Network Working Group I. Hickson
Internet-Draft Google, Inc.
Intended status: Standards Track October 5, 2009
Expires: April 8, 2010
The Web Socket protocol
draft-hixie-thewebsocketprotocol-45
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Abstract
This protocol enables two-way communication between a user agent
running untrusted code running in a controlled environment to a
remote host that understands the protocol. It is intended to fail to
communicate with servers of pre-existing protocols like SMTP or HTTP,
while allowing HTTP servers to opt-in to supporting this protocol if
desired. It is designed to be easy to implement on the server side.
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Author's note
This document is automatically generated from the same source
document as the HTML5 specification. [HTML5]
Please send feedback to either the hybi@ietf.org list or the
whatwg@whatwg.org list.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Protocol overview . . . . . . . . . . . . . . . . . . . . 4
1.3. Design philosophy . . . . . . . . . . . . . . . . . . . . 6
1.4. Security model . . . . . . . . . . . . . . . . . . . . . . 6
1.5. Relationship to TCP/IP and HTTP . . . . . . . . . . . . . 6
1.6. Establishing a connection . . . . . . . . . . . . . . . . 7
2. Conformance requirements . . . . . . . . . . . . . . . . . . . 8
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 8
3. Web Socket URLs . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Parsing Web Socket URLs . . . . . . . . . . . . . . . . . 9
3.2. Constructing Web Socket URLs . . . . . . . . . . . . . . . 10
4. Client-side requirements . . . . . . . . . . . . . . . . . . . 11
4.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Data framing . . . . . . . . . . . . . . . . . . . . . . . 19
4.3. Closing the connection . . . . . . . . . . . . . . . . . . 20
4.4. Handling errors in UTF-8 . . . . . . . . . . . . . . . . . 20
5. Server-side requirements . . . . . . . . . . . . . . . . . . . 22
5.1. Minimal handshake . . . . . . . . . . . . . . . . . . . . 22
5.2. Handshake details . . . . . . . . . . . . . . . . . . . . 23
5.3. Data framing . . . . . . . . . . . . . . . . . . . . . . . 24
6. Closing the connection . . . . . . . . . . . . . . . . . . . . 25
7. Security considerations . . . . . . . . . . . . . . . . . . . 26
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 27
8.1. Registration of ws: scheme . . . . . . . . . . . . . . . . 27
8.2. Registration of wss: scheme . . . . . . . . . . . . . . . 28
8.3. Registration of the "WebSocket" HTTP Upgrade keyword . . . 29
9. Using the Web Socket protocol from other specifications . . . 30
10. Normative References . . . . . . . . . . . . . . . . . . . . . 31
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 32
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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 Web Socket protocol
provides. Combined with the Web Socket 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 /demo HTTP/1.1
Upgrade: WebSocket
Connection: Upgrade
Host: example.com
Origin: http://example.com
WebSocket-Protocol: sample
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The handshake from the server looks as follows:
HTTP/1.1 101 Web Socket Protocol Handshake
Upgrade: WebSocket
Connection: Upgrade
WebSocket-Origin: http://example.com
WebSocket-Location: ws://example.com/demo
WebSocket-Protocol: sample
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.
Data is sent in the form of UTF-8 text. Each frame of data starts
with a 0x00 byte and ends with a 0xFF byte, with the UTF-8 text in
between.
The Web Socket protocol uses this framing so that specifications that
use the Web Socket protocol can expose such connections using an
event-based mechanism instead of requiring users of those
specifications to implement buffering and piecing together of
messages manually.
The protocol is designed to support other frame types in future.
Instead of the 0x00 byte, other bytes might in future be defined.
Frames denoted by bytes that do not have the high bit set (0x00 to
0x7F) are treated as described above (a stream of bytes terminated by
0xFF). Frames denoted by bytes that have the high bit set (0x80 to
0xFF) or equal to 0x80) have a leading length indicator, which is
encoded as a series of 7-bit bytes stored in octets with the 8th bit
being set for all but the last byte. The remainder of the frame is
then as much data as was specified.
The following diagrams summarise the protocol:
Handshake
|
\|/
Frame type byte <-------------------------------------.
| | |
| `-- (0x00 .. 0x7F) --> Data... --> 0xFF -->-+
| |
`-- (0x80 .. 0xFF) --> Length --> Data... ------->-'
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1.3. Design philosophy
_This section is non-normative._
The Web Socket 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 Web Socket by the
application layer, in the same way that metadata is layered on top of
TCP/IP by the application layer (HTTP).
Conceptually, Web Socket is really just a layer on top of TCP/IP 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; and 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. Other
than that, it adds nothing. Basically it is intended to be as close
as possible to just exposing raw TCP/IP 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.
1.4. Security model
_This section is non-normative._
The Web Socket protocol uses the origin model used by Web browsers to
restrict which Web pages can contact a Web Socket server when the Web
Socket protocol is used from a Web page. Naturally, when the Web
Socket protocol is used directly (not from a Web page), the origin
model is not useful, as the client can provide any arbitrary origin
string.
1.5. Relationship to TCP/IP and HTTP
_This section is non-normative._
The Web Socket 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 Web Socket
protocol by default uses port 80 for regular Web Socket connections
and port 443 for Web Socket connections tunneled over TLS.
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1.6. Establishing a connection
_This section is non-normative._
There are several options for establishing a Web Socket connection.
The simplest method is to use port 80 to get a direct connection to a
Web Socket server. Port 80 traffic, however, will often be
intercepted by HTTP proxies, which can lead to the connection failing
to be established.
The second simplest method is to use TLS encryption and port 443 to
connect directly to a Web Socket 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
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 Web Socket protocol to be deployed. In more elaborate
setups (e.g. with load balancers and multiple servers), a dedicated
set of hosts for Web Socket connections separate from the HTTP
servers is probably easier to manage.
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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
*Converting a string to ASCII lowercase* means replacing all
characters in the range U+0041 .. U+005A (i.e. LATIN CAPITAL LETTER
A to LATIN CAPITAL LETTER Z) with the corresponding characters in the
range U+0061 .. U+007A (i.e. LATIN SMALL LETTER A to LATIN SMALL
LETTER Z).
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.
[HTML5]
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3. Web Socket URLs
3.1. Parsing Web Socket URLs
The steps to *parse a Web Socket 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 /protocol/ is specified but is either the empty string or
contains characters that are not in the range U+0021 .. U+007E,
then fail this algorithm.
2. If the /url/ string is not an absolute URL, then fail this
algorithm. [WEBADDRESSES]
3. 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. [WEBADDRESSES] [RFC3629]
NOTE: It doesn't matter what it is resolved relative to, since
we already know it is an absolute URL at this point.
4. If /url/ does not have a <scheme> component whose value is
either "ws" or "wss", when compared in an ASCII case-insensitive
manner, 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 Web Socket URLs
The steps to *construct a Web Socket 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/.
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4. Client-side requirements
_This section only applies to user agents, not to servers._
NOTE: This specification doesn't currently define a limit to the
number of simultaneous connections that a client can establish to a
server.
4.1. Handshake
When the user agent is to *establish a Web Socket connection* to a
host /host/, on a port /port/, from an origin whose ASCII
serialization is /origin/, with a flag /secure/, with a string giving
a /resource name/, and optionally with a string giving a /protocol/,
it must run the following steps. The /resource name/ string must
start with a U+002F SOLIDUS character (/). [ORIGIN]
1. If the user agent already has a Web Socket connection to the
remote host (IP address) identified by /host/, even if known by
another name, wait until that connection has been established or
for that connection to have failed.
NOTE: This makes it harder for a script to perform a denial of
service attack by just opening a large number of Web Socket
connections to a remote host.
NOTE: There is no limit to the number of established Web Socket
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
high load.
2. _Connect_: If the user agent is configured to use a proxy when
using the Web Socket protocol to connect to host /host/ and/or
port /port/, then connect to that proxy and ask it to open a
TCP/IP 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:
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CONNECT example.com:80 HTTP/1.1
Host: example.com
Proxy-authorization: Basic ZWRuYW1vZGU6bm9jYXBlcyE=
Otherwise, if the user agent is not configured to use a proxy,
then open a TCP/IP connection 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 Web Socket connections separate from other
proxies are encouraged to use a SOCKS proxy for Web Socket
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 Web Socket URL.
NOTE: The WebSocket protocol can be identified in proxy
autoconfiguration scripts from the scheme ("ws:" for unencrypted
connections and "wss:" for encrypted connections).
3. If the connection could not be opened, then fail the Web Socket
connection and abort these steps.
4. If /secure/ is true, perform a TLS handshake over the
connection. If this fails (e.g. the server's certificate could
not be verified), then fail the Web Socket connection and abort
these steps. Otherwise, all further communication on this
channel must run through the encrypted tunnel. [RFC2246]
5. Send the following bytes to the remote side (the server):
47 45 54 20
Send the /resource name/ value, encoded as US-ASCII.
Send the following bytes:
20 48 54 54 50 2F 31 2E 31 0D 0A 55 70 67 72 61
64 65 3A 20 57 65 62 53 6F 63 6B 65 74 0D 0A 43
6F 6E 6E 65 63 74 69 6F 6E 3A 20 55 70 67 72 61
64 65 0D 0A
NOTE: The string "GET ", the path, " HTTP/1.1", CRLF, the string
"Upgrade: WebSocket", CRLF, and the string "Connection:
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Upgrade", CRLF.
6. Send the following bytes:
48 6F 73 74 3A 20
Send the /host/ value, converted to ASCII lowercase, and encoded
as US-ASCII.
If /secure/ is false, and /port/ is not 80, or if /secure/ is
true, and /port/ is not 443, then send an 0x3A byte (ASCII :)
followed by the value of /port/, expressed as a base-ten
integer, encoded as US-ASCII.
Send the following bytes:
0D 0A
NOTE: The string "Host: ", the host, and CRLF.
7. Send the following bytes:
4F 72 69 67 69 6E 3A 20
Send the /origin/ value, converted to ASCII lowercase, encoded
as US-ASCII. [ORIGIN]
NOTE: The /origin/ value is a string that was passed to this
algorithm.
Send the following bytes:
0D 0A
NOTE: The string "Origin: ", the origin, and CRLF.
8. If there is no /protocol/, then skip this step.
Otherwise, send the following bytes:
57 65 62 53 6F 63 6B 65 74 2D 50 72 6F 74 6F 63
6F 6C 3A 20
Send the /protocol/ value, encoded as US-ASCII.
Send the following bytes:
0d 0a
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NOTE: The string "WebSocket-Protocol: ", the protocol, and CRLF.
9. If the client has any authentication information or cookies that
would be relevant to a resource accessed over HTTP, if /secure/
is false, or HTTPS, if it is true, on host /host/, port /port/,
with /resource name/ as the path (and possibly query
parameters), then HTTP headers that would be appropriate for
that information should be sent at this point. [RFC2616]
[RFC2109] [RFC2965]
Each header must be on a line of its own (each ending with a CR
LF sequence). For the purposes of this step, each header must
not be split into multiple lines (despite HTTP otherwise
allowing this with continuation lines).
EXAMPLE: For example, if the server had a username and
password that applied to |http://example.com/socket|, and the
Web Socket was being opened to |ws://example.com/socket|, it
could send them:
Authorization: Basic d2FsbGU6ZXZl
10. Send the following bytes:
0d 0a
NOTE: Just a CRLF (a blank line).
11. Read bytes from the server until either the connection closes,
or a 0x0A byte is read. Let /header/ be these bytes, including
the 0x0A byte.
If /header/ is not at least two bytes long, or if the last two
bytes aren't 0x0D and 0x0A respectively, then fail the Web
Socket connection and abort these steps.
User agents may apply a timeout to this step, failing the Web
Socket connection if the server does not send back data in a
suitable time period.
12. If /header/ consists of 44 bytes that exactly match the
following, then let /mode/ be _normal_.
48 54 54 50 2F 31 2E 31 20 31 30 31 20 57 65 62
20 53 6F 63 6B 65 74 20 50 72 6F 74 6F 63 6F 6C
20 48 61 6E 64 73 68 61 6B 65 0D 0A
NOTE: The string "HTTP/1.1 101 Web Socket Protocol Handshake"
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followed by a CRLF pair.
Otherwise, let /code/ be the substring of /header/ that starts
from the byte after the first 0x20 byte, and ends with the byte
before the second 0x20 byte. If there are not at least two 0x20
bytes in /header/, then fail the Web Socket connection and abort
these steps.
If /code/, interpreted as ASCII, is "401", then let /mode/ be
_authenticate_.
Otherwise, fail the Web Socket connection and abort these steps.
13. If /mode/ is _normal_, then read 41 bytes from the server.
If the connection closes before 41 bytes are received, or if the
41 bytes aren't exactly equal to the following bytes, then fail
the Web Socket connection and abort these steps.
55 70 67 72 61 64 65 3A 20 57 65 62 53 6F 63 6B
65 74 0D 0A 43 6F 6E 6E 65 63 74 69 6F 6E 3A 20
55 70 67 72 61 64 65 0D 0A
NOTE: The string "Upgrade: WebSocket", CRLF, the string
"Connection: Upgrade", CRLF.
User agents may apply a timeout to this step, failing the Web
Socket connection if the server does not respond with the above
bytes within a suitable time period.
NOTE: This step is skipped if /mode/ is _authenticate_.
14. Let /headers/ be a list of name-value pairs, initially empty.
15. _Header_: Let /name/ and /value/ be empty byte arrays.
16. Read a byte from the server.
If the connection closes before this byte is received, then fail
the Web Socket connection and abort these steps.
Otherwise, handle the byte as described in the appropriate entry
below:
-> If the byte is 0x0D (ASCII CR)
If the /name/ byte array is empty, then jump to the headers
processing step. Otherwise, fail the Web Socket connection
and abort these steps.
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-> If the byte is 0x0A (ASCII LF)
Fail the Web Socket connection and abort these steps.
-> If the byte is 0x3A (ASCII :)
Move on to the next step.
-> If the byte is in the range 0x41 .. 0x5A (ASCII A .. Z)
Append a byte whose value is the byte's value plus 0x20 to
the /name/ byte array and redo this step for the next byte.
-> Otherwise
Append the byte to the /name/ byte array and redo this step
for the next byte.
NOTE: This reads a header name, terminated by a colon,
converting upper-case ASCII letters to lowercase, and aborting
if a stray CR or LF is found.
17. Read a byte from the server.
If the connection closes before this byte is received, then fail
the Web Socket connection and abort these steps.
Otherwise, handle the byte as described in the appropriate entry
below:
-> If the byte is 0x20 (ASCII space)
Ignore the byte and move on to the next step.
-> Otherwise
Treat the byte as described by the list in the next step,
then move on to that next step for real.
NOTE: This skips past a space character after the colon, if
necessary.
18. Read a byte from the server.
If the connection closes before this byte is received, then fail
the Web Socket connection and abort these steps.
Otherwise, handle the byte as described in the appropriate entry
below:
-> If the byte is 0x0D (ASCII CR)
Move on to the next step.
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-> If the byte is 0x0A (ASCII LF)
Fail the Web Socket connection and abort these steps.
-> Otherwise
Append the byte to the /value/ byte array and redo this step
for the next byte.
NOTE: This reads a header value, terminated by a CRLF.
19. Read a byte from the server.
If the connection closes before this byte is received, or if the
byte is not a 0x0A byte (ASCII LF), then fail the Web Socket
connection and abort these steps.
NOTE: This skips past the LF byte of the CRLF after the header.
20. Append an entry to the /headers/ list that has the name given by
the string obtained by interpreting the /name/ byte array as a
UTF-8 byte stream and the value given by the string obtained by
interpreting the /value/ byte array as a UTF-8 byte stream.
21. Return to the "Header" step above.
22. _Headers processing_: Read a byte from the server.
If the connection closes before this byte is received, or if the
byte is not a 0x0A byte (ASCII LF), then fail the Web Socket
connection and abort these steps.
NOTE: This skips past the LF byte of the CRLF after the blank
line after the headers.
23. If /mode/ is _normal_, then: If there is not exactly one entry
in the /headers/ list whose name is "websocket-origin", or if
there is not exactly one entry in the /headers/ list whose name
is "websocket-location", or if the /protocol/ was specified but
there is not exactly one entry in the /headers/ list whose name
is "websocket-protocol", or if there are any entries in the
/headers/ list whose names are the empty string, then fail the
Web Socket connection and abort these steps. Otherwise, handle
each entry in the /headers/ list as follows:
-> If the entry's name is "websocket-origin"
If the value is not exactly equal to /origin/, converted to
ASCII lowercase, then fail the Web Socket connection and
abort these steps. [ORIGIN]
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-> If the entry's name is "websocket-location"
If the value is not exactly equal to a string obtained from
the steps to construct a Web Socket URL from /host/, /port/,
/resource name/, and the /secure/ flag, then fail the Web
Socket connection and abort these steps.
-> If the entry's name is "websocket-protocol"
If there was a /protocol/ specified, and the value is not
exactly equal to /protocol/, then fail the Web Socket
connection and abort these steps. (If no /protocol/ was
specified, the header is ignored.)
-> If the entry's name is "set-cookie" or "set-cookie2" or
another cookie-related header name
Handle the cookie as defined by the appropriate
specification, with the resource being the one with the host
/host/, the port /port/, the path (and possibly query
parameters) /resource name/, and the scheme |http| if
/secure/ is false and |https| if /secure/ is true. [RFC2109]
[RFC2965]
-> Any other name
Ignore it.
If /mode/ is _authenticate_, then: If there is not exactly one
entry in the /headers/ list whose name is "www-authenticate",
then fail the Web Socket connection and abort these steps.
Otherwise, handle each entry in the /headers/ list as follows:
-> If the entry's name is "www-authenticate"
Obtain credentials in a manner consistent with the
requirements for handling the |WWW-Authenticate| header in
HTTP, and then close the connection (if the server has not
already done so) and jump back to the step labeled _connect_,
including the relevant authentication headers in the new
request. [RFC2616]
-> Any other name
Ignore it.
24. The *Web Socket connection is established*. Now the user agent
must send and receive to and from the connection as described in
the next section.
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4.2. Data framing
Once a Web Socket connection is established, the user agent must run
through the following state machine for the bytes sent by the server.
1. Try to read a byte from the server. Let /frame type/ be that
byte.
If no byte could be read because the Web Socket connection is
closed, then abort.
2. Handle the /frame type/ byte as follows:
If the high-order bit of the /frame type/ byte is set (i.e. if
/frame type/ _and_ed with 0x80 returns 0x80)
Run these steps. If at any point during these steps a read is
attempted but fails because the Web Socket connection is
closed, then abort.
1. Let /length/ be zero.
2. _Length_: Read a byte, let /b/ be that byte.
3. Let /b_v/ be integer corresponding to the low 7 bits of
/b/ (the value you would get by _and_ing /b/ with 0x7F).
4. Multiply /length/ by 128, add /b_v/ to that result, and
store the final result in /length/.
5. If the high-order bit of /b/ is set (i.e. if /b/ _and_ed
with 0x80 returns 0x80), then return to the step above
labeled _length_.
6. Read /length/ bytes.
7. Discard the read bytes.
If the high-order bit of the /frame type/ byte is _not_ set (i.e.
if /frame type/ _and_ed with 0x80 returns 0x00)
Run these steps. If at any point during these steps a read is
attempted but fails because the Web Socket connection is
closed, then abort.
1. Let /raw data/ be an empty byte array.
2. _Data_: Read a byte, let /b/ be that byte. If the client
runs out of resources for buffering the incoming data, or
hits an artificial resource limit intended to avoid
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resource starvation, then it must fail the Web Socket
connection and abort these steps.
3. If /b/ is not 0xFF, then append /b/ to /raw data/ and
return to the previous step (labeled _data_).
4. Interpret /raw data/ as a UTF-8 string, and store that
string in /data/.
5. If /frame type/ is 0x00, then *a message has been
received* with text /data/. Otherwise, discard the data.
3. Return to the first step to read the next byte.
If the user agent is faced with content that is too large to be
handled appropriately, then it must fail the Web Socket connection.
Once a Web Socket connection is established, the user agent must use
the following steps to *send /data/ using the Web Socket*:
1. Send a 0x00 byte to the server.
2. Encode /data/ using UTF-8 and send the resulting byte stream to
the server.
3. Send a 0xFF byte to the server.
If at any point there is a fatal problem with sending data to the
server, the user agent must fail the Web Socket connection.
4.3. Closing the connection
To *fail the Web Socket connection*, the user agent must close the
Web Socket connection, and may report the problem to the user (which
would be especially useful for developers). However, user agents
must not convey the failure information to the script that attempted
the connection in a way distinguishable from the Web Socket being
closed normally.
Except as indicated above or as specified by the application layer
(e.g. a script using the Web Socket API), user agents should not
close the connection.
4.4. Handling errors in UTF-8
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
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or sequences of bytes that are not valid UTF-8 sequences must be
interpreted as a U+FFFD REPLACEMENT CHARACTER.
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5. Server-side requirements
_This section only applies to servers._
5.1. Minimal handshake
NOTE: This section describes the minimal requirements for a server-
side implementation of Web Sockets.
Listen on a port for TCP/IP. Upon receiving a connection request,
open a connection and send the following bytes back to the client:
48 54 54 50 2F 31 2E 31 20 31 30 31 20 57 65 62
20 53 6F 63 6B 65 74 20 50 72 6F 74 6F 63 6F 6C
20 48 61 6E 64 73 68 61 6B 65 0D 0A 55 70 67 72
61 64 65 3A 20 57 65 62 53 6F 63 6B 65 74 0D 0A
43 6F 6E 6E 65 63 74 69 6F 6E 3A 20 55 70 67 72
61 64 65 0D 0A
Send the string "WebSocket-Origin" followed by a U+003A COLON (:) and
a U+0020 SPACE, followed by the ASCII serialization of the origin
from which the server is willing to accept connections, followed by a
CRLF pair (0x0D 0x0A). [ORIGIN]
For instance:
WebSocket-Origin: http://example.com
Send the string "WebSocket-Location" followed by a U+003A COLON (:)
and a U+0020 SPACE, followed by the URL of the Web Socket script,
followed by a CRLF pair (0x0D 0x0A).
For instance:
WebSocket-Location: ws://example.com/demo
NOTE: Do not include the port if it is the default port for Web
Socket protocol connections of the type in question (80 for
unencrypted connections and 443 for encrypted connections).
Send another CRLF pair (0x0D 0x0A).
Read data from the client until four bytes 0x0D 0x0A 0x0D 0x0A are
read. This data must either be discarded or handled as described in
the following section describing the handshake details.
If the connection isn't dropped at this point, go to the data framing
section.
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5.2. Handshake details
The previous section ignores the data that is transmitted by the
client during the handshake.
The data sent by the client consists of a number of fields separated
by CR LF pairs (bytes 0x0D 0x0A).
The first field consists of three tokens separated by space
characters (byte 0x20). The middle token is the path being opened.
If the server supports multiple paths, then the server should echo
the value of this field in the initial handshake, as part of the URL
given on the |WebSocket-Location| line (after the appropriate scheme
and host).
If the first field does not have three tokens, the server should
abort the connection as it probably represents an errorneous client.
The remaining fields consist of name-value pairs, with the name part
separated from the value part by a colon and a space (bytes 0x3A
0x20). Of these, several are interesting:
Host (bytes 48 6F 73 74)
The value gives the hostname that the client intended to use when
opening the Web Socket. It would be of interest in particular to
virtual hosting environments, where one server might serve
multiple hosts, and might therefore want to return different data.
The right host has to be output as part of the URL given on the
|WebSocket-Location| line of the handshake described above, to
verify that the server knows that it is really representing that
host.
Origin (bytes 4F 72 69 67 69 6E)
The value gives the scheme, hostname, and port (if it's not the
default port for the given scheme) of the page that asked the
client to open the Web Socket. It would be interesting if the
server's operator had deals with operators of other sites, since
the server could then decide how to respond (or indeed, _whether_
to respond) based on which site was requesting a connection.
If the server supports connections from more than one origin, then
the server should echo the value of this field in the initial
handshake, on the |WebSocket-Origin| line.
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Other fields
Other fields can be used, such as "Cookie" or "Authorization", for
authentication purposes.
Any fields that lack the colon-space separator should be discarded
and may cause the server to disconnect.
5.3. Data framing
NOTE: This section only describes how to handle content that this
specification allows user agents to send (text). It doesn't handle
any arbitrary content in the same way that the requirements on user
agents defined earlier handle any content including possible future
extensions to the protocols.
The server must run through the following steps to process the bytes
sent by the client:
1. Read a byte from the client. Assuming everything is going
according to plan, it will be a 0x00 byte. If the byte is not a
0x00 byte, then the server may disconnect.
2. Let /raw data/ be an empty byte array.
3. _Data_: Read a byte, let /b/ be that byte.
4. If /b/ is not 0xFF, then append /b/ to /raw data/ and return to
the previous step (labeled _data_).
5. Interpret /raw data/ as a UTF-8 string, and apply whatever
server-specific processing is to occur for the resulting string.
6. Return to the first step to read the next byte.
The server must run through the following steps to send strings to
the client:
1. Send a 0x00 byte to the client to indicate the start of a string.
2. Encode /data/ using UTF-8 and send the resulting byte stream to
the client.
3. Send a 0xFF byte to the client to indicate the end of the
message.
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6. Closing the connection
To *close the Web Socket connection*, either the user agent or the
server closes the TCP/IP connection. There is no closing handshake.
Whether the user agent or the server closes the connection, it is
said that the *Web Socket connection is closed*.
When a user agent is to close the Web Socket connection, it must drop
all subsequent data from the server and must act as if the server had
immediately closed its side of the connection.
When a user agent notices that the Web Socket connection is closed,
it must immediately close its side of the connection.
Servers may close the Web Socket connection whenever desired.
User agents should not close the Web Socket connection arbitrarily.
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7. 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" headers,
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" header is an origin
they expect, and should only respond with the corresponding
"WebSocket-Origin" if it is an accepted origin. Servers that only
accept input from one origin can just send back that value in the
"WebSocket-Origin" header, 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.
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8. IANA considerations
8.1. Registration of ws: scheme
A |ws:| URL identifies a Web Socket 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 Web Socket 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.
Web Socket 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.
8.2. Registration of wss: scheme
A |wss:| URL identifies a Web Socket 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 Web Socket 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.
Web Socket 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.
8.3. 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.
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9. Using the Web Socket protocol from other specifications
The Web Socket 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 Web Socket
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. [ORIGIN]
o Optionally a string identifying a protocol that is to be layered
over the Web Socket connection.
The /host/, /port/, /resource name/, and /secure/ flag are usually
obtained from a URL using the steps to parse a Web Socket URL's
components. These steps fail if the URL does not specify a Web
Socket.
If a connection can be established, then it is said that the "Web
Socket connection is established".
If at any time the connection is to be closed, then the specification
needs to use the "close the Web Socket 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 "Web
Socket connection is closed".
While a connection is open, the specification will need to handle the
cases when "a Web Socket message has been received" with text /data/.
To send some text /data/ to an open connection, the specification
needs to "send /data/ using the Web Socket".
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10. Normative References
[HTML5] Hickson, I., "HTML5", October 2009.
[ORIGIN] Barth, A., Jackson, C., and I. Hickson, "The HTTP Origin
Header", September 2009.
[RFC2109] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2109, February 1997.
[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.
[RFC2965] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 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.
[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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[WEBADDRESSES]
Connolly, D. and C. Sperberg-McQueen, "Web addresses in
HTML 5", May 2009.
[WSAPI] Hickson, I., "The Web Sockets API", October 2009.
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Author's Address
Ian Hickson
Google, Inc.
Email: ian@hixie.ch
URI: http://ln.hixie.ch/
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