[hybi] Opera's Pre-Last Call review of websocket -06

"Simon Pieters" <simonp@opera.com> Mon, 04 April 2011 12:40 UTC

Return-Path: <simonp@opera.com>
X-Original-To: hybi@core3.amsl.com
Delivered-To: hybi@core3.amsl.com
Received: from localhost (localhost [127.0.0.1]) by core3.amsl.com (Postfix) with ESMTP id 7001F3A67D1 for <hybi@core3.amsl.com>; Mon, 4 Apr 2011 05:40:40 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -7.999
X-Spam-Level:
X-Spam-Status: No, score=-7.999 tagged_above=-999 required=5 tests=[BAYES_00=-2.599, GB_I_LETTER=-2, J_CHICKENPOX_14=0.6, RCVD_IN_DNSWL_MED=-4]
Received: from mail.ietf.org ([64.170.98.32]) by localhost (core3.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id RZnYaR0s-3Fn for <hybi@core3.amsl.com>; Mon, 4 Apr 2011 05:40:28 -0700 (PDT)
Received: from smtp.opera.com (smtp.opera.com [213.236.208.81]) by core3.amsl.com (Postfix) with ESMTP id 997C83A67D8 for <hybi@ietf.org>; Mon, 4 Apr 2011 05:40:27 -0700 (PDT)
Received: from simon-pieterss-macbook.local ([87.253.73.138]) (authenticated bits=0) by smtp.opera.com (8.14.3/8.14.3/Debian-5+lenny1) with ESMTP id p34Cg70Z004677 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NOT); Mon, 4 Apr 2011 12:42:07 GMT
Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes
To: "hybi@ietf.org" <hybi@ietf.org>
References: <op.vs9bponnidj3kv@simon-pieterss-macbook.local> <op.vs9li6der4mipi@emoller-pc.gothenburg.osa>
Date: Mon, 04 Apr 2011 14:42:05 +0200
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
From: "Simon Pieters" <simonp@opera.com>
Message-ID: <op.vteywfw6idj3kv@simon-pieterss-macbook.local>
In-Reply-To: <op.vs9li6der4mipi@emoller-pc.gothenburg.osa>
User-Agent: Opera Mail/11.10 (MacIntel)
Subject: [hybi] Opera's Pre-Last Call review of websocket -06
X-BeenThere: hybi@ietf.org
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: Server-Initiated HTTP <hybi.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/listinfo/hybi>, <mailto:hybi-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/hybi>
List-Post: <mailto:hybi@ietf.org>
List-Help: <mailto:hybi-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/hybi>, <mailto:hybi-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 04 Apr 2011 12:40:40 -0000

Hi,

We have reviewed  
http://tools.ietf.org/html/draft-ietf-hybi-thewebsocketprotocol-06

The introduction section is non-normative but has a number of MUSTs.  
Please don't have any requirements in the introduction.

Why was Sec-WebSocket-Location removed?

The spec does not define "WebSocket connection is established", "a  
WebSocket message has been received", "a WebSocket error has been  
detected", "the WebSocket closing handshake has started", which means that  
the API spec's hooks don't work and you would never get any 'open',  
'message' or 'error' events.

Should probably have some text about when pings may be sent.

Should better cover error handling, e.g. what should happen when the high  
bit is set on the 63-bit length, what happens when the RSV bits are set,  
what should happen when FIN is set but opcode is 0x00, or a control frame  
is fragmented or has length greater than 125? I'd prefer detailed  
algorithms that covered every possible case, so that it is easy to argue  
that all cases are covered and so that it is clear when to fire relevant  
events and how many, etc. Just having a list with cases that are 'errors'  
does not make it clear when the error is to be detected or what should be  
done when multiple error cases match.


> 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]

It seems this specification uses a mix of lowercase and all uppercase.

>    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.
>   The term "URI" 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.
>    [RFC3986]

HTML calls it "URL", so doesn't seem particularly consistent.

>    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.
> 3.  WebSocket URIs
> 3.1.  Parsing WebSocket URIs
>   The steps to *parse a WebSocket URI's components* from a string /uri/
>    are as follows.  These steps return either a /host/, a /port/, a
>    /resource name/, and a /secure/ flag, or they fail.
>   1.   If the /uri/ string is not an absolute URI, then fail this
>         algorithm.  [RFC3986] [RFC3987]
>   2.   Resolve the /uri/ string using the resolve a Web address
>         algorithm defined by the Web addresses specification, with the
>         URI 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 URI at this point.
>   3.   If /uri/ does not have a <scheme> component whose value, when
>         converted to ASCII lowercase, is either "ws" or "wss", then fail
>         this algorithm.
>   4.   If /uri/ has a <fragment> component, then fail this algorithm.
>   5.   If the <scheme> component of /uri/ is "ws", set /secure/ to
>         false; otherwise, if the <scheme> component is "wss", set
>         /secure/ to true; otherwise, fail this algorithm.

We already know it's either "ws" or "wss", so this can't fail.

>    6.   Let /host/ be the value of the <host> component of /uri/,
>         converted to ASCII lowercase.
>   7.   If /uri/ 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 /uri/.
>   10.  If /resource name/ is the empty string, set it to a single
>         character U+002F SOLIDUS (/).
>   11.  If /uri/ has a <query> component, then append a single U+003F
>         QUESTION MARK character (?) to /resource name/, followed by the
>         value of the <query> component.
>   12.  Return /host/, /port/, /resource name/, and /secure/.
> 3.2.  Constructing WebSocket URIs
>   The steps to *construct a WebSocket URI* from a /host/, a /port/, a
>    /resource name/, and a /secure/ flag, are as follows:
>   1.  Let /uri/ be the empty string.
>   2.  If the /secure/ flag is false, then append the string "ws://" to
>        /uri/.  Otherwise, append the string "wss://" to /uri/.
>   3.  Append /host/ to /uri/.
>   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 /uri/.
>   5.  Append /resource name/ to /uri/.
>   6.  Return /uri/.
> 3.3.  Valid WebSocket URIs
>   For a WebSocket URI 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 /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 (/).
>   Any WebSocket URIs not meeting the above criteria are considered
>    invalid, and a client MUST NOT attempt to make a connection to an
>    invalid WebSocket URI.  A client SHOULD attempt to parse a URI
>    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
>    URI, but MUST NOT attempt to connect with such an unparsed URI, and
>    instead only use the parsed version and only if that version is
>    considered valid by the criteria above.
> 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 endpoint has sent
>    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 contained completely within the frame.
>   The masking-key is a 32-bit value chosen at random by the client.
>    The masking-key MUST be derived from a strong source of entropy, and
>    the masking-key for a given frame MUST NOT make it simple for a
>    server to predict the masking-key for a subsequent frame.
>   Each masked frame consists of a 32-bit masking-key followed by
>    masked-data:
>     masked-frame  = masking-key masked-data
>      masking-key   = 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.
>   Octet i of the masked-data is the XOR of octet i of the clear text
>    frame with octet i modulo 4 of the masking-key:
>     j              = i MOD 4
>      masked-octet-i = clear-text-octet-i XOR octet-j-of-masking-key
>   When preparing a masked-frame, the client MUST pick a fresh masking-
>    key 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]
>      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
>       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]:
>      ws-frame               = frame-fin
>                                frame-rsv1
>                                frame-rsv2
>                                frame-rsv3
>                                frame-opcode
>                                frame-rsv4
>                                frame-length
>                                frame-extension
>                                application-data;
>      frame-fin              = %x0 ; more frames of this message follow
>                              / %x1 ; final frame of message
>      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 primary purpose of fragmentation is to allow sending a message
>    that is of unknown size when the message is started without having to
>    buffer that message.  If messages couldn't be fragmented, then an
>    endpoint would have to buffer the entire message so its length could
>    be counted before first byte is sent.  With fragmentation, a server
>    or intermediary may choose a reasonable size buffer, and when the
>    buffer is full write a fragment to the network.
>   A secondary use-case for fragmentation is for multiplexing, where it
>    is not desirable for a large message on one logical channel to
>    monopolize the output channel, so the MUX needs to be free to split
>    the message into smaller fragments to better share the output
>    channel.
>   The following rules apply to fragmentation:
>   o  An unfragmented message consists of a single frame with the FIN
>       bit set and an opcode other than 0.
>   o  A fragmented message consists of a single frame with the FIN bit
>       clear and an opcode other than 0, followed by zero or more frames
>       with the FIN bit clear and the opcode set to 0, and terminated by
>       a single frame with the FIN bit set and an opcode of 0.  Its
>       content is the concatenation of the application data from each of
>       those frames in order.  As an example, for a text message sent as
>       three fragments, the first fragment would have an opcode of 0x4
>       and a FIN bit clear, the second fragment would have an opcode of
>       0x0 and a FIN bit clear, and the third fragment would have an
>       opcode of 0x0 and a FIN bit that is set.
>   o  Control frames MAY be injected in the middle of a fragmented
>       message.  Control frames themselves MUST NOT be fragmented. _Note:
>       if control frames could not be interjected, the latency of a ping,
>       for example, would be very long if behind a large message.  As
>       such, an endpoint MUST be capable of handling control frames in
>       the middle of a fragmented message._

Please don't have MUSTs inside notes, since the conformance section
says notes are non-normative.

>    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.
>   o  As a consequence of these rules, all fragments of a message are of
>       the same type, as set by the first fragment's opcode.  Since
>       Control frames cannot be fragmented, the type for all fragments in
>       a message MUST be either text or binary, or one of the reserved
>       opcodes.
> 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.  Control frames can be interjected in the middle of a
>    fragmented message.
>   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 Close message MAY contain a body (the "application data" portion
>    of the frame) that indicates a reason for closing, such as an
>    endpoint shutting down, an endpoint having received a message too
>    large, or an endpoint having received a message that does not conform
>    to the format expected by the other endpoint.  If there is a body,
>    the first two bytes of the body MUST be a 2-byte integer (in network
>    byte order) representing a status code defined in Section 7.4.
>    Following the 2-byte integer the body MAY contain UTF-8 encoded data,
>    the interpretation of which is not defined by this specification.
>   The application MUST NOT send any more data messages after sending a
>    close message.

What are 'data messages'? I see data frames, but not data messages. Are
control frames allowed to be sent after close?

>    If an endpoint receives a Close message and that endpoint did not
>    previously send a Close message, the endpoint MUST send a Close
>    message in response.  It SHOULD do so as soon as is practical.
>   After both sending and receiving a close message, an endpoint
>    considers the websocket connection closed, and SHOULD close the
>    underlying TCP connection.
>   If a client and server both send a Close message at the same time,
>    both endpoints will have sent and received a Close message and should
>    consider the websocket connection closed and close the underlying TCP
>    connection.
> 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.  A Pong is issued only
>    in response to the most recent Ping.

This text is identical to the text in the previous section, except for
the last sentence. I suggest stating the requirements only once, and
making the last sentence normative by including a MUST.

> 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
>      *  0x84 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains "Hello")
>   o  A fragmented text message
>      *  0x04 0x03 0x48 0x65 0x6c (contains "Hel")
>      *  0x80 0x02 0x6c 0x6f (contains "lo")
>   o  Ping request and response
>      *  0x82 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains a body of "Hello",
>          but the contents of the body are arbitrary)
>      *  0x83 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains a body of "Hello",
>          matching the body of the ping)
>   o  256 bytes binary message in a single frame
>      *  0x85 0x7E 0x0100 [256 bytes of binary data]
>   o  64KiB binary message in a single frame
>      *  0x85 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.  The negotiation of
>    extensions is discussed in further detail in Section 8.1.  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.
> 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 URI /uri/, 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.

Section 11 says that specifications are to feed this algorithm with
/host/, /port/, /resource name/, /secure/, /origin/ and /subprotocol/.
Not /uri/. The WebSocket API invokes this algorithm in accordance with
section 11. Please make this text closer to what it is in -00.

Actually the WebSocket API also has a /defer cookies/ flag. It seems
this has not been incorporated into the spec, or has been dropped at
some point. Please take in the defer cookies stuff from
http://www.whatwg.org/specs/web-socket-protocol/ (the opening paragraph
in section 5, step 46 and 47 in the algorithm, and the *apply the
cookies* definition.

>    1.  The WebSocket URI 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.

Checking this is the responsibility of the API spec, by invoking "parse
a WebSocket URI's components" defined in this specification. If it
fails to parse, this algorithm is not invoked to begin with.

>    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.  There
>        MUST be no more than one connection in a CONNECTING state.  If

Regardless of host? So we serialize tabs as well?

>        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.

No upper limit?

>        Servers can refuse to connect users with an excessive number of
>        connections, or disconnect resource-hogging users when suffering
>        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 URI to
>        pass the function must be constructed from /host/, /port/,
>        /resource name/, and the /secure/ flag using the steps to
>        construct a WebSocket URI.
>       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.
>   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

What about popping open a dialogue if the cert is self signed?

>        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 URI is "ws://example.com/chat",
>         The first line sent SHOULD be "GET /chat HTTP/1.1"

Please don't use SHOULD in an example, since examples are non-normative.

>    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 URI.

Make it equal to /host/ since parsing a WebSocket URI's components will
convert it to lowercase.

>    5.   The request MUST contain an "Upgrade" header whose value is
>         equal to "websocket".
>   6.   The request MUST contain a "Connection" header whose value MUST
>         include the "Upgrade" token.
>   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.

Double randomly.

>         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=="
>   8.   The request MUST include a header with the name "Sec-WebSocket-
>         Origin" if the request is coming from a browser client.  If the

Maybe the conformance section should have different conformance classes
for browesr clients and non-browser clients.

>         connection is from a non-browser client, the request MAY include
>         this header if the semantics of that client match the use-case
>         described here for browser clients.  The value of this header
>         MUST be the ASCII serialization of origin of the context in
>         which the code establishing the connection is running, and MUST
>         be lower-case.  The value MUST NOT contain letters in the range
>         U+0041 to U+005A (i.e.  LATIN CAPITAL LETTER A to LATIN CAPITAL
>         LETTER Z) [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 6.
>   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 elements that comprise this
>         value MUST be non-empty strings with characters in the range
>         U+0021 to U+007E and MUST all be unique.  The ABNF for the value

and MUST all be unique strings. (just to make sure you don't think the
characters must be unique)

>         of this header is 1#(token | quoted-string), where the
>         definitions of constructs and rules are as given in [RFC2616].

I'd like this to say that, at least for browser clients, if the
algorithm was invoked with a non-empty list of /subprotocols/ then the
header MUST be included, with the values of /subprotocols/ joined by a
comma and a space, and otherwise MUST NOT be included. Otherwise a
browser would be conforming for requesting subprotocols at random.

>    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
>         interpretation and format of this header is described in
>         Section 8.1.
>   12.  The request MAY include headers associated with sending cookies,
>         as defined by the appropriate specifications
>         [I-D.ietf-httpstate-cookie].

Any cookies at random? I'd like, at least for browser clients, for this
to be tighter, as it was in -00.

>    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
>       SHA-1 of the concatenation of the Sec-WebSocket-Key (as a string,
>       not base64-decoded) with the string "258EAFA5-E914-47DA-95CA-
>       C5AB0DC85B11", the client MUST fail the WebSocket connection.

-00 had rules for failing the websocket connection if the response had
certain other errors, like the wrong type of linebreaks. What's the
deal now? I haven't reviewed the security implications, but there may
be some if clients are tolerant in their parsing of the server's
handshake.

>    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.

It seems these two paragraphs aren't needed anymore when you don't have
a detailed algorithm but just some bullet points.

> 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 WebSocket requests with an appropriate handshake, and then passes
>    the connection to another server to actually process the data frames.
>    For the purposes of this specification, the "server" is the
>    combination of both computers.
> 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,
>    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-Version" header, with a value of 6.
>   5.  Optionally, a "Sec-WebSocket-Origin" header.  This header is sent
>        by all browser clients.  A connection attempt lacking this header
>        SHOULD NOT be interpreted as coming from a browser client.
>   6.  Optionally, a "Sec-WebSocket-Protocol header, with a list of
>        values indicating which protocols the client would like to speak,
>        ordered by preference.

Missing quote.

-00 was stricter about the Sec-WebSocket-Protocol header: if the algorithm  
was fed with an empty /subprotocols/ then the header must not be included,  
else the header must be included with the values of /subprotocols/. I  
prefer that over anything-goes "optinally".

>    7.  Optionally, a "Sec-WebSocket-Extensions" header, with a list of
>        values indicating which extensions the client would like to
>        speak.  The interpretation of this header is discussed in
>        Section 8.1.
>   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

If the server supports encryption? A bit unclear... if can support
encryption but the requested URL might be ws:

>        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
>           to lowercase.  The server MAY use this information as part of
>           a determination of whether to accept the incoming connection.

I'd like a warning here that if the server doesn't validate the origin,
it means that it will accept connections from anywhere. Normally it's
the browser's responsibility to enforce same-origin restrictions, but
with websockets it's the server application developer's responsibility,
and this needs to be pointed out explicitly IMHO.

I see now that there's a paragraph discussing this in security
considerations. I'd be happy with a pointer to security considerations
here.

>        /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 or more of
>           the values from the "Sec-WebSocket-Extensions" field.  The
>           absence of such a field is equivalent to the null value.  The
>           empty string is not the same as the null value for these
>           purposes.  Extensions not listed by the client MUST NOT be
>           listed.  The method by which these values should be selected
>           and interpreted is discussed in Section 8.1.
>   3.  If the server chooses to accept the incoming connection, it must
>        reply with a valid HTTP response indicating the following.
>       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 /key/, defined above in
>            Paragraph 2 of Section 5.2.2, with the string "258EAFA5-E914-
>            47DA-95CA-C5AB0DC85B11", taking the SHA-1 hash of this
>            concatenated value to obtain a 20-byte value, and base64-
>            encoding 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.  Optionally, a "Sec-WebSocket-Protocol" header, with a value
>            /subprotocol/ as defined in Paragraph 2 of Section 5.2.2.
>       4.  Optionally, a "Sec-WebSocket-Extensions" header, with a value
>            /extensions/ as defined in Paragraph 2 of Section 5.2.2.
>   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.

The next section doesn't describe sending and receiving data.

> 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.

Maybe use the HTML spec's definition of UTF-8 with error handling:
http://www.whatwg.org/specs/web-apps/current-work/complete/infrastructure.html#decoded-as-utf-8,-with-error-handling

> 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.
> 7.  Closing the connection
> 7.1.  Definitions
> 7.1.1.  Close the WebSocket Connection
>   To _Close the WebSocket Connection_, an endpoint closes the
>    underlying TCP connection.  An endpoint SHOULD use a method that
>    cleanly closes the TCP connection, discarding any trailing bytes that
>    may be received.  And endpoint MAY close the connection via any means

s/And/An/

>    available when necessary, such as when under attack.
>   As an example of how to obtain a clean closure in C using Berkeley
>    sockets, one would call shutdown() with SHUT_WR on the socket, call
>    recv() until obtaining a return value of 0 indicating that the peer
>    has also performed an orderly shutdown, and finally calling close()
>    on the socket.

Hmm, this example seems a bit out of place.

> 7.1.2.  Start the WebSocket Closing Handshake
>   To _start the WebSocket closing handshake_, and endpoint MUST send a

s/and/an/

>    Close control frame, as described in Section 4.5.1.  Upon receiving a
>    Close control frame, the other party sends a Close control frame in
>    response.  Once an endpoint has both sent and received a Close
>    control frame, that endpoint should _Close the WebSocket Connection_
>    as defined in Section 7.1.1.

Again this repeats the same requirements from 4.5.1, but subtly
different, such that it's not clear which to follow. Please only have
the same requirement once.

> 7.1.3.  The WebSocket Connection Is Closed
>   When the underlying TCP connection is closed, it is said that _the
>    WebSocket connection is closed_.  If the tcp connection was closed
>    after the WebSocket closing handshake was completed, the WebSocket
>    connection is said to have been closed _cleanly_.
> 7.1.4.  Fail the WebSocket Connection
>   Certain algorithms and specifications require a 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) in an appropriate manner.
>   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.
> 7.2.  Abnormal closures
> 7.2.1.  Client-initiated closure
>   Certain algorithms, namely during the initial handshake, require the
>    user agent to *fail the WebSocket connection*.  To do so, the user
>    agent must _Close the WebSocket connection_ as previously defined,
>    and may report the problem to the user via an appropriate mechanism
>    (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.
> 7.2.2.  Server-initiated closure
>   Certain algorithms require or recommend that the server _abort the
>    WebSocket connection_ during the opening handshake.  To do so, the
>    server must simply _close the WebSocket connection_ (Section 7.1.1).
> 7.3.  Normal closure of connections
>   Servers MAY close the WebSocket connection whenever desired.  User
>    agents SHOULD NOT close the WebSocket connection arbitrarily.  In
>    either case, an endpoint initiates a closure by following the
>    procedures to _start the WebSocket closing handshake_
>    (Section 7.1.2).
> 7.4.  Status codes
>   When closing an established connection (e.g. when sending a Close
>    frame, after the handshake has completed), an endpoint MAY indicate a
>    reason for closure.  The interpretation of this reason by an
>    endpoint, and the action an endpoint should take given this reason,
>    are left undefined by this specification.  This specification defines
>    a set of pre-defined status codes, and specifies which ranges may be
>    used by extensions, frameworks, and end applications.  The status
>    code and any associated textual message are optional components of a
>    Close frame.
> 7.4.1.  Defined Status Codes
>   Endpoints MAY use the following pre-defined status codes when sending
>    a Close frame.
>   1000
>      1000 indicates a normal closure, meaning whatever purpose the
>       connection was established for has been fulfilled.
>   1001
>      1001 indicates that an endpoint is "going away", such as a server
>       going down, or a browser having navigated away from a page.
>   1002
>      1002 indicates that an endpoint is terminating the connection due
>       to a protocol error.
>   1003
>      1003 indicates that an endpoint is terminating the connection
>       because it has received a type of data it cannot accept (e.g. an
>       endpoint that understands only text data may send this if it
>       receives a binary message.)
>   1004
>      1004 indicates that an endpoint is terminating the connection
>       because it has received a message that is too large.
> 7.4.2.  Reserved status code ranges
>   0-999
>      Status codes in the range 0-999 are not used.
>   1000-1999
>      Status codes in the range 1000-1999 are reserved for definition by
>       this protocol.
>   2000-2999
>      Status codes in the range 2000-2999 are reserved for use by
>       extensions.
>   3000-3999
>      Status codes in the range 3000-3999 MAY be used by libraries and
>       frameworks.  The interpretation of these codes is undefined by
>       this protocol.  End applications MUST NOT use status codes in this
>       range.
>   4000-4999
>      Status codes in the range 4000-4999 MAY be used by application
>       code.  The interpretaion of these codes is undefined by this
>       protocol.
> 8.  Extensions
>   WebSocket clients MAY request extensions to this specification, and
>    WebSocket servers MAY accept some or all extensions requested by the
>    client.  A server MUST NOT respond with any extension not requested
>    by the client.  If extension parameters are included in negotiations
>    between the client and the server, those parameters MUST be chosen in
>    accordance with the specification of the extension to which the
>    parameters apply.
> 8.1.  Negotiating extensions
>   A client requests extensions by including a "Sec-WebSocket-
>    Extensions" header, which follows the normal rules for HTTP headers
>    (see [RFC2616] section 4.2) and the value of the header is defined by
>    the following ABNF:
>         extension-list = 1#extension
>          extension = extension-token *( ";" extension-param )
>          extension-token = registered-token | private-use-token
>          registered-token = token
>          private-use-token = "x-" token
>          extension-param = token [ "=" ( token | quoted-string ) ]
>   Note that like other HTTP headers, this header may be split or
>    combined across multiple lines.  Ergo, the following are equivalent:
>         Sec-WebSocket-Extensions: foo
>          Sec-WebSocket-Extensions: bar; baz=2
>   is exactly equivalent to
>         Sec-WebSocket-Extensions: foo, bar; baz=2
>   Any extension-token used must either be a registered token
>    (registration TBD), or have a prefix of "x-" to indicate a private-
>    use token.  The parameters supplied with any given extension MUST be
>    defined for that extension.  Note that the client is only offering to
>    use any advertised extensions, and MUST NOT use them unless the
>    server accepts the extension.
>   Note that the order of extensions is significant.  Any interactions
>    between multiple extensions MAY be defined in the documents defining
>    the extensions.  In the absence of such definition, the
>    interpretation is that the headers listed by the client in its
>    request represent a preference of the headers it wishes to use, with
>    the first options listed being most preferable.  The extensions
>    listed by the server in response represent the extensions actually in
>    use.  Should the extensions modify the data and/or framing, the order
>    of operations on the data should be assumed to be the same as the
>    order in which the extensions are listed in the server's response in
>    the opening handshake.
>   For example, if there are two extensions "foo" and "bar", if the
>    header |Sec-WebSocket-Extensions| sent by the server has the value
>    "foo, bar" then operations on the data will be made as
>    bar(foo(data)), be those changes to the data itself (such as
>    compression) or changes to the framing thay may "stack".
>   Non-normative examples of acceptable extension headers:
>      Sec-WebSocket-Extensions: deflate-stream
>       Sec-WebSocket-Extensions: mux; max-channels=4; flow-control,  
> deflate-stream
>       Sec-WebSocket-Extensions: x-private-extension
>   A server accepts one or more extensions by including a |Sec-
>    WebSocket-Extensions| header containing one or more extensions which
>    were requested by the client.  The interpretation of any extension
>    parameters, and what constitutes a valid response by a server to a
>    requested set of parameters by a client, will be defined by each such
>    extension.
> 8.2.  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.
> 8.2.1.  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.
> 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.
>   In addition to endpoints being the target of attacks via WebSockets,
>    other parts of web infrastructure, such as proxies, may be the
>    subject of an attack.  In particular, an intermediary may interpret a
>    WebSocket message from a client as a request, and a message from the
>    server as a response to that request.  For instance, an attacker
>    could get a browser to establish a connection to its server, get the
>    browser to send a message that looks to an intermediary like a GET
>    request for a common piece of JavaScript on another domain, and send
>    back a message that is interpreted as a cacheable response to that
>    request, thus poisioning the cache for other users.  To prevent this
>    attack, messages sent from clients are masked on the wire with a 32-
>    bit value, to prevent an attacker from controlling the bits on the
>    wire and thus lessen the probability of an attacker being able to
>    construct a message that can be misinterpreted by a proxy as a non-
>    WebSocket request.
> 10.  IANA considerations
> 10.1.  Registration of ws: scheme
>   A |ws:| URI identifies a WebSocket server and resource name.
>   URI scheme name.
>       ws
>   Status.
>       Permanent.
>   URI scheme syntax.
>       In ABNF terms using the terminals from the URI specifications:
>       [RFC5234] [RFC3986]
>           "ws" ":" 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.
>   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:| URI 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
>       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
>   This section describes a header field for registration in the
>    Permanent Message Header Field Registry.  [RFC3864]
>   Header field name
>       Sec-WebSocket-Key
>   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| header is used in the WebSocket handshake.
>    It is sent from the client to the server to provide part of the
>    information used by the server to prove that it received a valid
>    WebSocket handshake.  This helps ensure that the server does not
>    accept connections from non-WebSocket clients (e.g.  HTTP clients)
>    that are being abused to send data to unsuspecting WebSocket servers.
> 10.5.  Sec-WebSocket-Extensions
>   This section describes a header field for registration in the
>    Permanent Message Header Field Registry.  [RFC3864]
>   Header field name
>       Sec-WebSocket-Extensions
>   Applicable protocol
>       http
>   Status
>       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-Extensions| header is used in the WebSocket
>    handshake.  It is initially sent from the client to the server, and
>    then subsequently sent from the servver to the client, to agree on a
>    set of protocol-level extensions to use during the connection.
> 10.6.  Sec-WebSocket-Accept
>   This section describes a header field for registration in the
>    Permanent Message Header Field Registry.  [RFC3864]
>   Header field name
>       Sec-WebSocket-Accept
>   Applicable protocol
>       http
>   Status
>       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-Accept| header is used in the WebSocket handshake.
>    It is sent from the server to the client to confirm that the server
>    is willing to initiate the connection.
> 10.7.  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
>    verify that the server is willing to serve the script that opened the
>    connection.
> 10.8.  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.
> 10.9.  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
>   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.
> 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 URI using the steps to parse a WebSocket URI's
>    components.  These steps fail if the URI 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".

-- 
Simon Pieters
Opera Software