Incremental HTTP Messages
draft-kazuho-httpbis-incremental-http-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Kazuho Oku , Tommy Pauly , Martin Thomson | ||
| Last updated | 2024-10-15 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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draft-kazuho-httpbis-incremental-http-00
httpbis 奥 一穂 (K. Oku)
Internet-Draft Fastly
Intended status: Standards Track T. Pauly
Expires: 18 April 2025 Apple
M. Thomson
Mozilla
15 October 2024
Incremental HTTP Messages
draft-kazuho-httpbis-incremental-http-00
Abstract
This document specifies the "Incremental" HTTP header field, which
instructs HTTP intermediaries to forward the HTTP message
incrementally.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the HTTP Working Group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/.
Source for this draft and an issue tracker can be found at
https://github.com/kazuho/draft-kazuho-httpbis-incremental-http.
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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 18 April 2025.
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Copyright Notice
Copyright (c) 2024 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. The Incremental Header Field . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4.1. Applying Concurrency Limits . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
HTTP [HTTP] permits receivers to begin processing portions of HTTP
messages as they arrive, rather than requiring them to wait for the
entire HTTP message to be received before acting.
Some applications are specifically designed to take advantage of this
capability.
For example, Server-Sent Events [SSE] uses a long-running HTTP
response, where the server continually sends notifications as they
become available.
In the case of Chunked Oblivious HTTP Messages [CHUNKED-OHTTP], the
client opens an HTTP request and incrementally sends application
messages, while the server can start responding even before the HTTP
request is fully complete. In this way, the HTTP request-response
pair effectively serves as a bi-directional communication channel.
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However, these applications are fragile when HTTP intermediaries are
involved. This is because HTTP intermediaries are not only permitted
but are frequently deployed to buffer complete HTTP messages before
forwarding them downstream (Section 7.6 of [HTTP]).
If such a buffering HTTP intermediary exists between the client and
the server, these applications may fail to function as intended.
In the case of Server-Sent Events, when an intermediary tries to
buffer the HTTP response completely before forwarding it, the client
might time out before receiving any portion of the HTTP response.
In the case of Chunked Oblivious HTTP Messages, when an intermediary
tries to buffer the entire HTTP request, the client will not start
receiving application messages from the server until the client
closes the request, effectively disrupting the intended incremental
processing of the request.
To help avoid such behavior, this document specifies the
"Incremental" HTTP header field, which instructs HTTP intermediaries
to begin forwarding the HTTP message downstream before receiving the
complete message.
2. 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.
The term Boolean is imported from [STRUCTURED-FIELDS].
3. The Incremental Header Field
The Incremental HTTP header field expresses the sender's intent for
HTTP intermediaries to start forwarding the message downstream before
the entire message is received.
This header field has just one valid value of type Boolean: "?1".
Incremental = ?1
Upon receiving a header section that includes the Incremental header
field, HTTP intermediaries SHOULD NOT buffer the entire message
before forwarding it. Instead, intermediaries SHOULD transmit the
header section downstream and continuously forward the bytes of the
message body as they arrive.
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The Incremental HTTP header field applies to each HTTP message.
Therefore, if both the HTTP request and response need to be forwarded
incrementally, the Incremental HTTP header field MUST be set for both
the HTTP request and the response.
The Incremental field is advisory. Intermediaries that are unaware
of the field or that do not support the field might buffer messages,
even when explicitly requested otherwise. Clients and servers
therefore cannot expect all intermediaries to understand and respect
a request to deliver messages incrementally. Clients can rely on
prior knowledge or probe for support on individual resources.
4. Security Considerations
4.1. Applying Concurrency Limits
To conserve resources required to handle HTTP requests or
connections, it is common for intermediaries to impose limits on the
maximum number of concurrent HTTP requests that they forward, while
buffering requests that exceed this limit.
Such intermediaries could apply a more restrictive concurrency limit
to requests marked as incremental to ensure that capacity remains
available for non-incremental requests, even when the maximum number
of incremental requests is reached. This approach helps balance the
processing of different types of requests and maintains service
availability across all requests.
When rejecting incremental requests due to reaching the concurrency
limit, intermediaries SHOULD respond with a 503 Service Unavailable
error, accompanied by a connection_limit_reached Proxy-Status
response header field (Section 2.3.12 of [PROXY-STATUS]).
5. IANA Considerations
TBD
6. References
6.1. Normative References
[HTTP] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
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[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>.
[STRUCTURED-FIELDS]
Nottingham, M. and P. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
6.2. Informative References
[CHUNKED-OHTTP]
Pauly, T. and M. Thomson, "Chunked Oblivious HTTP
Messages", Work in Progress, Internet-Draft, draft-ietf-
ohai-chunked-ohttp-01, 8 July 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ohai-
chunked-ohttp-01>.
[PROXY-STATUS]
Nottingham, M. and P. Sikora, "The Proxy-Status HTTP
Response Header Field", RFC 9209, DOI 10.17487/RFC9209,
June 2022, <https://www.rfc-editor.org/rfc/rfc9209>.
[SSE] WHATWG, "Server-Sent Events", n.d.,
<https://html.spec.whatwg.org/multipage/server-sent-
events.html>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Kazuho Oku
Fastly
Email: kazuhooku@gmail.com
Additional contact information:
奥 一穂
Fastly
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Tommy Pauly
Apple
Email: tpauly@apple.com
Martin Thomson
Mozilla
Email: mt@lowentropy.net
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