Bootstrapping WebSockets with HTTP/2
RFC 8441

Internet Engineering Task Force (IETF)                        P. McManus
Request for Comments: 8441                                       Mozilla
Updates: 6455                                             September 2018
Category: Standards Track
ISSN: 2070-1721

                  Bootstrapping WebSockets with HTTP/2

Abstract

   This document defines a mechanism for running the WebSocket Protocol
   (RFC 6455) over a single stream of an HTTP/2 connection.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8441.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

McManus                      Standards Track                    [Page 1]
RFC 8441                      H2 WebSockets               September 2018

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  The SETTINGS_ENABLE_CONNECT_PROTOCOL SETTINGS Parameter . . .   3
   4.  The Extended CONNECT Method . . . . . . . . . . . . . . . . .   4
   5.  Using Extended CONNECT to Bootstrap the WebSocket Protocol  .   4
     5.1.  Example . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Design Considerations . . . . . . . . . . . . . . . . . . . .   6
   7.  About Intermediaries  . . . . . . . . . . . . . . . . . . . .   6
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  A New HTTP/2 Setting  . . . . . . . . . . . . . . . . . .   7
     9.2.  A New HTTP Upgrade Token  . . . . . . . . . . . . . . . .   7
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Hypertext Transfer Protocol (HTTP) [RFC7230] provides compatible
   resource-level semantics across different versions, but it does not
   offer compatibility at the connection-management level.  Other
   protocols that rely on connection-management details of HTTP, such as
   WebSockets, must be updated for new versions of HTTP.

   The WebSocket Protocol [RFC6455] uses the HTTP/1.1 Upgrade mechanism
   (Section 6.7 of [RFC7230]) to transition a TCP connection from HTTP
   into a WebSocket connection.  A different approach must be taken with
   HTTP/2 [RFC7540].  Due to its multiplexing nature, HTTP/2 does not
   allow connection-wide header fields or status codes, such as the
   Upgrade and Connection request-header fields or the 101 (Switching
   Protocols) response code.  These are all required by the [RFC6455]
   opening handshake.

   Being able to bootstrap WebSockets from HTTP/2 allows one TCP
   connection to be shared by both protocols and extends HTTP/2's more
   efficient use of the network to WebSockets.

   This document extends the HTTP CONNECT method, as specified for
   HTTP/2 in Section 8.3 of [RFC7540].  The extension allows the
   substitution of a new protocol name to connect to rather than the
   external host normally used by CONNECT.  The result is a tunnel on a
   single HTTP/2 stream that can carry data for WebSockets (or any other
   protocol).  The other streams on the connection may carry more
   extended CONNECT tunnels, traditional HTTP/2 data, or a mixture of
   both.

McManus                      Standards Track                    [Page 2]
RFC 8441                      H2 WebSockets               September 2018

   This tunneled stream will be multiplexed with other regular streams
   on the connection and enjoys the normal priority, cancellation, and
   flow-control features of HTTP/2.

   Streams that successfully establish a WebSocket connection using a
   tunneled stream and the modifications to the opening handshake
   defined in this document then use the traditional WebSocket Protocol,
   treating the stream as if it were the TCP connection in that
   specification.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  The SETTINGS_ENABLE_CONNECT_PROTOCOL SETTINGS Parameter

   This document adds a new SETTINGS parameter to those defined by
   [RFC7540], Section 6.5.2.

   The new parameter name is SETTINGS_ENABLE_CONNECT_PROTOCOL.  The
   value of the parameter MUST be 0 or 1.

   Upon receipt of SETTINGS_ENABLE_CONNECT_PROTOCOL with a value of 1, a
   client MAY use the Extended CONNECT as defined in this document when
   creating new streams.  Receipt of this parameter by a server does not
   have any impact.

   A sender MUST NOT send a SETTINGS_ENABLE_CONNECT_PROTOCOL parameter
   with the value of 0 after previously sending a value of 1.

   Using a SETTINGS parameter to opt into an otherwise incompatible
   protocol change is a use of "Extending HTTP/2" defined by Section 5.5
   of [RFC7540].  Specifically, the addition a new pseudo-header field,
   ":protocol", and the change in meaning of the :authority pseudo-
   header field in Section 4 require opt-in negotiation.  If a client
   were to use the provisions of the extended CONNECT method defined in
   this document without first receiving a
   SETTINGS_ENABLE_CONNECT_PROTOCOL parameter, a non-supporting peer
   would detect a malformed request and generate a stream error
   (Section 8.1.2.6 of [RFC7540]).

McManus                      Standards Track                    [Page 3]
RFC 8441                      H2 WebSockets               September 2018

4.  The Extended CONNECT Method

   Usage of the CONNECT method in HTTP/2 is defined by Section 8.3 of
   [RFC7540].  This extension modifies the method in the following ways:

   o  A new pseudo-header field :protocol MAY be included on request
      HEADERS indicating the desired protocol to be spoken on the tunnel
      created by CONNECT.  The pseudo-header field is single valued and
      contains a value from the "Hypertext Transfer Protocol (HTTP)
      Upgrade Token Registry" located at
      <https://www.iana.org/assignments/http-upgrade-tokens/>

   o  On requests that contain the :protocol pseudo-header field, the
      :scheme and :path pseudo-header fields of the target URI (see
      Section 5) MUST also be included.

   o  On requests bearing the :protocol pseudo-header field, the
      :authority pseudo-header field is interpreted according to
      Section 8.1.2.3 of [RFC7540] instead of Section 8.3 of that
      document.  In particular, the server MUST NOT create a tunnel to
      the host indicated by the :authority as it would with a CONNECT
      method request that was not modified by this extension.

   Upon receiving a CONNECT request bearing the :protocol pseudo-header
   field, the server establishes a tunnel to another service of the
   protocol type indicated by the pseudo-header field.  This service may
   or may not be co-located with the server.

5.  Using Extended CONNECT to Bootstrap the WebSocket Protocol

   The :protocol pseudo-header field MUST be included in the CONNECT
   request, and it MUST have a value of "websocket" to initiate a
   WebSocket connection on an HTTP/2 stream.  Other HTTP request and
   response-header fields, such as those for manipulating cookies, may
   be included in the HEADERS with the CONNECT method as usual.  This
   request replaces the GET-based request in [RFC6455] and is used to
   process the WebSockets opening handshake.

   The scheme of the target URI (Section 5.1 of [RFC7230]) MUST be
   "https" for "wss"-schemed WebSockets and "http" for "ws"-schemed
   WebSockets.  The remainder of the target URI is the same as the
   WebSocket URI.  The WebSocket URI is still used for proxy
   autoconfiguration.  The security requirements for the HTTP/2
   connection used by this specification are established by [RFC7540]
   for https requests and [RFC8164] for http requests.

McManus                      Standards Track                    [Page 4]
RFC 8441                      H2 WebSockets               September 2018

   [RFC6455] requires the use of Connection and Upgrade header fields
   that are not part of HTTP/2.  They MUST NOT be included in the
   CONNECT request defined here.

   [RFC6455] requires the use of a Host header field that is also not
   part of HTTP/2.  The Host information is conveyed as part of the
   :authority pseudo-header field, which is required on every HTTP/2
   transaction.

   Implementations using this extended CONNECT to bootstrap WebSockets
   do not do the processing of the Sec-WebSocket-Key and Sec-WebSocket-
   Accept header fields of [RFC6455] as that functionality has been
   superseded by the :protocol pseudo-header field.

   The Origin [RFC6454], Sec-WebSocket-Version, Sec-WebSocket-Protocol,
   and Sec-WebSocket-Extensions header fields are used in the CONNECT
   request and response-header fields as defined in [RFC6455].  Note
   that HTTP/1 header field names were case insensitive, whereas HTTP/2
   requires they be encoded as lowercase.

   After successfully processing the opening handshake, the peers should
   proceed with the WebSocket Protocol [RFC6455] using the HTTP/2 stream
   from the CONNECT transaction as if it were the TCP connection
   referred to in [RFC6455].  The state of the WebSocket connection at
   this point is OPEN, as defined by [RFC6455], Section 4.1.

   The HTTP/2 stream closure is also analogous to the TCP connection
   closure of [RFC6455].  Orderly TCP-level closures are represented as
   END_STREAM flags ([RFC7540], Section 6.1).  RST exceptions are
   represented with the RST_STREAM frame ([RFC7540], Section 6.4) with
   the CANCEL error code ([RFC7540], Section 7).

McManus                      Standards Track                    [Page 5]
RFC 8441                      H2 WebSockets               September 2018

5.1.  Example

[[ From Client ]]                       [[ From Server ]]

                                        SETTINGS
                                        SETTINGS_ENABLE_CONNECT_[..] = 1

HEADERS + END_HEADERS
:method = CONNECT
:protocol = websocket
:scheme = https
:path = /chat
:authority = server.example.com
sec-websocket-protocol = chat, superchat
sec-websocket-extensions = permessage-deflate
sec-websocket-version = 13
origin = http://www.example.com

                                        HEADERS + END_HEADERS
                                        :status = 200
                                        sec-websocket-protocol = chat

DATA
WebSocket Data

                                        DATA + END_STREAM
                                        WebSocket Data

DATA + END_STREAM
WebSocket Data

6.  Design Considerations

   A more native integration with HTTP/2 is certainly possible with
   larger additions to HTTP/2.  This design was selected to minimize the
   solution complexity while still addressing the primary concern of
   running HTTP/2 and WebSockets concurrently.

7.  About Intermediaries

   This document does not change how WebSockets interacts with HTTP
   forward proxies.  If a client wishing to speak WebSockets connects
   via HTTP/2 to an HTTP proxy, it should continue to use a traditional
   CONNECT (i.e., not with a :protocol pseudo-header field) to tunnel
   through that proxy to the WebSocket server via HTTP.

McManus                      Standards Track                    [Page 6]
RFC 8441                      H2 WebSockets               September 2018

   The resulting version of HTTP on that tunnel determines whether
   WebSockets is initiated directly or via a modified CONNECT request
   described in this document.

8.  Security Considerations

   [RFC6455] ensures that non-WebSockets clients, especially
   XMLHttpRequest-based clients, cannot make a WebSocket connection.
   Its primary mechanism for doing that is the use of Sec-prefixed
   request-header fields that cannot be created by XMLHttpRequest-based
   clients.  This specification addresses that concern in two ways:

   o  XMLHttpRequest also prohibits use of the CONNECT method in
      addition to Sec-prefixed request-header fields.

   o  The use of a pseudo-header field is something that is connection
      specific, and HTTP/2 never allows a pseudo-header to be created
      outside of the protocol stack.

   The security considerations of [RFC6455], Section 10 continue to
   apply to the use of the WebSocket Protocol when using this
   specification, with the exception of 10.8.  That section is not
   relevant, because it is specific to the bootstrapping handshake that
   is changed in this document.

9.  IANA Considerations

9.1.  A New HTTP/2 Setting

   This document registers an entry in the "HTTP/2 Settings" registry
   that was established by Section 11.3 of [RFC7540].

      Code: 0x8
      Name: SETTINGS_ENABLE_CONNECT_PROTOCOL
      Initial Value: 0
      Specification: This document

9.2.  A New HTTP Upgrade Token

   This document registers an entry in the "HTTP Upgrade Tokens"
   registry that was established by [RFC7230].

      Value: websocket
      Description: The Web Socket Protocol
      Expected Version Tokens:
      References: [RFC6455] [RFC8441]

McManus                      Standards Track                    [Page 7]
RFC 8441                      H2 WebSockets               September 2018

10.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6454]  Barth, A., "The Web Origin Concept", RFC 6454,
              DOI 10.17487/RFC6454, December 2011,
              <https://www.rfc-editor.org/info/rfc6454>.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, DOI 10.17487/RFC6455, December 2011,
              <https://www.rfc-editor.org/info/rfc6455>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [RFC8164]  Nottingham, M. and M. Thomson, "Opportunistic Security for
              HTTP/2", RFC 8164, DOI 10.17487/RFC8164, May 2017,
              <https://www.rfc-editor.org/info/rfc8164>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Acknowledgments

   The 2017 HTTP Workshop had a very productive discussion that helped
   determine the key problem and acceptable level of solution
   complexity.

Author's Address

   Patrick McManus
   Mozilla

   Email: mcmanus@ducksong.com

McManus                      Standards Track                    [Page 8]