Network Working Group L. Pardue
Internet-Draft BBC Research & Development
Intended status: Informational July 1, 2018
Expires: January 2, 2019
Unbound Server Push (USP) for HTTP/QUIC
draft-pardue-quic-http-unbound-server-push-01
Abstract
This document defines an HTTP semantic extension, Unbound Server Push
(USP), which allows HTTP resources to be pushed without the need for
a prior HTTP request. HTTP/QUIC clients opt in to this feature via
an HTTP/QUIC setting.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. The Unbound Promise Stream Type . . . . . . . . . . . . . . . 3
3. The SETTINGS_ENABLE_UNBOUND_PUSH Parameter . . . . . . . . . 3
4. Usage of Unbound Server Push . . . . . . . . . . . . . . . . 3
5. 0-RTT Considerations . . . . . . . . . . . . . . . . . . . . 4
6. Handling Multiple Clients . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8.1. Registration of Unbound Promise Stream Type . . . . . . . 4
8.2. Registration of SETTINGS_ENABLE_UNBOUND_PUSH Parameter . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
HTTP server push is a feature of HTTP/2 [RFC7540] and HTTP/QUIC
[QUIC-HTTP] that allows a server to pre-emptively send HTTP resources
to a client in association with a previous client-initiated request.
This binding to a request object aligns with paradigms familiar to
client and server implementations. Unbound server push, in contrast,
may provide benefits for use cases where holding a request object
open for long periods (long polling) is undesirable, or where a
request object does not exist (unidirectional flows). (The
introduction of unidirectional streams in the QUIC transport
[QUIC-TRANSPORT] provides a direct expression of this message
exchange pattern.)
This document defines an HTTP/QUIC protocol extension that allows a
server to send one or more HTTP/QUIC "PUSH_PROMISE" frame on a new
server-initiated unidirectional stream type: the unbound promise
stream Section 2. Endpoints opt in to the unbound server push
feature using a "SETTINGS" parameter (Section 3) in accordance with
Section 5.5 of [RFC7540]. This is the only behavioural change to
server push as described in [QUIC-HTTP]. Unbound server push
operates in addition to bound server push for any HTTP/QUIC
connection.
Unbound server push should be used with care. It may introduce
complexities for implementations, particularly intermediaries, and it
can pose challenges for presentation to the application above HTTP.
In deployments where multiple client connections are trunked by a
reverse proxy onto a single upstream connection, unbound server push
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is effectively a mechanism for achieving application-level multicast
to all downstream clients that have enabled this feature.
*Authors' Note:* Unbound server push is proposed as an extension
to HTTP/QUIC in order to start a discussion on whether this
feature should be incorporated into the core HTTP/QUIC
specification document.
1.1. Notational Conventions
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.
2. The Unbound Promise Stream Type
An unbound promise stream is indicated by a stream type of "0xTBD".
Data on this stream consists of one or more "PUSH_PROMISE" frames,
sent in accordance with [QUIC-HTTP]. Only servers can promise; if a
server receives a client-initiated unbound promise stream, this MUST
be treated as a stream error of type HTTP_WRONG_DIRECTION.
3. The SETTINGS_ENABLE_UNBOUND_PUSH Parameter
This document adds a new HTTP/QUIC "SETTINGS" Parameter to those
defined by Section 7.3 of [QUIC-HTTP].
The new parameter is "SETTINGS_ENABLE_UNBOUND_PUSH" (type = 0xTBD).
This setting can be used to enable unbound server push. The value of
the parameter is an integer that MUST be 0 or 1. Any value other
than 0 or 1 MUST be treated as a connection error of type
"PROTOCOL_ERROR".
The initial value is 0, which indicates that unbound server push is
disabled by default.
4. Usage of Unbound Server Push
Unbound server push changes only one aspect of HTTP/QUIC server push:
the stream type on which an HTTP/QUIC "PUSH_PROMISE" frame can be
sent. It does not prevent the conventional use of bound server push;
both types MAY be used concurrently. The Push ID number space is
shared across both types. Unbound server push is subject to the
limits imposed by the HTTP/QUIC "MAX_PUSH_ID" frame.
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An endpoint that receives the "SETTINGS_ENABLE_UNBOUND_PUSH"
parameter set to a value of 0 MUST only send an HTTP/QUIC
"PUSH_PROMISE" frame on an appropriate client-initiated bidirectional
request stream. An endpoint that has set this parameter to 0 and had
it acknowledged MUST treat the reception of an HTTP/QUIC
"PUSH_PROMISE" frame on any other stream type as a connection error
of type "PROTOCOL_ERROR".
A server that receives the "SETTINGS_ENABLE_UNBOUND_PUSH" parameter
set to a value of 1 MAY send an HTTP/QUIC "PUSH_PROMISE" frame on an
unbound promise stream.
A client that has sent the "SETTINGS_ENABLE_UNBOUND_PUSH" parameter
set to 1, and received this parameter set to a value of 1, SHOULD be
ready for a server to send an HTTP/QUIC "PUSH_PROMISE" frame on
unbound push streams at any time.
5. 0-RTT Considerations
Client 0-RTT is not affected by server push configuration. There are
no additional consideration to be made beyond those defined in
[QUIC-HTTP].
6. Handling Multiple Clients
Unbound server push was discussed during the development of HTTP/2
[RFC7540]. The assessment was that servers that handle multiple
clients within the same stack or context (such as an HTTP
intermediary) may have a difficult time routing promises to the
correct client. The applicability of unbound server push should be
assessed and enabled where the risk of misdirected promises is
determined to be acceptable.
7. Security Considerations
There are no additional consideration beyond those presented in
[QUIC-HTTP].
8. IANA Considerations
8.1. Registration of Unbound Promise Stream Type
This document establishes an entry for the HTTP/QUIC Stream Type
registry that is established by [QUIC-HTTP].
Stream Type: Unbound Promise Stream
Code: 0xTBD
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Specification: This document
Sender: Server
8.2. Registration of SETTINGS_ENABLE_UNBOUND_PUSH Parameter
This document establishes an entry for the HTTP/QUIC Settings
Registry that is established by [QUIC-HTTP].
Name: "SETTINGS_ENABLE_UNBOUND_PUSH"
Code: 0xTBD
Specification: This document
9. Normative References
[QUIC-HTTP]
Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
QUIC", draft-ietf-quic-http-13 (work in progress).
[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic-
transport-13 (work in progress).
[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>.
[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>.
[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>.
Appendix A. Acknowledgements
The author would like to thank the following for review prior to
publication: Richard Bradbury.
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Author's Address
Lucas Pardue
BBC Research & Development
Email: lucas.pardue@bbc.co.uk
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