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Hypertext Transfer Protocol Working Group                    C. Benfield
Internet-Draft                                          October 09, 2015
Intended status: Standards Track
Expires: April 11, 2016


                    Peer-to-peer Extension to HTTP/2
                      draft-benfield-http2-p2p-02

Abstract

   This document introduces a negotiated extension to HTTP/2 that turns
   a single HTTP/2 connection into a bi-directional communication
   channel.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 11, 2016.

Copyright Notice

   Copyright (c) 2015 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
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   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Additions to HTTP/2 . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  SETTINGS_PEER_TO_PEER Setting . . . . . . . . . . . . . .   3
     2.2.  CLIENT_AUTHORITY Frame  . . . . . . . . . . . . . . . . .   4
       2.2.1.  Payload . . . . . . . . . . . . . . . . . . . . . . .   4
       2.2.2.  Semantics . . . . . . . . . . . . . . . . . . . . . .   4
     2.3.  HTTP Changes  . . . . . . . . . . . . . . . . . . . . . .   5
       2.3.1.  Client and Server . . . . . . . . . . . . . . . . . .   5
       2.3.2.  Stream IDs  . . . . . . . . . . . . . . . . . . . . .   5
     2.4.  Dialer Behavioral Changes . . . . . . . . . . . . . . . .   5
     2.5.  Listener Behavioral Changes . . . . . . . . . . . . . . .   6
     2.6.  PUSH_PROMISE  . . . . . . . . . . . . . . . . . . . . . .   6
     2.7.  Other Extensions  . . . . . . . . . . . . . . . . . . . .   6
   3.  Authority Validation  . . . . . . . . . . . . . . . . . . . .   6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  HTTP/2 Frame Type Registry Update . . . . . . . . . . . .   7
     4.2.  HTTP/2 Settings Registry Update . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Changelog  . . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The HTTP/2 [RFC7540] specification provides an alternative framing
   layer for the semantics of HTTP/1.1 [RFC7231].  This framing layer in
   principle allows for both parties in a HTTP/2 session to send
   requests and responses.  However, the HTTP/2 specification also
   requires that the semantics of HTTP/1.1 be preserved.  This means
   that one party of the conversation is considered the client, and one
   the server.  Only the client may send requests, and only the server
   may send responses.

   This document introduces an extension that can be advertised by a
   HTTP/2 client.  This extension allows both the client and the server
   to send requests and responses.  Essentially, this extension changes
   the protocol such that the notion of 'client' and 'server' are
   defined on a per-stream basis, rather than a per-connection basis.

   The principle of this extension is similar to the Reverse HTTP
   [I-D.lentczner-rhttp] proposal made in 2009.  HTTP/2's framing makes
   this a substantially more flexible extension than Reverse HTTP by



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   allowing the client and server to vary on a per-stream basis, rather
   than affecting the whole connection.

1.1.  Notational Conventions

   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 RFC 2119 [RFC2119].

1.2.  Terminology

   The nature of this specification is that which peer is a 'client' and
   which is a 'server' changes from stream-to-stream.  Therefore, the
   terms 'listener' and 'dialer' are introduced to unambiguously refer
   to peers.

   The 'dialer', or dialing peer, is the peer that initiated the HTTP/2
   connection.  In a standard, non-peer-to-peer HTTP/2 transaction, the
   'dialer' and the 'client' are the same.

   The 'listener', or listening peer, is the peer that accepted the
   HTTP/2 connection.  In a standard, non-peer-to-peer HTTP/2
   transaction, the 'listener' and the 'server' are the same.

   'Client' and 'server' are defined on a per-stream basis, following
   the rules in Section 2.3.1.

2.  Additions to HTTP/2

   This document introduces a new HTTP/2 setting ([RFC7540],
   Section 11.3) and a new HTTP/2 frame type ([RFC7540], Section 11.2),
   to allow for a HTTP/2 dialer to advertise its support for receiving
   server-initiated streams, and to allow a listener to advertise its
   support for receiving client-initiated pushed streams.

2.1.  SETTINGS_PEER_TO_PEER Setting

   The following new SETTINGS parameters ([RFC7540], Section 6.5.2) are
   defined:

   o  SETTINGS_PEER_TO_PEER (0xTBA): Informs the remote endpoint of
      whether the sender supports the peer-to-peer extension to HTTP/2.
      A value of 1 indicates that the peer-to-peer extension is
      supported.  Any other value, or the absence of this setting,
      indicates that the peer-to-peer extension is not supported.

      This setting MUST NOT be emitted by the listener on the HTTP/2
      connection.  If the dialer receives this setting from the listener



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      it MUST respond with a connection error ([RFC7540] Section 5.4.1)
      of type PROTOCOL_ERROR.

2.2.  CLIENT_AUTHORITY Frame

   This document introduces the CLIENT_AUTHORITY frame.  This frame MUST
   be emitted by a dialer after it sends a value of
   SETTINGS_PEER_TO_PEER of 1, and MUST NOT be emitted by a dialer any
   time after.  The purpose of this frame is to allow a dialer to
   advertise the authority or authorities for which it is prepared to
   accept requests.

   This frame always applies to a whole connection.  Therefore, the
   stream identifier for CLIENT_AUTHORITY frames MUST be 0.  If a
   listener receives a CLIENT_AUTHORITY frame whose stream identifier
   field is anything other than 0, it MUST respond with a connection
   error ([RFC7540] Section 5.4.1) of type PROTOCOL_ERROR.

2.2.1.  Payload

   Each CLIENT_AUTHORITY frame is made up of one or more of the
   following authority segments:

       +----------------------+
       | Authority Length (8) |
       +----------------------+----------------------------------+
       |                      Authority (*)                      |
       +---------------------------------------------------------+

                 Figure 1: Client Authority Frame Payload

   Each segment begins with a one-byte field indicating the length of
   the authority string the client is asserting.  That field is then
   followed by a single authority field.  The authority MUST be sent in
   whatever character encoding is going to be expected by the dialer on
   receipt of the :authority pseudo-header field.

2.2.2.  Semantics

   Generally speaking, a listener or coalescing intermediary has no in-
   band method of validating that a dialer's authority claims are valid.
   Therefore, a conforming listener MUST confirm a dialer's authority
   claims using some out-of-band method: see Section 3 for more.

   A dialer MUST NOT send a CLIENT_AUTHORITY frame after the first one.
   The CLIENT_AUTHORITY frame is considered to be a complete list of
   authorities: therefore, a dialer MUST start a new connection if it
   would like to change the list of authorities it claims.



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2.3.  HTTP Changes

   From the perspective of other HTTP RFCs, such as RFC 7231 [RFC7231]
   and RFC 7540 [RFC7540], this extension changes whether a peer is
   considered a 'client' or a 'server' on a per-stream basis, instead of
   a per-connection basis, based on which peer opened the stream and how
   they did so.

   The rest of the requirements of RFC 7231 [RFC7231] are preserved.

2.3.1.  Client and Server

   For the purpose of the rest of this document, 'client' and 'server'
   are defined on a per-stream basis.  For a stream that is opened by
   means of a HEADERS frame, the peer that sent the initial headers
   frame is 'client' and the other peer is 'server'.  For a stream that
   is opened by means of a PUSH_PROMISE frame, the peer that sent the
   PUSH_PROMISE frame is 'server' and the other peer is 'client'.

2.3.2.  Stream IDs

   RFC 7540 [RFC7540] Section 5.1.1 applies restrictions on what stream
   IDs MUST be used by a given peer.

   This document amends that section to state that streams initiated by
   a dialer MUST use odd-numbered stream identifiers, and streams
   initiated by a listener MUST use even-numbered stream identifiers.
   This ensures that there will be no conflict when both peers are
   actively creating streams.

   The other limitations of RFC 7540 [RFC7540] Section 5.1.1 continue to
   apply.

2.4.  Dialer Behavioral Changes

   When a dialer emits the SETTINGS_PEER_TO_PEER setting with a value of
   1, it is informing the listener that it is willing to accept HTTP
   requests from the server, allowing the listener to open streams with
   HEADERS frames.  This lifts some of the restrictions of RFC 7540
   [RFC7540] Section 8.

   If a dialer has sent the SETTINGS_PEER_TO_PEER setting with a value
   of 1, the dialer MUST NOT reject an attempt by the listener to change
   the value of SETTINGS_ENABLE_PUSH to 1.

   If the dialer, subsequent to sending SETTINGS_PEER_TO_PEER with value
   1, receives from the listener a value of SETTINGS_ENABLE_PUSH of 1,
   it MAY open streams by sending PUSH_PROMISE frames.



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2.5.  Listener Behavioral Changes

   When a listener receives the SETTINGS_PEER_TO_PEER setting from the
   dialer with a value of 1, it MAY at any point afterwards issue a non-
   zero value for SETTINGS_ENABLE_PUSH.  This allows dialers to open
   streams with PUSH_PROMISE, subject to some limitations (see
   Section 2.6), and also lifts some of the restrictions of RFC 7540
   [RFC7540] Section 8: specifically those sections that only allow
   listeners to send PUSH_PROMISE frames, and only allow dialers to
   receive them.

   A HTTP/2 listener, before receiving SETTINGS_PEER_TO_PEER, must have
   SETTINGS_ENABLE_PUSH equal to 0, as per [RFC7540] Section 8.2.
   However, once a listener has received SETTINGS_PEER_TO_PEER, it MAY
   set SETTINGS_ENABLE_PUSH equal to 1.  If it does not, it is assumed
   that SETTINGS_ENABLE_PUSH remains at 0, and the listener is unwilling
   to accept pushed streams.

2.6.  PUSH_PROMISE

   Whichever peer is client on a given stream MUST NOT send PUSH_PROMISE
   frames on that stream.  All other limitations about PUSH_PROMISE
   frames in RFC 7540 [RFC7540] continue to apply.

   If a peer attempts to send a PUSH_PROMISE frame on a stream in which
   it is the client, the peer that is server for that stream MUST treat
   this event as a connection error ([RFC7540] Section 5.4.1) of type
   PROTOCOL_ERROR.

2.7.  Other Extensions

   When this extension is deployed with other extensions to HTTP/2, the
   behaviour of this extension does not change.  All other extensions
   that refer to 'client' or 'server' SHOULD be treated as though those
   terms apply on a per-stream basis.

   If other extensions apply 'server' or 'client' to the whole
   connection (e.g.  for settings in SETTINGS frames, which are sent on
   stream 0), then both peers SHOULD be considered clients and both
   peers should be considered servers.

3.  Authority Validation

   Generally speaking, a listener or coalescing intermediary has no in-
   band method of validating that a dialer's authority claims are valid.
   Therefore, a conforming listener MUST confirm a dialer's authority
   claims using some out-of-band method.




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   This specification does not lay out in detail any proposed mechanism
   for doing this validation, as the best approach may vary from
   deployment to deployment.  However, some options include:

   o  validating authorities against a TLS certificate presented by the
      dialer during TLS handshake.

   o  confirming that a reverse DNS lookup for the dialer IP returns the
      authority asserted by the dialer.

   o  a static list of IP addresses trusted for a given authority.

   The only requirement is that a listener MUST implement some form of
   validation, and then MUST treat any attempt by a dialer to assert an
   authority that it cannot validate as a connection error ([RFC7540]
   Section 5.4.1) of type PROTOCOL_ERROR.

4.  IANA Considerations

4.1.  HTTP/2 Frame Type Registry Update

   This document updates the HTTP/2 Frame Type registry ([RFC7540],
   Section 11.2).  The entries in the following table are registered by
   this document.

                 +------------------+------+-------------+
                 | Name             | Code | Section     |
                 +------------------+------+-------------+
                 | CLIENT_AUTHORITY | TBD  | Section 2.2 |
                 +------------------+------+-------------+

4.2.  HTTP/2 Settings Registry Update

   This document updates the registry for HTTP/2 Settings ([RFC7540],
   Section 11.4).  The entries in the following table are registered by
   this document.

           +--------------+------+---------------+-------------+
           | Name         | Code | Initial Value | Section     |
           +--------------+------+---------------+-------------+
           | PEER_TO_PEER | TBD  | 0             | Section 2.1 |
           +--------------+------+---------------+-------------+

5.  Acknowledgements

   Thanks to David Dias, Juan Benet, and Fedor Indutny for the original
   idea, and Amos Jeffries, Mike Bishop, and Ilari Liusvaara for their
   follow-up.



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   Thanks also to Tyrel Souza, Donald Stufft, and Paul Kehrer for
   proofreading.

   Thanks to David Reid for pointing out the Reverse HTTP proposal
   [I-D.lentczner-rhttp].

   Thanks to Amos Jeffries for proposing an advertised extension, rather
   than a negotiated one.

6.  References

6.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI
              10.17487/RFC7231, June 2014,
              <http://www.rfc-editor.org/info/rfc7231>.

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

6.2.  Informative References

   [I-D.lentczner-rhttp]
              Lentczner, M. and D. Preston, "Reverse HTTP", draft-
              lentczner-rhttp-00 (work in progress), March 2009.

Appendix A.  Changelog

   (This appendix to be deleted by the RFC Editor.)

   Since -01:

   o  Introduce the terms 'dialer' and 'listener'.

   o  Clarify the terms 'client' and 'server'.

   o  Clarify what stream IDs are used by which peer.

   o  Remove the ability to send multiple CLIENT_AUTHORITY frames.




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   o  Correctly credit David Dias and Juan Benet for their role.

   Since -00:

   o  Clarified the semantics behind multiple CLIENT_AUTHORITY frames.

   o  Removed the requirement for servers to issue
      SETTINGS_PEER_TO_PEER, instead allowing the extension to be purely
      client-advertised.

Author's Address

   Cory Benfield

   Email: cory@lukasa.co.uk




































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