generating the WebSocket connection
request. If the server does not wish to accept connections from this
origin, it can choose to reject the connection by sending an
appropriate HTTP error code. This header field is sent by browser
clients, for non-browser clients this header field may be sent if it
makes sense in the context of those clients.
Finally, the server has to prove to the client that it received the
client's WebSocket handshake, so that the server doesn't accept
connections that are not WebSocket connections. This prevents an
attacker from tricking a WebSocket server by sending it carefully-
crafted packets using |XMLHttpRequest| or a |form| submission.
To prove that the handshake was received, the server has to take two
pieces of information and combine them to form a response. The first
piece of information comes from the |Sec-WebSocket-Key| header field
in the client handshake:
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
For this header field, the server has to take the value (as present
in the header field, e.g. the base64-encoded [RFC4648] version minus
any leading and trailing whitespace), and concatenate this with the
Globally Unique Identifier (GUID, [RFC4122]) "258EAFA5-E914-47DA-
95CA-C5AB0DC85B11" in string form, which is unlikely to be used by
network endpoints that do not understand the WebSocket protocol. A
SHA-1 hash (160 bits), base64-encoded (see Section 4 of [RFC4648]),
of this concatenation is then returned in the server's handshake
[FIPS.180-2.2002].
Concretely, if as in the example above, |Sec-WebSocket-Key| header
field had the value "dGhlIHNhbXBsZSBub25jZQ==", the server would
concatenate the string "258EAFA5-E914-47DA-95CA-C5AB0DC85B11" to form
the string "dGhlIHNhbXBsZSBub25jZQ==258EAFA5-E914-47DA-95CA-
C5AB0DC85B11". The server would then take the SHA-1 hash of this,
giving the value 0xb3 0x7a 0x4f 0x2c 0xc0 0x62 0x4f 0x16 0x90 0xf6
0x46 0x06 0xcf 0x38 0x59 0x45 0xb2 0xbe 0xc4 0xea. This value is
then base64-encoded (see Section 4 of [RFC4648]), to give the value
"s3pPLMBiTxaQ9kYGzzhZRbK+xOo=". This value would then be echoed in
the |Sec-WebSocket-Accept| header field.
The handshake from the server is much simpler than the client
handshake. The first line is an HTTP Status-Line, with the status
code 101:
Fette & Melnikov Expires March 3, 2012 [Page 8]
Internet-Draft The WebSocket protocol August 2011
HTTP/1.1 101 Switching Protocols
Any status code other than 101 indicates that the WebSocket handshake
has not completed, and that the semantics of HTTP still apply. The
headers follow the status code.
The |Connection| and |Upgrade| header fields complete the HTTP
Upgrade. The |Sec-WebSocket-Accept| header field indicates whether
the server is willing to accept the connection. If present, this
header field must include a hash of the client's nonce sent in |Sec-
WebSocket-Key| along with a predefined GUID. Any other value must
not be interpreted as an acceptance of the connection by the server.
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
These fields are checked by the |WebSocket| client for scripted
pages. If the |Sec-WebSocket-Accept| value does not match the
expected value, or if the header field is missing, or if the HTTP
status code is not 101, the connection will not be established and
WebSocket frames will not be sent.
Option fields can also be included. In this version of the protocol,
the main option field is |Sec-WebSocket-Protocol|, which indicates
the subprotocol that the server has selected. WebSocket clients
verify that the server included one of the values as was specified in
the WebSocket client's handshake. A server that speaks multiple
subprotocols has to make sure it selects one based on the client's
handshake and specifies it in its handshake.
Sec-WebSocket-Protocol: chat
The server can also set cookie-related option fields to _set_
cookies, as described in [RFC6265].
1.4. Closing Handshake
_This section is non-normative._
The closing handshake is far simpler than the opening handshake.
Either peer can send a control frame with data containing a specified
control sequence to begin the closing handshake (detailed in
Section 5.5.1). Upon receiving such a frame, the other peer sends a
close frame in response, if it hasn't already sent one. Upon
Fette & Melnikov Expires March 3, 2012 [Page 9]
Internet-Draft The WebSocket protocol August 2011
receiving _that_ control frame, the first peer then closes the
connection, safe in the knowledge that no further data is
forthcoming.
After sending a control frame indicating the connection should be
closed, a peer does not send any further data; after receiving a
control frame indicating the connection should be closed, a peer
discards any further data received.
It is safe for both peers to initiate this handshake simultaneously.
The closing handshake is intended to complement the TCP closing
handshake (FIN/ACK), on the basis that the TCP closing handshake is
not always reliable end-to-end, especially in the presence of
intercepting proxies and other intermediaries.
By sending a close frame and waiting for a close frame in response,
certain cases are avoided where data may be unnecessarily lost. For
instance, on some platforms, if a socket is closed with data in the
receive queue, a RST packet is sent, which will then cause recv() to
fail for the party that received the RST, even if there was data
waiting to be read.
1.5. Design Philosophy
_This section is non-normative._
The WebSocket protocol is designed on the principle that there should
be minimal framing (the only framing that exists is to make the
protocol frame-based instead of stream-based, and to support a
distinction between Unicode text and binary frames). It is expected
that metadata would be layered on top of WebSocket by the application
layer, in the same way that metadata is layered on top of TCP by the
application layer (e.g., HTTP).
Conceptually, WebSocket is really just a layer on top of TCP that
does the following:
o adds a Web "origin"-based security model for browsers
o adds an addressing and protocol naming mechanism to support
multiple services on one port and multiple host names on one IP
address;
o layers a framing mechanism on top of TCP to get back to the IP
packet mechanism that TCP is built on, but without length limits
Fette & Melnikov Expires March 3, 2012 [Page 10]
Internet-Draft The WebSocket protocol August 2011
o includes an additional closing handshake in-band that is designed
to work in the presence of proxies and other intermediaries
Other than that, WebSocket adds nothing. Basically it is intended to
be as close to just exposing raw TCP to script as possible given the
constraints of the Web. It's also designed in such a way that its
servers can share a port with HTTP servers, by having its handshake
be a valid HTTP Upgrade request mechanism also. One could
conceptually use other protocols to establish client-server
messaging, but the intent of WebSockets was to provide a relatively
simple protocol that can coexist with HTTP and deployed HTTP
infrastructure (such as proxies) that is as close to TCP as is safe
for use with such infrastructure given security considerations, with
targeted additions to simplify usage and make simple things simple
(such as the addition of message semantics).
The protocol is intended to be extensible; future versions will
likely introduce additional concepts such as multiplexing.
1.6. Security Model
_This section is non-normative._
The WebSocket protocol uses the origin model used by Web browsers to
restrict which Web pages can contact a WebSocket server when the
WebSocket protocol is used from a Web page. Naturally, when the
WebSocket protocol is used by a dedicated client directly (i.e. not
from a Web page through a Web browser), the origin model is not
useful, as the client can provide any arbitrary origin string.
This protocol is intended to fail to establish a connection with
servers of pre-existing protocols like SMTP [RFC5321] and HTTP, while
allowing HTTP servers to opt-in to supporting this protocol if
desired. This is achieved by having a strict and elaborate
handshake, and by limiting the data that can be inserted into the
connection before the handshake is finished (thus limiting how much
the server can be influenced).
It is similarly intended to fail to establish a connection when data
from other protocols, especially HTTP, is sent to a WebSocket server,
for example as might happen if an HTML |form| were submitted to a
WebSocket server. This is primarily achieved by requiring that the
server prove that it read the handshake, which it can only do if the
handshake contains the appropriate parts which themselves can only be
sent by a WebSocket handshake. In particular, at the time of writing
of this specification, fields starting with |Sec-| cannot be set by
an attacker from a Web browser using only HTML and JavaScript APIs
such as |XMLHttpRequest|.
Fette & Melnikov Expires March 3, 2012 [Page 11]
Internet-Draft The WebSocket protocol August 2011
1.7. Relationship to TCP and HTTP
_This section is non-normative._
The WebSocket protocol is an independent TCP-based protocol. Its
only relationship to HTTP is that its handshake is interpreted by
HTTP servers as an Upgrade request.
By default the WebSocket protocol uses port 80 for regular WebSocket
connections and port 443 for WebSocket connections tunneled over TLS
[RFC2818].
1.8. Establishing a Connection
_This section is non-normative._
When a connection is to be made to a port that is shared by an HTTP
server (a situation that is quite likely to occur with traffic to
ports 80 and 443), the connection will appear to the HTTP server to
be a regular GET request with an Upgrade offer. In relatively simple
setups with just one IP address and a single server for all traffic
to a single hostname, this might allow a practical way for systems
based on the WebSocket protocol to be deployed. In more elaborate
setups (e.g. with load balancers and multiple servers), a dedicated
set of hosts for WebSocket connections separate from the HTTP servers
is probably easier to manage. At the time of writing of this
specification, it should be noted that connections on port 80 and 443
have significantly different success rates, with connections on port
443 being significantly more likely to succeed, though this may
change with time.
1.9. Subprotocols Using the WebSocket protocol
_This section is non-normative._
The client can request that the server use a specific subprotocol by
including the |Sec-WebSocket-Protocol| field in its handshake. If it
is specified, the server needs to include the same field and one of
the selected subprotocol values in its response for the connection to
be established.
These subprotocol names should be registered as per Section 11.5. To
avoid potential collisions, it is recommended to use names that
contain the ASCII version of the domain name of the subprotocol's
originator. For example, if Example Corporation were to create a
Chat subprotocol to be implemented by many servers around the Web,
they could name it "chat.example.com". If the Example Organization
called their competing subprotocol "chat.example.org", then the two
Fette & Melnikov Expires March 3, 2012 [Page 12]
Internet-Draft The WebSocket protocol August 2011
subprotocols could be implemented by servers simultaneously, with the
server dynamically selecting which subprotocol to use based on the
value sent by the client.
Subprotocols can be versioned in backwards-incompatible ways by
changing the subprotocol name, e.g. going from "bookings.example.net"
to "v2.bookings.example.net". These subprotocols would be considered
completely separate by WebSocket clients. Backwards-compatible
versioning can be implemented by reusing the same subprotocol string
but carefully designing the actual subprotocol to support this kind
of extensibility.
Fette & Melnikov Expires March 3, 2012 [Page 13]
Internet-Draft The WebSocket protocol August 2011
2. Conformance Requirements
All diagrams, examples, and notes in this specification are non-
normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
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. [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 MAY
be implemented in any manner, so long as the end result is
equivalent. (In particular, the algorithms defined in this
specification are intended to be easy to follow, and not intended to
be performant.)
The conformance classes defined by this specification are clients and
servers.
2.1. Terminology
_ASCII_ shall mean the character-encoding scheme defined in
[ANSI.X3-4.1986].
This document makes reference to UTF-8 values and uses UTF-8
notational formats as defined in STD 63 [RFC3629].
Key Terms such as named algorithms or definitions are indicated like
_this_.
Names of header fields or variables are indicated like |this|.
Variable values are indicated like /this/.
This document references the procedure to _Fail the WebSocket
Connection_. This procedure is defined in Section 7.1.7.
_Converting a string to ASCII lowercase_ means replacing all
characters in the range U+0041 to U+005A (i.e. LATIN CAPITAL LETTER
A to LATIN CAPITAL LETTER Z) with the corresponding characters in the
range U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL
LETTER Z).
Fette & Melnikov Expires March 3, 2012 [Page 14]
Internet-Draft The WebSocket protocol August 2011
Comparing two strings in an _ASCII case-insensitive_ manner means
comparing them exactly, code point for code point, except that the
characters in the range U+0041 to U+005A (i.e. LATIN CAPITAL LETTER
A to LATIN CAPITAL LETTER Z) and the corresponding characters in the
range U+0061 to U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL
LETTER Z) are considered to also match.
The term "URI" is used in this document as defined in [RFC3986].
When an implementation is required to _send_ data as part of the
WebSocket protocol, the implementation MAY delay the actual
transmission arbitrarily, e.g. buffering data so as to send fewer IP
packets.
Fette & Melnikov Expires March 3, 2012 [Page 15]
Internet-Draft The WebSocket protocol August 2011
3. WebSocket URIs
This specification defines two URI schemes, using the ABNF syntax
defined in RFC 5234 [RFC5234], and terminology and ABNF productions
defined by the URI specification RFC 3986 [RFC3986].
ws-URI = "ws:" "//" host [ ":" port ] path [ "?" query ]
wss-URI = "wss:" "//" host [ ":" port ] path [ "?" query ]
host = <host, defined in [RFC3986], Section 3.2.2>
port = <port, defined in [RFC3986], Section 3.2.3>
path = <path-abempty, defined in [RFC3986], Section 3.3>
query = <query, defined in [RFC3986], Section 3.4>
The port component is OPTIONAL; the default for "ws" is port 80,
while the default for "wss" is port 443.
The URI is called "secure" (and it said that "the secure flag is
set") if the scheme component matches "wss" case-insensitively.
The "resource-name" (also known as /resource name/ in Section 4.1)
can be constructed by concatenating
o "/" if the path component is empty
o the path component
o "?" if the query component is non-empty
o the query component
Fragment identifiers are meaningless in the context of WebSocket
URIs, and MUST NOT be used on these URIs. The character "#" in URIs
MUST be escaped as %23 if used as part of the query component.
Fette & Melnikov Expires March 3, 2012 [Page 16]
Internet-Draft The WebSocket protocol August 2011
4. Opening Handshake
4.1. Client Requirements
To _Establish a WebSocket Connection_, a client opens a connection
and sends a handshake as defined in this section. A connection is
defined to initially be in a CONNECTING state. A client will need to
supply a /host/, /port/, /resource name/, and a /secure/ flag, which
are the components of a WebSocket URI as discussed in Section 3,
along with a list of /protocols/ and /extensions/ to be used.
Additionally, if the client is a web browser, an /origin/ MUST be
supplied.
Clients running in controlled environments, e.g. browsers on mobile
handsets tied to specific carriers, MAY offload the management of the
connection to another agent on the network. In such a situation, the
client for the purposes of conformance is considered to include both
the handset software and any such agents.
When the client is to _Establish a WebSocket Connection_ given a set
of (/host/, /port/, /resource name/, and /secure/ flag), along with a
list of /protocols/ and /extensions/ to be used, and an /origin/ in
the case of web browsers, it MUST open a connection, send an opening
handshake, and read the server's handshake in response. The exact
requirements of how the connection should be opened, what should be
sent in the opening handshake, and how the server's response should
be interpreted, are as follows in this section. In the following
text, we will use terms from Section 3 such as "/host/" and "/secure/
flag" as defined in that section.
1. The components of the WebSocket URI passed into this algorithm
(/host/, /port/, /resource name/ and /secure/ flag) MUST be valid
according to the specification of WebSocket URIs specified in
Section 3. If any of the components are invalid, the client MUST
_Fail the WebSocket Connection_ and abort these steps.
2. If the client already has a WebSocket connection to the remote
host (IP address) identified by /host/ and port /port/ pair, even
if the remote host is known by another name, the client MUST wait
until that connection has been established or for that connection
to have failed. There MUST be no more than one connection in a
CONNECTING state. If multiple connections to the same IP address
are attempted simultaneously, the client MUST serialize them so
that there is no more than one connection at a time running
through the following steps.
If the client cannot determine the IP address of the remote host
(for example because all communication is being done through a
Fette & Melnikov Expires March 3, 2012 [Page 17]
Internet-Draft The WebSocket protocol August 2011
proxy server that performs DNS queries itself), then the client
MUST assume for the purposes of this step that each host name
refers to a distinct remote host, and instead the client SHOULD
limit the total number of simultaneous pending connections to a
reasonably low number (e.g., the client might allow simultaneous
pending connections to a.example.com and b.example.com, but if
thirty simultaneous connections to a single host are requested,
that may not be allowed). In a Web browser context, the client
SHOULD consider the number of tabs the user has open in setting a
limit to the number of simultaneous pending connections.
NOTE: This makes it harder for a script to perform a denial of
service attack by just opening a large number of WebSocket
connections to a remote host. A server can further reduce the
load on itself when attacked by pausing before closing the
connection, as that will reduce the rate at which the client
reconnects.
NOTE: There is no limit to the number of established WebSocket
connections a client can have with a single remote host. Servers
can refuse to accept connections from hosts/IP addresses with an
excessive number of existing connections, or disconnect resource-
hogging connections when suffering high load.
3. _Proxy Usage_: If the client is configured to use a proxy when
using the WebSocket protocol to connect to host /host/ and port
/port/, then the client SHOULD connect to that proxy and ask it
to open a TCP connection to the host given by /host/ and the port
given by /port/.
EXAMPLE: For example, if the client uses an HTTP proxy for all
traffic, then if it was to try to connect to port 80 on server
example.com, it might send the following lines to the proxy
server:
CONNECT example.com:80 HTTP/1.1
Host: example.com
If there was a password, the connection might look like:
CONNECT example.com:80 HTTP/1.1
Host: example.com
Proxy-authorization: Basic ZWRuYW1vZGU6bm9jYXBlcyE=
If the client is not configured to use a proxy, then a direct TCP
connection SHOULD be opened to the host given by /host/ and the
Fette & Melnikov Expires March 3, 2012 [Page 18]
Internet-Draft The WebSocket protocol August 2011
port given by /port/.
NOTE: Implementations that do not expose explicit UI for
selecting a proxy for WebSocket connections separate from other
proxies are encouraged to use a SOCKS5 [RFC1928] proxy for
WebSocket connections, if available, or failing that, to prefer
the proxy configured for HTTPS connections over the proxy
configured for HTTP connections.
For the purpose of proxy autoconfiguration scripts, the URI to
pass the function MUST be constructed from /host/, /port/,
/resource name/, and the /secure/ flag using the definition of a
WebSocket URI as given in Section 3.
NOTE: The WebSocket protocol can be identified in proxy
autoconfiguration scripts from the scheme ("ws" for unencrypted
connections and "wss" for encrypted connections).
4. If the connection could not be opened, either because a direct
connection failed or because any proxy used returned an error,
then the client MUST _Fail the WebSocket Connection_ and abort
the connection attempt.
5. If /secure/ is true, the client MUST perform a TLS handshake over
the connection after opening the connection and before sending
the handshake data [RFC2818]. If this fails (e.g. the server's
certificate could not be verified), then the client MUST _Fail
the WebSocket Connection_ and abort the connection. Otherwise,
all further communication on this channel MUST run through the
encrypted tunnel. [RFC5246]
Clients MUST use the Server Name Indication extension in the TLS
handshake. [RFC6066]
Once a connection to the server has been established (including a
connection via a proxy or over a TLS-encrypted tunnel), the client
MUST send an opening handshake to the server. The handshake consists
of an HTTP upgrade request, along with a list of required and
optional header fields. The requirements for this handshake are as
follows.
1. The handshake MUST be a valid HTTP request as specified by
[RFC2616].
2. The Method of the request MUST be GET and the HTTP version MUST
be at least 1.1.
For example, if the WebSocket URI is "ws://example.com/chat",
Fette & Melnikov Expires March 3, 2012 [Page 19]
Internet-Draft The WebSocket protocol August 2011
The first line sent should be "GET /chat HTTP/1.1"
3. The "Request-URI" part of the request MUST match the /resource
name/ Section 3 (a relative URI), or be an absolute http/https
URI that, when parsed, has a /resource name/, /host/ and /port/
that match the corresponding ws/wss URI.
4. The request MUST contain a "Host" header field whose value is
equal to /host/.
5. The request MUST contain an "Upgrade" header field whose value
is equal to "websocket".
6. The request MUST contain a "Connection" header field whose value
MUST include the "Upgrade" token.
7. The request MUST include a header field with the name "Sec-
WebSocket-Key". The value of this header field MUST be a nonce
consisting of a randomly selected 16-byte value that has been
base64-encoded (see Section 4 of [RFC4648]). The nonce MUST be
selected randomly for each connection.
NOTE: As an example, if the randomly selected value was the
sequence of bytes 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09
0x0a 0x0b 0x0c 0x0d 0x0e 0x0f 0x10, the value of the header
field would be "AQIDBAUGBwgJCgsMDQ4PEC=="
8. The request MUST include a header field with the name "Origin"
[I-D.ietf-websec-origin] if the request is coming from a browser
client. If the connection is from a non-browser client, the
request MAY include this header field if the semantics of that
client match the use-case described here for browser clients.
The value of this header field is the ASCII serialization of
origin of the context in which the code establishing the
connection is running. See [I-D.ietf-websec-origin] for the
details of how this header field value is constructed.
As an example, if code is running on www.example.com attempting
to establish a connection to ww2.example.com, the value of the
header field would be "http://www.example.com".
9. The request MUST include a header field with the name "Sec-
WebSocket-Version". The value of this header field MUST be 13.
_Note: Although drafts -09, -10, -11 and -12 were published, as
they were mostly comprised of editorial changes and
clarifications and not changes to the wire protocol, values 9,
10, 11 and 12 were not used as valid values for Sec-WebSocket-
Version. These values were reserved in the IANA registry but
Fette & Melnikov Expires March 3, 2012 [Page 20]
Internet-Draft The WebSocket protocol August 2011
were not and will not be used._
10. The request MAY include a header field with the name "Sec-
WebSocket-Protocol". If present, this value indicates one or
more comma separated subprotocol the client wishes to speak,
ordered by preference. The elements that comprise this value
MUST be non-empty strings with characters in the range U+0021 to
U+007E not including separator characters as defined in
[RFC2616], and MUST all be unique strings. The ABNF for the
value of this header field is 1#token, where the definitions of
constructs and rules are as given in [RFC2616].
11. The request MAY include a header field with the name "Sec-
WebSocket-Extensions". If present, this value indicates the
protocol-level extension(s) the client wishes to speak. The
interpretation and format of this header field is described in
Section 9.1.
12. The request MAY include any other header fields, for example
cookies [RFC6265] and/or authentication related header fields
such as Authorization header field [RFC2616].
Once the client's opening handshake has been sent, the client MUST
wait for a response from the server before sending any further data.
The client MUST validate the server's response as follows:
1. If the status code received from the server is not 101, the
client handles the response per HTTP [RFC2616] procedures, in
particular the client might perform authentication if it receives
401 status code, the server might redirect the client using a 3xx
status code (but clients are not required to follow them), etc.
Otherwise, proceed as follows.
2. If the response lacks an "Upgrade" header field or the "Upgrade"
header field contains a value that is not an ASCII case-
insensitive match for the value "websocket", the client MUST
_Fail the WebSocket Connection _.
3. If the response lacks a "Connection" header field or the
"Connection" header field doesn't contains a token that is an
ASCII case-insensitive match for the value "Upgrade", the client
MUST _Fail the WebSocket Connection_.
4. If the response lacks a "Sec-WebSocket-Accept" header field or
the "Sec-WebSocket-Accept" contains a value other than the
base64-encoded SHA-1 of the concatenation of the "Sec-WebSocket-
Key" (as a string, not base64-decoded) with the string "258EAFA5-
E914-47DA-95CA-C5AB0DC85B11", but ignoring any leading and
Fette & Melnikov Expires March 3, 2012 [Page 21]
Internet-Draft The WebSocket protocol August 2011
trailing whitespace, the client MUST _Fail the WebSocket
Connection_
5. If the response includes a "Sec-WebSocket-Extensions" header
field, and this header field indicates the use of an extension
that was not present in the client' handshake (the server has
indicated an extension not requested by the client), the client
MUST _Fail the WebSocket Connection_. (The parsing of this
header field to determine which extensions are requested is
discussed in Section 9.1.)
6. If the response includes a "Sec-WebSocket-Protocol" header field,
and this header field indicates the use of a subprotocol that was
not present in the client' handshake (the server has indicated a
subprotocol not requested by the client), the client MUST _Fail
the WebSocket Connection_. (The parsing of this header field to
determine which extensions are requested is discussed in
Section 9.1.)
If the server's response does not conform to the requirements for the
server's handshake as defined in this section and in Section 4.2.2,
the client MUST _Fail the WebSocket Connection_.
If the server's response is validated as provided for above, it is
said that _The WebSocket Connection is Established_ and that the
WebSocket Connection is in the OPEN state. The _Extensions In Use_
is defined to be a (possibly empty) string, the value of which is
equal to the value of the |Sec-WebSocket-Extensions| header field
supplied by the server's handshake, or the null value if that header
field was not present in the server's handshake. The _Subprotocol In
Use_ is defined to be the value of the |Sec-WebSocket-Protocol|
header field in the server's handshake, or the null value if that
header field was not present in the server's handshake.
Additionally, if any header fields in the server's handshake indicate
that cookies should be set (as defined by [RFC6265]), these cookies
are referred to as _Cookies Set During the Server's Opening
Handshake_.
4.2. Server-side Requirements
_This section only applies to servers._
Servers MAY offload the management of the connection to other agents
on the network, for example load balancers and reverse proxies. In
such a situation, the server for the purposes of conformance is
considered to include all parts of the server-side infrastructure
from the first device to terminate the TCP connection all the way to
the server that processes requests and sends responses.
Fette & Melnikov Expires March 3, 2012 [Page 22]
Internet-Draft The WebSocket protocol August 2011
EXAMPLE: For example, a data center might have a server that responds
to WebSocket requests with an appropriate handshake, and then passes
the connection to another server to actually process the data frames.
For the purposes of this specification, the "server" is the
combination of both computers.
4.2.1. Reading the Client's Opening Handshake
When a client starts a WebSocket connection, it sends its part of the
opening handshake. The server must parse at least part of this
handshake in order to obtain the necessary information to generate
the server part of the handshake.
The client's opening handshake consists of the following parts. If
the server, while reading the handshake, finds that the client did
not send a handshake that matches the description below (note that as
per [RFC2616] the order of the header fields is not important),
including but not limited to any violations of the grammar (ABNF)
specified for the components of the handshake, the server MUST stop
processing the client's handshake, and return an HTTP response with
an appropriate error code (such as 400 Bad Request).
1. An HTTP/1.1 or higher GET request, including a "Request-URI"
[RFC2616] that should be interpreted as a /resource name/
Section 3 (or an absolute HTTP/HTTPS URI containing the
/resource name/).
2. A "Host" header field containing the server's authority.
3. An "Upgrade" header field containing the value "websocket",
treated as an ASCII case-insensitive value.
4. A "Connection" header field that includes the token "Upgrade",
treated as an ASCII case-insensitive value.
5. A "Sec-WebSocket-Key" header field with a base64-encoded (see
Section 4 of [RFC4648]) value that, when decoded, is 16 bytes in
length.
6. A "Sec-WebSocket-Version" header field, with a value of 8.
7. Optionally, a "Origin" header field. This header field is sent
by all browser clients. A connection attempt lacking this
header field SHOULD NOT be interpreted as coming from a browser
client.
8. Optionally, a "Sec-WebSocket-Protocol" header field, with a list
of values indicating which protocols the client would like to
Fette & Melnikov Expires March 3, 2012 [Page 23]
Internet-Draft The WebSocket protocol August 2011
speak, ordered by preference.
9. Optionally, a "Sec-WebSocket-Extensions" header field, with a
list of values indicating which extensions the client would like
to speak. The interpretation of this header field is discussed
in Section 9.1.
10. Optionally, other header fields, such as those used to send
cookies or request authentication to a server. Unknown header
fields are ignored, as per [RFC2616].
4.2.2. Sending the Server's Opening Handshake
When a client establishes a WebSocket connection to a server, the
server MUST complete the following steps to accept the connection and
send the server's opening handshake.
1. If the server supports encryption, perform a TLS handshake over
the connection. If this fails (e.g. the client indicated a host
name in the extended client hello "server_name" extension that
the server does not host), then close the connection; otherwise,
all further communication for the connection (including the
server's handshake) MUST run through the encrypted tunnel.
[RFC5246]
2. If the server wishes to perform additional client authentication,
it might return 401 status code with the corresponding WWW-
Authenticate header field as described in [RFC2616].
3. The server MAY redirect the client using a 3xx status code
[RFC2616]. Note that this step can happen together with, before
or after the optional authentication step described above.
4. Establish the following information:
/origin/
The |Origin| header field in the client's handshake indicates
the origin of the script establishing the connection. The
origin is serialized to ASCII and converted to lowercase. The
server MAY use this information as part of a determination of
whether to accept the incoming connection. If the server does
not validate the origin, it will accept connections from
anywhere. If the server does not wish to accept this
connection, it MUST return an appropriate HTTP error code
(e.g. 403 Forbidden) and abort the WebSocket handshake
described in this section. For more detail, refer to
Section 10.
Fette & Melnikov Expires March 3, 2012 [Page 24]
Internet-Draft The WebSocket protocol August 2011
/key/
The |Sec-WebSocket-Key| header field in the client's handshake
includes a base64-encoded value that, if decoded, is 16 bytes
in length. This (encoded) value is used in the creation of
the server's handshake to indicate an acceptance of the
connection. It is not necessary for the server to base64-
decode the "Sec-WebSocket-Key" value.
/version/
The |Sec-WebSocket-Version| header field in the client's
handshake includes the version of the WebSocket protocol the
client is attempting to communicate with. If this version
does not match a version understood by the server, the server
MUST abort the websocket handshake described in this section
and instead send an appropriate HTTP error code (such as 426
Upgrade Required), and a |Sec-WebSocket-Version| header field
indicating the version(s) the server is capable of
understanding.
/resource name/
An identifier for the service provided by the server. If the
server provides multiple services, then the value should be
derived from the resource name given in the client's handshake
from the Request-URI [RFC2616] of the GET method. If the
requested service is not available, the server MUST send an
appropriate HTTP error code (such as 404 Not Found) and abort
the WebSocket handshake.
/subprotocol/
Either a single value representing the subprotocol the server
is ready to use or null. The value chosen MUST be derived
from the client's handshake, specifically by selecting one of
the values from the "Sec-WebSocket-Protocol" field that the
server is willing to use for this connection (if any). If the
client's handshake did not contain such a header field, or if
the server does not agree to any of the client's requested
subprotocols, the only acceptable value is null. The absence
of such a field is equivalent to the null value (meaning that
if the server does not wish to agree to one of the suggested
subprotocols, it MUST NOT send back a |Sec-WebSocket-Protocol|
header field in its response). The empty string is not the
same as the null value for these purposes, and is not a legal
value for this field. The ABNF for the value of this header
field is (token), where the definitions of constructs and
rules are as given in [RFC2616].
Fette & Melnikov Expires March 3, 2012 [Page 25]
Internet-Draft The WebSocket protocol August 2011
/extensions/
A (possibly empty) list representing the protocol-level
extensions the server is ready to use. If the server supports
multiple extensions, then the value MUST be derived from the
client's handshake, specifically by selecting one or more of
the values from the "Sec-WebSocket-Extensions" field. The
absence of such a field is equivalent to the null value. The
empty string is not the same as the null value for these
purposes. Extensions not listed by the client MUST NOT be
listed. The method by which these values should be selected
and interpreted is discussed in Section 9.1.
5. If the server chooses to accept the incoming connection, it MUST
reply with a valid HTTP response indicating the following.
1. A Status-Line with a 101 response code as per RFC 2616
[RFC2616]. Such a response could look like "HTTP/1.1 101
Switching Protocols"
2. An "Upgrade" header field with value "websocket" as per RFC
2616 [RFC2616].
3. A "Connection" header field with value "Upgrade"
4. A "Sec-WebSocket-Accept" header field. The value of this
header field is constructed by concatenating /key/, defined
above in Paragraph 4 of Section 4.2.2, with the string
"258EAFA5-E914-47DA-95CA-C5AB0DC85B11", taking the SHA-1 hash
of this concatenated value to obtain a 20-byte value, and
base64-encoding (see Section 4 of [RFC4648]) this 20-byte
hash.
The ABNF of this header field is defined as follows:
Sec-WebSocket-Accept = base64-value
base64-value = *base64-data [ base64-padding ]
base64-data = 4base64-character
base64-padding = (2base64-character "==") |
(3base64-character "=")
base64-character = ALPHA | DIGIT | "+" | "/"
NOTE: As an example, if the value of the "Sec-WebSocket-Key"
header field in the client's handshake were
"dGhlIHNhbXBsZSBub25jZQ==", the server would append the
string "258EAFA5-E914-47DA-95CA-C5AB0DC85B11" to form the
string "dGhlIHNhbXBsZSBub25jZQ==258EAFA5-E914-47DA-95CA-
C5AB0DC85B11". The server would then take the SHA-1 hash of
Fette & Melnikov Expires March 3, 2012 [Page 26]
Internet-Draft The WebSocket protocol August 2011
this string, giving the value 0xb3 0x7a 0x4f 0x2c 0xc0 0x62
0x4f 0x16 0x90 0xf6 0x46 0x06 0xcf 0x38 0x59 0x45 0xb2 0xbe
0xc4 0xea. This value is then base64-encoded, to give the
value "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=", which would be returned
in the "Sec-WebSocket-Accept" header field.
5. Optionally, a "Sec-WebSocket-Protocol" header field, with a
value /subprotocol/ as defined in Paragraph 4 of
Section 4.2.2.
6. Optionally, a "Sec-WebSocket-Extensions" header field, with a
value /extensions/ as defined in Paragraph 4 of
Section 4.2.2. If multiple extensions are to be used, they
must all be listed in a single Sec-WebSocket-Extensions
header field. This header field MUST NOT be repeated.
This completes the server's handshake. If the server finishes these
steps without aborting the WebSocket handshake, the server considers
the WebSocket connection to be established and that the WebSocket
connection is in the OPEN state. At this point, the server may begin
sending (and receiving) data.
4.3. Collected ABNF for new header fields used in handshake
Unlike other section of the document this section is using ABNF
syntax/rules from Section 2.1 of [RFC2616], including "implied *LWS
rule".
Note that the following ABNF conventions are used in this section:
Some names of the rules correspond to names of the corresponding
header fields. Such rules express values of the corresponding header
fields, for example the Sec-WebSocket-Key ABNF rule describes syntax
of the Sec-WebSocket-Key header field value. ABNF rules with the
"-Client" suffix in the name are only used in requests sent by the
client to the server; ABNF rules with the "-Server" suffix in the
name are only used in responses sent by the server to the client.
For example, the ABNF rule Sec-WebSocket-Protocol-Client describes
syntax of the Sec-WebSocket-Protocol header field value sent by the
client to the server.
The following new header field can be sent during the handshake from
the client to the server:
Fette & Melnikov Expires March 3, 2012 [Page 27]
Internet-Draft The WebSocket protocol August 2011
Sec-WebSocket-Key = base64-value
Sec-WebSocket-Extensions = extension-list
Sec-WebSocket-Protocol-Client = 1#token
Sec-WebSocket-Version-Client = version
base64-value = *base64-data [ base64-padding ]
base64-data = 4base64-character
base64-padding = (2base64-character "==") |
(3base64-character "=")
base64-character = ALPHA | DIGIT | "+" | "/"
extension-list = 1#extension
extension = extension-token *( ";" extension-param )
extension-token = registered-token
registered-token = token
extension-param = token [ "=" token ]
NZDIGIT = "1" | "2" | "3" | "4" | "5" | "6" |
"7" | "8" | "9"
version = DIGIT | (NZDIGIT DIGIT) |
("1" DIGIT DIGIT) | ("2" DIGIT DIGIT)
; Limited to 0-255 range, with no leading zeros
The following new header field can be sent during the handshake from
the server to the client:
Sec-WebSocket-Extensions = extension-list
Sec-WebSocket-Accept = base64-value
Sec-WebSocket-Protocol-Server = token
Sec-WebSocket-Version-Server = 1#version
Fette & Melnikov Expires March 3, 2012 [Page 28]
Internet-Draft The WebSocket protocol August 2011
5. Data Framing
5.1. Overview
In the WebSocket protocol, data is transmitted using a sequence of
frames. All frames sent from the client to the server are masked to
avoid confusing network intermediaries, such as intercepting proxies.
All frames sent from the server to the client are not masked.
The base framing protocol defines a frame type with an opcode, a
payload length, and designated locations for extension and
application data, which together define the _payload_ data. Certain
bits and opcodes are reserved for future expansion of the protocol.
A data frame MAY be transmitted by either the client or the server at
any time after opening handshake completion and before that endpoint
has sent a close frame (Section 5.5.1).
5.2. Base Framing Protocol
This wire format for the data transfer part is described by the ABNF
[RFC5234] given in detail in this section. A high level overview of
the framing is given in the following figure.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-------+-+-------------+-------------------------------+
|F|R|R|R| opcode|M| Payload len | Extended payload length |
|I|S|S|S| (4) |A| (7) | (16/63) |
|N|V|V|V| |S| | (if payload len==126/127) |
| |1|2|3| |K| | |
+-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
| Extended payload length continued, if payload len == 127 |
+ - - - - - - - - - - - - - - - +-------------------------------+
| |Masking-key, if MASK set to 1 |
+-------------------------------+-------------------------------+
| Masking-key (continued) | Payload Data |
+-------------------------------- - - - - - - - - - - - - - - - +
: Payload Data continued ... :
+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
| Payload Data continued ... |
+---------------------------------------------------------------+
Fette & Melnikov Expires March 3, 2012 [Page 29]
Internet-Draft The WebSocket protocol August 2011
FIN: 1 bit
Indicates that this is the final fragment in a message. The first
fragment MAY also be the final fragment.
RSV1, RSV2, RSV3: 1 bit each
MUST be 0 unless an extension is negotiated which defines meanings
for non-zero values. If a nonzero value is received and none of
the negotiated extensions defines the meaning of such a nonzero
value, the receiving endpoint MUST _Fail the WebSocket
Connection_.
Opcode: 4 bits
Defines the interpretation of the payload data. If an unknown
opcode is received, the receiving endpoint MUST _Fail the
WebSocket Connection_. The following values are defined.
* %x0 denotes a continuation frame
* %x1 denotes a text frame
* %x2 denotes a binary frame
* %x3-7 are reserved for further non-control frames
* %x8 denotes a connection close
* %x9 denotes a ping
* %xA denotes a pong
* %xB-F are reserved for further control frames
Mask: 1 bit
Defines whether the payload data is masked. If set to 1, a
masking key is present in masking-key, and this is used to unmask
the payload data as per Section 5.3. All frames sent from client
to server have this bit set to 1.
Payload length: 7 bits, 7+16 bits, or 7+64 bits
The length of the payload data, in bytes: if 0-125, that is the
payload length. If 126, the following 2 bytes interpreted as a 16
bit unsigned integer are the payload length. If 127, the
following 8 bytes interpreted as a 64-bit unsigned integer (the
Fette & Melnikov Expires March 3, 2012 [Page 30]
Internet-Draft The WebSocket protocol August 2011
most significant bit MUST be 0) are the payload length. Multibyte
length quantities are expressed in network byte order. The
payload length is the length of the extension data + the length of
the application data. The length of the extension data may be
zero, in which case the payload length is the length of the
application data.
Masking-key: 0 or 4 bytes
All frames sent from the client to the server are masked by a 32-
bit value that is contained within the frame. This field is
present if the mask bit is set to 1, and is absent if the mask bit
is set to 0. See Section 5.3 for further information on client-
to-server masking.
Payload data: (x+y) bytes
The payload data is defined as extension data concatenated with
application data.
Extension data: x bytes
The extension data is 0 bytes unless an extension has been
negotiated. Any extension MUST specify the length of the
extension data, or how that length may be calculated, and how the
extension use MUST be negotiated during the opening handshake. If
present, the extension data is included in the total payload
length.
Application data: y bytes
Arbitrary application data, taking up the remainder of the frame
after any extension data. The length of the application data is
equal to the payload length minus the length of the extension
data.
The base framing protocol is formally defined by the following ABNF
[RFC5234]:
ws-frame = frame-fin
frame-rsv1
frame-rsv2
frame-rsv3
frame-opcode
frame-masked
frame-payload-length
[ frame-masking-key ]
frame-payload-data
Fette & Melnikov Expires March 3, 2012 [Page 31]
Internet-Draft The WebSocket protocol August 2011
frame-fin = %x0 ; more frames of this message follow
/ %x1 ; final frame of this message
frame-rsv1 = %x0
; 1 bit, MUST be 0 unless negotiated
; otherwise
frame-rsv2 = %x0
; 1 bit, MUST be 0 unless negotiated
; otherwise
frame-rsv3 = %x0
; 1 bit, MUST be 0 unless negotiated
; otherwise
frame-opcode = %x0 ; continuation frame
/ %x1 ; text frame
/ %x2 ; binary frame
/ %x3-7
; reserved for further non-control frames
/ %x8 ; connection close
/ %x9 ; ping
/ %xA ; pong
/ %xB-F ; reserved for further control frames
frame-masked = %x0
; frame is not masked, no frame-masking-key
/ %x1
; frame is masked, frame-masking-key present
frame-payload-length = %x00-7D
/ %x7E frame-payload-length-16
/ %x7F frame-payload-length-63
frame-payload-length-16 = %x0000-FFFF
frame-payload-length-63 = %x0000000000000000-7FFFFFFFFFFFFFFF
frame-masking-key = 4( %0x00-FF )
; present only if frame-masked is 1
frame-payload-data = (frame-masked-extension-data
frame-masked-application-data)
; frame-masked 1
/ (frame-unmasked-extension-data
frame-unmasked-application-data)
; frame-masked 0
Fette & Melnikov Expires March 3, 2012 [Page 32]
Internet-Draft The WebSocket protocol August 2011
frame-masked-extension-data = *( %x00-FF ) ; to be defined later
frame-masked-application-data = *( %x00-FF )
frame-unmasked-extension-data = *( %x00-FF ) ; to be defined later
frame-unmasked-application-data = *( %x00-FF )
5.3. Client-to-Server Masking
The client MUST mask all frames sent to the server. This is required
for security reasons which are further discussed in Section 10.3. A
server MUST close the connection upon receiving a frame with the MASK
bit set to 0. In this case, a server MAY send a close frame with a
status code of 1002 (protocol error) as defined in Section 7.4.1.
A masked frame MUST have the field frame-masked set to 1, as defined
in Section 5.2.
The masking key is contained completely within the frame, as defined
in Section 5.2 as frame-masking-key. It is used to mask the payload
data defined in the same section as frame-payload-data, which
includes extension and application data.
The masking key is a 32-bit value chosen at random by the client.
The masking key MUST be derived from a strong source of entropy, and
the masking key for a given frame MUST NOT make it simple for a
server to predict the masking key for a subsequent frame. RFC 4086
[RFC4086] discusses what entails a suitable source of entropy for
security-sensitive applications.
The masking does not affect the length of the payload data. To
convert masked data into unmasked data, or vice versa, the following
algorithm is applied. The same algorithm applies regardless of the
direction of the translation - e.g. the same steps are applied to
mask the data as to unmask the data.
Octet i of the transformed data ("transformed-octet-i") is the XOR of
octet i of the original data ("original-octet-i") with octet at index
i modulo 4 of the masking key ("masking-key-octet-j"):
j = i MOD 4
transformed-octet-i = original-octet-i XOR masking-key-octet-j
When preparing a masked frame, the client MUST pick a fresh masking
key from the set of allowed 32-bit values. The masking key must be
Fette & Melnikov Expires March 3, 2012 [Page 33]
Internet-Draft The WebSocket protocol August 2011
unpredictable. The unpredictability of the masking key is essential
to prevent the author of malicious applications from selecting the
bytes that appear on the wire.
The payload length, indicated in the framing as frame-payload-length,
does NOT include the length of the masking key. It is the length of
the payload data, e.g. the number of bytes following the masking key.
5.4. Fragmentation
The primary purpose of fragmentation is to allow sending a message
that is of unknown size when the message is started without having to
buffer that message. If messages couldn't be fragmented, then an
endpoint would have to buffer the entire message so its length could
be counted before first byte is sent. With fragmentation, a server
or intermediary may choose a reasonable size buffer, and when the
buffer is full write a fragment to the network.
A secondary use-case for fragmentation is for multiplexing, where it
is not desirable for a large message on one logical channel to
monopolize the output channel, so the MUX needs to be free to split
the message into smaller fragments to better share the output
channel.
Unless specified otherwise by an extension, frames have no semantic
meaning. An intermediary might coalesce and/or split frames, if no
extensions were negotiated by the client and the server, or if some
extensions were negotiated, but the intermediary understood all the
extensions negotiated and knows how to coalesce and/or split frames
in presence of these extensions. One implication of this is that in
absence of extensions senders and receivers must not depend on
presence of specific frame boundaries.
The following rules apply to fragmentation:
o An unfragmented message consists of a single frame with the FIN
bit set and an opcode other than 0.
o A fragmented message consists of a single frame with the FIN bit
clear and an opcode other than 0, followed by zero or more frames
with the FIN bit clear and the opcode set to 0, and terminated by
a single frame with the FIN bit set and an opcode of 0. A
fragmented message is conceptually equivalent to a single larger
message whose payload is equal to the concatenation of the
payloads of the fragments in order, however in the presence of
extensions this may not hold true as the extension defines the
interpretation of the extension data present. For instance,
extension data may only be present at the beginning of the first
Fette & Melnikov Expires March 3, 2012 [Page 34]
Internet-Draft The WebSocket protocol August 2011
fragment and apply to subsequent fragments, or there may be
extension data present in each of the fragments that applies only
to that particular fragment. In absence of extension data, the
following example demonstrates how fragmentation works.
EXAMPLE: For a text message sent as three fragments, the first
fragment would have an opcode of 0x1 and a FIN bit clear, the
second fragment would have an opcode of 0x0 and a FIN bit clear,
and the third fragment would have an opcode of 0x0 and a FIN bit
that is set.
o Control frames MAY be injected in the middle of a fragmented
message. Control frames themselves MUST NOT be fragmented.
o Message fragments MUST be delivered to the recipient in the order
sent by the sender.
o The fragments of one message MUST NOT be interleaved between the
fragments of another message unless an extension has been
negotiated that can interpret the interleaving.
o An endpoint MUST be capable of handling control frames in the
middle of a fragmented message.
o A sender MAY create fragments of any size for non-control
messages.
o Clients and servers MUST support receiving both fragmented and
unfragmented messages.
o As control frames cannot be fragmented, an intermediary MUST NOT
attempt to change the fragmentation of a control frame.
o An intermediary MUST NOT change the fragmentation of a message if
any reserved bit values are used and the meaning of these values
is not known to the intermediary.
o An intermediary MUST NOT change the fragmentation of any message
in the context of a connection where extensions have been
negotiated and the intermediary is not aware of the semantics of
the negotiated extensions.
o As a consequence of these rules, all fragments of a message are of
the same type, as set by the first fragment's opcode. Since
Control frames cannot be fragmented, the type for all fragments in
a message MUST be either text or binary, or one of the reserved
opcodes.
Fette & Melnikov Expires March 3, 2012 [Page 35]
Internet-Draft The WebSocket protocol August 2011
_Note: if control frames could not be interjected, the latency of a
ping, for example, would be very long if behind a large message.
Hence, the requirement of handling control frames in the middle of a
fragmented message._
_Implementation Note: in absence of any extension a receiver doesn't
have to buffer the whole frame in order to process it. For example
if streaming API is used, a part of a frame can be delivered to the
application. But note that that assumption might not hold true for
all future WebSocket extensions._
5.5. Control Frames
Control frames are identified by opcodes where the most significant
bit of the opcode is 1. Currently defined opcodes for control frames
include 0x8 (Close), 0x9 (Ping), and 0xA (Pong). Opcodes 0xB-0xF are
reserved for further control frames yet to be defined.
Control frames are used to communicate state about the WebSocket.
Control frames can be interjected in the middle of a fragmented
message.
All control frames MUST have a payload length of 125 bytes or less
and MUST NOT be fragmented.
5.5.1. Close
The Close frame contains an opcode of 0x8.
The Close frame MAY contain a body (the "application data" portion of
the frame) that indicates a reason for closing, such as an endpoint
shutting down, an endpoint having received a frame too large, or an
endpoint having received a frame that does not conform to the format
expected by the other endpoint. If there is a body, the first two
bytes of the body MUST be a 2-byte unsigned integer (in network byte
order) representing a status code with value /code/ defined in
Section 7.4. Following the 2-byte integer the body MAY contain UTF-8
encoded data with value /reason/, the interpretation of which is not
defined by this specification. This data is not necessarily human
readable, but may be useful for debugging or passing information
relevant to the script that opened the connection. As the data is
not guaranteed to be human readable, clients MUST NOT show it to end
users.
Close frames sent from client to server must be masked as per
Section 5.3.
The application MUST NOT send any more data frames after sending a
Fette & Melnikov Expires March 3, 2012 [Page 36]
Internet-Draft The WebSocket protocol August 2011
close frame.
If an endpoint receives a Close frame and that endpoint did not
previously send a Close frame, the endpoint MUST send a Close frame
in response. It SHOULD do so as soon as is practical. An endpoint
MAY delay sending a close frame until its current message is sent
(for instance, if the majority of a fragmented message is already
sent, an endpoint MAY send the remaining fragments before sending a
Close frame). However, there is no guarantee that the endpoint which
has already sent a Close frame will continue to process data.
After both sending and receiving a close message, an endpoint
considers the WebSocket connection closed, and MUST close the
underlying TCP connection. The server MUST close the underlying TCP
connection immediately; the client SHOULD wait for the server to
close the connection but MAY close the connection at any time after
sending and receiving a close message, e.g. if it has not received a
TCP close from the server in a reasonable time period.
If a client and server both send a Close message at the same time,
both endpoints will have sent and received a Close message and should
consider the WebSocket connection closed and close the underlying TCP
connection.
5.5.2. Ping
The Ping frame contains an opcode of 0x9.
Upon receipt of a Ping frame, an endpoint MUST send a Pong frame in
response. It SHOULD do so as soon as is practical. Pong frames are
discussed in Section 5.5.3.
An endpoint MAY send a Ping frame any time after the connection is
established and before the connection is closed. NOTE: A ping frame
may serve either as a keepalive, or to verify that the remote
endpoint is still responsive.
5.5.3. Pong
The Pong frame contains an opcode of 0xA.
Section 5.5.2 details requirements that apply to both Ping and Pong
frames.
A Pong frame sent in response to a Ping frame must have identical
Application Data as found in the message body of the Ping frame being
replied to.
Fette & Melnikov Expires March 3, 2012 [Page 37]
Internet-Draft The WebSocket protocol August 2011
If an endpoint receives a Ping frame and has not yet sent Pong
frame(s) in response to previous Ping frame(s), the endpoint MAY
elect to send a Pong frame for only the most recently processed Ping
frame.
A Pong frame MAY be sent unsolicited. This serves as a
unidirectional heartbeat. A response to an unsolicited pong is not
expected.
5.6. Data Frames
Data frames (e.g. non-control frames) are identified by opcodes where
the most significant bit of the opcode is 0. Currently defined
opcodes for data frames include 0x1 (Text), 0x2 (Binary). Opcodes
0x3-0x7 are reserved for further non-control frames yet to be
defined.
Data frames carry application-layer and/or extension-layer data. The
opcode determines the interpretation of the data:
Text
The payload data is text data encoded as UTF-8. Note that a
particular text frame might include a partial UTF-8 sequence,
however the whole message MUST contain valid UTF-8. Invalid UTF-8
in reassembled messages is handled as described in Section 8.1.
Binary
The payload data is arbitrary binary data whose interpretation is
solely up to the application layer.
5.7. Examples
_This section is non-normative._
o A single-frame unmasked text message
* 0x81 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains "Hello")
o A single-frame masked text message
* 0x81 0x85 0x37 0xfa 0x21 0x3d 0x7f 0x9f 0x4d 0x51 0x58
(contains "Hello")
o A fragmented unmasked text message
Fette & Melnikov Expires March 3, 2012 [Page 38]
Internet-Draft The WebSocket protocol August 2011
* 0x01 0x03 0x48 0x65 0x6c (contains "Hel")
* 0x80 0x02 0x6c 0x6f (contains "lo")
o Unmasked Ping request and masked Ping response
* 0x89 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains a body of "Hello",
but the contents of the body are arbitrary)
* 0x8a 0x85 0x37 0xfa 0x21 0x3d 0x7f 0x9f 0x4d 0x51 0x58
(contains a body of "Hello", matching the body of the ping)
o 256 bytes binary message in a single unmasked frame
* 0x82 0x7E 0x0100 [256 bytes of binary data]
o 64KiB binary message in a single unmasked frame
* 0x82 0x7F 0x0000000000010000 [65536 bytes of binary data]
5.8. Extensibility
The protocol is designed to allow for extensions, which will add
capabilities to the base protocols. The endpoints of a connection
MUST negotiate the use of any extensions during the opening
handshake. This specification provides opcodes 0x3 through 0x7 and
0xB through 0xF, the extension data field, and the frame-rsv1, frame-
rsv2, and frame-rsv3 bits of the frame header for use by extensions.
The negotiation of extensions is discussed in further detail in
Section 9.1. Below are some anticipated uses of extensions. This
list is neither complete nor prescriptive.
o Extension data may be placed in the payload data before the
application data.
o Reserved bits can be allocated for per-frame needs.
o Reserved opcode values can be defined.
o Reserved bits can be allocated to the opcode field if more opcode
values are needed.
o A reserved bit or an "extension" opcode can be defined which
allocates additional bits out of the payload data to define larger
opcodes or more per-frame bits.
Fette & Melnikov Expires March 3, 2012 [Page 39]
Internet-Draft The WebSocket protocol August 2011
6. Sending and Receiving Data
6.1. Sending Data
To _Send a WebSocket Message_ comprising of /data/ over a WebSocket
connection, an endpoint MUST perform the following steps.
1. The endpoint MUST ensure the WebSocket connection is in the OPEN
state (cf. Section 4.1 and Section 4.2.2.) If at any point the
state of the WebSocket connection changes, the endpoint MUST
abort the following steps.
2. An endpoint MUST encapsulate the /data/ in a WebSocket frame as
defined in Section 5.2. If the data to be sent is large, or if
the data is not available in its entirety at the point the
endpoint wishes to begin sending the data, the endpoint MAY
alternately encapsulate the data in a series of frames as defined
in Section 5.4.
3. The opcode (frame-opcode) of the first frame containing the data
MUST be set to the appropriate value from Section 5.2 for data
that is to be interpreted by the recipient as text or binary
data.
4. The FIN bit (frame-fin) of the last frame containing the data
MUST be set to 1 as defined in Section 5.2.
5. If the data is being sent by the client, the frame(s) MUST be
masked as defined in Section 5.3.
6. If any extensions (Section 9) have been negotiated for the
WebSocket connection, additional considerations may apply as per
the definition of those extensions.
7. The frame(s) that have been formed MUST be transmitted over the
underlying network connection.
6.2. Receiving Data
To receive WebSocket data, an endpoint listens on the underlying
network connection. Incoming data MUST be parsed as WebSocket frames
as defined in Section 5.2. If a control frame (Section 5.5) is
received, the frame MUST be handled as defined by Section 5.5. Upon
receiving a data frame (Section 5.6), the endpoint MUST note the
/type/ of the data as defined by the Opcode (frame-opcode) from
Section 5.2. The _Application Data_ from this frame is defined as
the /data/ of the message. If the frame comprises an unfragmented
message (Section 5.4), it is said that _A WebSocket Message Has Been
Fette & Melnikov Expires March 3, 2012 [Page 40]
Internet-Draft The WebSocket protocol August 2011
Received_ with type /type/ and data /data/. If the frame is part of
a fragmented message, the _Application Data_ of the subsequent data
frames is concatenated to form the /data/. When the last fragment is
received as indicated by the FIN bit (frame-fin), it is said that _A
WebSocket Message Has Been Received_ with data /data/ (comprised of
the concatenation of the _Application Data_ of the fragments) and
type /type/ (noted from the first frame of the fragmented message).
Subsequent data frames MUST be interpreted as belonging to a new
WebSocket Message.
Extensions (Section 9) MAY change the semantics of how data is read,
specifically including what comprises a message boundary.
Extensions, in addition to adding "Extension data" before the
"Application data" in a payload, MAY also modify the "Application
data" (such as by compressing it).
A server MUST remove masking for data frames received from a client
as described in Section 5.3.
Fette & Melnikov Expires March 3, 2012 [Page 41]
Internet-Draft The WebSocket protocol August 2011
7. Closing the connection
7.1. Definitions
7.1.1. Close the WebSocket Connection
To _Close the WebSocket Connection_, an endpoint closes the
underlying TCP connection. An endpoint SHOULD use a method that
cleanly closes the TCP connection, as well as the TLS session, if
applicable, discarding any trailing bytes that may be received. An
endpoint MAY close the connection via any means available when
necessary, such as when under attack.
The underlying TCP connection, in most normal cases, SHOULD be closed
first by the server, so that it holds the TIME_WAIT state and not the
client (as this would prevent it from re-opening the connection for 2
MSL, while there is no corresponding server impact as a TIME_WAIT
connection is immediately reopened upon a new SYN with a higher seq
number). In abnormal cases (such as not having received a TCP Close
from the server after a reasonable amount of time) a client MAY
initiate the TCP Close. As such, when a server is instructed to
_Close the WebSocket Connection_ it SHOULD initiate a TCP Close
immediately, and when a client is instructed to do the same, it
SHOULD wait for a TCP Close from the server.
As an example of how to obtain a clean closure in C using Berkeley
sockets, one would call shutdown() with SHUT_WR on the socket, call
recv() until obtaining a return value of 0 indicating that the peer
has also performed an orderly shutdown, and finally calling close()
on the socket.
7.1.2. Start the WebSocket Closing Handshake
To _Start the WebSocket Closing Handshake_ with a status code
(Section 7.4) /code/ and an optional close reason (Section 7.1.6)
/reason/, an endpoint MUST send a Close control frame, as described
in Section 5.5.1 whose status code is set to /code/ and whose close
reason is set to /reason/. Once an endpoint has both sent and
received a Close control frame, that endpoint SHOULD _Close the
WebSocket Connection_ as defined in Section 7.1.1.
7.1.3. The WebSocket Closing Handshake is Started
Upon either sending or receiving a Close control frame, it is said
that _The WebSocket Closing Handshake is Started_ and that the
WebSocket connection is in the CLOSING state.
Fette & Melnikov Expires March 3, 2012 [Page 42]
Internet-Draft The WebSocket protocol August 2011
7.1.4. The WebSocket Connection is Closed
When the underlying TCP connection is closed, it is said that _The
WebSocket Connection is Closed_ and that the WebSocket connection is
in the CLOSED state. If the tcp connection 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.
7.1.5. The WebSocket Connection Close Code
As defined in Section 5.5.1 and Section 7.4, a Close control frame
may contain a status code indicating a reason for closure. A closing
of the WebSocket connection may be initiated by either endpoint,
potentially simultaneously. _The WebSocket Connection Close Code_ is
defined as the status code (Section 7.4) contained in the first Close
control frame received by the application implementing this protocol.
If this Close control frame contains no status code, _The WebSocket
Connection Close Code_ is considered to be 1005. If _The WebSocket
Connection is Closed_ and no Close control frame was received by the
endpoint (such as could occur if the underlying transport connection
is lost), _The WebSocket Connection Close Code_ is considered to be
1006.
NOTE: Two endpoints may not agree on the value of _The WebSocket
Connection Close Code_. As an example, if the remote endpoint sent a
Close frame but the local application has not yet read the data
containing the Close frame from its socket's receive buffer, and the
local application independently decided to close the connection and
send a Close frame, both endpoints will have sent and received a
Close frame, and will not send further Close frames. Each endpoint
will see the Connection Close Code sent by the other end as the
_WebSocket Connection Close Code_. As such, it is possible that the
two endpoints may not agree on the value of _The WebSocket Connection
Close Code_ in the case that both endpoints _Start the WebSocket
Closing Handshake_ independently and at roughly the same time.
7.1.6. The WebSocket Connection Close Reason
As defined in Section 5.5.1 and Section 7.4, a Close control frame
may contain a status code indicating a reason for closure, followed
by UTF-8 encoded data, the interpretation of said data being left to
the endpoints and not defined by this protocol. A closing of the
WebSocket connection may be initiated by either endpoint, potentially
simultaneously. _The WebSocket Connection Close Reason_ is defined as
the UTF-8 encoded data following the status code (Section 7.4)
Fette & Melnikov Expires March 3, 2012 [Page 43]
Internet-Draft The WebSocket protocol August 2011
contained in the first Close control frame received by the
application implementing this protocol. If there is no such data in
the Close control frame, _The WebSocket Connection Close Reason_ is
the empty string.
NOTE: Following the same logic as noted in Section 7.1.5, two
endpoints may not agree on _The WebSocket Connection Close Reason_.
7.1.7. Fail the WebSocket Connection
Certain algorithms and specifications require an endpoint to _Fail
the WebSocket Connection_. To do so, the client MUST _Close the
WebSocket Connection_, and MAY report the problem to the user (which
would be especially useful for developers) in an appropriate manner.
Similarly, to do so, the server MUST _Close the WebSocket
Connection_, and SHOULD log the problem.
If _The WebSocket Connection is Established_ prior to the point where
the endpoint is required to _Fail the WebSocket Connection_, the
endpoint SHOULD send a Close frame with an appropriate status code
Section 7.4 before proceeding to _Close the WebSocket Connection_.
An endpoint MAY omit sending a Close frame if it believes the other
side is unlikely to be able to receive and process the close frame,
due to the nature of the error that led to the WebSocket connection
being failed in the first place. An endpoint MUST NOT continue to
attempt to process data (including a responding Close frame) from the
remote endpoint after being instructed to _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.
7.2. Abnormal Closures
7.2.1. Client-Initiated Closure
Certain algorithms, namely during the opening handshake, require the
client to _Fail the WebSocket Connection_. To do so, the client MUST
_Fail the WebSocket Connection_ as defined in Section 7.1.7.
If at any point the underlying transport layer connection is
unexpectedly lost, 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.
Fette & Melnikov Expires March 3, 2012 [Page 44]
Internet-Draft The WebSocket protocol August 2011
7.2.2. Server-Initiated Closure
Certain algorithms require or recommend that the server _Abort the
WebSocket Connection_ during the opening handshake. To do so, the
server MUST simply _Close the WebSocket Connection_ (Section 7.1.1).
7.2.3. Recovering From Abnormal Closure
Abnormal closures may be caused by any number of reasons. Such
closures could be the result of a transient error, in which case
reconnecting may lead to a good connection and a resumption of normal
operations. Such closures may also be the result of a nontransient
problem, in which case if each deployed client experiences an
abnormal closure and immediately and persistently tries to reconnect,
the server may experience what amounts to a denial of service attack
by a large number of clients trying to reconnect. The end result of
such a scenario could be that the service is unable to recover, or
recovey is made much more difficult, in any sort of timely manner.
To prevent this, clients SHOULD use some form of backoff when trying
to reconnect after abnormal closures as described in this section.
The first reconnect attempt SHOULD be delayed by a random amount of
time. The parameters by which this random delay is chosen are left
to the client to decide; a value chosen randomly between 0 and 5
seconds is a reasonable initial delay though clients MAY choose a
different interval from which to select a delay length based on
implementation experience and particular application.
Should the first reconnect attempt fail, subsequent reconnect
attempts SHOULD be delayed by increasingly longer amounts of time,
using a method such as truncated binary exponential backoff.
7.3. Normal Closure of Connections
Servers MAY close the WebSocket connection whenever desired. Clients
SHOULD NOT close the WebSocket connection arbitrarily. In either
case, an endpoint initiates a closure by following the procedures to
_Start the WebSocket Closing Handshake_ (Section 7.1.2).
7.4. Status Codes
When closing an established connection (e.g. when sending a Close
frame, after the opening handshake has completed), an endpoint MAY
indicate a reason for closure. The interpretation of this reason by
an endpoint, and the action an endpoint should take given this
reason, are left undefined by this specification. This specification
defines a set of pre-defined status codes, and specifies which ranges
Fette & Melnikov Expires March 3, 2012 [Page 45]
Internet-Draft The WebSocket protocol August 2011
may be used by extensions, frameworks, and end applications. The
status code and any associated textual message are optional
components of a Close frame.
7.4.1. Defined Status Codes
Endpoints MAY use the following pre-defined status codes when sending
a Close frame.
1000
1000 indicates a normal closure, meaning whatever purpose the
connection was established for has been fulfilled.
1001
1001 indicates that an endpoint is "going away", such as a server
going down, or a browser having navigated away from a page.
1002
1002 indicates that an endpoint is terminating the connection due
to a protocol error.
1003
1003 indicates that an endpoint is terminating the connection
because it has received a type of data it cannot accept (e.g. an
endpoint that understands only text data MAY send this if it
receives a binary message).
1004
Reserved. The specific meaning might be defined in the future.
1005
1005 is a reserved value and MUST NOT be set as a status code in a
Close control frame by an endpoint. It is designated for use in
applications expecting a status code to indicate that no status
code was actually present.
1006
1006 is a reserved value and MUST NOT be set as a status code in a
Close control frame by an endpoint. It is designated for use in
applications expecting a status code to indicate that the
connection was closed abnormally, e.g. without sending or
Fette & Melnikov Expires March 3, 2012 [Page 46]
Internet-Draft The WebSocket protocol August 2011
receiving a Close control frame.
1007
1007 indicates that an endpoint is terminating the connection
because it has received data that was supposed to be UTF-8 (such
as in a text frame) that was in fact not valid UTF-8 [RFC3629].
1008
1008 indicates that an endpoint is terminating the connection
because it has received a message that violates its policy. This
is a generic status code that can be returned when there is no
other more suitable status code (e.g. 1003 or 1009), or if there
is a need to hide specific details about the policy.
1009
1009 indicates that an endpoint is terminating the connection
because it has received a message which is too big for it to
process.
1010
1010 indicates that an endpoint (client) is terminating the
connection because it has expected the server to negotiate one or
more extension, but the server didn't return them in the response
message of the WebSocket handshake. The list of extensions which
are needed SHOULD appear in the /reason/ part of the Close frame.
Note that this status code is not used by the server, because it
can fail the WebSocket handshake instead.
7.4.2. Reserved Status Code Ranges
0-999
Status codes in the range 0-999 are not used.
1000-2999
Status codes in the range 1000-2999 are reserved for definition by
this protocol, its future revisions, and extensions specified in a
permanent and readily available public specification.
3000-3999
Status codes in the range 3000-3999 are reserved for use by
libraries, frameworks and application. These status codes are
Fette & Melnikov Expires March 3, 2012 [Page 47]
Internet-Draft The WebSocket protocol August 2011
registered directly with IANA. The interpretation of these codes
is undefined by this protocol.
4000-4999
Status codes in the range 4000-4999 are reserved for private use
and thus can't be registered. Such codes can be used by prior
agreements between WebSocket applications. The interpretation of
these codes is undefined by this protocol.
Fette & Melnikov Expires March 3, 2012 [Page 48]
Internet-Draft The WebSocket protocol August 2011
8. Error Handling
8.1. Handling Errors in UTF-8 Encoded Data
When an endpoint is to interpret a byte stream as UTF-8 but finds
that the byte stream is not in fact a valid UTF-8 stream, that
endpoint MUST _Fail the WebSocket Connection_. This rule applies
both during the opening handshake and during subsequent data
exchange.
Fette & Melnikov Expires March 3, 2012 [Page 49]
Internet-Draft The WebSocket protocol August 2011
9. Extensions
WebSocket clients MAY request extensions to this specification, and
WebSocket servers MAY accept some or all extensions requested by the
client. A server MUST NOT respond with any extension not requested
by the client. If extension parameters are included in negotiations
between the client and the server, those parameters MUST be chosen in
accordance with the specification of the extension to which the
parameters apply.
9.1. Negotiating Extensions
A client requests extensions by including a "Sec-WebSocket-
Extensions" header field, which follows the normal rules for HTTP
header fields (see [RFC2616] section 4.2) and the value of the header
field is defined by the following ABNF. Note that unlike other
section of the document this section is using ABNF syntax/rules from
[RFC2616], including "implied *LWS rule". If a value is received by
either the client or the server during negotiation that does not
conform to the ABNF below, the recipient of such malformed data MUST
immediately _Fail the WebSocket Connection_.
Sec-WebSocket-Extensions = extension-list
extension-list = 1#extension
extension = extension-token *( ";" extension-param )
extension-token = registered-token
registered-token = token
extension-param = token [ "=" token ]
Note that like other HTTP header fields, this header field MAY be
split or combined across multiple lines. Ergo, the following are
equivalent:
Sec-WebSocket-Extensions: foo
Sec-WebSocket-Extensions: bar; baz=2
is exactly equivalent to
Sec-WebSocket-Extensions: foo, bar; baz=2
Any extension-token used MUST be a registered token (see
Section 11.4). The parameters supplied with any given extension MUST
be defined for that extension. Note that the client is only offering
to use any advertised extensions, and MUST NOT use them unless the
server indicates that it wishes to use the extension.
Note that the order of extensions is significant. Any interactions
between multiple extensions MAY be defined in the documents defining
Fette & Melnikov Expires March 3, 2012 [Page 50]
Internet-Draft The WebSocket protocol August 2011
the extensions. In the absence of such definition, the
interpretation is that the header fields listed by the client in its
request represent a preference of the header fields it wishes to use,
with the first options listed being most preferable. The extensions
listed by the server in response represent the extensions actually in
use for the connection. Should the extensions modify the data and/or
framing, the order of operations on the data should be assumed to be
the same as the order in which the extensions are listed in the
server's response in the opening handshake.
For example, if there are two extensions "foo" and "bar", if the
header field |Sec-WebSocket-Extensions| sent by the server has the
value "foo, bar" then operations on the data will be made as
bar(foo(data)), be those changes to the data itself (such as
compression) or changes to the framing thay may "stack".
Non-normative examples of acceptable extension header fields (note
that long lines are folded for readability):
Sec-WebSocket-Extensions: deflate-stream
Sec-WebSocket-Extensions: mux; max-channels=4; flow-control,
deflate-stream
Sec-WebSocket-Extensions: private-extension
A server accepts one or more extensions by including a |Sec-
WebSocket-Extensions| header field containing one or more extensions
which were requested by the client. The interpretation of any
extension parameters, and what constitutes a valid response by a
server to a requested set of parameters by a client, will be defined
by each such extension.
9.2. Known Extensions
Extensions provide a mechanism for implementations to opt-in to
additional protocol features. This document doesn't define any
extension but implementations MAY use extensions defined separately.
Fette & Melnikov Expires March 3, 2012 [Page 51]
Internet-Draft The WebSocket protocol August 2011
10. Security Considerations
This section describes some security considerations applicable to the
WebSocket protocol. Specific security considerations are described
in subsections of this section.
10.1. Non-Browser Clients
Many threats anticipated by the WebSocket protocol protect from
malicious JavaScript running inside a trusted application such as a
web browser, for example checking of the "Origin" header field (see
below). See Section 1.6 for additional details. Such assumptions
don't hold true in a case of a more capable client.
While this protocol is intended to be used by scripts in Web pages,
it can also be used directly by hosts. Such hosts are acting on
their own behalf, and can therefore send fake "Origin" header fields,
misleading the server. Servers should therefore be careful about
assuming that they are talking directly to scripts from known
origins, and must consider that they might be accessed in unexpected
ways. In particular, a server should not trust that any input is
valid.
EXAMPLE: For example, if the server uses input as part of SQL
queries, all input text should be escaped before being passed to the
SQL server, lest the server be susceptible to SQL injection.
10.2. Origin Considerations
Servers that are not intended to process input from any Web page but
only for certain sites SHOULD verify the "Origin" field is an origin
they expect, and should only respond with the corresponding "Sec-
WebSocket-Accept" if it is an accepted origin.
The "Origin" header field protects from the attack cases when the
untrusted party is typically the author of a JavaScript application
that is executing in the context of the trusted client. The client
itself can contact the server and via the mechanism of the "Origin"
header field, determine whether to extend those communication
privileges to the JavaScript application. The intent is not to
prevent non-browsers from establishing connections, but rather to
ensure that trusted browsers under the control of potentially
malicious JavaScript cannot fake a WebSocket handshake.
Fette & Melnikov Expires March 3, 2012 [Page 52]
Internet-Draft The WebSocket protocol August 2011
10.3. Attacks On Infrastructure (Masking)
In addition to endpoints being the target of attacks via WebSockets,
other parts of web infrastructure, such as proxies, may be the
subject of an attack.
As this protocol was being developed, an experiment was conducted to
demonstrate a class of attacks on proxies that led to the poisoning
of caching proxies deployed in the wild. The general form of the
attack was to establish a connection to a server under the
"attacker's" control, perform an UPGRADE on the HTTP connection
similar to what the WebSocket protocol does to establish a
connection, and to subsequently send data over that UPGRADEd
connection that looked like a GET request for a specific known
resource (which in an attack would likely be something like a widely
deployed script for tracking hits, or a resource on an ad-serving
network). The remote server would respond with something that looked
like a response to the fake GET request, and this response would be
cached by a nonzero percentage of deployed intermediaries, thus
poisioning the cache. The net effect of this attack would be that if
a user could be convinced to visit a website the attacker controlled,
the attacker could potentially poison the cache for that user and
other users behind the same cache and run malicious script on other
origins, compromising the web security model.
To avoid such attacks on deployed intermediaries, the working group
decided to adopt a solution that would provably protect against such
attacks. There were many proposed solutions that people argued
"should" protect against the above attacks, such as adding in more
random data and null bytes to the handshake, starting each frame with
a byte that has the first (highest order) bit set such that the data
appears to be non-ASCII, and so forth, but in the end none of these
solutions were provably secure. The deployed intermediaries were
already not conforming to existing specifications, and given that we
can't possibly enumerate all of the ways in which such
nonconformities could exhibit themselves and that we cannot
exhaustively discover and test each nonconformant intermediary
against each possible attack, there was consensus to adopt an
approach that did not require people to reason about how
nonconformant intermediaries might behave. Namely, the working group
decided to mask all data from the client to the server, so that the
remote script (attacker) does not have control over how the data
being sent appears on the wire, and thus cannot construct a message
that could be mis- interpreted by an intermediary as an HTTP request.
It is necessary that the masking key is chosen randomly for each
frame. If the same key is used, or a decipherable pattern exists for
how the next key is chosen, the attacker can send a message that,
Fette & Melnikov Expires March 3, 2012 [Page 53]
Internet-Draft The WebSocket protocol August 2011
when masked, could appear to be an HTTP request (by taking the
message the attacker wishes to see on the wire, and masking it with
the next masking key to be used, when the client applies the masking
key it will effectively unmask the data.)
It is also necessary that once the transmission of a frame from a
client has begun, the payload (application supplied data) of that
frame must not be capable of being modified by the application.
Otherwise, an attacker could send a long frame where the initial data
was a known value (such as all zeros), compute the masking key being
used upon receipt of the first part of the data, and then modify the
data that is yet to be sent in the frame to appear as an HTTP request
when masked. (This is essentially the same problem described in the
previous paragraph with using a known or predictable masking key.)
If additional data is to be sent or data to be sent is somehow
changed, that new or changed data must be sent in a new frame and
thus with a new masking key. In short, once transmission of a frame
begins, the contents must not be modifiable by the remote script
(application).
The threat model being protected against is one in which the client
sends data that appears to be a HTTP request. As such, the channel
that needs to be masked is the data from the client to the server.
The data from the server to the client can be made to look like a
response, but to accomplish this request the client must also be able
to forge a request. As such, it was not deemend necessary to mask
data in both directions (the data from the server to the client is
not masked).
10.4. Implementation-Specific Limits
Implementations MAY impose implementation-specific limits on
otherwise unconstrained inputs, e.g. to prevent denial of service
attacks, to guard against running out of memory, or to work around
platform-specific limitations. For example implementations might
impose limit on frame sizes and the total message size after
reassembly from multiple frames.
10.5. WebSocket client authentication
This protocol doesn't prescribe any particular way that servers can
authenticate clients during the WebSocket handshake. The WebSocket
server can use any client authentication mechanism available to a
generic HTTP server, such as Cookies, HTTP Authentication, TLS
authentication.
Fette & Melnikov Expires March 3, 2012 [Page 54]
Internet-Draft The WebSocket protocol August 2011
10.6. Connection confidentiality and integrity
Communications confidentiality and integrity is provided by running
the WebSocket protocol over TLS (wss URIs).
For connections using TLS, the amount of benefit provided by TLS
depends greatly on the strength of the algorithms negotiated during
the TLS handshake. For example some TLS cipher mechanisms don't
provide connection confidentiality. To achieve reasonable levels of
protections, clients should use only Strong TLS algorithms. "Web
Security Context: User Interface Guidelines"
[W3C.REC-wsc-ui-20100812] discusses what constitutes Strong TLS
algorithms.
10.7. Handling of invalid data
Incoming data MUST always be validated by both clients and servers.
If at any time an endpoint is faced with data that it does not
understand, or that violates some criteria by which the endpoint
determines safety of input, or when the endpoint sees an opening
handshake that does not correspond to the values it is expecting
(e.g. incorrect path or origin in the client request), the endpoint
MAY drop the TCP connection. If the invalid data received after a
successful WebSocket handshake, the endpoint SHOULD send a Close
frame with an appropriate status code Section 7.4 before proceeding
to _Close the WebSocket Connection_. Use of a Close frame with an
appropriate status code can help in diagnosing the problem. If the
invalid data is sent during the WebSocket handshake the server SHOULD
return an appropriate HTTP [RFC2616] status code.
A common class of security problems arise when sending text data
using using the wrong encoding. This protocol specifies that
messages with a Text data type (as opposed to Binary or other types)
contain UTF-8 encoded data. Although the length is still indicated
and applications implementing this protocol should use the length to
determine where the frame actually ends, sending data in an improper
encoding may still break assumptions applications built on top of
this protocol may make, leading from anything to misinterpretation of
data to loss of data to potential security bugs.
Fette & Melnikov Expires March 3, 2012 [Page 55]
Internet-Draft The WebSocket protocol August 2011
11. IANA Considerations
11.1. Registration of new URI Schemes
11.1.1. Registration of "ws" Scheme
A |ws| URI identifies a WebSocket server and resource name.
URI scheme name.
ws
Status.
Permanent.
URI scheme syntax.
In ABNF terms using the terminals from the URI specifications:
[RFC5234] [RFC3986]
"ws:" "//" authority path-abempty [ "?" query ]
The <path-abempty> and <query> [RFC3986] components form the
resource name sent to the server to identify the kind of service
desired. Other components have the meanings described in RFC3986.
URI scheme semantics.
The only operation for this scheme is to open a connection using
the WebSocket protocol.
Encoding considerations.
Characters in the host component that are excluded by the syntax
defined above MUST be converted from Unicode to ASCII by applying
the IDNA ToASCII algorithm to the Unicode host name, with both the
AllowUnassigned and UseSTD3ASCIIRules flags set, and using the
result of this algorithm as the host in the URI. [RFC3490]
Characters in other components that are excluded by the syntax
defined above MUST be converted from Unicode to ASCII by first
encoding the characters as UTF-8 and then replacing the
corresponding bytes using their percent-encoded form as defined in
the URI and IRI specifications. [RFC3986] [RFC3987]
Applications/protocols that use this URI scheme name.
WebSocket protocol.
Interoperability considerations.
Use of WebSocket requires use of HTTP version 1.1 or higher.
Fette & Melnikov Expires March 3, 2012 [Page 56]
Internet-Draft The WebSocket protocol August 2011
Security considerations.
See "Security considerations" section above.
Contact.
HYBI WG <hybi@ietf.org>
Author/Change controller.
IETF <iesg@ietf.org>
References.
RFC XXXX
11.1.2. Registration of "wss" Scheme
A |wss| URI identifies a WebSocket server and resource name, and
indicates that traffic over that connection is to be protected via
TLS (including standard benefits of TLS such as data confidentiality
and integrity, and endpoint authentication).
URI scheme name.
wss
Status.
Permanent.
URI scheme syntax.
In ABNF terms using the terminals from the URI specifications:
[RFC5234] [RFC3986]
"wss:" "//" authority path-abempty [ "?" query ]
The <path-abempty> and <query> components form the resource name
sent to the server to identify the kind of service desired. Other
components have the meanings described in RFC3986.
URI scheme semantics.
The only operation for this scheme is to open a connection using
the WebSocket protocol, encrypted using TLS.
Encoding considerations.
Characters in the host component that are excluded by the syntax
defined above MUST be converted from Unicode to ASCII by applying
the IDNA ToASCII algorithm to the Unicode host name, with both the
AllowUnassigned and UseSTD3ASCIIRules flags set, and using the
result of this algorithm as the host in the URI. [RFC3490]
Characters in other components that are excluded by the syntax
defined above MUST be converted from Unicode to ASCII by first
Fette & Melnikov Expires March 3, 2012 [Page 57]
Internet-Draft The WebSocket protocol August 2011
encoding the characters as UTF-8 and then replacing the
corresponding bytes using their percent-encoded form as defined in
the URI and IRI specification. [RFC3986] [RFC3987]
Applications/protocols that use this URI scheme name.
WebSocket protocol over TLS.
Interoperability considerations.
Use of WebSocket requires use of HTTP version 1.1 or higher.
Security considerations.
See "Security considerations" section above.
Contact.
HYBI WG <hybi@ietf.org>
Author/Change controller.
IETF <iesg@ietf.org>
References.
RFC XXXX
11.2. Registration of the "WebSocket" HTTP Upgrade Keyword
This section defines a keyword for registration in the "HTTP Upgrade
Tokens" registry as per RFC 2817 [RFC2817].
Name of token.
WebSocket
Author/Change controller.
IETF <iesg@ietf.org>
Contact.
HYBI <hybi@ietf.org>
References.
RFC XXXX
11.3. Registration of new HTTP Header Fields
11.3.1. Sec-WebSocket-Key
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Fette & Melnikov Expires March 3, 2012 [Page 58]
Internet-Draft The WebSocket protocol August 2011
Header field name
Sec-WebSocket-Key
Applicable protocol
http
Status
standard
Author/Change controller
IETF
Specification document(s)
RFC XXXX
Related information
This header field is only used for WebSocket opening handshake.
The |Sec-WebSocket-Key| header field is used in the WebSocket opening
handshake. It is sent from the client to the server to provide part
of the information used by the server to prove that it received a
valid WebSocket opening handshake. This helps ensure that the server
does not accept connections from non-WebSocket clients (e.g. HTTP
clients) that are being abused to send data to unsuspecting WebSocket
servers.
11.3.2. Sec-WebSocket-Extensions
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Extensions
Applicable protocol
http
Status
standard
Author/Change controller
IETF
Specification document(s)
RFC XXXX
Fette & Melnikov Expires March 3, 2012 [Page 59]
Internet-Draft The WebSocket protocol August 2011
Related information
This header field is only used for WebSocket opening handshake.
The |Sec-WebSocket-Extensions| header field is used in the WebSocket
opening handshake. It is initially sent from the client to the
server, and then subsequently sent from the server to the client, to
agree on a set of protocol-level extensions to use for the duration
of the connection.
11.3.3. Sec-WebSocket-Accept
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Accept
Applicable protocol
http
Status
standard
Author/Change controller
IETF
Specification document(s)
RFC XXXX
Related information
This header field is only used for WebSocket opening handshake.
The |Sec-WebSocket-Accept| header field is used in the WebSocket
opening handshake. It is sent from the server to the client to
confirm that the server is willing to initiate the connection.
11.3.4. Sec-WebSocket-Protocol
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Protocol
Applicable protocol
http
Fette & Melnikov Expires March 3, 2012 [Page 60]
Internet-Draft The WebSocket protocol August 2011
Status
standard
Author/Change controller
IETF
Specification document(s)
RFC XXXX
Related information
This header field is only used for WebSocket opening handshake.
The |Sec-WebSocket-Protocol| header field is used in the WebSocket
opening handshake. It is sent from the client to the server and back
from the server to the client to confirm the subprotocol of the
connection. This enables scripts to both select a subprotocol and be
sure that the server agreed to serve that subprotocol.
11.3.5. Sec-WebSocket-Version
This section describes a header field for registration in the
Permanent Message Header Field Registry [RFC3864].
Header field name
Sec-WebSocket-Version
Applicable protocol
http
Status
standard
Author/Change controller
IETF
Specification document(s)
RFC XXXX
Related information
This header field is only used for WebSocket opening handshake.
The |Sec-WebSocket-Version| header field is used in the WebSocket
opening handshake. It is sent from the client to the server to
indicate the protocol version of the connection. This enables
servers to correctly interpret the opening handshake and subsequent
data being sent from the data, and close the connection if the server
cannot interpret that data in a safe manner. The |Sec-WebSocket-
Version| header field is also sent from the server to the client on
Fette & Melnikov Expires March 3, 2012 [Page 61]
Internet-Draft The WebSocket protocol August 2011
WebSocket handshake error, when the version received from the client
does not match a version understood by the server. In such a case
the header field includes the protocol version(s) supported by the
server.
Note that there is no expectation that higher version numbers are
necessarily backward compatible with lower version numbers.
11.4. WebSocket Extension Name Registry
This specification requests the creation of a new IANA registry for
WebSocket Extension names to be used with the WebSocket protocol in
accordance with the principles set out in RFC 5226 [RFC5226].
As part of this registry IANA will maintain the following
information:
Extension Identifier
The identifier of the extension, as will be used in the Sec-
WebSocket-Extension header field registered in Section 11.3.2 of
this specification. The value must conform to the requirements
for an extension-token as defined in Section 9.1 of this
specification.
Extension Common Name
The name of the extension, as the extension is generally referred
to.
Extension Definition
A reference to the document in which the extension being used with
the WebSocket protocol is defined.
Known Incompatible Extensions
A list of extension identifiers with which this extension is known
to be incompatible.
WebSocket Extension names are to be subject to "First Come First
Served" IANA registration policy [RFC5226].
There are no initial values in this registry.
11.5. WebSocket Subprotocol Name Registry
This specification requests the creation of a new IANA registry for
WebSocket Subprotocol names to be used with the WebSocket protocol in
accordance with the principles set out in RFC 5226 [RFC5226].
As part of this registry IANA will maintain the following
Fette & Melnikov Expires March 3, 2012 [Page 62]
Internet-Draft The WebSocket protocol August 2011
information:
Subprotocol Identifier
The identifier of the subprotocol, as will be used in the Sec-
WebSocket-Protocol header field registered in Section 11.3.4 of
this specification. The value must conform to the requirements
given in Paragraph 10 of Section 4.1 of this specification, namely
the value must be a token as defined by RFC 2616 [RFC2616].
Subprotocol Common Name
The name of the subprotocol, as the subprotocol is generally
referred to.
Subprotocol Definition
A reference to the document in which the subprotocol being used
with the WebSocket protocol is defined.
WebSocket Subprotocol names are to be subject to "First Come First
Served" IANA registration policy [RFC5226].
11.6. WebSocket Version Number Registry
This specification requests the creation of a new IANA registry for
WebSocket Version Numbers to be used with the WebSocket protocol in
accordance with the principles set out in RFC 5226 [RFC5226].
As part of this registry IANA will maintain the following
information:
Version Number
The version number to be used in the Sec-WebSocket-Version as
specified in Section 4.1 of this specification. The value must be
a non negative integer in the range between 0 and 255 (inclusive).
Reference
The RFC requesting a new version number.
WebSocket Version Numbers are to be subject to "IETF Review" IANA
registration policy [RFC5226]. In order to improve interoperability
with intermediate versions published in Internet Drafts, version
numbers associated with such drafts might be registered in this
registry. Note that "IETF Review" applies to registrations
corresponding to Internet Drafts.
IANA is asked to add initial values to the registry, with suggested
numerical values as these have been used in past versions of this
protocol.
Fette & Melnikov Expires March 3, 2012 [Page 63]
Internet-Draft The WebSocket protocol August 2011
Version Number | Reference
-+----------------+-----------------------------------------+-
| 0 + draft-ietf-hybi-thewebsocketprotocol-00 |
-+----------------+-----------------------------------------+-
| 1 + draft-ietf-hybi-thewebsocketprotocol-01 |
-+----------------+-----------------------------------------+-
| 2 + draft-ietf-hybi-thewebsocketprotocol-02 |
-+----------------+-----------------------------------------+-
| 3 + draft-ietf-hybi-thewebsocketprotocol-03 |
-+----------------+-----------------------------------------+-
| 4 + draft-ietf-hybi-thewebsocketprotocol-04 |
-+----------------+-----------------------------------------+-
| 5 + draft-ietf-hybi-thewebsocketprotocol-05 |
-+----------------+-----------------------------------------+-
| 6 + draft-ietf-hybi-thewebsocketprotocol-06 |
-+----------------+-----------------------------------------+-
| 7 + draft-ietf-hybi-thewebsocketprotocol-07 |
-+----------------+-----------------------------------------+-
| 8 + draft-ietf-hybi-thewebsocketprotocol-08 |
-+----------------+-----------------------------------------+-
| 9 + Reserved |
-+----------------+-----------------------------------------+-
| 10 + Reserved |
-+----------------+-----------------------------------------+-
| 11 + Reserved |
-+----------------+-----------------------------------------+-
| 12 + Reserved |
-+----------------+-----------------------------------------+-
| 13 + draft-ietf-hybi-thewebsocketprotocol-13 |
-+----------------+-----------------------------------------+-
11.7. WebSocket Close Code Number Registry
This specification requests the creation of a new IANA registry for
WebSocket Connection Close Code Numbers in accordance with the
principles set out in RFC 5226 [RFC5226].
As part of this registry IANA will maintain the following
information:
Status Code
The Status Code which denotes a reson for a WebSocket connection
closure as per Section 7.4 of this document. The status code is
an integer number between 1000 and 4999 (inclusive).
Fette & Melnikov Expires March 3, 2012 [Page 64]
Internet-Draft The WebSocket protocol August 2011
Meaning
The meaning of the status code. Each status code has to have a
unique meaning.
Contact
A contact for the entity reserving the status code.
Reference
The stable document requesting the status codes and defining their
meaning. This is required for status codes in the range 1000-
2999, and recommended for status codes in the range 3000-3999.
WebSocket Close Code Numbers are to be subject to different
registration requirements depending on their range. Unless otherwise
specified, requests are subject to "Standards Action" IANA
registration policy [RFC5226]. Requests for status codes for use by
this protocol, its subsequent versions or extensions are subject to
any one of "Standards Action", "Specification Required" (which
implies "Designated Expert") or "IESG Review" IANA registration
policies and should be granted status codes in the range 1000-2999.
Requests for status codes for use by libraries, frameworks and
applications are subject to "First Come First Served" IANA
registration policy and should be granted in the range 3000-3999.
The range of status codes from 4000-4999 is designated for Private
Use. Requests should indicate whether they are requesting status
codes for use by the WebSocket protocol (or a future version of the
protocol) or by extensions, or by libraries/frameworks/applications.
IANA is asked to add initial values to the registry, with suggested
numerical values as these have been used in past versions of this
protocol.
Fette & Melnikov Expires March 3, 2012 [Page 65]
Internet-Draft The WebSocket protocol August 2011
|Status Code | Meaning | Contact | Reference |
-+------------+-----------------+---------------+-----------|
| 1000 | Normal Closure | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1001 | Going Away | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1002 | Protocol error | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1003 | Unsupported Data| hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1004 | ---Reserved---- | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1005 | No Status Rcvd | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1006 | Abnormal Closure| hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1007 | Invalid UTF-8 | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1008 | Policy Violation| hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1009 | Message Too Big | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
| 1010 | Mandatory Ext. | hybi@ietf.org | RFC XXXX |
-+------------+-----------------+---------------+-----------|
11.8. WebSocket Opcode Registry
This specification requests the creation of a new IANA registry for
WebSocket Opcodes in accordance with the principles set out in RFC
5226 [RFC5226].
As part of this registry IANA will maintain the following
information:
Opcode
The opcode denotes the frame type of the WebSocket frame, as
defined in Section 5.2. The status code is an integer number
between 0 and 15, inclusive.
Meaning
The meaning of the opcode code.
Reference
The specification requesting the opcode.
WebSocket Opcode numbers are subject to "Standards Action" IANA
registration policy [RFC5226].
Fette & Melnikov Expires March 3, 2012 [Page 66]
Internet-Draft The WebSocket protocol August 2011
IANA is asked to add initial values to the registry, with suggested
numerical values as these have been used in past versions of this
protocol.
|Opcode | Meaning | Reference |
-+--------+-------------------------------------+-----------|
| 0 | Continuation Frame | RFC XXXX |
-+--------+-------------------------------------+-----------|
| 1 | Text Frame | RFC XXXX |
-+--------+-------------------------------------+-----------|
| 2 | Binary Frame | RFC XXXX |
-+--------+-------------------------------------+-----------|
| 8 | Connection Close Frame | RFC XXXX |
-+--------+-------------------------------------+-----------|
| 9 | Ping Frame | RFC XXXX |
-+--------+-------------------------------------+-----------|
| 10 | Pong Frame | RFC XXXX |
-+--------+-------------------------------------+-----------|
11.9. WebSocket Framing Header Bits Registry
This specification requests the creation of a new IANA registry for
WebSocket Framing Header Bits in accordance with the principles set
out in RFC 5226 [RFC5226]. This registry controls assignment of the
bits marked RSV1, RSV2, and RSV3 in Section 5.2.
These bits are reserved for future versions or extensions of this
specification.
WebSocket Framing Header Bits assignments are subject to "Standards
Action" IANA registration policy [RFC5226].
Fette & Melnikov Expires March 3, 2012 [Page 67]
Internet-Draft The WebSocket protocol August 2011
12. Using the WebSocket protocol from Other Specifications
The WebSocket protocol is intended to be used by another
specification to provide a generic mechanism for dynamic author-
defined content, e.g. in a specification defining a scripted API.
Such a specification first needs to _Establish a WebSocket
Connection_, providing that algorithm with:
o The destination, consisting of a /host/ and a /port/.
o A /resource name/, which allows for multiple services to be
identified at one host and port.
o A /secure/ flag, which is true if the connection is to be
encrypted, and false otherwise.
o An ASCII serialization of an origin that is being made responsible
for the connection. [I-D.ietf-websec-origin]
o Optionally a string identifying a protocol that is to be layered
over the WebSocket connection.
The /host/, /port/, /resource name/, and /secure/ flag are usually
obtained from a URI using the steps to parse a WebSocket URI's
components. These steps fail if the URI does not specify a
WebSocket.
If at any time the connection is to be closed, then the specification
needs to use the _Close the WebSocket Connection_ algorithm
(Section 7.1.1).
Section 7.1.4 defines when _The WebSocket Connection is Closed_.
While a connection is open, the specification will need to handle the
cases when _A WebSocket Message Has Been Received_ (Section 6.2).
To send some data /data/ to an open connection, the specification
needs to _Send a WebSocket Message_ (Section 6.1).
Fette & Melnikov Expires March 3, 2012 [Page 68]
Internet-Draft The WebSocket protocol August 2011
13. Acknowledgements
Special thanks are due to Ian Hickson, who was the original author
and editor of this protocol. The initial design of this
specification benefitted from the participation of many people in the
WHATWG and WHATWG mailing list. Contributions to that specification
are not tracked by section, but a list of all who contributed to that
specification is given in the WHATWG HTML specification at
http://whatwg.org/html5.
Special thanks also to John Tamplin for providing a significant
amount of text for the Data Framing section of this specification.
Special thanks also to Adam Barth for providing a significant amount
of text and background research for the Data Masking section of this
specification.
Special thanks to Lisa Dusseault for the Apps Area review (and for
helping to start this work), Richard Barnes for the Gen-Art review
and Magnus Westerlund for the Transport Area Review. Special thanks
to HYBI WG past and present WG chairs who tirelessly worked behind
the scene to move this work toward completion: Joe Hildebrand,
Salvatore Loreto and Gabriel Montenegro. And last but not least,
special thank you to the responsible Area Director Peter Saint-Andre.
Thank you to the following people who participated in discussions on
the HYBI WG mailing list and contributed ideas and/or provided
detailed reviews (the list is likely to be incomplete): Greg Wilkins,
John Tamplin, Willy Tarreau, Maciej Stachowiak, Jamie Lokier, Scott
Ferguson, Bjoern Hoehrmann, Julian Reschke, Dave Cridland, Andy
Green, Eric Rescorla, Inaki Baz Castillo, Martin Thomson, Roberto
Peon, Patrick McManus, Zhong Yu, Bruce Atherton, Takeshi Yoshino,
Martin J. Duerst, James Graham, Simon Pieters, Roy T. Fielding,
Mykyta Yevstifeyev, Len Holgate, Paul Colomiets, Piotr Kulaga, Brian
Raymor, Jan Koehler, Joonas Lehtolahti. Note that people listed
above didn't necessarily endorsed the end result of this work.
Fette & Melnikov Expires March 3, 2012 [Page 69]
Internet-Draft The WebSocket protocol August 2011
14. References
14.1. Normative References
[ANSI.X3-4.1986]
American National Standards Institute, "Coded Character
Set - 7-bit American Standard Code for Information
Interchange", ANSI X3.4, 1986.
[FIPS.180-2.2002]
National Institute of Standards and Technology, "Secure
Hash Standard", FIPS PUB 180-2, August 2002, <http://
csrc.nist.gov/publications/fips/fips180-2/fips180-2.pdf>.
[RFC1928] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
L. Jones, "SOCKS Protocol Version 5", RFC 1928,
March 1996.
[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
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864,
September 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
Fette & Melnikov Expires March 3, 2012 [Page 70]
Internet-Draft The WebSocket protocol August 2011
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness
Requirements for Security", BCP 106, RFC 4086, June 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[I-D.ietf-websec-origin]
Barth, A., "The Web Origin Concept",
draft-ietf-websec-origin-04 (work in progress),
August 2011.
14.2. Informative References
[WSAPI] Hickson, I., "The Web Sockets API", August 2010,
<http://dev.w3.org/html5/websockets/>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
April 2011.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[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.
[W3C.REC-wsc-ui-20100812]
Saldhana, A. and T. Roessler, "Web Security Context: User
Interface Guidelines", World Wide Web Consortium
Recommendation REC-wsc-ui-20100812, August 2010,
Fette & Melnikov Expires March 3, 2012 [Page 71]
Internet-Draft The WebSocket protocol August 2011
<http://www.w3.org/TR/2010/REC-wsc-ui-20100812>.
Fette & Melnikov Expires March 3, 2012 [Page 72]
Internet-Draft The WebSocket protocol August 2011
Authors' Addresses
Ian Fette
Google, Inc.
Email: ifette+ietf@google.com
URI: http://www.ianfette.com/
Alexey Melnikov
Isode Ltd
5 Castle Business Village
36 Station Road
Hampton, Middlesex TW12 2BX
UK
Email: Alexey.Melnikov@isode.com
Fette & Melnikov Expires March 3, 2012 [Page 73]
Html markup produced by rfcmarkup 1.129c, available from
https://tools.ietf.org/tools/rfcmarkup/