Network Working Group J. Cohen
Internet-Draft Self
Intended status: Informational 21 October 2024
Expires: 24 April 2025
Symmetric HTTP/2 Extension
draft-joshco-symmetric-h2-01
Abstract
This draft defines an HTTP/2 [RFC9113] extension to support Symmetric
HTTP, which makes a simplifying assumption that the client-side HTTP
server is only accessible and addressible by the server that accepted
the HTTP/2 connection.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/joshco/sh2.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 24 April 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Simplifying Assumption . . . . . . . . . . . . . . . . . 3
2. HTTP/2 Extensions . . . . . . . . . . . . . . . . . . . . . . 3
2.1. HTTP/2 SETTINGS_SYMMETRIC . . . . . . . . . . . . . . . . 4
2.2. Client Authority . . . . . . . . . . . . . . . . . . . . 4
2.2.1. HTTP/2 Authority . . . . . . . . . . . . . . . . . . 4
2.2.2. Client Known URN . . . . . . . . . . . . . . . . . . 4
3. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. HTTP/2 Settings Registry Update . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
This extension allows the client or browser to act as a web server
which receives HTTP requests from the origin server and send
responses back. This is enabled by allowing server initiated streams
to the client.
Resources on the client side of an HTTP/2 connection are addressed
using a URN prefix. The path /foo on the client is addressed as
urn:symmetric_http:client/foo
To avoid confusion over terminology...
1.1. Terminology
This document uses the following terminology.
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+========+========================================+
| Term | Definition |
+========+========================================+
| Client | The HTTP/2 client that initiates an |
| | HTTP/2 connection to a server |
+--------+----------------------------------------+
| Server | The HTTP/2 server that accepts an |
| | inbound connection from the client |
+--------+----------------------------------------+
| Agent | An HTTP engine that processes incoming |
| | requests and generates responses |
+--------+----------------------------------------+
| Client | The Agent on the client |
| Agent | |
+--------+----------------------------------------+
| Server | The Agent on the server |
| Agent | |
+--------+----------------------------------------+
Table 1
1.2. Simplifying Assumption
A previous draft "Peer-to-peer Extension to HTTP/2" ([P2P]) attempted
to create bidirectional HTTP/2 extension, but specified that the
client authority needed to be verified out of band.
Section 3 of ([P2P]) states:
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.
This document attempts to sidestep that issue by having the client
only accessible, or addressable by the HTTP/2 server that it opened
an HTTP/2 connected to. As a result, a real-world authority isn't
necessary.
Instead the client, known only to the server, is simply the "other
side" of an HTTP/2 connection, and is specified according to the
Client Authority section of this document.
2. HTTP/2 Extensions
This document overrides HTTP/2 [RFC9113] section 5.1, where it says:
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"If this stream is initiated by the server, as described in
Section 5.1.1, then receiving a HEADERS frame MUST also be treated
as a connection error (Section 5.4.1) of type PROTOCOL_ERROR."
When operating in symmetric HTTP mode, this restriction is removed.
2.1. HTTP/2 SETTINGS_SYMMETRIC
This document introduces a new HTTP/2 setting SETTINGS_SYMMETRIC.
When SETTINGS_SYMMETRIC (0xTBA) is set to 1, it informs the server
that the client supports server initiated streams which carry HTTP/2
requests to the client and responses to the server.
This setting MUST NOT be emitted by the server. If the client
receives this setting from the server, it must respond with a
conection error [HTTP2] Section 5.4.1) of type PROTOCOL ERROR.
2.2. Client Authority
2.2.1. HTTP/2 Authority
In the use of symmetric HTTP, when the server sends an HTTP message
to the client agent, the authority header is either:
* Omitted
* Set to the value of TBA_TOKEN
2.2.2. Client Known URN
In situations where a client needs to provide a URI to the server,
for example to register a subscription, it MUST use the following URN
as a prefix.
For example, if the client wishes to receive HTTP messages as a
specific path, /foo, the URI would be:
urn:symmetric_http:client/foo
3. Conventions and Definitions
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.
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4. Security Considerations
This document defines the client and client agent to be only
accessible and addressable from the HTTP/2 server it has connected
to. It is not yet known if there are viable exploits that would
allow a third party to access the client agent using symmetric HTTP.
5. IANA Considerations
5.1. HTTP/2 Settings Registry Update
This document updates the registry for HTTP/2 Settings to add
SETTINGS_SYMMETRIC, ID=0xTBA, which can have a value of 1 or 0.
6. Normative References
[HTTP2] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
[P2P] Benfield, C., "Peer-to-peer Extension to HTTP/2", Work in
Progress, Internet-Draft, draft-benfield-http2-p2p-02, 9
October 2015, <https://datatracker.ietf.org/doc/html/
draft-benfield-http2-p2p-02>.
[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
[RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
Appendix A. Acknowledgments
This document draws wisdom and inspiration from Cory Benfield's
Intenet Draft from 2015, "Peer-to-peer Extension to HTTP/2", draft-
benfield-http2-p2p-02 ([P2P]).
Author's Address
Josh Cohen
Self
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Email: joshco@gmail.com
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