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rfc:rfc6455

Internet Engineering Task Force (IETF) I. Fette Request for Comments: 6455 Google, Inc. Category: Standards Track A. Melnikov ISSN: 2070-1721 Isode Ltd.

                                                         December 2011
                       The WebSocket Protocol

Abstract

 The WebSocket Protocol enables two-way communication between a client
 running untrusted code in a controlled environment to a remote host
 that has opted-in to communications from that code.  The security
 model used for this is the origin-based security model commonly used
 by web browsers.  The protocol consists of an opening handshake
 followed by basic message framing, layered over TCP.  The goal of
 this technology is to provide a mechanism for browser-based
 applications that need two-way communication with servers that does
 not rely on opening multiple HTTP connections (e.g., using
 XMLHttpRequest or <iframe>s and long polling).

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6455.

Copyright Notice

 Copyright (c) 2011 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must

Fette & Melnikov Standards Track [Page 1] RFC 6455 The WebSocket Protocol December 2011

 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.1.  Background . . . . . . . . . . . . . . . . . . . . . . . .  4
   1.2.  Protocol Overview  . . . . . . . . . . . . . . . . . . . .  5
   1.3.  Opening Handshake  . . . . . . . . . . . . . . . . . . . .  6
   1.4.  Closing Handshake  . . . . . . . . . . . . . . . . . . . .  9
   1.5.  Design Philosophy  . . . . . . . . . . . . . . . . . . . .  9
   1.6.  Security Model . . . . . . . . . . . . . . . . . . . . . . 10
   1.7.  Relationship to TCP and HTTP . . . . . . . . . . . . . . . 11
   1.8.  Establishing a Connection  . . . . . . . . . . . . . . . . 11
   1.9.  Subprotocols Using the WebSocket Protocol  . . . . . . . . 12
 2.  Conformance Requirements . . . . . . . . . . . . . . . . . . . 12
   2.1.  Terminology and Other Conventions  . . . . . . . . . . . . 13
 3.  WebSocket URIs . . . . . . . . . . . . . . . . . . . . . . . . 14
 4.  Opening Handshake  . . . . . . . . . . . . . . . . . . . . . . 14
   4.1.  Client Requirements  . . . . . . . . . . . . . . . . . . . 14
   4.2.  Server-Side Requirements . . . . . . . . . . . . . . . . . 20
     4.2.1.  Reading the Client's Opening Handshake . . . . . . . . 21
     4.2.2.  Sending the Server's Opening Handshake . . . . . . . . 22
   4.3.  Collected ABNF for New Header Fields Used in Handshake . . 25
   4.4.  Supporting Multiple Versions of WebSocket Protocol . . . . 26
 5.  Data Framing . . . . . . . . . . . . . . . . . . . . . . . . . 27
   5.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . 27
   5.2.  Base Framing Protocol  . . . . . . . . . . . . . . . . . . 28
   5.3.  Client-to-Server Masking . . . . . . . . . . . . . . . . . 32
   5.4.  Fragmentation  . . . . . . . . . . . . . . . . . . . . . . 33
   5.5.  Control Frames . . . . . . . . . . . . . . . . . . . . . . 36
     5.5.1.  Close  . . . . . . . . . . . . . . . . . . . . . . . . 36
     5.5.2.  Ping . . . . . . . . . . . . . . . . . . . . . . . . . 37
     5.5.3.  Pong . . . . . . . . . . . . . . . . . . . . . . . . . 37
   5.6.  Data Frames  . . . . . . . . . . . . . . . . . . . . . . . 38
   5.7.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . 38
   5.8.  Extensibility  . . . . . . . . . . . . . . . . . . . . . . 39
 6.  Sending and Receiving Data . . . . . . . . . . . . . . . . . . 39
   6.1.  Sending Data . . . . . . . . . . . . . . . . . . . . . . . 39
   6.2.  Receiving Data . . . . . . . . . . . . . . . . . . . . . . 40
 7.  Closing the Connection . . . . . . . . . . . . . . . . . . . . 41
   7.1.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . 41
     7.1.1.  Close the WebSocket Connection . . . . . . . . . . . . 41
     7.1.2.  Start the WebSocket Closing Handshake  . . . . . . . . 42
     7.1.3.  The WebSocket Closing Handshake is Started . . . . . . 42
     7.1.4.  The WebSocket Connection is Closed . . . . . . . . . . 42
     7.1.5.  The WebSocket Connection Close Code  . . . . . . . . . 42

Fette & Melnikov Standards Track [Page 2] RFC 6455 The WebSocket Protocol December 2011

     7.1.6.  The WebSocket Connection Close Reason  . . . . . . . . 43
     7.1.7.  Fail the WebSocket Connection  . . . . . . . . . . . . 43
   7.2.  Abnormal Closures  . . . . . . . . . . . . . . . . . . . . 44
     7.2.1.  Client-Initiated Closure . . . . . . . . . . . . . . . 44
     7.2.2.  Server-Initiated Closure . . . . . . . . . . . . . . . 44
     7.2.3.  Recovering from Abnormal Closure . . . . . . . . . . . 44
   7.3.  Normal Closure of Connections  . . . . . . . . . . . . . . 45
   7.4.  Status Codes . . . . . . . . . . . . . . . . . . . . . . . 45
     7.4.1.  Defined Status Codes . . . . . . . . . . . . . . . . . 45
     7.4.2.  Reserved Status Code Ranges  . . . . . . . . . . . . . 47
 8.  Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 48
   8.1.  Handling Errors in UTF-8-Encoded Data  . . . . . . . . . . 48
 9.  Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 48
   9.1.  Negotiating Extensions . . . . . . . . . . . . . . . . . . 48
   9.2.  Known Extensions . . . . . . . . . . . . . . . . . . . . . 50
 10. Security Considerations  . . . . . . . . . . . . . . . . . . . 50
   10.1. Non-Browser Clients  . . . . . . . . . . . . . . . . . . . 50
   10.2. Origin Considerations  . . . . . . . . . . . . . . . . . . 50
   10.3. Attacks On Infrastructure (Masking)  . . . . . . . . . . . 51
   10.4. Implementation-Specific Limits . . . . . . . . . . . . . . 52
   10.5. WebSocket Client Authentication  . . . . . . . . . . . . . 53
   10.6. Connection Confidentiality and Integrity . . . . . . . . . 53
   10.7. Handling of Invalid Data . . . . . . . . . . . . . . . . . 53
   10.8. Use of SHA-1 by the WebSocket Handshake  . . . . . . . . . 54
 11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 54
   11.1. Registration of New URI Schemes  . . . . . . . . . . . . . 54
     11.1.1. Registration of "ws" Scheme  . . . . . . . . . . . . . 54
     11.1.2. Registration of "wss" Scheme . . . . . . . . . . . . . 55
   11.2. Registration of the "WebSocket" HTTP Upgrade Keyword . . . 56
   11.3. Registration of New HTTP Header Fields . . . . . . . . . . 57
     11.3.1. Sec-WebSocket-Key  . . . . . . . . . . . . . . . . . . 57
     11.3.2. Sec-WebSocket-Extensions . . . . . . . . . . . . . . . 58
     11.3.3. Sec-WebSocket-Accept . . . . . . . . . . . . . . . . . 58
     11.3.4. Sec-WebSocket-Protocol . . . . . . . . . . . . . . . . 59
     11.3.5. Sec-WebSocket-Version  . . . . . . . . . . . . . . . . 60
   11.4. WebSocket Extension Name Registry  . . . . . . . . . . . . 61
   11.5. WebSocket Subprotocol Name Registry  . . . . . . . . . . . 61
   11.6. WebSocket Version Number Registry  . . . . . . . . . . . . 62
   11.7. WebSocket Close Code Number Registry . . . . . . . . . . . 64
   11.8. WebSocket Opcode Registry  . . . . . . . . . . . . . . . . 65
   11.9. WebSocket Framing Header Bits Registry . . . . . . . . . . 66
 12. Using the WebSocket Protocol from Other Specifications . . . . 66
 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 67
 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 68
   14.1. Normative References . . . . . . . . . . . . . . . . . . . 68
   14.2. Informative References . . . . . . . . . . . . . . . . . . 69

Fette & Melnikov Standards Track [Page 3] RFC 6455 The WebSocket Protocol December 2011

1. Introduction

1.1. Background

 _This section is non-normative._
 Historically, creating web applications that need bidirectional
 communication between a client and a server (e.g., instant messaging
 and gaming applications) has required an abuse of HTTP to poll the
 server for updates while sending upstream notifications as distinct
 HTTP calls [RFC6202].
 This results in a variety of problems:
 o  The server is forced to use a number of different underlying TCP
    connections for each client: one for sending information to the
    client and a new one for each incoming message.
 o  The wire protocol has a high overhead, with each client-to-server
    message having an HTTP header.
 o  The client-side script is forced to maintain a mapping from the
    outgoing connections to the incoming connection to track replies.
 A simpler solution would be to use a single TCP connection for
 traffic in both directions.  This is what the WebSocket Protocol
 provides.  Combined with the WebSocket API [WSAPI], it provides an
 alternative to HTTP polling for two-way communication from a web page
 to a remote server.
 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.
 The WebSocket Protocol is designed to supersede existing
 bidirectional communication technologies that use HTTP as a transport
 layer to benefit from existing infrastructure (proxies, filtering,
 authentication).  Such technologies were implemented as trade-offs
 between efficiency and reliability because HTTP was not initially
 meant to be used for bidirectional communication (see [RFC6202] for
 further discussion).  The WebSocket Protocol attempts to address the
 goals of existing bidirectional HTTP technologies in the context of
 the existing HTTP infrastructure; as such, it is designed to work
 over HTTP ports 80 and 443 as well as to support HTTP proxies and
 intermediaries, even if this implies some complexity specific to the
 current environment.  However, the design does not limit WebSocket to
 HTTP, and future implementations could use a simpler handshake over a

Fette & Melnikov Standards Track [Page 4] RFC 6455 The WebSocket Protocol December 2011

 dedicated port without reinventing the entire protocol.  This last
 point is important because the traffic patterns of interactive
 messaging do not closely match standard HTTP traffic and can induce
 unusual loads on some components.

1.2. Protocol Overview

 _This section is non-normative._
 The protocol has two parts: a handshake and the data transfer.
 The handshake from the client looks as follows:
      GET /chat HTTP/1.1
      Host: server.example.com
      Upgrade: websocket
      Connection: Upgrade
      Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
      Origin: http://example.com
      Sec-WebSocket-Protocol: chat, superchat
      Sec-WebSocket-Version: 13
 The handshake from the server looks as follows:
      HTTP/1.1 101 Switching Protocols
      Upgrade: websocket
      Connection: Upgrade
      Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
      Sec-WebSocket-Protocol: chat
 The leading line from the client follows the Request-Line format.
 The leading line from the server follows the Status-Line format.  The
 Request-Line and Status-Line productions are defined in [RFC2616].
 An unordered set of header fields comes after the leading line in
 both cases.  The meaning of these header fields is specified in
 Section 4 of this document.  Additional header fields may also be
 present, such as cookies [RFC6265].  The format and parsing of
 headers is as defined in [RFC2616].
 Once the client and server have both sent their handshakes, and if
 the handshake was successful, then the data transfer part starts.
 This is a two-way communication channel where each side can,
 independently from the other, send data at will.
 After a successful handshake, clients and servers transfer data back
 and forth in conceptual units referred to in this specification as
 "messages".  On the wire, a message is composed of one or more

Fette & Melnikov Standards Track [Page 5] RFC 6455 The WebSocket Protocol December 2011

 frames.  The WebSocket message does not necessarily correspond to a
 particular network layer framing, as a fragmented message may be
 coalesced or split by an intermediary.
 A frame has an associated type.  Each frame belonging to the same
 message contains the same type of data.  Broadly speaking, there are
 types for textual data (which is interpreted as UTF-8 [RFC3629]
 text), binary data (whose interpretation is left up to the
 application), and control frames (which are not intended to carry
 data for the application but instead for protocol-level signaling,
 such as to signal that the connection should be closed).  This
 version of the protocol defines six frame types and leaves ten
 reserved for future use.

1.3. Opening Handshake

 _This section is non-normative._
 The opening handshake is intended to be compatible with HTTP-based
 server-side software and intermediaries, so that a single port can be
 used by both HTTP clients talking to that server and WebSocket
 clients talking to that server.  To this end, the WebSocket client's
 handshake is an HTTP Upgrade request:
      GET /chat HTTP/1.1
      Host: server.example.com
      Upgrade: websocket
      Connection: Upgrade
      Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
      Origin: http://example.com
      Sec-WebSocket-Protocol: chat, superchat
      Sec-WebSocket-Version: 13
 In compliance with [RFC2616], header fields in the handshake may be
 sent by the client in any order, so the order in which different
 header fields are received is not significant.
 The "Request-URI" of the GET method [RFC2616] is used to identify the
 endpoint of the WebSocket connection, both to allow multiple domains
 to be served from one IP address and to allow multiple WebSocket
 endpoints to be served by a single server.
 The client includes the hostname in the |Host| header field of its
 handshake as per [RFC2616], so that both the client and the server
 can verify that they agree on which host is in use.

Fette & Melnikov Standards Track [Page 6] RFC 6455 The WebSocket Protocol December 2011

 Additional header fields are used to select options in the WebSocket
 Protocol.  Typical options available in this version are the
 subprotocol selector (|Sec-WebSocket-Protocol|), list of extensions
 support by the client (|Sec-WebSocket-Extensions|), |Origin| header
 field, etc.  The |Sec-WebSocket-Protocol| request-header field can be
 used to indicate what subprotocols (application-level protocols
 layered over the WebSocket Protocol) are acceptable to the client.
 The server selects one or none of the acceptable protocols and echoes
 that value in its handshake to indicate that it has selected that
 protocol.
      Sec-WebSocket-Protocol: chat
 The |Origin| header field [RFC6454] is used to protect against
 unauthorized cross-origin use of a WebSocket server by scripts using
 the WebSocket API in a web browser.  The server is informed of the
 script origin generating the WebSocket connection request.  If the
 server does not wish to accept connections from this origin, it can
 choose to reject the connection by sending an appropriate HTTP error
 code.  This header field is sent by browser clients; for non-browser
 clients, this header field may be sent if it makes sense in the
 context of those clients.
 Finally, the server has to prove to the client that it received the
 client's WebSocket handshake, so that the server doesn't accept
 connections that are not WebSocket connections.  This prevents an
 attacker from tricking a WebSocket server by sending it carefully
 crafted packets using XMLHttpRequest [XMLHttpRequest] or a form
 submission.
 To prove that the handshake was received, the server has to take two
 pieces of information and combine them to form a response.  The first
 piece of information comes from the |Sec-WebSocket-Key| header field
 in the client handshake:
      Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
 For this header field, the server has to take the value (as present
 in the header field, e.g., the base64-encoded [RFC4648] version minus
 any leading and trailing whitespace) and concatenate this with the
 Globally Unique Identifier (GUID, [RFC4122]) "258EAFA5-E914-47DA-
 95CA-C5AB0DC85B11" in string form, which is unlikely to be used by
 network endpoints that do not understand the WebSocket Protocol.  A
 SHA-1 hash (160 bits) [FIPS.180-3], base64-encoded (see Section 4 of
 [RFC4648]), of this concatenation is then returned in the server's
 handshake.

Fette & Melnikov Standards Track [Page 7] RFC 6455 The WebSocket Protocol December 2011

 Concretely, if as in the example above, the |Sec-WebSocket-Key|
 header field had the value "dGhlIHNhbXBsZSBub25jZQ==", the server
 would concatenate the string "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
 to form the string "dGhlIHNhbXBsZSBub25jZQ==258EAFA5-E914-47DA-95CA-
 C5AB0DC85B11".  The server would then take the SHA-1 hash of this,
 giving the value 0xb3 0x7a 0x4f 0x2c 0xc0 0x62 0x4f 0x16 0x90 0xf6
 0x46 0x06 0xcf 0x38 0x59 0x45 0xb2 0xbe 0xc4 0xea.  This value is
 then base64-encoded (see Section 4 of [RFC4648]), to give the value
 "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=".  This value would then be echoed in
 the |Sec-WebSocket-Accept| header field.
 The handshake from the server is much simpler than the client
 handshake.  The first line is an HTTP Status-Line, with the status
 code 101:
      HTTP/1.1 101 Switching Protocols
 Any status code other than 101 indicates that the WebSocket handshake
 has not completed and that the semantics of HTTP still apply.  The
 headers follow the status code.
 The |Connection| and |Upgrade| header fields complete the HTTP
 Upgrade.  The |Sec-WebSocket-Accept| header field indicates whether
 the server is willing to accept the connection.  If present, this
 header field must include a hash of the client's nonce sent in
 |Sec-WebSocket-Key| along with a predefined GUID.  Any other value
 must not be interpreted as an acceptance of the connection by the
 server.
      HTTP/1.1 101 Switching Protocols
      Upgrade: websocket
      Connection: Upgrade
      Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
 These fields are checked by the WebSocket client for scripted pages.
 If the |Sec-WebSocket-Accept| value does not match the expected
 value, if the header field is missing, or if the HTTP status code is
 not 101, the connection will not be established, and WebSocket frames
 will not be sent.
 Option fields can also be included.  In this version of the protocol,
 the main option field is |Sec-WebSocket-Protocol|, which indicates
 the subprotocol that the server has selected.  WebSocket clients
 verify that the server included one of the values that was specified
 in the WebSocket client's handshake.  A server that speaks multiple
 subprotocols has to make sure it selects one based on the client's
 handshake and specifies it in its handshake.

Fette & Melnikov Standards Track [Page 8] RFC 6455 The WebSocket Protocol December 2011

      Sec-WebSocket-Protocol: chat
 The server can also set cookie-related option fields to _set_
 cookies, as described in [RFC6265].

1.4. Closing Handshake

 _This section is non-normative._
 The closing handshake is far simpler than the opening handshake.
 Either peer can send a control frame with data containing a specified
 control sequence to begin the closing handshake (detailed in
 Section 5.5.1).  Upon receiving such a frame, the other peer sends a
 Close frame in response, if it hasn't already sent one.  Upon
 receiving _that_ control frame, the first peer then closes the
 connection, safe in the knowledge that no further data is
 forthcoming.
 After sending a control frame indicating the connection should be
 closed, a peer does not send any further data; after receiving a
 control frame indicating the connection should be closed, a peer
 discards any further data received.
 It is safe for both peers to initiate this handshake simultaneously.
 The closing handshake is intended to complement the TCP closing
 handshake (FIN/ACK), on the basis that the TCP closing handshake is
 not always reliable end-to-end, especially in the presence of
 intercepting proxies and other intermediaries.
 By sending a Close frame and waiting for a Close frame in response,
 certain cases are avoided where data may be unnecessarily lost.  For
 instance, on some platforms, if a socket is closed with data in the
 receive queue, a RST packet is sent, which will then cause recv() to
 fail for the party that received the RST, even if there was data
 waiting to be read.

1.5. Design Philosophy

 _This section is non-normative._
 The WebSocket Protocol is designed on the principle that there should
 be minimal framing (the only framing that exists is to make the
 protocol frame-based instead of stream-based and to support a
 distinction between Unicode text and binary frames).  It is expected
 that metadata would be layered on top of WebSocket by the application

Fette & Melnikov Standards Track [Page 9] RFC 6455 The WebSocket Protocol December 2011

 layer, in the same way that metadata is layered on top of TCP by the
 application layer (e.g., HTTP).
 Conceptually, WebSocket is really just a layer on top of TCP that
 does the following:
 o  adds a web origin-based security model for browsers
 o  adds an addressing and protocol naming mechanism to support
    multiple services on one port and multiple host names on one IP
    address
 o  layers a framing mechanism on top of TCP to get back to the IP
    packet mechanism that TCP is built on, but without length limits
 o  includes an additional closing handshake in-band that is designed
    to work in the presence of proxies and other intermediaries
 Other than that, WebSocket adds nothing.  Basically it is intended to
 be as close to just exposing raw TCP to script as possible given the
 constraints of the Web.  It's also designed in such a way that its
 servers can share a port with HTTP servers, by having its handshake
 be a valid HTTP Upgrade request.  One could conceptually use other
 protocols to establish client-server messaging, but the intent of
 WebSockets is to provide a relatively simple protocol that can
 coexist with HTTP and deployed HTTP infrastructure (such as proxies)
 and that is as close to TCP as is safe for use with such
 infrastructure given security considerations, with targeted additions
 to simplify usage and keep simple things simple (such as the addition
 of message semantics).
 The protocol is intended to be extensible; future versions will
 likely introduce additional concepts such as multiplexing.

1.6. Security Model

 _This section is non-normative._
 The WebSocket Protocol uses the origin model used by web browsers to
 restrict which web pages can contact a WebSocket server when the
 WebSocket Protocol is used from a web page.  Naturally, when the
 WebSocket Protocol is used by a dedicated client directly (i.e., not
 from a web page through a web browser), the origin model is not
 useful, as the client can provide any arbitrary origin string.
 This protocol is intended to fail to establish a connection with
 servers of pre-existing protocols like SMTP [RFC5321] and HTTP, while
 allowing HTTP servers to opt-in to supporting this protocol if

Fette & Melnikov Standards Track [Page 10] RFC 6455 The WebSocket Protocol December 2011

 desired.  This is achieved by having a strict and elaborate handshake
 and by limiting the data that can be inserted into the connection
 before the handshake is finished (thus limiting how much the server
 can be influenced).
 It is similarly intended to fail to establish a connection when data
 from other protocols, especially HTTP, is sent to a WebSocket server,
 for example, as might happen if an HTML "form" were submitted to a
 WebSocket server.  This is primarily achieved by requiring that the
 server prove that it read the handshake, which it can only do if the
 handshake contains the appropriate parts, which can only be sent by a
 WebSocket client.  In particular, at the time of writing of this
 specification, fields starting with |Sec-| cannot be set by an
 attacker from a web browser using only HTML and JavaScript APIs such
 as XMLHttpRequest [XMLHttpRequest].

1.7. Relationship to TCP and HTTP

 _This section is non-normative._
 The WebSocket Protocol is an independent TCP-based protocol.  Its
 only relationship to HTTP is that its handshake is interpreted by
 HTTP servers as an Upgrade request.
 By default, the WebSocket Protocol uses port 80 for regular WebSocket
 connections and port 443 for WebSocket connections tunneled over
 Transport Layer Security (TLS) [RFC2818].

1.8. Establishing a Connection

 _This section is non-normative._
 When a connection is to be made to a port that is shared by an HTTP
 server (a situation that is quite likely to occur with traffic to
 ports 80 and 443), the connection will appear to the HTTP server to
 be a regular GET request with an Upgrade offer.  In relatively simple
 setups with just one IP address and a single server for all traffic
 to a single hostname, this might allow a practical way for systems
 based on the WebSocket Protocol to be deployed.  In more elaborate
 setups (e.g., with load balancers and multiple servers), a dedicated
 set of hosts for WebSocket connections separate from the HTTP servers
 is probably easier to manage.  At the time of writing of this
 specification, it should be noted that connections on ports 80 and
 443 have significantly different success rates, with connections on
 port 443 being significantly more likely to succeed, though this may
 change with time.

Fette & Melnikov Standards Track [Page 11] RFC 6455 The WebSocket Protocol December 2011

1.9. Subprotocols Using the WebSocket Protocol

 _This section is non-normative._
 The client can request that the server use a specific subprotocol by
 including the |Sec-WebSocket-Protocol| field in its handshake.  If it
 is specified, the server needs to include the same field and one of
 the selected subprotocol values in its response for the connection to
 be established.
 These subprotocol names should be registered as per Section 11.5.  To
 avoid potential collisions, it is recommended to use names that
 contain the ASCII version of the domain name of the subprotocol's
 originator.  For example, if Example Corporation were to create a
 Chat subprotocol to be implemented by many servers around the Web,
 they could name it "chat.example.com".  If the Example Organization
 called their competing subprotocol "chat.example.org", then the two
 subprotocols could be implemented by servers simultaneously, with the
 server dynamically selecting which subprotocol to use based on the
 value sent by the client.
 Subprotocols can be versioned in backward-incompatible ways by
 changing the subprotocol name, e.g., going from
 "bookings.example.net" to "v2.bookings.example.net".  These
 subprotocols would be considered completely separate by WebSocket
 clients.  Backward-compatible versioning can be implemented by
 reusing the same subprotocol string but carefully designing the
 actual subprotocol to support this kind of extensibility.

2. Conformance Requirements

 All diagrams, examples, and notes in this specification are non-
 normative, as are all sections explicitly marked non-normative.
 Everything else in this specification is normative.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].
 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.

Fette & Melnikov Standards Track [Page 12] RFC 6455 The WebSocket Protocol December 2011

 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.)

2.1. Terminology and Other Conventions

 _ASCII_ shall mean the character-encoding scheme defined in
 [ANSI.X3-4.1986].
 This document makes reference to UTF-8 values and uses UTF-8
 notational formats as defined in STD 63 [RFC3629].
 Key terms such as named algorithms or definitions are indicated like
 _this_.
 Names of header fields or variables are indicated like |this|.
 Variable values are indicated like /this/.
 This document references the procedure to _Fail the WebSocket
 Connection_.  This procedure is defined in Section 7.1.7.
 _Converting a string to ASCII lowercase_ means replacing all
 characters in the range U+0041 to U+005A (i.e., LATIN CAPITAL LETTER
 A to LATIN CAPITAL LETTER Z) with the corresponding characters in the
 range U+0061 to U+007A (i.e., LATIN SMALL LETTER A to LATIN SMALL
 LETTER Z).
 Comparing two strings in an _ASCII case-insensitive_ manner means
 comparing them exactly, code point for code point, except that the
 characters in the range U+0041 to U+005A (i.e., LATIN CAPITAL LETTER
 A to LATIN CAPITAL LETTER Z) and the corresponding characters in the
 range U+0061 to U+007A (i.e., LATIN SMALL LETTER A to LATIN SMALL
 LETTER Z) are considered to also match.
 The term "URI" is used in this document as defined in [RFC3986].
 When an implementation is required to _send_ data as part of the
 WebSocket Protocol, the implementation MAY delay the actual
 transmission arbitrarily, e.g., buffering data so as to send fewer IP
 packets.
 Note that this document uses both [RFC5234] and [RFC2616] variants of
 ABNF in different sections.

Fette & Melnikov Standards Track [Page 13] RFC 6455 The WebSocket Protocol December 2011

3. WebSocket URIs

 This specification defines two URI schemes, using the ABNF syntax
 defined in RFC 5234 [RFC5234], and terminology and ABNF productions
 defined by the URI specification RFC 3986 [RFC3986].
        ws-URI = "ws:" "//" host [ ":" port ] path [ "?" query ]
        wss-URI = "wss:" "//" host [ ":" port ] path [ "?" query ]
        host = <host, defined in [RFC3986], Section 3.2.2>
        port = <port, defined in [RFC3986], Section 3.2.3>
        path = <path-abempty, defined in [RFC3986], Section 3.3>
        query = <query, defined in [RFC3986], Section 3.4>
 The port component is OPTIONAL; the default for "ws" is port 80,
 while the default for "wss" is port 443.
 The URI is called "secure" (and it is said that "the secure flag is
 set") if the scheme component matches "wss" case-insensitively.
 The "resource-name" (also known as /resource name/ in Section 4.1)
 can be constructed by concatenating the following:
 o  "/" if the path component is empty
 o  the path component
 o  "?" if the query component is non-empty
 o  the query component
 Fragment identifiers are meaningless in the context of WebSocket URIs
 and MUST NOT be used on these URIs.  As with any URI scheme, the
 character "#", when not indicating the start of a fragment, MUST be
 escaped as %23.

4. Opening Handshake

4.1. Client Requirements

 To _Establish a WebSocket Connection_, a client opens a connection
 and sends a handshake as defined in this section.  A connection is
 defined to initially be in a CONNECTING state.  A client will need to
 supply a /host/, /port/, /resource name/, and a /secure/ flag, which
 are the components of a WebSocket URI as discussed in Section 3,
 along with a list of /protocols/ and /extensions/ to be used.
 Additionally, if the client is a web browser, it supplies /origin/.

Fette & Melnikov Standards Track [Page 14] RFC 6455 The WebSocket Protocol December 2011

 Clients running in controlled environments, e.g., browsers on mobile
 handsets tied to specific carriers, MAY offload the management of the
 connection to another agent on the network.  In such a situation, the
 client for the purposes of this specification is considered to
 include both the handset software and any such agents.
 When the client is to _Establish a WebSocket Connection_ given a set
 of (/host/, /port/, /resource name/, and /secure/ flag), along with a
 list of /protocols/ and /extensions/ to be used, and an /origin/ in
 the case of web browsers, it MUST open a connection, send an opening
 handshake, and read the server's handshake in response.  The exact
 requirements of how the connection should be opened, what should be
 sent in the opening handshake, and how the server's response should
 be interpreted are as follows in this section.  In the following
 text, we will use terms from Section 3, such as "/host/" and
 "/secure/ flag" as defined in that section.
 1.  The components of the WebSocket URI passed into this algorithm
     (/host/, /port/, /resource name/, and /secure/ flag) MUST be
     valid according to the specification of WebSocket URIs specified
     in Section 3.  If any of the components are invalid, the client
     MUST _Fail the WebSocket Connection_ and abort these steps.
 2.  If the client already has a WebSocket connection to the remote
     host (IP address) identified by /host/ and port /port/ pair, even
     if the remote host is known by another name, the client MUST wait
     until that connection has been established or for that connection
     to have failed.  There MUST be no more than one connection in a
     CONNECTING state.  If multiple connections to the same IP address
     are attempted simultaneously, the client MUST serialize them so
     that there is no more than one connection at a time running
     through the following steps.
     If the client cannot determine the IP address of the remote host
     (for example, because all communication is being done through a
     proxy server that performs DNS queries itself), then the client
     MUST assume for the purposes of this step that each host name
     refers to a distinct remote host, and instead the client SHOULD
     limit the total number of simultaneous pending connections to a
     reasonably low number (e.g., the client might allow simultaneous
     pending connections to a.example.com and b.example.com, but if
     thirty simultaneous connections to a single host are requested,
     that may not be allowed).  For example, in a web browser context,
     the client needs to consider the number of tabs the user has open
     in setting a limit to the number of simultaneous pending
     connections.

Fette & Melnikov Standards Track [Page 15] RFC 6455 The WebSocket Protocol December 2011

     NOTE: This makes it harder for a script to perform a denial-of-
     service attack by just opening a large number of WebSocket
     connections to a remote host.  A server can further reduce the
     load on itself when attacked by pausing before closing the
     connection, as that will reduce the rate at which the client
     reconnects.
     NOTE: There is no limit to the number of established WebSocket
     connections a client can have with a single remote host.  Servers
     can refuse to accept connections from hosts/IP addresses with an
     excessive number of existing connections or disconnect resource-
     hogging connections when suffering high load.
 3.  _Proxy Usage_: If the client is configured to use a proxy when
     using the WebSocket Protocol to connect to host /host/ and port
     /port/, then the client SHOULD connect to that proxy and ask it
     to open a TCP connection to the host given by /host/ and the port
     given by /port/.
        EXAMPLE: For example, if the client uses an HTTP proxy for all
        traffic, then if it was to try to connect to port 80 on server
        example.com, it might send the following lines to the proxy
        server:
            CONNECT example.com:80 HTTP/1.1
            Host: example.com
        If there was a password, the connection might look like:
            CONNECT example.com:80 HTTP/1.1
            Host: example.com
            Proxy-authorization: Basic ZWRuYW1vZGU6bm9jYXBlcyE=
     If the client is not configured to use a proxy, then a direct TCP
     connection SHOULD be opened to the host given by /host/ and the
     port given by /port/.
     NOTE: Implementations that do not expose explicit UI for
     selecting a proxy for WebSocket connections separate from other
     proxies are encouraged to use a SOCKS5 [RFC1928] proxy for
     WebSocket connections, if available, or failing that, to prefer
     the proxy configured for HTTPS connections over the proxy
     configured for HTTP connections.
     For the purpose of proxy autoconfiguration scripts, the URI to
     pass the function MUST be constructed from /host/, /port/,
     /resource name/, and the /secure/ flag using the definition of a
     WebSocket URI as given in Section 3.

Fette & Melnikov Standards Track [Page 16] RFC 6455 The WebSocket Protocol December 2011

     NOTE: The WebSocket Protocol can be identified in proxy
     autoconfiguration scripts from the scheme ("ws" for unencrypted
     connections and "wss" for encrypted connections).
 4.  If the connection could not be opened, either because a direct
     connection failed or because any proxy used returned an error,
     then the client MUST _Fail the WebSocket Connection_ and abort
     the connection attempt.
 5.  If /secure/ is true, the client MUST perform a TLS handshake over
     the connection after opening the connection and before sending
     the handshake data [RFC2818].  If this fails (e.g., the server's
     certificate could not be verified), then the client MUST _Fail
     the WebSocket Connection_ and abort the connection.  Otherwise,
     all further communication on this channel MUST run through the
     encrypted tunnel [RFC5246].
     Clients MUST use the Server Name Indication extension in the TLS
     handshake [RFC6066].
 Once a connection to the server has been established (including a
 connection via a proxy or over a TLS-encrypted tunnel), the client
 MUST send an opening handshake to the server.  The handshake consists
 of an HTTP Upgrade request, along with a list of required and
 optional header fields.  The requirements for this handshake are as
 follows.
 1.   The handshake MUST be a valid HTTP request as specified by
      [RFC2616].
 2.   The method of the request MUST be GET, and the HTTP version MUST
      be at least 1.1.
      For example, if the WebSocket URI is "ws://example.com/chat",
      the first line sent should be "GET /chat HTTP/1.1".
 3.   The "Request-URI" part of the request MUST match the /resource
      name/ defined in Section 3 (a relative URI) or be an absolute
      http/https URI that, when parsed, has a /resource name/, /host/,
      and /port/ that match the corresponding ws/wss URI.
 4.   The request MUST contain a |Host| header field whose value
      contains /host/ plus optionally ":" followed by /port/ (when not
      using the default port).
 5.   The request MUST contain an |Upgrade| header field whose value
      MUST include the "websocket" keyword.

Fette & Melnikov Standards Track [Page 17] RFC 6455 The WebSocket Protocol December 2011

 6.   The request MUST contain a |Connection| header field whose value
      MUST include the "Upgrade" token.
 7.   The request MUST include a header field with the name
      |Sec-WebSocket-Key|.  The value of this header field MUST be a
      nonce consisting of a randomly selected 16-byte value that has
      been base64-encoded (see Section 4 of [RFC4648]).  The nonce
      MUST be selected randomly for each connection.
      NOTE: As an example, if the randomly selected value was the
      sequence of bytes 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09
      0x0a 0x0b 0x0c 0x0d 0x0e 0x0f 0x10, the value of the header
      field would be "AQIDBAUGBwgJCgsMDQ4PEC=="
 8.   The request MUST include a header field with the name |Origin|
      [RFC6454] if the request is coming from a browser client.  If
      the connection is from a non-browser client, the request MAY
      include this header field if the semantics of that client match
      the use-case described here for browser clients.  The value of
      this header field is the ASCII serialization of origin of the
      context in which the code establishing the connection is
      running.  See [RFC6454] for the details of how this header field
      value is constructed.
      As an example, if code downloaded from www.example.com attempts
      to establish a connection to ww2.example.com, the value of the
      header field would be "http://www.example.com".
 9.   The request MUST include a header field with the name
      |Sec-WebSocket-Version|.  The value of this header field MUST be
      13.
      NOTE: Although draft versions of this document (-09, -10, -11,
      and -12) were posted (they were mostly comprised of editorial
      changes and clarifications and not changes to the wire
      protocol), values 9, 10, 11, and 12 were not used as valid
      values for Sec-WebSocket-Version.  These values were reserved in
      the IANA registry but were not and will not be used.
 10.  The request MAY include a header field with the name
      |Sec-WebSocket-Protocol|.  If present, this value indicates one
      or more comma-separated subprotocol the client wishes to speak,
      ordered by preference.  The elements that comprise this value
      MUST be non-empty strings with characters in the range U+0021 to
      U+007E not including separator characters as defined in
      [RFC2616] and MUST all be unique strings.  The ABNF for the
      value of this header field is 1#token, where the definitions of
      constructs and rules are as given in [RFC2616].

Fette & Melnikov Standards Track [Page 18] RFC 6455 The WebSocket Protocol December 2011

 11.  The request MAY include a header field with the name
      |Sec-WebSocket-Extensions|.  If present, this value indicates
      the protocol-level extension(s) the client wishes to speak.  The
      interpretation and format of this header field is described in
      Section 9.1.
 12.  The request MAY include any other header fields, for example,
      cookies [RFC6265] and/or authentication-related header fields
      such as the |Authorization| header field [RFC2616], which are
      processed according to documents that define them.
 Once the client's opening handshake has been sent, the client MUST
 wait for a response from the server before sending any further data.
 The client MUST validate the server's response as follows:
 1.  If the status code received from the server is not 101, the
     client handles the response per HTTP [RFC2616] procedures.  In
     particular, the client might perform authentication if it
     receives a 401 status code; the server might redirect the client
     using a 3xx status code (but clients are not required to follow
     them), etc.  Otherwise, proceed as follows.
 2.  If the response lacks an |Upgrade| header field or the |Upgrade|
     header field contains a value that is not an ASCII case-
     insensitive match for the value "websocket", the client MUST
     _Fail the WebSocket Connection_.
 3.  If the response lacks a |Connection| header field or the
     |Connection| header field doesn't contain a token that is an
     ASCII case-insensitive match for the value "Upgrade", the client
     MUST _Fail the WebSocket Connection_.
 4.  If the response lacks a |Sec-WebSocket-Accept| header field or
     the |Sec-WebSocket-Accept| contains a value other than the
     base64-encoded SHA-1 of the concatenation of the |Sec-WebSocket-
     Key| (as a string, not base64-decoded) with the string "258EAFA5-
     E914-47DA-95CA-C5AB0DC85B11" but ignoring any leading and
     trailing whitespace, the client MUST _Fail the WebSocket
     Connection_.
 5.  If the response includes a |Sec-WebSocket-Extensions| header
     field and this header field indicates the use of an extension
     that was not present in the client's handshake (the server has
     indicated an extension not requested by the client), the client
     MUST _Fail the WebSocket Connection_.  (The parsing of this
     header field to determine which extensions are requested is
     discussed in Section 9.1.)

Fette & Melnikov Standards Track [Page 19] RFC 6455 The WebSocket Protocol December 2011

 6.  If the response includes a |Sec-WebSocket-Protocol| header field
     and this header field indicates the use of a subprotocol that was
     not present in the client's handshake (the server has indicated a
     subprotocol not requested by the client), the client MUST _Fail
     the WebSocket Connection_.
 If the server's response does not conform to the requirements for the
 server's handshake as defined in this section and in Section 4.2.2,
 the client MUST _Fail the WebSocket Connection_.
 Please note that according to [RFC2616], all header field names in
 both HTTP requests and HTTP responses are case-insensitive.
 If the server's response is validated as provided for above, it is
 said that _The WebSocket Connection is Established_ and that the
 WebSocket Connection is in the OPEN state.  The _Extensions In Use_
 is defined to be a (possibly empty) string, the value of which is
 equal to the value of the |Sec-WebSocket-Extensions| header field
 supplied by the server's handshake or the null value if that header
 field was not present in the server's handshake.  The _Subprotocol In
 Use_ is defined to be the value of the |Sec-WebSocket-Protocol|
 header field in the server's handshake or the null value if that
 header field was not present in the server's handshake.
 Additionally, if any header fields in the server's handshake indicate
 that cookies should be set (as defined by [RFC6265]), these cookies
 are referred to as _Cookies Set During the Server's Opening
 Handshake_.

4.2. Server-Side Requirements

 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 this specification
 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: 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.

Fette & Melnikov Standards Track [Page 20] RFC 6455 The WebSocket Protocol December 2011

4.2.1. Reading the Client's Opening Handshake

 When a client starts a WebSocket connection, it sends its part of the
 opening handshake.  The server must parse at least part of this
 handshake in order to obtain the necessary information to generate
 the server part of the handshake.
 The client's opening handshake consists of the following parts.  If
 the server, while reading the handshake, finds that the client did
 not send a handshake that matches the description below (note that as
 per [RFC2616], the order of the header fields is not important),
 including but not limited to any violations of the ABNF grammar
 specified for the components of the handshake, the server MUST stop
 processing the client's handshake and return an HTTP response with an
 appropriate error code (such as 400 Bad Request).
 1.   An HTTP/1.1 or higher GET request, including a "Request-URI"
      [RFC2616] that should be interpreted as a /resource name/
      defined in Section 3 (or an absolute HTTP/HTTPS URI containing
      the /resource name/).
 2.   A |Host| header field containing the server's authority.
 3.   An |Upgrade| header field containing the value "websocket",
      treated as an ASCII case-insensitive value.
 4.   A |Connection| header field that includes the token "Upgrade",
      treated as an ASCII case-insensitive value.
 5.   A |Sec-WebSocket-Key| header field with a base64-encoded (see
      Section 4 of [RFC4648]) value that, when decoded, is 16 bytes in
      length.
 6.   A |Sec-WebSocket-Version| header field, with a value of 13.
 7.   Optionally, an |Origin| header field.  This header field is sent
      by all browser clients.  A connection attempt lacking this
      header field SHOULD NOT be interpreted as coming from a browser
      client.
 8.   Optionally, a |Sec-WebSocket-Protocol| header field, with a list
      of values indicating which protocols the client would like to
      speak, ordered by preference.
 9.   Optionally, a |Sec-WebSocket-Extensions| header field, with a
      list of values indicating which extensions the client would like
      to speak.  The interpretation of this header field is discussed
      in Section 9.1.

Fette & Melnikov Standards Track [Page 21] RFC 6455 The WebSocket Protocol December 2011

 10.  Optionally, other header fields, such as those used to send
      cookies or request authentication to a server.  Unknown header
      fields are ignored, as per [RFC2616].

4.2.2. Sending the Server's Opening Handshake

 When a client establishes a WebSocket connection to a server, the
 server MUST complete the following steps to accept the connection and
 send the server's opening handshake.
 1.  If the connection is happening on an HTTPS (HTTP-over-TLS) port,
     perform a TLS handshake over the connection.  If this fails
     (e.g., the client indicated a host name in the extended client
     hello "server_name" extension that the server does not host),
     then close the connection; otherwise, all further communication
     for the connection (including the server's handshake) MUST run
     through the encrypted tunnel [RFC5246].
 2.  The server can perform additional client authentication, for
     example, by returning a 401 status code with the corresponding
     |WWW-Authenticate| header field as described in [RFC2616].
 3.  The server MAY redirect the client using a 3xx status code
     [RFC2616].  Note that this step can happen together with, before,
     or after the optional authentication step described above.
 4.  Establish the following information:
     /origin/
        The |Origin| header field in the client's handshake indicates
        the origin of the script establishing the connection.  The
        origin is serialized to ASCII and converted to lowercase.  The
        server MAY use this information as part of a determination of
        whether to accept the incoming connection.  If the server does
        not validate the origin, it will accept connections from
        anywhere.  If the server does not wish to accept this
        connection, it MUST return an appropriate HTTP error code
        (e.g., 403 Forbidden) and abort the WebSocket handshake
        described in this section.  For more detail, refer to
        Section 10.
     /key/
        The |Sec-WebSocket-Key| header field in the client's handshake
        includes a base64-encoded value that, if decoded, is 16 bytes
        in length.  This (encoded) value is used in the creation of
        the server's handshake to indicate an acceptance of the
        connection.  It is not necessary for the server to base64-
        decode the |Sec-WebSocket-Key| value.

Fette & Melnikov Standards Track [Page 22] RFC 6455 The WebSocket Protocol December 2011

     /version/
        The |Sec-WebSocket-Version| header field in the client's
        handshake includes the version of the WebSocket Protocol with
        which the client is attempting to communicate.  If this
        version does not match a version understood by the server, the
        server MUST abort the WebSocket handshake described in this
        section and instead send an appropriate HTTP error code (such
        as 426 Upgrade Required) and a |Sec-WebSocket-Version| header
        field indicating the version(s) the server is capable of
        understanding.
     /resource name/
        An identifier for the service provided by the server.  If the
        server provides multiple services, then the value should be
        derived from the resource name given in the client's handshake
        in the "Request-URI" [RFC2616] of the GET method.  If the
        requested service is not available, the server MUST send an
        appropriate HTTP error code (such as 404 Not Found) and abort
        the WebSocket handshake.
     /subprotocol/
        Either a single value representing the subprotocol the server
        is ready to use or null.  The value chosen MUST be derived
        from the client's handshake, specifically by selecting one of
        the values from the |Sec-WebSocket-Protocol| field that the
        server is willing to use for this connection (if any).  If the
        client's handshake did not contain such a header field or if
        the server does not agree to any of the client's requested
        subprotocols, the only acceptable value is null.  The absence
        of such a field is equivalent to the null value (meaning that
        if the server does not wish to agree to one of the suggested
        subprotocols, it MUST NOT send back a |Sec-WebSocket-Protocol|
        header field in its response).  The empty string is not the
        same as the null value for these purposes and is not a legal
        value for this field.  The ABNF for the value of this header
        field is (token), where the definitions of constructs and
        rules are as given in [RFC2616].
     /extensions/
        A (possibly empty) list representing the protocol-level
        extensions the server is ready to use.  If the server supports
        multiple extensions, then the value MUST be derived from the
        client's handshake, specifically by selecting one or more of
        the values from the |Sec-WebSocket-Extensions| field.  The
        absence of such a field is equivalent to the null value.  The
        empty string is not the same as the null value for these

Fette & Melnikov Standards Track [Page 23] RFC 6455 The WebSocket Protocol December 2011

        purposes.  Extensions not listed by the client MUST NOT be
        listed.  The method by which these values should be selected
        and interpreted is discussed in Section 9.1.
 5.  If the server chooses to accept the incoming connection, it MUST
     reply with a valid HTTP response indicating the following.
     1.  A Status-Line with a 101 response code as per RFC 2616
         [RFC2616].  Such a response could look like "HTTP/1.1 101
         Switching Protocols".
     2.  An |Upgrade| header field with value "websocket" as per RFC
         2616 [RFC2616].
     3.  A |Connection| header field with value "Upgrade".
     4.  A |Sec-WebSocket-Accept| header field.  The value of this
         header field is constructed by concatenating /key/, defined
         above in step 4 in Section 4.2.2, with the string "258EAFA5-
         E914-47DA-95CA-C5AB0DC85B11", taking the SHA-1 hash of this
         concatenated value to obtain a 20-byte value and base64-
         encoding (see Section 4 of [RFC4648]) this 20-byte hash.
         The ABNF [RFC2616] of this header field is defined as
         follows:
         Sec-WebSocket-Accept     = base64-value-non-empty
         base64-value-non-empty = (1*base64-data [ base64-padding ]) |
                                  base64-padding
         base64-data      = 4base64-character
         base64-padding   = (2base64-character "==") |
                            (3base64-character "=")
         base64-character = ALPHA | DIGIT | "+" | "/"
 NOTE: As an example, if the value of the |Sec-WebSocket-Key| header
 field in the client's handshake were "dGhlIHNhbXBsZSBub25jZQ==", the
 server would append the string "258EAFA5-E914-47DA-95CA-C5AB0DC85B11"
 to form the string "dGhlIHNhbXBsZSBub25jZQ==258EAFA5-E914-47DA-95CA-
 C5AB0DC85B11".  The server would then take the SHA-1 hash of this
 string, giving the value 0xb3 0x7a 0x4f 0x2c 0xc0 0x62 0x4f 0x16 0x90
 0xf6 0x46 0x06 0xcf 0x38 0x59 0x45 0xb2 0xbe 0xc4 0xea.  This value
 is then base64-encoded, to give the value
 "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=", which would be returned in the
 |Sec-WebSocket-Accept| header field.
     5.  Optionally, a |Sec-WebSocket-Protocol| header field, with a
         value /subprotocol/ as defined in step 4 in Section 4.2.2.

Fette & Melnikov Standards Track [Page 24] RFC 6455 The WebSocket Protocol December 2011

     6.  Optionally, a |Sec-WebSocket-Extensions| header field, with a
         value /extensions/ as defined in step 4 in Section 4.2.2.  If
         multiple extensions are to be used, they can all be listed in
         a single |Sec-WebSocket-Extensions| header field or split
         between multiple instances of the |Sec-WebSocket-Extensions|
         header field.
 This completes the server's handshake.  If the server finishes these
 steps without aborting the WebSocket handshake, the server considers
 the WebSocket connection to be established and that the WebSocket
 connection is in the OPEN state.  At this point, the server may begin
 sending (and receiving) data.

4.3. Collected ABNF for New Header Fields Used in Handshake

 This section is using ABNF syntax/rules from Section 2.1 of
 [RFC2616], including the "implied *LWS rule".
 Note that the following ABNF conventions are used in this section.
 Some names of the rules correspond to names of the corresponding
 header fields.  Such rules express values of the corresponding header
 fields, for example, the Sec-WebSocket-Key ABNF rule describes syntax
 of the |Sec-WebSocket-Key| header field value.  ABNF rules with the
 "-Client" suffix in the name are only used in requests sent by the
 client to the server; ABNF rules with the "-Server" suffix in the
 name are only used in responses sent by the server to the client.
 For example, the ABNF rule Sec-WebSocket-Protocol-Client describes
 syntax of the |Sec-WebSocket-Protocol| header field value sent by the
 client to the server.
 The following new header fields can be sent during the handshake from
 the client to the server:
    Sec-WebSocket-Key = base64-value-non-empty
    Sec-WebSocket-Extensions = extension-list
    Sec-WebSocket-Protocol-Client = 1#token
    Sec-WebSocket-Version-Client = version
    base64-value-non-empty = (1*base64-data [ base64-padding ]) |
                              base64-padding
    base64-data      = 4base64-character
    base64-padding   = (2base64-character "==") |
                       (3base64-character "=")
    base64-character = ALPHA | DIGIT | "+" | "/"
    extension-list = 1#extension
    extension = extension-token *( ";" extension-param )
    extension-token = registered-token
    registered-token = token

Fette & Melnikov Standards Track [Page 25] RFC 6455 The WebSocket Protocol December 2011

    extension-param = token [ "=" (token | quoted-string) ]
         ; When using the quoted-string syntax variant, the value
         ; after quoted-string unescaping MUST conform to the
         ; 'token' ABNF.
    NZDIGIT       =  "1" | "2" | "3" | "4" | "5" | "6" |
                     "7" | "8" | "9"
    version = DIGIT | (NZDIGIT DIGIT) |
              ("1" DIGIT DIGIT) | ("2" DIGIT DIGIT)
              ; Limited to 0-255 range, with no leading zeros
 The following new header fields can be sent during the handshake from
 the server to the client:
    Sec-WebSocket-Extensions = extension-list
    Sec-WebSocket-Accept     = base64-value-non-empty
    Sec-WebSocket-Protocol-Server = token
    Sec-WebSocket-Version-Server = 1#version

4.4. Supporting Multiple Versions of WebSocket Protocol

 This section provides some guidance on supporting multiple versions
 of the WebSocket Protocol in clients and servers.
 Using the WebSocket version advertisement capability (the
 |Sec-WebSocket-Version| header field), a client can initially request
 the version of the WebSocket Protocol that it prefers (which doesn't
 necessarily have to be the latest supported by the client).  If the
 server supports the requested version and the handshake message is
 otherwise valid, the server will accept that version.  If the server
 doesn't support the requested version, it MUST respond with a
 |Sec-WebSocket-Version| header field (or multiple
 |Sec-WebSocket-Version| header fields) containing all versions it is
 willing to use.  At this point, if the client supports one of the
 advertised versions, it can repeat the WebSocket handshake using a
 new version value.
 The following example demonstrates version negotiation described
 above:
    GET /chat HTTP/1.1
    Host: server.example.com
    Upgrade: websocket
    Connection: Upgrade
    ...
    Sec-WebSocket-Version: 25

Fette & Melnikov Standards Track [Page 26] RFC 6455 The WebSocket Protocol December 2011

 The response from the server might look as follows:
    HTTP/1.1 400 Bad Request
    ...
    Sec-WebSocket-Version: 13, 8, 7
 Note that the last response from the server might also look like:
    HTTP/1.1 400 Bad Request
    ...
    Sec-WebSocket-Version: 13
    Sec-WebSocket-Version: 8, 7
 The client now repeats the handshake that conforms to version 13:
    GET /chat HTTP/1.1
    Host: server.example.com
    Upgrade: websocket
    Connection: Upgrade
    ...
    Sec-WebSocket-Version: 13

5. Data Framing

5.1. Overview

 In the WebSocket Protocol, data is transmitted using a sequence of
 frames.  To avoid confusing network intermediaries (such as
 intercepting proxies) and for security reasons that are further
 discussed in Section 10.3, a client MUST mask all frames that it
 sends to the server (see Section 5.3 for further details).  (Note
 that masking is done whether or not the WebSocket Protocol is running
 over TLS.)  The server MUST close the connection upon receiving a
 frame that is not masked.  In this case, a server MAY send a Close
 frame with a status code of 1002 (protocol error) as defined in
 Section 7.4.1.  A server MUST NOT mask any frames that it sends to
 the client.  A client MUST close a connection if it detects a masked
 frame.  In this case, it MAY use the status code 1002 (protocol
 error) as defined in Section 7.4.1.  (These rules might be relaxed in
 a future specification.)
 The base framing protocol defines a frame type with an opcode, a
 payload length, and designated locations for "Extension data" and
 "Application data", which together define the "Payload data".
 Certain bits and opcodes are reserved for future expansion of the
 protocol.

Fette & Melnikov Standards Track [Page 27] RFC 6455 The WebSocket Protocol December 2011

 A data frame MAY be transmitted by either the client or the server at
 any time after opening handshake completion and before that endpoint
 has sent a Close frame (Section 5.5.1).

5.2. Base Framing Protocol

 This wire format for the data transfer part is described by the ABNF
 [RFC5234] given in detail in this section.  (Note that, unlike in
 other sections of this document, the ABNF in this section is
 operating on groups of bits.  The length of each group of bits is
 indicated in a comment.  When encoded on the wire, the most
 significant bit is the leftmost in the ABNF).  A high-level overview
 of the framing is given in the following figure.  In a case of
 conflict between the figure below and the ABNF specified later in
 this section, the figure is authoritative.
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-------+-+-------------+-------------------------------+
   |F|R|R|R| opcode|M| Payload len |    Extended payload length    |
   |I|S|S|S|  (4)  |A|     (7)     |             (16/64)           |
   |N|V|V|V|       |S|             |   (if payload len==126/127)   |
   | |1|2|3|       |K|             |                               |
   +-+-+-+-+-------+-+-------------+ - - - - - - - - - - - - - - - +
   |     Extended payload length continued, if payload len == 127  |
   + - - - - - - - - - - - - - - - +-------------------------------+
   |                               |Masking-key, if MASK set to 1  |
   +-------------------------------+-------------------------------+
   | Masking-key (continued)       |          Payload Data         |
   +-------------------------------- - - - - - - - - - - - - - - - +
   :                     Payload Data continued ...                :
   + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - +
   |                     Payload Data continued ...                |
   +---------------------------------------------------------------+
 FIN:  1 bit
    Indicates that this is the final fragment in a message.  The first
    fragment MAY also be the final fragment.
 RSV1, RSV2, RSV3:  1 bit each
    MUST be 0 unless an extension is negotiated that defines meanings
    for non-zero values.  If a nonzero value is received and none of
    the negotiated extensions defines the meaning of such a nonzero
    value, the receiving endpoint MUST _Fail the WebSocket
    Connection_.

Fette & Melnikov Standards Track [Page 28] RFC 6455 The WebSocket Protocol December 2011

 Opcode:  4 bits
    Defines the interpretation of the "Payload data".  If an unknown
    opcode is received, the receiving endpoint MUST _Fail the
    WebSocket Connection_.  The following values are defined.
  • %x0 denotes a continuation frame
  • %x1 denotes a text frame
  • %x2 denotes a binary frame
  • %x3-7 are reserved for further non-control frames
  • %x8 denotes a connection close
  • %x9 denotes a ping
  • %xA denotes a pong
  • %xB-F are reserved for further control frames
 Mask:  1 bit
    Defines whether the "Payload data" is masked.  If set to 1, a
    masking key is present in masking-key, and this is used to unmask
    the "Payload data" as per Section 5.3.  All frames sent from
    client to server have this bit set to 1.
 Payload length:  7 bits, 7+16 bits, or 7+64 bits
    The length of the "Payload data", in bytes: if 0-125, that is the
    payload length.  If 126, the following 2 bytes interpreted as a
    16-bit unsigned integer are the payload length.  If 127, the
    following 8 bytes interpreted as a 64-bit unsigned integer (the
    most significant bit MUST be 0) are the payload length.  Multibyte
    length quantities are expressed in network byte order.  Note that
    in all cases, the minimal number of bytes MUST be used to encode
    the length, for example, the length of a 124-byte-long string
    can't be encoded as the sequence 126, 0, 124.  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".

Fette & Melnikov Standards Track [Page 29] RFC 6455 The WebSocket Protocol December 2011

 Masking-key:  0 or 4 bytes
    All frames sent from the client to the server are masked by a
    32-bit value that is contained within the frame.  This field is
    present if the mask bit is set to 1 and is absent if the mask bit
    is set to 0.  See Section 5.3 for further information on client-
    to-server masking.
 Payload data:  (x+y) bytes
    The "Payload data" is defined as "Extension data" concatenated
    with "Application data".
 Extension data:  x bytes
    The "Extension data" is 0 bytes unless an extension has been
    negotiated.  Any extension MUST specify the length of the
    "Extension data", or how that length may be calculated, and how
    the extension use MUST be negotiated during the opening handshake.
    If present, the "Extension data" is included in the total payload
    length.
 Application data:  y bytes
    Arbitrary "Application data", taking up the remainder of the frame
    after any "Extension data".  The length of the "Application data"
    is equal to the payload length minus the length of the "Extension
    data".
 The base framing protocol is formally defined by the following ABNF
 [RFC5234].  It is important to note that the representation of this
 data is binary, not ASCII characters.  As such, a field with a length
 of 1 bit that takes values %x0 / %x1 is represented as a single bit
 whose value is 0 or 1, not a full byte (octet) that stands for the
 characters "0" or "1" in the ASCII encoding.  A field with a length
 of 4 bits with values between %x0-F again is represented by 4 bits,
 again NOT by an ASCII character or full byte (octet) with these
 values.  [RFC5234] does not specify a character encoding: "Rules
 resolve into a string of terminal values, sometimes called
 characters.  In ABNF, a character is merely a non-negative integer.
 In certain contexts, a specific mapping (encoding) of values into a
 character set (such as ASCII) will be specified."  Here, the
 specified encoding is a binary encoding where each terminal value is
 encoded in the specified number of bits, which varies for each field.

Fette & Melnikov Standards Track [Page 30] RFC 6455 The WebSocket Protocol December 2011

  ws-frame                = frame-fin           ; 1 bit in length
                            frame-rsv1          ; 1 bit in length
                            frame-rsv2          ; 1 bit in length
                            frame-rsv3          ; 1 bit in length
                            frame-opcode        ; 4 bits in length
                            frame-masked        ; 1 bit in length
                            frame-payload-length   ; either 7, 7+16,
                                                   ; or 7+64 bits in
                                                   ; length
                            [ frame-masking-key ]  ; 32 bits in length
                            frame-payload-data     ; n*8 bits in
                                                   ; length, where
                                                   ; n >= 0
  frame-fin               = %x0 ; more frames of this message follow
                          / %x1 ; final frame of this message
                                ; 1 bit in length
  frame-rsv1              = %x0 / %x1
                            ; 1 bit in length, MUST be 0 unless
                            ; negotiated otherwise
  frame-rsv2              = %x0 / %x1
                            ; 1 bit in length, MUST be 0 unless
                            ; negotiated otherwise
  frame-rsv3              = %x0 / %x1
                            ; 1 bit in length, MUST be 0 unless
                            ; negotiated otherwise
  frame-opcode            = frame-opcode-non-control /
                            frame-opcode-control /
                            frame-opcode-cont
  frame-opcode-cont       = %x0 ; frame continuation
  frame-opcode-non-control= %x1 ; text frame
                          / %x2 ; binary frame
                          / %x3-7
                          ; 4 bits in length,
                          ; reserved for further non-control frames
  frame-opcode-control    = %x8 ; connection close
                          / %x9 ; ping
                          / %xA ; pong
                          / %xB-F ; reserved for further control
                                  ; frames
                                  ; 4 bits in length

Fette & Melnikov Standards Track [Page 31] RFC 6455 The WebSocket Protocol December 2011

  frame-masked            = %x0
                          ; frame is not masked, no frame-masking-key
                          / %x1
                          ; frame is masked, frame-masking-key present
                          ; 1 bit in length
  frame-payload-length    = ( %x00-7D )
                          / ( %x7E frame-payload-length-16 )
                          / ( %x7F frame-payload-length-63 )
                          ; 7, 7+16, or 7+64 bits in length,
                          ; respectively
  frame-payload-length-16 = %x0000-FFFF ; 16 bits in length
  frame-payload-length-63 = %x0000000000000000-7FFFFFFFFFFFFFFF
                          ; 64 bits in length
  frame-masking-key       = 4( %x00-FF )
                            ; present only if frame-masked is 1
                            ; 32 bits in length
  frame-payload-data      = (frame-masked-extension-data
                             frame-masked-application-data)
                          ; when frame-masked is 1
                            / (frame-unmasked-extension-data
                              frame-unmasked-application-data)
                          ; when frame-masked is 0
  frame-masked-extension-data     = *( %x00-FF )
                          ; reserved for future extensibility
                          ; n*8 bits in length, where n >= 0
  frame-masked-application-data   = *( %x00-FF )
                          ; n*8 bits in length, where n >= 0
  frame-unmasked-extension-data   = *( %x00-FF )
                          ; reserved for future extensibility
                          ; n*8 bits in length, where n >= 0
  frame-unmasked-application-data = *( %x00-FF )
                          ; n*8 bits in length, where n >= 0

5.3. Client-to-Server Masking

 A masked frame MUST have the field frame-masked set to 1, as defined
 in Section 5.2.

Fette & Melnikov Standards Track [Page 32] RFC 6455 The WebSocket Protocol December 2011

 The masking key is contained completely within the frame, as defined
 in Section 5.2 as frame-masking-key.  It is used to mask the "Payload
 data" defined in the same section as frame-payload-data, which
 includes "Extension data" and "Application data".
 The masking key is a 32-bit value chosen at random by the client.
 When preparing a masked frame, the client MUST pick a fresh masking
 key from the set of allowed 32-bit values.  The masking key needs to
 be unpredictable; thus, 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/proxy to predict the masking key for a
 subsequent frame.  The unpredictability of the masking key is
 essential to prevent authors of malicious applications from selecting
 the bytes that appear on the wire.  RFC 4086 [RFC4086] discusses what
 entails a suitable source of entropy for security-sensitive
 applications.
 The masking does not affect the length of the "Payload data".  To
 convert masked data into unmasked data, or vice versa, the following
 algorithm is applied.  The same algorithm applies regardless of the
 direction of the translation, e.g., the same steps are applied to
 mask the data as to unmask the data.
 Octet i of the transformed data ("transformed-octet-i") is the XOR of
 octet i of the original data ("original-octet-i") with octet at index
 i modulo 4 of the masking key ("masking-key-octet-j"):
   j                   = i MOD 4
   transformed-octet-i = original-octet-i XOR masking-key-octet-j
 The payload length, indicated in the framing as frame-payload-length,
 does NOT include the length of the masking key.  It is the length of
 the "Payload data", e.g., the number of bytes following the masking
 key.

5.4. Fragmentation

 The primary purpose of fragmentation is to allow sending a message
 that is of unknown size when the message is started without having to
 buffer that message.  If messages couldn't be fragmented, then an
 endpoint would have to buffer the entire message so its length could
 be counted before the 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 multiplexing needs to be free

Fette & Melnikov Standards Track [Page 33] RFC 6455 The WebSocket Protocol December 2011

 to split the message into smaller fragments to better share the
 output channel.  (Note that the multiplexing extension is not
 described in this document.)
 Unless specified otherwise by an extension, frames have no semantic
 meaning.  An intermediary might coalesce and/or split frames, if no
 extensions were negotiated by the client and the server or if some
 extensions were negotiated, but the intermediary understood all the
 extensions negotiated and knows how to coalesce and/or split frames
 in the presence of these extensions.  One implication of this is that
 in absence of extensions, senders and receivers must not depend on
 the presence of specific frame boundaries.
 The following rules apply to fragmentation:
 o  An unfragmented message consists of a single frame with the FIN
    bit set (Section 5.2) and an opcode other than 0.
 o  A fragmented message consists of a single frame with the FIN bit
    clear and an opcode other than 0, followed by zero or more frames
    with the FIN bit clear and the opcode set to 0, and terminated by
    a single frame with the FIN bit set and an opcode of 0.  A
    fragmented message is conceptually equivalent to a single larger
    message whose payload is equal to the concatenation of the
    payloads of the fragments in order; however, in the presence of
    extensions, this may not hold true as the extension defines the
    interpretation of the "Extension data" present.  For instance,
    "Extension data" may only be present at the beginning of the first
    fragment and apply to subsequent fragments, or there may be
    "Extension data" present in each of the fragments that applies
    only to that particular fragment.  In the absence of "Extension
    data", the following example demonstrates how fragmentation works.
    EXAMPLE: For a text message sent as three fragments, the first
    fragment would have an opcode of 0x1 and a FIN bit clear, the
    second fragment would have an opcode of 0x0 and a FIN bit clear,
    and the third fragment would have an opcode of 0x0 and a FIN bit
    that is set.
 o  Control frames (see Section 5.5) MAY be injected in the middle of
    a fragmented message.  Control frames themselves MUST NOT be
    fragmented.
 o  Message fragments MUST be delivered to the recipient in the order
    sent by the sender.

Fette & Melnikov Standards Track [Page 34] RFC 6455 The WebSocket Protocol December 2011

 o  The fragments of one message MUST NOT be interleaved between the
    fragments of another message unless an extension has been
    negotiated that can interpret the interleaving.
 o  An endpoint MUST be capable of handling control frames in the
    middle of a fragmented message.
 o  A sender MAY create fragments of any size for non-control
    messages.
 o  Clients and servers MUST support receiving both fragmented and
    unfragmented messages.
 o  As control frames cannot be fragmented, an intermediary MUST NOT
    attempt to change the fragmentation of a control frame.
 o  An intermediary MUST NOT change the fragmentation of a message if
    any reserved bit values are used and the meaning of these values
    is not known to the intermediary.
 o  An intermediary MUST NOT change the fragmentation of any message
    in the context of a connection where extensions have been
    negotiated and the intermediary is not aware of the semantics of
    the negotiated extensions.  Similarly, an intermediary that didn't
    see the WebSocket handshake (and wasn't notified about its
    content) that resulted in a WebSocket connection MUST NOT change
    the fragmentation of any message of such connection.
 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, binary, or one of the reserved
    opcodes.
 NOTE: If control frames could not be interjected, the latency of a
 ping, for example, would be very long if behind a large message.
 Hence, the requirement of handling control frames in the middle of a
 fragmented message.
 IMPLEMENTATION NOTE: In the absence of any extension, a receiver
 doesn't have to buffer the whole frame in order to process it.  For
 example, if a streaming API is used, a part of a frame can be
 delivered to the application.  However, note that this assumption
 might not hold true for all future WebSocket extensions.

Fette & Melnikov Standards Track [Page 35] RFC 6455 The WebSocket Protocol December 2011

5.5. Control Frames

 Control frames are identified by opcodes where the most significant
 bit of the opcode is 1.  Currently defined opcodes for control frames
 include 0x8 (Close), 0x9 (Ping), and 0xA (Pong).  Opcodes 0xB-0xF are
 reserved for further control frames yet to be defined.
 Control frames are used to communicate state about the WebSocket.
 Control frames can be interjected in the middle of a fragmented
 message.
 All control frames MUST have a payload length of 125 bytes or less
 and MUST NOT be fragmented.

5.5.1. Close

 The Close frame contains an opcode of 0x8.
 The Close frame MAY contain a body (the "Application data" portion of
 the frame) that indicates a reason for closing, such as an endpoint
 shutting down, an endpoint having received a frame too large, or an
 endpoint having received a frame that does not conform to the format
 expected by the endpoint.  If there is a body, the first two bytes of
 the body MUST be a 2-byte unsigned integer (in network byte order)
 representing a status code with value /code/ defined in Section 7.4.
 Following the 2-byte integer, the body MAY contain UTF-8-encoded data
 with value /reason/, the interpretation of which is not defined by
 this specification.  This data is not necessarily human readable but
 may be useful for debugging or passing information relevant to the
 script that opened the connection.  As the data is not guaranteed to
 be human readable, clients MUST NOT show it to end users.
 Close frames sent from client to server must be masked as per
 Section 5.3.
 The application MUST NOT send any more data frames after sending a
 Close frame.
 If an endpoint receives a Close frame and did not previously send a
 Close frame, the endpoint MUST send a Close frame in response.  (When
 sending a Close frame in response, the endpoint typically echos the
 status code it received.)  It SHOULD do so as soon as practical.  An
 endpoint MAY delay sending a Close frame until its current message is
 sent (for instance, if the majority of a fragmented message is
 already sent, an endpoint MAY send the remaining fragments before
 sending a Close frame).  However, there is no guarantee that the
 endpoint that has already sent a Close frame will continue to process
 data.

Fette & Melnikov Standards Track [Page 36] RFC 6455 The WebSocket Protocol December 2011

 After both sending and receiving a Close message, an endpoint
 considers the WebSocket connection closed and MUST close the
 underlying TCP connection.  The server MUST close the underlying TCP
 connection immediately; the client SHOULD wait for the server to
 close the connection but MAY close the connection at any time after
 sending and receiving a Close message, e.g., if it has not received a
 TCP Close from the server in a reasonable time period.
 If a client and server both send a Close message at the same time,
 both endpoints will have sent and received a Close message and should
 consider the WebSocket connection closed and close the underlying TCP
 connection.

5.5.2. Ping

 The Ping frame contains an opcode of 0x9.
 A Ping frame MAY include "Application data".
 Upon receipt of a Ping frame, an endpoint MUST send a Pong frame in
 response, unless it already received a Close frame.  It SHOULD
 respond with Pong frame as soon as is practical.  Pong frames are
 discussed in Section 5.5.3.
 An endpoint MAY send a Ping frame any time after the connection is
 established and before the connection is closed.
 NOTE: A Ping frame may serve either as a keepalive or as a means to
 verify that the remote endpoint is still responsive.

5.5.3. Pong

 The Pong frame contains an opcode of 0xA.
 Section 5.5.2 details requirements that apply to both Ping and Pong
 frames.
 A Pong frame sent in response to a Ping frame must have identical
 "Application data" as found in the message body of the Ping frame
 being replied to.
 If an endpoint receives a Ping frame and has not yet sent Pong
 frame(s) in response to previous Ping frame(s), the endpoint MAY
 elect to send a Pong frame for only the most recently processed Ping
 frame.

Fette & Melnikov Standards Track [Page 37] RFC 6455 The WebSocket Protocol December 2011

 A Pong frame MAY be sent unsolicited.  This serves as a
 unidirectional heartbeat.  A response to an unsolicited Pong frame is
 not expected.

5.6. Data Frames

 Data frames (e.g., non-control frames) are identified by opcodes
 where the most significant bit of the opcode is 0.  Currently defined
 opcodes for data frames include 0x1 (Text), 0x2 (Binary).  Opcodes
 0x3-0x7 are reserved for further non-control frames yet to be
 defined.
 Data frames carry application-layer and/or extension-layer data.  The
 opcode determines the interpretation of the data:
 Text
    The "Payload data" is text data encoded as UTF-8.  Note that a
    particular text frame might include a partial UTF-8 sequence;
    however, the whole message MUST contain valid UTF-8.  Invalid
    UTF-8 in reassembled messages is handled as described in
    Section 8.1.
 Binary
    The "Payload data" is arbitrary binary data whose interpretation
    is solely up to the application layer.

5.7. Examples

 o  A single-frame unmasked text message
  • 0x81 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains "Hello")
 o  A single-frame masked text message
  • 0x81 0x85 0x37 0xfa 0x21 0x3d 0x7f 0x9f 0x4d 0x51 0x58

(contains "Hello")

 o  A fragmented unmasked text message
  • 0x01 0x03 0x48 0x65 0x6c (contains "Hel")
  • 0x80 0x02 0x6c 0x6f (contains "lo")

Fette & Melnikov Standards Track [Page 38] RFC 6455 The WebSocket Protocol December 2011

 o  Unmasked Ping request and masked Ping response
  • 0x89 0x05 0x48 0x65 0x6c 0x6c 0x6f (contains a body of "Hello",

but the contents of the body are arbitrary)

  • 0x8a 0x85 0x37 0xfa 0x21 0x3d 0x7f 0x9f 0x4d 0x51 0x58

(contains a body of "Hello", matching the body of the ping)

 o  256 bytes binary message in a single unmasked frame
  • 0x82 0x7E 0x0100 [256 bytes of binary data]
 o  64KiB binary message in a single unmasked frame
  • 0x82 0x7F 0x0000000000010000 [65536 bytes of binary data]

5.8. Extensibility

 The protocol is designed to allow for extensions, which will add
 capabilities to the base protocol.  The endpoints of a connection
 MUST negotiate the use of any extensions during the opening
 handshake.  This specification provides opcodes 0x3 through 0x7 and
 0xB through 0xF, the "Extension data" field, and the frame-rsv1,
 frame-rsv2, and frame-rsv3 bits of the frame header for use by
 extensions.  The negotiation of extensions is discussed in further
 detail in Section 9.1.  Below are some anticipated uses of
 extensions.  This list is neither complete nor prescriptive.
 o  "Extension data" may be placed in the "Payload data" before the
    "Application data".
 o  Reserved bits can be allocated for per-frame needs.
 o  Reserved opcode values can be defined.
 o  Reserved bits can be allocated to the opcode field if more opcode
    values are needed.
 o  A reserved bit or an "extension" opcode can be defined that
    allocates additional bits out of the "Payload data" to define
    larger opcodes or more per-frame bits.

6. Sending and Receiving Data

6.1. Sending Data

 To _Send a WebSocket Message_ comprising of /data/ over a WebSocket
 connection, an endpoint MUST perform the following steps.

Fette & Melnikov Standards Track [Page 39] RFC 6455 The WebSocket Protocol December 2011

 1.  The endpoint MUST ensure the WebSocket connection is in the OPEN
     state (cf. Sections 4.1 and 4.2.2.)  If at any point the state of
     the WebSocket connection changes, the endpoint MUST abort the
     following steps.
 2.  An endpoint MUST encapsulate the /data/ in a WebSocket frame as
     defined in Section 5.2.  If the data to be sent is large or if
     the data is not available in its entirety at the point the
     endpoint wishes to begin sending the data, the endpoint MAY
     alternately encapsulate the data in a series of frames as defined
     in Section 5.4.
 3.  The opcode (frame-opcode) of the first frame containing the data
     MUST be set to the appropriate value from Section 5.2 for data
     that is to be interpreted by the recipient as text or binary
     data.
 4.  The FIN bit (frame-fin) of the last frame containing the data
     MUST be set to 1 as defined in Section 5.2.
 5.  If the data is being sent by the client, the frame(s) MUST be
     masked as defined in Section 5.3.
 6.  If any extensions (Section 9) have been negotiated for the
     WebSocket connection, additional considerations may apply as per
     the definition of those extensions.
 7.  The frame(s) that have been formed MUST be transmitted over the
     underlying network connection.

6.2. Receiving Data

 To receive WebSocket data, an endpoint listens on the underlying
 network connection.  Incoming data MUST be parsed as WebSocket frames
 as defined in Section 5.2.  If a control frame (Section 5.5) is
 received, the frame MUST be handled as defined by Section 5.5.  Upon
 receiving a data frame (Section 5.6), the endpoint MUST note the
 /type/ of the data as defined by the opcode (frame-opcode) from
 Section 5.2.  The "Application data" from this frame is defined as
 the /data/ of the message.  If the frame comprises an unfragmented
 message (Section 5.4), it is said that _A WebSocket Message Has Been
 Received_ with type /type/ and data /data/.  If the frame is part of
 a fragmented message, the "Application data" of the subsequent data
 frames is concatenated to form the /data/.  When the last fragment is
 received as indicated by the FIN bit (frame-fin), it is said that _A
 WebSocket Message Has Been Received_ with data /data/ (comprised of
 the concatenation of the "Application data" of the fragments) and

Fette & Melnikov Standards Track [Page 40] RFC 6455 The WebSocket Protocol December 2011

 type /type/ (noted from the first frame of the fragmented message).
 Subsequent data frames MUST be interpreted as belonging to a new
 WebSocket message.
 Extensions (Section 9) MAY change the semantics of how data is read,
 specifically including what comprises a message boundary.
 Extensions, in addition to adding "Extension data" before the
 "Application data" in a payload, MAY also modify the "Application
 data" (such as by compressing it).
 A server MUST remove masking for data frames received from a client
 as described in Section 5.3.

7. Closing the Connection

7.1. Definitions

7.1.1. Close the WebSocket Connection

 To _Close the WebSocket Connection_, an endpoint closes the
 underlying TCP connection.  An endpoint SHOULD use a method that
 cleanly closes the TCP connection, as well as the TLS session, if
 applicable, discarding any trailing bytes that may have been
 received.  An endpoint MAY close the connection via any means
 available when necessary, such as when under attack.
 The underlying TCP connection, in most normal cases, SHOULD be closed
 first by the server, so that it holds the TIME_WAIT state and not the
 client (as this would prevent it from re-opening the connection for 2
 maximum segment lifetimes (2MSL), while there is no corresponding
 server impact as a TIME_WAIT connection is immediately reopened upon
 a new SYN with a higher seq number).  In abnormal cases (such as not
 having received a TCP Close from the server after a reasonable amount
 of time) a client MAY initiate the TCP Close.  As such, when a server
 is instructed to _Close the WebSocket Connection_ it SHOULD initiate
 a TCP Close immediately, and when a client is instructed to do the
 same, it SHOULD wait for a TCP Close from the server.
 As an example of how to obtain a clean closure in C using Berkeley
 sockets, one would call shutdown() with SHUT_WR on the socket, call
 recv() until obtaining a return value of 0 indicating that the peer
 has also performed an orderly shutdown, and finally call close() on
 the socket.

Fette & Melnikov Standards Track [Page 41] RFC 6455 The WebSocket Protocol December 2011

7.1.2. Start the WebSocket Closing Handshake

 To _Start the WebSocket Closing Handshake_ with a status code
 (Section 7.4) /code/ and an optional close reason (Section 7.1.6)
 /reason/, an endpoint MUST send a Close control frame, as described
 in Section 5.5.1, whose status code is set to /code/ and whose close
 reason is set to /reason/.  Once an endpoint has both sent and
 received a Close control frame, that endpoint SHOULD _Close the
 WebSocket Connection_ as defined in Section 7.1.1.

7.1.3. The WebSocket Closing Handshake is Started

 Upon either sending or receiving a Close control frame, it is said
 that _The WebSocket Closing Handshake is Started_ and that the
 WebSocket connection is in the CLOSING state.

7.1.4. The WebSocket Connection is Closed

 When the underlying TCP connection is closed, it is said that _The
 WebSocket Connection is Closed_ and that the WebSocket connection is
 in the CLOSED state.  If the TCP connection was closed after the
 WebSocket closing handshake was completed, the WebSocket connection
 is said to have been closed _cleanly_.
 If the WebSocket connection could not be established, it is also said
 that _The WebSocket Connection is Closed_, but not _cleanly_.

7.1.5. The WebSocket Connection Close Code

 As defined in Sections 5.5.1 and 7.4, a Close control frame may
 contain a status code indicating a reason for closure.  A closing of
 the WebSocket connection may be initiated by either endpoint,
 potentially simultaneously. _The WebSocket Connection Close Code_ is
 defined as the status code (Section 7.4) contained in the first Close
 control frame received by the application implementing this protocol.
 If this Close control frame contains no status code, _The WebSocket
 Connection Close Code_ is considered to be 1005.  If _The WebSocket
 Connection is Closed_ and no Close control frame was received by the
 endpoint (such as could occur if the underlying transport connection
 is lost), _The WebSocket Connection Close Code_ is considered to be
 1006.
 NOTE: Two endpoints may not agree on the value of _The WebSocket
 Connection Close Code_.  As an example, if the remote endpoint sent a
 Close frame but the local application has not yet read the data
 containing the Close frame from its socket's receive buffer, and the
 local application independently decided to close the connection and
 send a Close frame, both endpoints will have sent and received a

Fette & Melnikov Standards Track [Page 42] RFC 6455 The WebSocket Protocol December 2011

 Close frame and will not send further Close frames.  Each endpoint
 will see the status code sent by the other end as _The WebSocket
 Connection Close Code_.  As such, it is possible that the two
 endpoints may not agree on the value of _The WebSocket Connection
 Close Code_ in the case that both endpoints _Start the WebSocket
 Closing Handshake_ independently and at roughly the same time.

7.1.6. The WebSocket Connection Close Reason

 As defined in Sections 5.5.1 and 7.4, a Close control frame may
 contain a status code indicating a reason for closure, followed by
 UTF-8-encoded data, the interpretation of said data being left to the
 endpoints and not defined by this protocol.  A closing of the
 WebSocket connection may be initiated by either endpoint, potentially
 simultaneously. _The WebSocket Connection Close Reason_ is defined as
 the UTF-8-encoded data following the status code (Section 7.4)
 contained in the first Close control frame received by the
 application implementing this protocol.  If there is no such data in
 the Close control frame, _The WebSocket Connection Close Reason_ is
 the empty string.
 NOTE: Following the same logic as noted in Section 7.1.5, two
 endpoints may not agree on _The WebSocket Connection Close Reason_.

7.1.7. Fail the WebSocket Connection

 Certain algorithms and specifications require an endpoint to _Fail
 the WebSocket Connection_.  To do so, the client MUST _Close the
 WebSocket Connection_, and MAY report the problem to the user (which
 would be especially useful for developers) in an appropriate manner.
 Similarly, to do so, the server MUST _Close the WebSocket
 Connection_, and SHOULD log the problem.
 If _The WebSocket Connection is Established_ prior to the point where
 the endpoint is required to _Fail the WebSocket Connection_, the
 endpoint SHOULD send a Close frame with an appropriate status code
 (Section 7.4) before proceeding to _Close the WebSocket Connection_.
 An endpoint MAY omit sending a Close frame if it believes the other
 side is unlikely to be able to receive and process the Close frame,
 due to the nature of the error that led the WebSocket connection to
 fail in the first place.  An endpoint MUST NOT continue to attempt to
 process data (including a responding Close frame) from the remote
 endpoint after being instructed to _Fail the WebSocket Connection_.
 Except as indicated above or as specified by the application layer
 (e.g., a script using the WebSocket API), clients SHOULD NOT close
 the connection.

Fette & Melnikov Standards Track [Page 43] RFC 6455 The WebSocket Protocol December 2011

7.2. Abnormal Closures

7.2.1. Client-Initiated Closure

 Certain algorithms, in particular during the opening handshake,
 require the client to _Fail the WebSocket Connection_.  To do so, the
 client MUST _Fail the WebSocket Connection_ as defined in
 Section 7.1.7.
 If at any point the underlying transport layer connection is
 unexpectedly lost, the client MUST _Fail the WebSocket Connection_.
 Except as indicated above or as specified by the application layer
 (e.g., a script using the WebSocket API), clients SHOULD NOT close
 the connection.

7.2.2. Server-Initiated Closure

 Certain algorithms require or recommend that the server _Abort the
 WebSocket Connection_ during the opening handshake.  To do so, the
 server MUST simply _Close the WebSocket Connection_ (Section 7.1.1).

7.2.3. Recovering from Abnormal Closure

 Abnormal closures may be caused by any number of reasons.  Such
 closures could be the result of a transient error, in which case
 reconnecting may lead to a good connection and a resumption of normal
 operations.  Such closures may also be the result of a nontransient
 problem, in which case if each deployed client experiences an
 abnormal closure and immediately and persistently tries to reconnect,
 the server may experience what amounts to a denial-of-service attack
 by a large number of clients trying to reconnect.  The end result of
 such a scenario could be that the service is unable to recover in a
 timely manner or recovery is made much more difficult.
 To prevent this, clients SHOULD use some form of backoff when trying
 to reconnect after abnormal closures as described in this section.
 The first reconnect attempt SHOULD be delayed by a random amount of
 time.  The parameters by which this random delay is chosen are left
 to the client to decide; a value chosen randomly between 0 and 5
 seconds is a reasonable initial delay though clients MAY choose a
 different interval from which to select a delay length based on
 implementation experience and particular application.
 Should the first reconnect attempt fail, subsequent reconnect
 attempts SHOULD be delayed by increasingly longer amounts of time,
 using a method such as truncated binary exponential backoff.

Fette & Melnikov Standards Track [Page 44] RFC 6455 The WebSocket Protocol December 2011

7.3. Normal Closure of Connections

 Servers MAY close the WebSocket connection whenever desired.  Clients
 SHOULD NOT close the WebSocket connection arbitrarily.  In either
 case, an endpoint initiates a closure by following the procedures to
 _Start the WebSocket Closing Handshake_ (Section 7.1.2).

7.4. Status Codes

 When closing an established connection (e.g., when sending a Close
 frame, after the opening handshake has completed), an endpoint MAY
 indicate a reason for closure.  The interpretation of this reason by
 an endpoint, and the action an endpoint should take given this
 reason, are left undefined by this specification.  This specification
 defines a set of pre-defined status codes and specifies which ranges
 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 that the purpose for
    which the connection was established 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).

Fette & Melnikov Standards Track [Page 45] RFC 6455 The WebSocket Protocol December 2011

 1004
    Reserved.  The specific meaning might be defined in the future.
 1005
    1005 is a reserved value and MUST NOT be set as a status code in a
    Close control frame by an endpoint.  It is designated for use in
    applications expecting a status code to indicate that no status
    code was actually present.
 1006
    1006 is a reserved value and MUST NOT be set as a status code in a
    Close control frame by an endpoint.  It is designated for use in
    applications expecting a status code to indicate that the
    connection was closed abnormally, e.g., without sending or
    receiving a Close control frame.
 1007
    1007 indicates that an endpoint is terminating the connection
    because it has received data within a message that was not
    consistent with the type of the message (e.g., non-UTF-8 [RFC3629]
    data within a text message).
 1008
    1008 indicates that an endpoint is terminating the connection
    because it has received a message that violates its policy.  This
    is a generic status code that can be returned when there is no
    other more suitable status code (e.g., 1003 or 1009) or if there
    is a need to hide specific details about the policy.
 1009
    1009 indicates that an endpoint is terminating the connection
    because it has received a message that is too big for it to
    process.
 1010
    1010 indicates that an endpoint (client) is terminating the
    connection because it has expected the server to negotiate one or
    more extension, but the server didn't return them in the response
    message of the WebSocket handshake.  The list of extensions that

Fette & Melnikov Standards Track [Page 46] RFC 6455 The WebSocket Protocol December 2011

    are needed SHOULD appear in the /reason/ part of the Close frame.
    Note that this status code is not used by the server, because it
    can fail the WebSocket handshake instead.
 1011
    1011 indicates that a server is terminating the connection because
    it encountered an unexpected condition that prevented it from
    fulfilling the request.
 1015
    1015 is a reserved value and MUST NOT be set as a status code in a
    Close control frame by an endpoint.  It is designated for use in
    applications expecting a status code to indicate that the
    connection was closed due to a failure to perform a TLS handshake
    (e.g., the server certificate can't be verified).

7.4.2. Reserved Status Code Ranges

 0-999
    Status codes in the range 0-999 are not used.
 1000-2999
    Status codes in the range 1000-2999 are reserved for definition by
    this protocol, its future revisions, and extensions specified in a
    permanent and readily available public specification.
 3000-3999
    Status codes in the range 3000-3999 are reserved for use by
    libraries, frameworks, and applications.  These status codes are
    registered directly with IANA.  The interpretation of these codes
    is undefined by this protocol.
 4000-4999
    Status codes in the range 4000-4999 are reserved for private use
    and thus can't be registered.  Such codes can be used by prior
    agreements between WebSocket applications.  The interpretation of
    these codes is undefined by this protocol.

Fette & Melnikov Standards Track [Page 47] RFC 6455 The WebSocket Protocol December 2011

8. Error Handling

8.1. Handling Errors in UTF-8-Encoded Data

 When an endpoint is to interpret a byte stream as UTF-8 but finds
 that the byte stream is not, in fact, a valid UTF-8 stream, that
 endpoint MUST _Fail the WebSocket Connection_.  This rule applies
 both during the opening handshake and during subsequent data
 exchange.

9. Extensions

 WebSocket clients MAY request extensions to this specification, and
 WebSocket servers MAY accept some or all extensions requested by the
 client.  A server MUST NOT respond with any extension not requested
 by the client.  If extension parameters are included in negotiations
 between the client and the server, those parameters MUST be chosen in
 accordance with the specification of the extension to which the
 parameters apply.

9.1. Negotiating Extensions

 A client requests extensions by including a |Sec-WebSocket-
 Extensions| header field, which follows the normal rules for HTTP
 header fields (see [RFC2616], Section 4.2) and the value of the
 header field is defined by the following ABNF [RFC2616].  Note that
 this section is using ABNF syntax/rules from [RFC2616], including the
 "implied *LWS rule".  If a value is received by either the client or
 the server during negotiation that does not conform to the ABNF
 below, the recipient of such malformed data MUST immediately _Fail
 the WebSocket Connection_.
       Sec-WebSocket-Extensions = extension-list
       extension-list = 1#extension
       extension = extension-token *( ";" extension-param )
       extension-token = registered-token
       registered-token = token
       extension-param = token [ "=" (token | quoted-string) ]
           ;When using the quoted-string syntax variant, the value
           ;after quoted-string unescaping MUST conform to the
           ;'token' ABNF.

Fette & Melnikov Standards Track [Page 48] RFC 6455 The WebSocket Protocol December 2011

 Note that like other HTTP header fields, this header field MAY be
 split or combined across multiple lines.  Ergo, the following are
 equivalent:
       Sec-WebSocket-Extensions: foo
       Sec-WebSocket-Extensions: bar; baz=2
 is exactly equivalent to
       Sec-WebSocket-Extensions: foo, bar; baz=2
 Any extension-token used MUST be a registered token (see
 Section 11.4).  The parameters supplied with any given extension MUST
 be defined for that extension.  Note that the client is only offering
 to use any advertised extensions and MUST NOT use them unless the
 server indicates that it wishes to use the extension.
 Note that the order of extensions is significant.  Any interactions
 between multiple extensions MAY be defined in the documents defining
 the extensions.  In the absence of such definitions, the
 interpretation is that the header fields listed by the client in its
 request represent a preference of the header fields it wishes to use,
 with the first options listed being most preferable.  The extensions
 listed by the server in response represent the extensions actually in
 use for the connection.  Should the extensions modify the data and/or
 framing, the order of operations on the data should be assumed to be
 the same as the order in which the extensions are listed in the
 server's response in the opening handshake.
 For example, if there are two extensions "foo" and "bar" and if the
 header field |Sec-WebSocket-Extensions| sent by the server has the
 value "foo, bar", then operations on the data will be made as
 bar(foo(data)), be those changes to the data itself (such as
 compression) or changes to the framing that may "stack".
 Non-normative examples of acceptable extension header fields (note
 that long lines are folded for readability):
       Sec-WebSocket-Extensions: deflate-stream
       Sec-WebSocket-Extensions: mux; max-channels=4; flow-control,
        deflate-stream
       Sec-WebSocket-Extensions: private-extension
 A server accepts one or more extensions by including a
 |Sec-WebSocket-Extensions| header field containing one or more
 extensions that were requested by the client.  The interpretation of

Fette & Melnikov Standards Track [Page 49] RFC 6455 The WebSocket Protocol December 2011

 any extension parameters, and what constitutes a valid response by a
 server to a requested set of parameters by a client, will be defined
 by each such extension.

9.2. Known Extensions

 Extensions provide a mechanism for implementations to opt-in to
 additional protocol features.  This document doesn't define any
 extension, but implementations MAY use extensions defined separately.

10. Security Considerations

 This section describes some security considerations applicable to the
 WebSocket Protocol.  Specific security considerations are described
 in subsections of this section.

10.1. Non-Browser Clients

 The WebSocket Protocol protects against malicious JavaScript running
 inside a trusted application such as a web browser, for example, by
 checking of the |Origin| header field (see below).  See Section 1.6
 for additional details.  Such assumptions don't hold true in the case
 of a more-capable client.
 While this protocol is intended to be used by scripts in web pages,
 it can also be used directly by hosts.  Such hosts are acting on
 their own behalf and can therefore send fake |Origin| header fields,
 misleading the server.  Servers should therefore be careful about
 assuming that they are talking directly to scripts from known origins
 and must consider that they might be accessed in unexpected ways.  In
 particular, a server should not trust that any input is valid.
 EXAMPLE: If the server uses input as part of SQL queries, all input
 text should be escaped before being passed to the SQL server, lest
 the server be susceptible to SQL injection.

10.2. Origin Considerations

 Servers that are not intended to process input from any web page but
 only for certain sites SHOULD verify the |Origin| field is an origin
 they expect.  If the origin indicated is unacceptable to the server,
 then it SHOULD respond to the WebSocket handshake with a reply
 containing HTTP 403 Forbidden status code.
 The |Origin| header field protects from the attack cases when the
 untrusted party is typically the author of a JavaScript application
 that is executing in the context of the trusted client.  The client
 itself can contact the server and, via the mechanism of the |Origin|

Fette & Melnikov Standards Track [Page 50] RFC 6455 The WebSocket Protocol December 2011

 header field, determine whether to extend those communication
 privileges to the JavaScript application.  The intent is not to
 prevent non-browsers from establishing connections but rather to
 ensure that trusted browsers under the control of potentially
 malicious JavaScript cannot fake a WebSocket handshake.

10.3. Attacks On Infrastructure (Masking)

 In addition to endpoints being the target of attacks via WebSockets,
 other parts of web infrastructure, such as proxies, may be the
 subject of an attack.
 As this protocol was being developed, an experiment was conducted to
 demonstrate a class of attacks on proxies that led to the poisoning
 of caching proxies deployed in the wild [TALKING].  The general form
 of the attack was to establish a connection to a server under the
 "attacker's" control, perform an UPGRADE on the HTTP connection
 similar to what the WebSocket Protocol does to establish a
 connection, and subsequently send data over that UPGRADEd connection
 that looked like a GET request for a specific known resource (which
 in an attack would likely be something like a widely deployed script
 for tracking hits or a resource on an ad-serving network).  The
 remote server would respond with something that looked like a
 response to the fake GET request, and this response would be cached
 by a nonzero percentage of deployed intermediaries, thus poisoning
 the cache.  The net effect of this attack would be that if a user
 could be convinced to visit a website the attacker controlled, the
 attacker could potentially poison the cache for that user and other
 users behind the same cache and run malicious script on other
 origins, compromising the web security model.
 To avoid such attacks on deployed intermediaries, it is not
 sufficient to prefix application-supplied data with framing that is
 not compliant with HTTP, as it is not possible to exhaustively
 discover and test that each nonconformant intermediary does not skip
 such non-HTTP framing and act incorrectly on the frame payload.
 Thus, the defense adopted is to mask all data from the client to the
 server, so that the remote script (attacker) does not have control
 over how the data being sent appears on the wire and thus cannot
 construct a message that could be misinterpreted by an intermediary
 as an HTTP request.
 Clients MUST choose a new masking key for each frame, using an
 algorithm that cannot be predicted by end applications that provide
 data.  For example, each masking could be drawn from a
 cryptographically strong random number generator.  If the same key is
 used or a decipherable pattern exists for how the next key is chosen,
 the attacker can send a message that, when masked, could appear to be

Fette & Melnikov Standards Track [Page 51] RFC 6455 The WebSocket Protocol December 2011

 an HTTP request (by taking the message the attacker wishes to see on
 the wire and masking it with the next masking key to be used, the
 masking key will effectively unmask the data when the client applies
 it).
 It is also necessary that once the transmission of a frame from a
 client has begun, the payload (application-supplied data) of that
 frame must not be capable of being modified by the application.
 Otherwise, an attacker could send a long frame where the initial data
 was a known value (such as all zeros), compute the masking key being
 used upon receipt of the first part of the data, and then modify the
 data that is yet to be sent in the frame to appear as an HTTP request
 when masked.  (This is essentially the same problem described in the
 previous paragraph with using a known or predictable masking key.)
 If additional data is to be sent or data to be sent is somehow
 changed, that new or changed data must be sent in a new frame and
 thus with a new masking key.  In short, once transmission of a frame
 begins, the contents must not be modifiable by the remote script
 (application).
 The threat model being protected against is one in which the client
 sends data that appears to be an HTTP request.  As such, the channel
 that needs to be masked is the data from the client to the server.
 The data from the server to the client can be made to look like a
 response, but to accomplish this request, the client must also be
 able to forge a request.  As such, it was not deemed necessary to
 mask data in both directions (the data from the server to the client
 is not masked).
 Despite the protection provided by masking, non-compliant HTTP
 proxies will still be vulnerable to poisoning attacks of this type by
 clients and servers that do not apply masking.

10.4. Implementation-Specific Limits

 Implementations that have implementation- and/or platform-specific
 limitations regarding the frame size or total message size after
 reassembly from multiple frames MUST protect themselves against
 exceeding those limits.  (For example, a malicious endpoint can try
 to exhaust its peer's memory or mount a denial-of-service attack by
 sending either a single big frame (e.g., of size 2**60) or by sending
 a long stream of small frames that are a part of a fragmented
 message.)  Such an implementation SHOULD impose a limit on frame
 sizes and the total message size after reassembly from multiple
 frames.

Fette & Melnikov Standards Track [Page 52] RFC 6455 The WebSocket Protocol December 2011

10.5. WebSocket Client Authentication

 This protocol doesn't prescribe any particular way that servers can
 authenticate clients during the WebSocket handshake.  The WebSocket
 server can use any client authentication mechanism available to a
 generic HTTP server, such as cookies, HTTP authentication, or TLS
 authentication.

10.6. Connection Confidentiality and Integrity

 Connection confidentiality and integrity is provided by running the
 WebSocket Protocol over TLS (wss URIs).  WebSocket implementations
 MUST support TLS and SHOULD employ it when communicating with their
 peers.
 For connections using TLS, the amount of benefit provided by TLS
 depends greatly on the strength of the algorithms negotiated during
 the TLS handshake.  For example, some TLS cipher mechanisms don't
 provide connection confidentiality.  To achieve reasonable levels of
 protection, clients should use only Strong TLS algorithms.  "Web
 Security Context: User Interface Guidelines"
 [W3C.REC-wsc-ui-20100812] discusses what constitutes Strong TLS
 algorithms.  [RFC5246] provides additional guidance in Appendix A.5
 and Appendix D.3.

10.7. Handling of Invalid Data

 Incoming data MUST always be validated by both clients and servers.
 If, at any time, an endpoint is faced with data that it does not
 understand or that violates some criteria by which the endpoint
 determines safety of input, or when the endpoint sees an opening
 handshake that does not correspond to the values it is expecting
 (e.g., incorrect path or origin in the client request), the endpoint
 MAY drop the TCP connection.  If the invalid data was received after
 a successful WebSocket handshake, the endpoint SHOULD send a Close
 frame with an appropriate status code (Section 7.4) before proceeding
 to _Close the WebSocket Connection_.  Use of a Close frame with an
 appropriate status code can help in diagnosing the problem.  If the
 invalid data is sent during the WebSocket handshake, the server
 SHOULD return an appropriate HTTP [RFC2616] status code.
 A common class of security problems arises when sending text data
 using the wrong encoding.  This protocol specifies that messages with
 a Text data type (as opposed to Binary or other types) contain UTF-8-
 encoded data.  Although the length is still indicated and
 applications implementing this protocol should use the length to
 determine where the frame actually ends, sending data in an improper

Fette & Melnikov Standards Track [Page 53] RFC 6455 The WebSocket Protocol December 2011

 encoding may still break assumptions that applications built on top
 of this protocol may make, leading to anything from misinterpretation
 of data to loss of data or potential security bugs.

10.8. Use of SHA-1 by the WebSocket Handshake

 The WebSocket handshake described in this document doesn't depend on
 any security properties of SHA-1, such as collision resistance or
 resistance to the second pre-image attack (as described in
 [RFC4270]).

11. IANA Considerations

11.1. Registration of New URI Schemes

11.1.1. Registration of "ws" Scheme

 A |ws| URI identifies a WebSocket server and resource name.
 URI scheme name
    ws
 Status
    Permanent
 URI scheme syntax
    Using the ABNF [RFC5234] syntax and ABNF terminals from the URI
    specification [RFC3986]:
         "ws:" "//" authority path-abempty [ "?" query ]
 The <path-abempty> and <query> [RFC3986] components form the resource
 name sent to the server to identify the kind of service desired.
 Other components have the meanings described in [RFC3986].
 URI scheme semantics
    The only operation for this scheme is to open a connection using
    the WebSocket Protocol.
 Encoding considerations
    Characters in the host component that are excluded by the syntax
    defined above MUST be converted from Unicode to ASCII as specified
    in [RFC3987] or its replacement.  For the purposes of scheme-based
    normalization, Internationalized Domain Name (IDN) forms of the
    host component and their conversions to punycode are considered
    equivalent (see Section 5.3.3 of [RFC3987]).

Fette & Melnikov Standards Track [Page 54] RFC 6455 The WebSocket Protocol December 2011

    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 [RFC3986] and Internationalized Resource Identifier (IRI)
    [RFC3987] specifications.
 Applications/protocols that use this URI scheme name
    WebSocket Protocol
 Interoperability considerations
    Use of WebSocket requires use of HTTP version 1.1 or higher.
 Security considerations
    See "Security Considerations" section.
 Contact
    HYBI WG <hybi@ietf.org>
 Author/Change controller
    IETF <iesg@ietf.org>
 References
    RFC 6455

11.1.2. Registration of "wss" Scheme

 A |wss| URI identifies a WebSocket server and resource name and
 indicates that traffic over that connection is to be protected via
 TLS (including standard benefits of TLS such as data confidentiality
 and integrity and endpoint authentication).
 URI scheme name
    wss
 Status
    Permanent
 URI scheme syntax
    Using the ABNF [RFC5234] syntax and ABNF terminals from the URI
    specification [RFC3986]:
         "wss:" "//" authority path-abempty [ "?" query ]
 The <path-abempty> and <query> components form the resource name sent
 to the server to identify the kind of service desired.  Other
 components have the meanings described in [RFC3986].

Fette & Melnikov Standards Track [Page 55] RFC 6455 The WebSocket Protocol December 2011

 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 as specified
    in [RFC3987] or its replacement.  For the purposes of scheme-based
    normalization IDN forms of the host component and their
    conversions to punycode are considered equivalent (see Section
    5.3.3 of [RFC3987]).
    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 [RFC3986] and IRI [RFC3987] specifications.
 Applications/protocols that use this URI scheme name
    WebSocket Protocol over TLS
 Interoperability considerations
    Use of WebSocket requires use of HTTP version 1.1 or higher.
 Security considerations
    See "Security Considerations" section.
 Contact
    HYBI WG <hybi@ietf.org>
 Author/Change controller
    IETF <iesg@ietf.org>
 References
    RFC 6455

11.2. Registration of the "WebSocket" HTTP Upgrade Keyword

 This section defines a keyword registered in the HTTP Upgrade Tokens
 Registry as per RFC 2817 [RFC2817].
 Name of token
    WebSocket
 Author/Change controller
    IETF <iesg@ietf.org>

Fette & Melnikov Standards Track [Page 56] RFC 6455 The WebSocket Protocol December 2011

 Contact
    HYBI <hybi@ietf.org>
 References
    RFC 6455

11.3. Registration of New HTTP Header Fields

11.3.1. Sec-WebSocket-Key

 This section describes a header field registered in the Permanent
 Message Header Field Names registry [RFC3864].
 Header field name
    Sec-WebSocket-Key
 Applicable protocol
    http
 Status
    standard
 Author/Change controller
    IETF
 Specification document(s)
    RFC 6455
 Related information
    This header field is only used for WebSocket opening handshake.
 The |Sec-WebSocket-Key| header field is used in the WebSocket opening
 handshake.  It is sent from the client to the server to provide part
 of the information used by the server to prove that it received a
 valid WebSocket opening handshake.  This helps ensure that the server
 does not accept connections from non-WebSocket clients (e.g., HTTP
 clients) that are being abused to send data to unsuspecting WebSocket
 servers.
 The |Sec-WebSocket-Key| header field MUST NOT appear more than once
 in an HTTP request.

Fette & Melnikov Standards Track [Page 57] RFC 6455 The WebSocket Protocol December 2011

11.3.2. Sec-WebSocket-Extensions

 This section describes a header field for registration in the
 Permanent Message Header Field Names registry [RFC3864].
 Header field name
    Sec-WebSocket-Extensions
 Applicable protocol
    http
 Status
    standard
 Author/Change controller
    IETF
 Specification document(s)
    RFC 6455
 Related information
    This header field is only used for WebSocket opening handshake.
 The |Sec-WebSocket-Extensions| header field is used in the WebSocket
 opening handshake.  It is initially sent from the client to the
 server, and then subsequently sent from the server to the client, to
 agree on a set of protocol-level extensions to use for the duration
 of the connection.
 The |Sec-WebSocket-Extensions| header field MAY appear multiple times
 in an HTTP request (which is logically the same as a single
 |Sec-WebSocket-Extensions| header field that contains all values.
 However, the |Sec-WebSocket-Extensions| header field MUST NOT appear
 more than once in an HTTP response.

11.3.3. Sec-WebSocket-Accept

 This section describes a header field registered in the Permanent
 Message Header Field Names registry [RFC3864].
 Header field name
    Sec-WebSocket-Accept
 Applicable protocol
    http
 Status
    standard

Fette & Melnikov Standards Track [Page 58] RFC 6455 The WebSocket Protocol December 2011

 Author/Change controller
    IETF
 Specification document(s)
    RFC 6455
 Related information
    This header field is only used for the WebSocket opening
    handshake.
 The |Sec-WebSocket-Accept| header field is used in the WebSocket
 opening handshake.  It is sent from the server to the client to
 confirm that the server is willing to initiate the WebSocket
 connection.
 The |Sec-WebSocket-Accept| header MUST NOT appear more than once in
 an HTTP response.

11.3.4. Sec-WebSocket-Protocol

 This section describes a header field registered in the Permanent
 Message Header Field Names registry [RFC3864].
 Header field name
    Sec-WebSocket-Protocol
 Applicable protocol
    http
 Status
    standard
 Author/Change controller
    IETF
 Specification document(s)
    RFC 6455
 Related information
    This header field is only used for the WebSocket opening
    handshake.
 The |Sec-WebSocket-Protocol| header field is used in the WebSocket
 opening handshake.  It is sent from the client to the server and back
 from the server to the client to confirm the subprotocol of the
 connection.  This enables scripts to both select a subprotocol and be
 sure that the server agreed to serve that subprotocol.

Fette & Melnikov Standards Track [Page 59] RFC 6455 The WebSocket Protocol December 2011

 The |Sec-WebSocket-Protocol| header field MAY appear multiple times
 in an HTTP request (which is logically the same as a single
 |Sec-WebSocket-Protocol| header field that contains all values).
 However, the |Sec-WebSocket-Protocol| header field MUST NOT appear
 more than once in an HTTP response.

11.3.5. Sec-WebSocket-Version

 This section describes a header field registered in the Permanent
 Message Header Field Names registry [RFC3864].
 Header field name
    Sec-WebSocket-Version
 Applicable protocol
    http
 Status
    standard
 Author/Change controller
    IETF
 Specification document(s)
    RFC 6455
 Related information
    This header field is only used for the WebSocket opening
    handshake.
 The |Sec-WebSocket-Version| header field is used in the WebSocket
 opening handshake.  It is sent from the client to the server to
 indicate the protocol version of the connection.  This enables
 servers to correctly interpret the opening handshake and subsequent
 data being sent from the data, and close the connection if the server
 cannot interpret that data in a safe manner.  The |Sec-WebSocket-
 Version| header field is also sent from the server to the client on
 WebSocket handshake error, when the version received from the client
 does not match a version understood by the server.  In such a case,
 the header field includes the protocol version(s) supported by the
 server.
 Note that there is no expectation that higher version numbers are
 necessarily backward compatible with lower version numbers.

Fette & Melnikov Standards Track [Page 60] RFC 6455 The WebSocket Protocol December 2011

 The |Sec-WebSocket-Version| header field MAY appear multiple times in
 an HTTP response (which is logically the same as a single
 |Sec-WebSocket-Version| header field that contains all values).
 However, the |Sec-WebSocket-Version| header field MUST NOT appear
 more than once in an HTTP request.

11.4. WebSocket Extension Name Registry

 This specification creates a new IANA registry for WebSocket
 Extension names to be used with the WebSocket Protocol in accordance
 with the principles set out in RFC 5226 [RFC5226].
 As part of this registry, IANA maintains the following information:
 Extension Identifier
    The identifier of the extension, as will be used in the
    |Sec-WebSocket-Extensions| header field registered in
    Section 11.3.2 of this specification.  The value must conform to
    the requirements for an extension-token as defined in Section 9.1
    of this specification.
 Extension Common Name
    The name of the extension, as the extension is generally referred
    to.
 Extension Definition
    A reference to the document in which the extension being used with
    the WebSocket Protocol is defined.
 Known Incompatible Extensions
    A list of extension identifiers with which this extension is known
    to be incompatible.
 WebSocket Extension names are to be subject to the "First Come First
 Served" IANA registration policy [RFC5226].
 There are no initial values in this registry.

11.5. WebSocket Subprotocol Name Registry

 This specification creates a new IANA registry for WebSocket
 Subprotocol names to be used with the WebSocket Protocol in
 accordance with the principles set out in RFC 5226 [RFC5226].

Fette & Melnikov Standards Track [Page 61] RFC 6455 The WebSocket Protocol December 2011

 As part of this registry, IANA maintains the following information:
 Subprotocol Identifier
    The identifier of the subprotocol, as will be used in the
    |Sec-WebSocket-Protocol| header field registered in Section 11.3.4
    of this specification.  The value must conform to the requirements
    given in item 10 of Section 4.1 of this specification -- namely,
    the value must be a token as defined by RFC 2616 [RFC2616].
 Subprotocol Common Name
    The name of the subprotocol, as the subprotocol is generally
    referred to.
 Subprotocol Definition
    A reference to the document in which the subprotocol being used
    with the WebSocket Protocol is defined.
 WebSocket Subprotocol names are to be subject to the "First Come
 First Served" IANA registration policy [RFC5226].

11.6. WebSocket Version Number Registry

 This specification creates a new IANA registry for WebSocket Version
 Numbers to be used with the WebSocket Protocol in accordance with the
 principles set out in RFC 5226 [RFC5226].
 As part of this registry, IANA maintains the following information:
 Version Number
    The version number to be used in the |Sec-WebSocket-Version| is
    specified in Section 4.1 of this specification.  The value must be
    a non-negative integer in the range between 0 and 255 (inclusive).
 Reference
    The RFC requesting a new version number or a draft name with
    version number (see below).
 Status
    Either "Interim" or "Standard".  See below for description.
 A version number is designated as either "Interim" or "Standard".
 A "Standard" version number is documented in an RFC and used to
 identify a major, stable version of the WebSocket protocol, such as
 the version defined by this RFC.  "Standard" version numbers are
 subject to the "IETF Review" IANA registration policy [RFC5226].

Fette & Melnikov Standards Track [Page 62] RFC 6455 The WebSocket Protocol December 2011

 An "Interim" version number is documented in an Internet-Draft and
 used to help implementors identify and interoperate with deployed
 versions of the WebSocket protocol, such as versions developed before
 the publication of this RFC.  "Interim" version numbers are subject
 to the "Expert Review" IANA registration policy [RFC5226], with the
 chairs of the HYBI Working Group (or, if the working group closes,
 the Area Directors for the IETF Applications Area) being the initial
 Designated Experts.
 IANA has added initial values to the registry as follows.
 +--------+-----------------------------------------+----------+
 |Version |                Reference                |  Status  |
 | Number |                                         |          |
 +--------+-----------------------------------------+----------+
 | 0      + draft-ietf-hybi-thewebsocketprotocol-00 | Interim  |
 +--------+-----------------------------------------+----------+
 | 1      + draft-ietf-hybi-thewebsocketprotocol-01 | Interim  |
 +--------+-----------------------------------------+----------+
 | 2      + draft-ietf-hybi-thewebsocketprotocol-02 | Interim  |
 +--------+-----------------------------------------+----------+
 | 3      + draft-ietf-hybi-thewebsocketprotocol-03 | Interim  |
 +--------+-----------------------------------------+----------+
 | 4      + draft-ietf-hybi-thewebsocketprotocol-04 | Interim  |
 +--------+-----------------------------------------+----------+
 | 5      + draft-ietf-hybi-thewebsocketprotocol-05 | Interim  |
 +--------+-----------------------------------------+----------+
 | 6      + draft-ietf-hybi-thewebsocketprotocol-06 | Interim  |
 +--------+-----------------------------------------+----------+
 | 7      + draft-ietf-hybi-thewebsocketprotocol-07 | Interim  |
 +--------+-----------------------------------------+----------+
 | 8      + draft-ietf-hybi-thewebsocketprotocol-08 | Interim  |
 +--------+-----------------------------------------+----------+
 | 9      +                Reserved                 |          |
 +--------+-----------------------------------------+----------+
 | 10     +                Reserved                 |          |
 +--------+-----------------------------------------+----------+
 | 11     +                Reserved                 |          |
 +--------+-----------------------------------------+----------+
 | 12     +                Reserved                 |          |
 +--------+-----------------------------------------+----------+
 | 13     +                RFC 6455                 | Standard |
 +--------+-----------------------------------------+----------+

Fette & Melnikov Standards Track [Page 63] RFC 6455 The WebSocket Protocol December 2011

11.7. WebSocket Close Code Number Registry

 This specification creates a new IANA registry for WebSocket
 Connection Close Code Numbers in accordance with the principles set
 out in RFC 5226 [RFC5226].
 As part of this registry, IANA maintains the following information:
 Status Code
    The Status Code denotes a reason for a WebSocket connection
    closure as per Section 7.4 of this document.  The status code is
    an integer number between 1000 and 4999 (inclusive).
 Meaning
    The meaning of the status code.  Each status code has to have a
    unique meaning.
 Contact
    A contact for the entity reserving the status code.
 Reference
    The stable document requesting the status codes and defining their
    meaning.  This is required for status codes in the range 1000-2999
    and recommended for status codes in the range 3000-3999.
 WebSocket Close Code Numbers are subject to different registration
 requirements depending on their range.  Requests for status codes for
 use by this protocol and its subsequent versions or extensions are
 subject to any one of the "Standards Action", "Specification
 Required" (which implies "Designated Expert"), or "IESG Review" IANA
 registration policies and should be granted in the range 1000-2999.
 Requests for status codes for use by libraries, frameworks, and
 applications are subject to the "First Come First Served" IANA
 registration policy and should be granted in the range 3000-3999.
 The range of status codes from 4000-4999 is designated for Private
 Use.  Requests should indicate whether they are requesting status
 codes for use by the WebSocket Protocol (or a future version of the
 protocol), by extensions, or by libraries/frameworks/applications.

Fette & Melnikov Standards Track [Page 64] RFC 6455 The WebSocket Protocol December 2011

 IANA has added initial values to the registry as follows.
   |Status Code | Meaning         | Contact       | Reference |
  -+------------+-----------------+---------------+-----------|
   | 1000       | Normal Closure  | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1001       | Going Away      | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1002       | Protocol error  | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1003       | Unsupported Data| hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1004       | ---Reserved---- | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1005       | No Status Rcvd  | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1006       | Abnormal Closure| hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1007       | Invalid frame   | hybi@ietf.org | RFC 6455  |
   |            | payload data    |               |           |
  -+------------+-----------------+---------------+-----------|
   | 1008       | Policy Violation| hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1009       | Message Too Big | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1010       | Mandatory Ext.  | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|
   | 1011       | Internal Server | hybi@ietf.org | RFC 6455  |
   |            | Error           |               |           |
  -+------------+-----------------+---------------+-----------|
   | 1015       | TLS handshake   | hybi@ietf.org | RFC 6455  |
  -+------------+-----------------+---------------+-----------|

11.8. WebSocket Opcode Registry

 This specification creates a new IANA registry for WebSocket Opcodes
 in accordance with the principles set out in RFC 5226 [RFC5226].
 As part of this registry, IANA maintains the following information:
 Opcode
    The opcode denotes the frame type of the WebSocket frame, as
    defined in Section 5.2.  The opcode is an integer number between 0
    and 15, inclusive.
 Meaning
    The meaning of the opcode value.

Fette & Melnikov Standards Track [Page 65] RFC 6455 The WebSocket Protocol December 2011

 Reference
    The specification requesting the opcode.
 WebSocket Opcode numbers are subject to the "Standards Action" IANA
 registration policy [RFC5226].
 IANA has added initial values to the registry as follows.
   |Opcode  | Meaning                             | Reference |
  -+--------+-------------------------------------+-----------|
   | 0      | Continuation Frame                  | RFC 6455  |
  -+--------+-------------------------------------+-----------|
   | 1      | Text Frame                          | RFC 6455  |
  -+--------+-------------------------------------+-----------|
   | 2      | Binary Frame                        | RFC 6455  |
  -+--------+-------------------------------------+-----------|
   | 8      | Connection Close Frame              | RFC 6455  |
  -+--------+-------------------------------------+-----------|
   | 9      | Ping Frame                          | RFC 6455  |
  -+--------+-------------------------------------+-----------|
   | 10     | Pong Frame                          | RFC 6455  |
  -+--------+-------------------------------------+-----------|

11.9. WebSocket Framing Header Bits Registry

 This specification creates a new IANA registry for WebSocket Framing
 Header Bits in accordance with the principles set out in RFC 5226
 [RFC5226].  This registry controls assignment of the bits marked
 RSV1, RSV2, and RSV3 in Section 5.2.
 These bits are reserved for future versions or extensions of this
 specification.
 WebSocket Framing Header Bits assignments are subject to the
 "Standards Action" IANA registration policy [RFC5226].

12. Using the WebSocket Protocol from Other Specifications

 The WebSocket Protocol is intended to be used by another
 specification to provide a generic mechanism for dynamic author-
 defined content, e.g., in a specification defining a scripted API.
 Such a specification first needs to _Establish a WebSocket
 Connection_, providing that algorithm with:
 o  The destination, consisting of a /host/ and a /port/.

Fette & Melnikov Standards Track [Page 66] RFC 6455 The WebSocket Protocol December 2011

 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 [RFC6454] that is being made
    responsible for the connection.
 o  Optionally, a string identifying a protocol that is to be layered
    over the WebSocket connection.
 The /host/, /port/, /resource name/, and /secure/ flag are usually
 obtained from a URI using the steps to parse a WebSocket URI's
 components.  These steps fail if the URI does not specify a
 WebSocket.
 If at any time the connection is to be closed, then the specification
 needs to use the _Close the WebSocket Connection_ algorithm
 (Section 7.1.1).
 Section 7.1.4 defines when _The WebSocket Connection is Closed_.
 While a connection is open, the specification will need to handle the
 cases when _A WebSocket Message Has Been Received_ (Section 6.2).
 To send some data /data/ to an open connection, the specification
 needs to _Send a WebSocket Message_ (Section 6.1).

13. Acknowledgements

 Special thanks are due to Ian Hickson, who was the original author
 and editor of this protocol.  The initial design of this
 specification benefitted from the participation of many people in the
 WHATWG and WHATWG mailing list.  Contributions to that specification
 are not tracked by section, but a list of all who contributed to that
 specification is given in the WHATWG HTML specification at
 http://whatwg.org/html5.
 Special thanks also to John Tamplin for providing a significant
 amount of text for the "Data Framing" section of this specification.
 Special thanks also to Adam Barth for providing a significant amount
 of text and background research for the "Data Masking" section of
 this specification.

Fette & Melnikov Standards Track [Page 67] RFC 6455 The WebSocket Protocol December 2011

 Special thanks to Lisa Dusseault for the Apps Area review (and for
 helping to start this work), Richard Barnes for the Gen-Art review,
 and Magnus Westerlund for the Transport Area Review.  Special thanks
 to HYBI WG past and present WG chairs who tirelessly worked behind
 the scene to move this work toward completion: Joe Hildebrand,
 Salvatore Loreto, and Gabriel Montenegro.  And last but not least,
 special thank you to the responsible Area Director Peter Saint-Andre.
 Thank you to the following people who participated in discussions on
 the HYBI WG mailing list and contributed ideas and/or provided
 detailed reviews (the list is likely to be incomplete): Greg Wilkins,
 John Tamplin, Willy Tarreau, Maciej Stachowiak, Jamie Lokier, Scott
 Ferguson, Bjoern Hoehrmann, Julian Reschke, Dave Cridland, Andy
 Green, Eric Rescorla, Inaki Baz Castillo, Martin Thomson, Roberto
 Peon, Patrick McManus, Zhong Yu, Bruce Atherton, Takeshi Yoshino,
 Martin J. Duerst, James Graham, Simon Pieters, Roy T. Fielding,
 Mykyta Yevstifeyev, Len Holgate, Paul Colomiets, Piotr Kulaga, Brian
 Raymor, Jan Koehler, Joonas Lehtolahti, Sylvain Hellegouarch, Stephen
 Farrell, Sean Turner, Pete Resnick, Peter Thorson, Joe Mason, John
 Fallows, and Alexander Philippou.  Note that people listed above
 didn't necessarily endorse the end result of this work.

14. References

14.1. Normative References

 [ANSI.X3-4.1986]
            American National Standards Institute, "Coded Character
            Set - 7-bit American Standard Code for Information
            Interchange", ANSI X3.4, 1986.
 [FIPS.180-3]
            National Institute of Standards and Technology, "Secure
            Hash Standard", FIPS PUB 180-3, October 2008,
            <http://csrc.nist.gov/publications/fips/fips180-3/
            fips180-3_final.pdf>.
 [RFC1928]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
            L. Jones, "SOCKS Protocol Version 5", RFC 1928,
            March 1996.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
            Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
            Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

Fette & Melnikov Standards Track [Page 68] RFC 6455 The WebSocket Protocol December 2011

 [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within
            HTTP/1.1", RFC 2817, May 2000.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
 [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
            10646", STD 63, RFC 3629, November 2003.
 [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
            Procedures for Message Header Fields", BCP 90, RFC 3864,
            September 2004.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66,
            RFC 3986, January 2005.
 [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
            Identifiers (IRIs)", RFC 3987, January 2005.
 [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
            Requirements for Security", BCP 106, RFC 4086, June 2005.
 [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
            Encodings", RFC 4648, October 2006.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", STD 68, RFC 5234, January 2008.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246, August 2008.
 [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
            Extension Definitions", RFC 6066, January 2011.
 [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
            December 2011.

14.2. Informative References

 [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
            Unique IDentifier (UUID) URN Namespace", RFC 4122,
            July 2005.

Fette & Melnikov Standards Track [Page 69] RFC 6455 The WebSocket Protocol December 2011

 [RFC4270]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic
            Hashes in Internet Protocols", RFC 4270, November 2005.
 [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
            October 2008.
 [RFC6202]  Loreto, S., Saint-Andre, P., Salsano, S., and G. Wilkins,
            "Known Issues and Best Practices for the Use of Long
            Polling and Streaming in Bidirectional HTTP", RFC 6202,
            April 2011.
 [RFC6265]  Barth, A., "HTTP State Management Mechanism", RFC 6265,
            April 2011.
 [TALKING]  Huang, L-S., Chen, E., Barth, A., Rescorla, E., and C.
            Jackson, "Talking to Yourself for Fun and Profit", 2010,
            <http://w2spconf.com/2011/papers/websocket.pdf>.
 [W3C.REC-wsc-ui-20100812]
            Roessler, T. and A. Saldhana, "Web Security Context: User
            Interface Guidelines", World Wide Web Consortium
            Recommendation REC-wsc-ui-20100812, August 2010,
            <http://www.w3.org/TR/2010/REC-wsc-ui-20100812/>.
            Latest version available at
            <http://www.w3.org/TR/wsc-ui/>.
 [WSAPI]    Hickson, I., "The WebSocket API", W3C Working Draft WD-
            websockets-20110929, September 2011,
            <http://www.w3.org/TR/2011/WD-websockets-20110929/>.
            Latest version available at
            <http://www.w3.org/TR/websockets/>.
 [XMLHttpRequest]
            van Kesteren, A., Ed., "XMLHttpRequest", W3C Candidate
            Recommendation CR-XMLHttpRequest-20100803, August 2010,
            <http://www.w3.org/TR/2010/CR-XMLHttpRequest-20100803/>.
            Latest version available at
            <http://www.w3.org/TR/XMLHttpRequest/>.

Fette & Melnikov Standards Track [Page 70] RFC 6455 The WebSocket Protocol December 2011

Authors' Addresses

 Ian Fette
 Google, Inc.
 EMail: ifette+ietf@google.com
 URI:   http://www.ianfette.com/
 Alexey Melnikov
 Isode Ltd.
 5 Castle Business Village
 36 Station Road
 Hampton, Middlesex  TW12 2BX
 UK
 EMail: Alexey.Melnikov@isode.com

Fette & Melnikov Standards Track [Page 71]

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