HyBi Working Group I. Fette
Internet-Draft Google, Inc.
Intended status: Standards Track January 11, 2011
Expires: July 15, 2011
The WebSocket protocol
draft-ietf-hybi-thewebsocketprotocol-04
Abstract
The WebSocket protocol enables two-way communication between a user
agent 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 initial
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
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Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on July 15, 2011.
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
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Protocol overview . . . . . . . . . . . . . . . . . . . . 4
1.3. Opening handshake . . . . . . . . . . . . . . . . . . . . 6
1.4. Closing handshake . . . . . . . . . . . . . . . . . . . . 8
1.5. Design philosophy . . . . . . . . . . . . . . . . . . . . 9
1.6. Security model . . . . . . . . . . . . . . . . . . . . . . 9
1.7. Relationship to TCP and HTTP . . . . . . . . . . . . . . . 10
1.8. Establishing a connection . . . . . . . . . . . . . . . . 10
1.9. Subprotocols using the WebSocket protocol . . . . . . . . 11
2. Conformance requirements . . . . . . . . . . . . . . . . . . . 12
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 12
3. WebSocket URLs . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1. Parsing WebSocket URLs . . . . . . . . . . . . . . . . . . 14
3.2. Constructing WebSocket URLs . . . . . . . . . . . . . . . 15
3.3. Valid WebSocket URLs . . . . . . . . . . . . . . . . . . . 15
4. Data Framing . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 17
4.2. Client-to-Server Masking . . . . . . . . . . . . . . . . . 17
4.3. Base Framing Protocol . . . . . . . . . . . . . . . . . . 18
4.4. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 21
4.5. Control Frames . . . . . . . . . . . . . . . . . . . . . . 22
4.5.1. Close . . . . . . . . . . . . . . . . . . . . . . . . 22
4.5.2. Ping . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.5.3. Pong . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.6. Data Frames . . . . . . . . . . . . . . . . . . . . . . . 23
4.7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.8. Extensibility . . . . . . . . . . . . . . . . . . . . . . 24
5. Opening Handshake . . . . . . . . . . . . . . . . . . . . . . 25
5.1. Client Requirements . . . . . . . . . . . . . . . . . . . 25
5.2. Server-side requirements . . . . . . . . . . . . . . . . . 29
5.2.1. Reading the client's opening handshake . . . . . . . . 29
5.2.2. Sending the server's opening handshake . . . . . . . . 30
6. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1. Handling errors in UTF-8 from the server . . . . . . . . . 33
6.2. Handling errors in UTF-8 from the client . . . . . . . . . 33
7. Closing the connection . . . . . . . . . . . . . . . . . . . . 34
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7.1. Client-initiated closure . . . . . . . . . . . . . . . . . 34
7.2. Server-initiated closure . . . . . . . . . . . . . . . . . 34
7.3. Closure . . . . . . . . . . . . . . . . . . . . . . . . . 34
8. Known extensions . . . . . . . . . . . . . . . . . . . . . . . 36
8.1. Compression . . . . . . . . . . . . . . . . . . . . . . . 36
9. Security considerations . . . . . . . . . . . . . . . . . . . 37
10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 38
10.1. Registration of ws: scheme . . . . . . . . . . . . . . . . 38
10.2. Registration of wss: scheme . . . . . . . . . . . . . . . 39
10.3. Registration of the "WebSocket" HTTP Upgrade keyword . . . 40
10.4. Sec-WebSocket-Key and Sec-WebSocket-Nonce . . . . . . . . 40
10.5. Sec-WebSocket-Location . . . . . . . . . . . . . . . . . . 41
10.6. Sec-WebSocket-Origin . . . . . . . . . . . . . . . . . . . 42
10.7. Sec-WebSocket-Protocol . . . . . . . . . . . . . . . . . . 43
10.8. Sec-WebSocket-Version . . . . . . . . . . . . . . . . . . 43
11. Using the WebSocket protocol from other specifications . . . . 45
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 46
13. Normative References . . . . . . . . . . . . . . . . . . . . . 47
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 49
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1. Introduction
1.1. Background
_This section is non-normative._
Historically, creating an instant messenger chat client as a Web
application has required an abuse of HTTP to poll the server for
updates while sending upstream notifications as distinct HTTP calls.
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:
GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Origin: http://example.com
Sec-WebSocket-Protocol: chat, superchat
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Sec-WebSocket-Version: 4
The handshake from the server looks as follows:
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: me89jWimTRKTWwrS3aRrL53YZSo=
Sec-WebSocket-Nonce: AQIDBAUGBwgJCgsMDQ4PEC==
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
headers. The meaning of these headers is specified in Section 5 of
this document. Additional headers may also be present, such as
cookies required to identify the user. 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". A message is a complete unit of data at an application
level, with the expectation that many or most applications
implementing this protocol (such as web user agents) provide APIs in
terms of sending and receiving messages. The websocket message does
not necessarily correspond to a particular network layer framing, as
a fragmented message may be coalesced, or vice versa, e.g. by an
intermediary.
Data is sent on the wire in the form of frames that have an
associated type. Broadly speaking, there are types for textual data,
which is interpreted as UTF-8 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 use.
The WebSocket protocol uses this framing so that specifications that
use the WebSocket protocol can expose such connections using an
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event-based mechanism instead of requiring users of those
specifications to implement buffering and piecing together of
messages manually.
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==
Sec-WebSocket-Origin: http://example.com
Sec-WebSocket-Protocol: chat, superchat
Sec-WebSocket-Version: 4
Headers in the handshake are sent by the client in a random order;
the order is not meaningful.
Additional headers are used to select options in the WebSocket
protocol. Options available in this version are the subprotocol
selector, |Sec-WebSocket-Protocol|, and |Cookie|, which can used for
sending cookies to the server (e.g. as an authentication mechanism).
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 of the acceptable protocols and echoes that value in its
handshake to indicate that it has selected that protocol.
Sec-WebSocket-Protocol: chat
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 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.
The |Sec-WebSocket-Origin| header is used to protect against
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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 abort the connection.
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 in the
client handshake:
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
For this header, the server has to take the value (as present in the
header, e.g. the base64-encoded version), and concatenate this with
the GUID "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, base64-encoded, of this
concatenation is then returned in the server's handshake
[FIPS.180-2.2002].
Concretely, if as in the example above, header |Sec-WebSocket-Key|
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, to give the value "s3pPLMBiTxaQ9kYGzzhZRbK+
xOo=".
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:
HTTP/1.1 101 Switching Protocols
Any status code other than 101 must be treated as a failure and the
websocket connection aborted. The headers follow the status code.
The |Connection| and |Upgrade| headers complete the HTTP Upgrade.
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The |Sec-WebSocket-Accept| header indicates whether the server is
willing to accept the connection. If present, this header 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: me89jWimTRKTWwrS3aRrL53YZSo=
These fields are checked by the Web browser when it is acting as a
|WebSocket| client for scripted pages. If the |Sec-WebSocket-Accept|
value does not match the expected value, or if the header is missing,
or if the HTTP status code is not 101, the connection will not be
established and WebSockets 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. Web browsers verify
that the server included one of the values as was specified in the
|WebSocket| constructor. 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 in HTTP.
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. Upon receiving such
a frame, the other peer sends an identical frame in acknowledgement,
if it hasn't already sent one. Upon 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.
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It is safe for both peers to initiate this handshake simultaneously.
The closing handshake is intended to replace 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 man-in-
the-middle proxies and other intermediaries.
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 (HTTP).
Conceptually, WebSocket is really just a layer on top of TCP that
adds a Web "origin"-based security model for browsers; adds an
addressing and protocol naming mechanism to support multiple services
on one port and multiple host names on one IP address; 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; and re-
implements the closing handshake in-band. Other than that, it 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
handshake also.
The protocol is intended to be extensible; future versions will
likely introduce a mechanism to compress data and might support
sending binary data.
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
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servers of pre-existing protocols like SMTP or 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, fields starting with
|Sec-| cannot be set by an attacker from a Web browser, even when
using |XMLHttpRequest|.
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.
Based on the expert recommendation of the IANA, the WebSocket
protocol by default uses port 80 for regular WebSocket connections
and port 443 for WebSocket connections tunneled over TLS.
1.8. Establishing a connection
_This section is non-normative._
There are several options for establishing a WebSocket connection.
On the face of it, the simplest method would seem to be to use port
80 to get a direct connection to a WebSocket server. Port 80
traffic, however, will often be intercepted by HTTP proxies, which
can lead to the connection failing to be established.
The most reliable method, therefore, is to use TLS encryption and
port 443 to connect directly to a WebSocket server. This has the
advantage of being more secure; however, TLS encryption can be
computationally expensive.
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
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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.
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 do not need to be registered, but if a
subprotocol is intended to be implemented by multiple independent
WebSocket servers, potential clashes with the names of subprotocols
defined independently can be avoided by using names that contain 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
"example.org's chat protocol", then the two 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.
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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", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this
document are to be interpreted as described in RFC2119. For
readability, these words do not appear in all uppercase letters in
this specification. [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.)
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.
The conformance classes defined by this specification are user agents
and servers.
2.1. Terminology
*ASCII* shall mean the character-encoding scheme defined in
[ANSI.X3-4.1986].
*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).
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.
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The term "URL" is used in this section in a manner consistent with
the terminology used in HTML, namely, to denote a string that might
or might not be a valid URI or IRI and to which certain error
handling behaviors will be applied when the string is parsed. [HTML]
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.
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3. WebSocket URLs
3.1. Parsing WebSocket URLs
The steps to *parse a WebSocket URL's components* from a string /url/
are as follows. These steps return either a /host/, a /port/, a
/resource name/, and a /secure/ flag, or they fail.
1. If the /url/ string is not an absolute URL, then fail this
algorithm. [RFC3986] [RFC3987]
2. Resolve the /url/ string using the resolve a Web address
algorithm defined by the Web addresses specification, with the
URL character encoding set to UTF-8. [RFC3629] [RFC3986]
[RFC3987]
NOTE: It doesn't matter what it is resolved relative to, since
we already know it is an absolute URL at this point.
3. If /url/ does not have a <scheme> component whose value, when
converted to ASCII lowercase, is either "ws" or "wss", then fail
this algorithm.
4. If /url/ has a <fragment> component, then fail this algorithm.
5. If the <scheme> component of /url/ is "ws", set /secure/ to
false; otherwise, the <scheme> component is "wss", set /secure/
to true.
6. Let /host/ be the value of the <host> component of /url/,
converted to ASCII lowercase.
7. If /url/ has a <port> component, then let /port/ be that
component's value; otherwise, there is no explicit /port/.
8. If there is no explicit /port/, then: if /secure/ is false, let
/port/ be 80, otherwise let /port/ be 443.
9. Let /resource name/ be the value of the <path> component (which
might be empty) of /url/.
10. If /resource name/ is the empty string, set it to a single
character U+002F SOLIDUS (/).
11. If /url/ has a <query> component, then append a single U+003F
QUESTION MARK character (?) to /resource name/, followed by the
value of the <query> component.
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12. Return /host/, /port/, /resource name/, and /secure/.
3.2. Constructing WebSocket URLs
The steps to *construct a WebSocket URL* from a /host/, a /port/, a
/resource name/, and a /secure/ flag, are as follows:
1. Let /url/ be the empty string.
2. If the /secure/ flag is false, then append the string "ws://" to
/url/. Otherwise, append the string "wss://" to /url/.
3. Append /host/ to /url/.
4. If the /secure/ flag is false and port is not 80, or if the
/secure/ flag is true and port is not 443, then append the string
":" followed by /port/ to /url/.
5. Append /resource name/ to /url/.
6. Return /url/.
3.3. Valid WebSocket URLs
For a WebSocket URL to be considered valid, the following conditions
MUST hold.
o The /host/ must be ASCII-only (i.e. it must have been punycode-
encoded already if necessary, and MUST NOT contain any characters
above U+007E).
o The /origin/ must not contain characters in the range U+0041 to
U+005A (i.e. LATIN CAPITAL LETTER A to LATIN CAPITAL LETTER Z).
o The /resource name/ string must be a non-empty string of
characters in the range U+0021 to U+007E that starts with a U+002F
SOLIDUS character (/).
o The various strings in /protocols/ MUST all be non-empty strings
with characters in the range U+0021 to U+007E and MUST all be
unique.
Any WebSocket URLs not meeting the above criteria are considered
invalid, and a client MUST NOT attempt to make a connection to an
invalid WebSocket URL. A client SHOULD attempt to parse a URL
obtained from any external source (such as a web site or a user)
using the steps specified in Section 3.1 to obtain a valid WebSocket
URL, but MUST NOT attempt to connect with such an unparsed URL, and
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instead only use the parsed version and only if that version is
considered valid by the criteria above.
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4. Data Framing
4.1. Overview
In the WebSocket protocol, data is transmitted using a sequence of
frames. Frames sent from the client to the server are masked to
avoid confusing network intermediaries, such as intercepting proxies.
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.
As such, In the absence of extensions negotiated during the opening
handshake (Section 5), all reserved bits MUST be 0 and reserved
opcode values MUST NOT be used.
A data frame MAY be transmitted by either the client or the server at
any time after handshake completion and before that host has
generated a close message (Section 4.5.1).
4.2. Client-to-Server Masking
The client MUST mask all frames sent to the server.
The masking-key is derived from information exchanged between the
client and the server in the handshake and is constant for the
duration of the WebSocket connection.
The masking-key is the SHA-1 hash of the concatenation of the value
of the Sec-WebSocket-Key header (sent from the client to the server),
the value of the Sec-WebSocket-Nonce header (sent from the server to
the client), and the string "61AC5F19-FBBA-4540-B96F-6561F1AB40A8"
(which is unique to the web socket protocol).
For example, if the Sec-WebSocket-Key header contains the value
"dGhlIHNhbXBsZSBub25jZQ==" and the Sec-WebSocket-Nonce header
contains the value "AQIDBAUGBwgJCgsMDQ4PEC==", the masking key is the
SHA-1 hash of the string "dGhlIHNhbXBsZSBub25jZQ==AQIDBAUGBwgJCgsMDQ4
PEC==61AC5F19-FBBA-4540-B96F-6561F1AB40A8", which is the sequence of
octets 0x41 0xe1 0x4f 0x78 0x31 0x1e 0x4c 0x34 0x28 0x3e 0x6d 0x8b
0x36 0x3b 0x88 0x48 0xd5 0x85 0x91 0xa7.
Each masked frame consists of a 32-bit masking-nonce followed by
masked-data:
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masked-frame = masking-nonce masked-data
masking-nonce = 4full-octet
masked-data = *full-octet
full-octet = %x00-FF
The masked-data is the clear-text frame "encrypted" using a simple
XOR cipher as follows.
1. Let the frame-key be the SHA-1 hash of the concatentation of the
masking-nonce followed by the masking-key.
2. Octet i of the masked-data is the XOR of octet i of the clear
text frame with octet i modulo 20 of the frame-key:
frame-key = SHA-1(masking-nonce || masking-key)
j = i MOD 20
masked-octet-i = clear-text-octet-i XOR octet-j-of-frame-key
When preparing a masked-frame, the client MUST pick a fresh masking-
nonce uniformly at random from the set of allowed 32-bit values. The
unpredictability of the masking-nonce is essential to prevent the
author of malicious application data from selecting the bytes that
appear on the wire.
4.3. Base Framing Protocol
This wire format for the data transfer part is described by the ABNF
given in detail in this section. A high level overview of the
framing is given in the following figure. [RFC5234]
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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|R| Payload len | Extended payload length |
|I|S|S|S| (4) |S| (7) | (16/63) |
|N|V|V|V| |V| | (if payload len==126/127) |
| |1|2|3| |4| | |
+-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
| Extended payload length continued, if payload len == 127 |
+ - - - - - - - - - - - - - - - +-------------------------------+
| | Extension data |
+-------------------------------+ - - - - - - - - - - - - - - - +
: :
+---------------------------------------------------------------+
: Application data :
+---------------------------------------------------------------+
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, RSV4: 1 bit each
Must be 0 unless an extension is negotiated which defines meanings
for non-zero values
Opcode: 4 bits
Defines the interpretation of the payload data
Payload length: 7 bits
The length of the payload: 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 high 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.
Extension data: n bytes
The extension data is 0 bytes unless there is a reserved op-code
or reserved bit present in the frame which indicates an extension
has been negotiated. Any extension MUST specify the length of the
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extension data, or how that length may be calculated, and its use
MUST be negotiated during the handshake. If present, the
extension data is included in the total payload length.
Application data: n 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]:
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ws-frame = frame-more
frame-rsv1
frame-rsv2
frame-rsv3
frame-opcode
frame-rsv4
frame-length
frame-extension
application-data;
frame-more = %x0 ; final frame of message
/ %x1 ; more frames of this message follow
frame-rsv1 = %x0 ; 1 bit, must be 0
frame-rsv2 = %x0 ; 1 bit, must be 0
frame-rsv3 = %x0 ; 1 bit, must be 0
frame-opcode = %x0 ; continuation frame
/ %x1 ; connection close
/ %x2 ; ping
/ %x3 ; pong
/ %x4 ; text frame
/ %x5 ; binary frame
/ %x6-F ; reserved
frame-rsv4 = %x0 ; 1 bit, must be 0
frame-length = %x00-7D
/ %x7E frame-length-16
/ %x7F frame-length-63
frame-length-16 = %x0000-FFFF
frame-length-63 = %x0000000000000000-7FFFFFFFFFFFFFFF
frame-extension = *( %x00-FF ) ; to be defined later
application-data = *( %x00-FF )
4.4. Fragmentation
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.
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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. Its
content is the concatenation of the application data from each of
those frames in order.
o _Note: There is an open question as to whether control frames be
interjected in the middle of a fragmented message. If so, it must
be decided whether they be fragmented (which would require keeping
a stack of "in-progress" messages)._
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 An intermediary MAY change the fragmentation of a message if the
message uses only opcode and reserved bit values known to the
intermediary.
4.5. Control Frames
Control frames have opcodes of 0x01 (Close), 0x02 (Ping), or 0x03
(Pong). Control frames are used to communicate state about the
websocket.
All control frames MUST be 125 bytes or less in length and MUST NOT
be fragmented.
4.5.1. Close
The Close message contains an opcode of 0x01.
The application MUST NOT send any more data messages after sending a
close message.
A received close message is deemed to be an acknowledgement if the
message body matches the body of a close message previously sent by
the receiver. Otherwise the close message is a close initiated by
the sender.
Upon receipt of an initiated close the endpoint MUST send a close
acknowledgment. It should do so as soon as is practical.
The websocket is considered fully closed when an endpoint has either
received a close acknowledgment or sent a close acknowledgment.
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4.5.2. Ping
The Ping message contains an opcode of 0x02.
Upon receipt of a Ping message, an endpoint MUST send a Pong message
in response. It SHOULD do so as soon as is practical. The message
bodies of the Ping and Pong MUST be the same.
4.5.3. Pong
The Pong message contains an opcode of 0x03.
Upon receipt of a Ping message, an endpoint MUST send a Pong message
in response. It SHOULD do so as soon as is practical. The message
bodies of the Ping and Pong MUST be the same.
4.6. Data Frames
All frame types not listed in Section 4.5 are data frames, which
transport application-layer data. The opcode determines the
interpretation of the application data:
Text
The payload data is text data encoded as UTF-8.
Binary
The payload data is arbitrary binary data whose interpretation is
solely up to the application layer.
4.7. Examples
_This section is non-normative._
o A single-frame text message
* 0x04 0x05 "Hello"
o A fragmented text message
* 0x84 0x03 "Hel"
* 0x00 0x02 "lo"
o Ping request and response
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* 0x02 0x05 "Hello"
* 0x03 0x05 "Hello"
o 256 bytes binary message in a single frame
* 0x05 0x7E 0x0100 [256 bytes of binary data]
o 64KiB binary message in a single frame
* 0x05 0x7F 0x0000000000010000 [65536 bytes of binary data]
4.8. 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 handshake. This
specification provides opcodes 0x6 through 0xF, the extension data
field, and the frame-rsv1, frame-rsv2, frame-rsv3, and frame-rsv4
bits of the frame header for use by extensions. Below are some
anticipated uses of extensions. This list is neither complete nor
proscriptive.
o Extension data may be placed in the payload 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 area to define larger
opcodes or more per-frame bits.
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5. Opening Handshake
5.1. Client Requirements
User agents 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 user agent for the purposes of conformance is
considered to include both the handset software and any such agents.
When the user agent is to *establish a WebSocket connection* to a
WebSocket URL /url/, it must meet the following requirements. In the
following text, we will use terms from Section 3 such as "/host/" and
"/secure/ flag" as defined in that section.
1. The WebSocket URL and its components MUST be valid according to
Section 3.3. If any of the requirements are not met, the client
MUST fail the WebSocket connection and abort these steps.
2. If the user agent already has a WebSocket connection to the
remote host (IP address) identified by /host/, even if known by
another name, the user agent MUST wait until that connection has
been established or for that connection to have failed. If
multiple connections to the same IP address are attempted
simultaneously, the user agent MUST serialize them so that there
is no more than one connection at a time running through the
following steps.
If the user agent cannot determine the IP address of the remote
host (for example because all communication is being done through
a proxy server that performs DNS queries itself), then the user
agent MUST assume for the purposes of this step that each host
name refers to a distinct remote host, but should instead limit
the total number of simultaneous connections that are not
established to a reasonably low number (e.g., in a Web browser,
to the number of tabs the user has open).
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 making use of this 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 user agent can have with a single remote host.
Servers can refuse to connect users with an excessive number of
connections, or disconnect resource-hogging users when suffering
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high load.
3. _Proxy Usage_: If the user agent is configured to use a proxy
when using the WebSocket protocol to connect to host /host/
and/or port /port/, then the user agent 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 user agent 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 user agent is not configured to use a proxy, then a direct
TCP connection SHOULD be opened to the host given by /host/ and
the 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 SOCKS 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 URL to
pass the function must be constructed from /host/, /port/,
/resource name/, and the /secure/ flag using the steps to
construct a WebSocket URL.
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 user agent MUST fail the WebSocket connection and abort
the connection attempt.
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5. If /secure/ is true, the user agent MUST perform a TLS handshake
over the connection. If this fails (e.g. the server's
certificate could not be verified), then the user agent MUST fail
the WebSocket connection and abort the connection. Otherwise,
all further communication on this channel MUST run through the
encrypted tunnel. [RFC2246]
User agents MUST use the Server Name Indication extension in the
TLS handshake. [RFC4366]
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 a handshake to the server. The handshake consists of an
HTTP upgrade request, along with a list of required and optional
headers. 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 URL is "ws://example.com/chat",
The first line sent SHOULD be "GET /chat HTTP/1.1"
3. The request must contain a "Request-URI" as part of the GET
method. This MUST match the /resource name/ Section 3.
4. The request MUST contain a "Host" header whose value is equal to
the authority component of the WebSocket URL.
5. The request MUST contain an "Upgrade" header whose value is
equal to "websocket".
6. The request MUST contain a "Connection" header whose value is
equal to "Upgrade".
7. The request MUST include a header with the name "Sec-WebSocket-
Key". The value of this header MUST be a nonce consisting of a
randomly selected 16-byte value that has been base64-encoded
[RFC3548]. The nonce MUST be randomly 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
would be "AQIDBAUGBwgJCgsMDQ4PEC=="
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8. The request MUST include a header with the name "Sec-WebSocket-
Origin". The value of this header MUST be the ASCII
serialization of origin of the context in which the code
establishing the connection is running [I-D.ietf-websec-origin].
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 would be "http://www.example.com".
9. The request MUST include a header with the name "Sec-WebSocket-
Version". The value of this header must be 4.
10. The request MAY include a header with the name "Sec-WebSocket-
Protocol". If present, this value indicates the subprotocol(s)
the client wishes to speak. The ABNF for the value of this
header is 1#(token | quoted-string), where the definitions of
/token/ and /quoted-string/ are as given in [RFC2616].
11. The request MAY include a header with the name "Sec-WebSocket-
Extensions". If present, this value indicates the protocol-
level extension(s) the client wishes to speak. The ABNF for the
value of this header is 1#(token | quoted-string), where the
definitions of /token/ and /quoted-string/ are as given in
[RFC2616].
12. The request MAY include headers associated with sending cookies,
as defined by the appropriate specifications
[I-D.ietf-httpstate-cookie].
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:
o If the status code received from the server is not 101, the client
MUST fail the WebSocket connection.
o If the response lacks an Upgrade header or the Upgrade header
contains a value that is not an ASCII case-insensitive match for
the value "websocket", the client MUST fail the WebSocket
connection.
o If the response lacks a Connection header or the Connection header
contains a value that is not an ASCII case-insensitive match for
the value "Upgrade", the client MUST fail the WebSocket
connection.
o If the response lacks a Sec-WebSocket-Accept header or the Sec-
WebSocket-Accept contains a value other than the base64-encoded
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SHA-1 of the concatenation of the Sec-WebSocket-Key with the
string "258EAFA5-E914-47DA-95CA-C5AB0DC85B11", the client MUST
fail the WebSocket connection.
Where the algorithm above requires that a user agent fail the
WebSocket connection, the user agent may first read an arbitrary
number of further bytes from the connection (and then discard them)
before actually *failing the WebSocket connection*. Similarly, if a
user agent can show that the bytes read from the connection so far
are such that there is no subsequent sequence of bytes that the
server can send that would not result in the user agent being
required to *fail the WebSocket connection*, the user agent may
immediately *fail the WebSocket connection* without waiting for those
bytes.
NOTE: The previous paragraph is intended to make it conforming for
user agents to implement the algorithm in subtly different ways that
are equivalent in all ways except that they terminate the connection
at earlier or later points. For example, it enables an
implementation to buffer the entire handshake response before
checking it, or to verify each field as it is received rather than
collecting all the fields and then checking them as a block.
5.2. 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.
EXAMPLE: For example, a data center might have a server that responds
to Web Socket 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.
5.2.1. 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 handshake consists of the following parts. If the server,
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while reading the handshake, finds that the client did not send a
handshake that matches the description below, the server must abort
the WebSocket connection.
1. An HTTP/1.1 or higher GET request, including a "Request-URI"
[RFC2616] that should be interpreted as a /resource name/
Section 3.
2. A "Host" header containing the server's authority.
3. A "Sec-WebSocket-Key" header with a base64-encoded value that,
when decoded, is 16 bytes in length.
4. A "Sec-WebSocket-Origin" header.
5. A "Sec-WebSocket-Version" header, with a value of 4.
6. Optionally, a "Sec-WebSocket-Protocol header, with a list of
values indicating which protocols the client would like to speak,
ordered by preference.
7. Optionally, a "Sec-WebSocket-Extensions" header, with a list of
values indicating which extensions the client would like to
speak.
8. Optionally, other headers, such as those used to send cookies to
a server. Unknown headers MUST be ignored.
5.2.2. 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 handshake) must run through the encrypted tunnel.
[RFC2246]
2. Establish the following information:
/origin/
The |Sec-WebSocket-Origin| header in the client's handshake
indicates the origin of the script establishing the
connection. The origin is serialized to ASCII and converted
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to lowercase. The server MAY use this information as part of
a determination of whether to accept the incoming connection.
/key/
The |Sec-WebSocket-Key| header 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 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 connection. The server MAY send a non-200
response code with a |Sec-WebSocket-Version| header indicating
the version(s) the server is capable of understanding along
with this non-200 response code.
/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.
/subprotocol/
A (possibly empty) list representing the subprotocol the
server is ready to use. If the server supports multiple
subprotocols, then the value should be derived from the
client's handshake, specifically by selecting one of the
values from the "Sec-WebSocket-Protocol" 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/
A (possibly empty) list representing the protocol-level
extensions the server is ready to use. If the server supports
multiple extensions, then the value should be derived from the
client's handshake, specifically by selecting one 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.
3. If the server chooses to accept the incoming connection, it must
reply with a valid HTTP response indicating the following.
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1. A 101 response code. Such a response could look like
"HTTP/1.1 101 Switching Protocols"
2. A "Sec-WebSocket-Accept" header. The value of this header is
constructed by concatenating the value of the client's "Sec-
WebSocket-Key" header in the client's handshake 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 this 20-byte hash.
NOTE: As an example, if the value of the "Sec-WebSocket-Key"
header 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
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.
3. A "Sec-WebSocket-Nonce" header. The value of this header
MUST be a nonce consisting of a randomly selected 16-byte
value that has been base64-encoded [RFC3548]. The nonce MUST
be randomly 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 would be "AQIDBAUGBwgJCgsMDQ4PEC==" value
4. Optionally, a "Sec-WebSocket-Protocol" header, indicating the
subprotocol, if any, the server is prepared to speak. The
value of this header must be equal to one of the values
specified by the client in its opening handshake.
5. Optionally, a "Sec-WebSocket-Extensions" header, indicating
the protocol level extensions, if any, the server is prepared
to speak. The value of this header must be a subset of the
values specified by the client in its opening handshake.
This completes the server's handshake. If the server finishes these
steps without aborting the WebSocket connection, and if the client
does not then fail the WebSocket connection, then the connection is
established and the server may begin sending and receiving data, as
described in the next section.
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6. Error Handling
6.1. Handling errors in UTF-8 from the server
When a client is to interpret a byte stream as UTF-8 but finds that
the byte stream is not in fact a valid UTF-8 stream, then any bytes
or sequences of bytes that are not valid UTF-8 sequences must be
interpreted as a U+FFFD REPLACEMENT CHARACTER.
6.2. Handling errors in UTF-8 from the client
When a server is to interpret a byte stream as UTF-8 but finds that
the byte stream is not in fact a valid UTF-8 stream, behavior is
undefined. A server could close the connection, convert invalid byte
sequences to U+FFFD REPLACEMENT CHARACTERs, store the data verbatim,
or perform application-specific processing. Subprotocols layered on
the WebSocket protocol might define specific behavior for servers.
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7. Closing the connection
7.1. Client-initiated closure
Certain algorithms require the user agent to *fail the WebSocket
connection*. To do so, the user agent must close the WebSocket
connection, and may report the problem to the user (which would be
especially useful for developers).
Except as indicated above or as specified by the application layer
(e.g. a script using the WebSocket API), user agents should not close
the connection.
User agents must not convey any failure information to scripts in a
way that would allow a script to distinguish the following
situations:
o A server whose host name could not be resolved.
o A server to which packets could not successfully be routed.
o A server that refused the connection on the specified port.
o A server that did not complete the opening handshake (e.g. because
it was not a WebSocket server).
o A WebSocket server that sent a correct opening handshake, but that
specified options that caused the client to drop the connection
(e.g. the server specified an origin that differed from the
script's).
o A WebSocket server that abruptly closed the connection after
successfully completing the opening handshake.
7.2. 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.
7.3. Closure
To *close the WebSocket connection*, the user agent or server must
close the TCP connection, using whatever mechanism possible (e.g.
either the TCP RST or FIN mechanisms). When a user agent notices
that the server has closed its connection, it must immediately close
its side of the connection also. Whether the user agent or the
server closes the connection first, it is said that the *WebSocket
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connection is closed*. If the connection was closed after the client
finished the WebSocket closing handshake, then the WebSocket
connection is said to have been closed _cleanly_.
Servers may close the WebSocket connection whenever desired. User
agents should not close the WebSocket connection arbitrarily.
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8. Known extensions
Extensions provide a mechanism for implementations to opt-in to
additional protocol features. This section defines the meaning of
well-known extensions but implementations may use extensions defined
separately as well.
8.1. Compression
The registered extension token for this compression extension is
"deflate-stream".
The extension does not have any per message extension data and it
does not define the use of any WebSocket reserved bits or op codes.
Senders using this extension MUST apply RFC 1951 encodings to all
bytes of the data stream following the handshake including both data
and control messages. The data stream MAY include multiple blocks of
both compressed and uncompressed types as defined by RFC 1951.
[RFC1951]
Senders MUST NOT delay the transmission of any portion of a WebSocket
message because the deflate encoding of the message does not end on a
byte boundary. The encodings for adjacent messages MAY appear in the
same byte if no delay in transmission is occurred by doing so.
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9. Security considerations
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" 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.
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-Origin" if it is an accepted origin. Servers that only
accept input from one origin can just send back that value in the
"Sec-WebSocket-Origin" field, without bothering to check the client's
value.
If at any time a server is faced with data that it does not
understand, or that violates some criteria by which the server
determines safety of input, or when the server sees a handshake that
does not correspond to the values the server is expecting (e.g.
incorrect path or origin), the server should just disconnect. It is
always safe to disconnect.
The biggest security risk when sending text data using this protocol
is sending data using the wrong encoding. If an attacker can trick
the server into sending data encoded as ISO-8859-1 verbatim (for
instance), rather than encoded as UTF-8, then the attacker could
inject arbitrary frames into the data stream.
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10. IANA considerations
10.1. Registration of ws: scheme
A |ws:| URL 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" ":" hier-part [ "?" query ]
The path 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.
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 specification. [RFC3986] [RFC3987]
Applications/protocols that use this URI scheme name.
WebSocket protocol.
Interoperability considerations.
None.
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Security considerations.
See "Security considerations" section above.
Contact.
Ian Hickson <ian@hixie.ch>
Author/Change controller.
Ian Hickson <ian@hixie.ch>
References.
This document.
10.2. Registration of wss: scheme
A |wss:| URL identifies a WebSocket server and resource name, and
indicates that traffic over that connection is to be encrypted.
URI scheme name.
wss
Status.
Permanent.
URI scheme syntax.
In ABNF terms using the terminals from the URI specifications:
[RFC5234] [RFC3986]
"wss" ":" hier-part [ "?" query ]
The path 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
encoding the characters as UTF-8 and then replacing the
corresponding bytes using their percent-encoded form as defined in
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the URI and IRI specification. [RFC3986] [RFC3987]
Applications/protocols that use this URI scheme name.
WebSocket protocol over TLS.
Interoperability considerations.
None.
Security considerations.
See "Security considerations" section above.
Contact.
Ian Hickson <ian@hixie.ch>
Author/Change controller.
Ian Hickson <ian@hixie.ch>
References.
This document.
10.3. Registration of the "WebSocket" HTTP Upgrade keyword
Name of token.
WebSocket
Author/Change controller.
Ian Hickson <ian@hixie.ch>
Contact.
Ian Hickson <ian@hixie.ch>
References.
This document.
10.4. Sec-WebSocket-Key and Sec-WebSocket-Nonce
This section describes two header fields for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Key
Applicable protocol
http
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Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
Header field name
Sec-WebSocket-Nonce
Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Key| and |Sec-WebSocket-Nonce| headers are used in
the WebSocket handshake. They are 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 handshake. This helps ensure that the
server does not accept connections from non-Web-Socket clients (e.g.
HTTP clients) that are being abused to send data to unsuspecting
WebSocket servers.
10.5. Sec-WebSocket-Location
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Location
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Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Location| header is used in the WebSocket
handshake. It is sent from the server to the client to confirm the
URL of the connection. This enables the client to verify that the
connection was established to the right server, port, and path,
instead of relying on the server to verify that the requested host,
port, and path are correct.
10.6. Sec-WebSocket-Origin
This section describes a header field for registration in the
Permanent Message Header Field Registry. [RFC3864]
Header field name
Sec-WebSocket-Origin
Applicable protocol
http
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Origin| header is used in the WebSocket handshake.
It is sent from the server to the client to confirm the origin of the
script that opened the connection. This enables user agents to
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verify that the server is willing to serve the script that opened the
connection.
10.7. 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
Status
reserved; do not use outside WebSocket handshake
Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Protocol| header is used in the WebSocket
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.
10.8. 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
reserved; do not use outside WebSocket handshake
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Author/Change controller
IETF
Specification document(s)
This document is the relevant specification.
Related information
None.
The |Sec-WebSocket-Version| header is used in the WebSocket
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 handshake and subsequent data being sent from
the data, and close the connection if the server cannot interpret
that data in a safe manner.
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11. 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 URL using the steps to parse a WebSocket URL's
components. These steps fail if the URL does not specify a
WebSocket.
If a connection can be established, then it is said that the
"WebSocket connection is established".
If at any time the connection is to be closed, then the specification
needs to use the "close the WebSocket connection" algorithm.
When the connection is closed, for any reason including failure to
establish the connection in the first place, it is said that 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" with text /data/.
To send some text /data/ to an open connection, the specification
needs to "send /data/ using the WebSocket".
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12. 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. [HTML]
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.
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13. Normative References
[HTML] Hickson, I., "HTML", August 2010,
<http://whatwg.org/html5>.
[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>.
[RFC1951] Deutsch, P., "DEFLATE Compressed Data Format Specification
version 1.3", RFC 1951, May 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[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.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 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.
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[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[I-D.ietf-httpstate-cookie]
Barth, A., "HTTP State Management Mechanism",
draft-ietf-httpstate-cookie-20 (work in progress),
December 2010.
[I-D.ietf-websec-origin]
Barth, A., "The Web Origin Concept",
draft-ietf-websec-origin-00 (work in progress),
December 2010.
[WSAPI] Hickson, I., "The Web Sockets API", August 2010,
<http://dev.w3.org/html5/websockets/>.
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Author's Address
Ian Fette
Google, Inc.
Email: ifette+ietf@google.com
URI: http://www.ianfette.com/
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