rfc9659.original   rfc9659.txt 
HTTPBIS N. Jaju, Ed. Internet Engineering Task Force (IETF) N. Jaju, Ed.
Internet-Draft Google Request for Comments: 9659 Google
Updates: 8878 (if approved) F. Handte, Ed. Updates: 8878 W. F. Handte, Ed.
Intended status: Informational Meta Platforms, Inc. Category: Informational Meta Platforms, Inc.
Expires: 24 February 2025 23 August 2024 ISSN: 2070-1721 September 2024
Window Sizing for Zstandard Content Encoding Window Sizing for Zstandard Content Encoding
draft-ietf-httpbis-zstd-window-size-03
Abstract Abstract
Deployments of Zstandard, or "zstd", can use different window sizes Deployments of Zstandard, or "zstd", can use different window sizes
to limit memory usage during compression and decompression. Some to limit memory usage during compression and decompression. Some
browsers and user agents limit window sizes to mitigate memory usage browsers and user agents limit window sizes to mitigate memory usage
concerns, causing interoperability issues. This document updates the concerns, thereby causing interoperability issues. This document
window size limit in RFC8878 from a recommendation to a requirement updates the window size limit in RFC 8878 from a recommendation to a
in HTTP contexts. requirement in HTTP contexts.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at https://httpwg.org/
http-extensions/draft-ietf-httpbis-zstd-window-size.html. Status
information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-httpbis-zstd-window-
size/.
Discussion of this document takes place on the HTTP Working Group
mailing list (mailto: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/httpwg/http-extensions/labels/zstd-window-size.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for informational purposes.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
This Internet-Draft will expire on 24 February 2025. 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/rfc9659.
Copyright Notice Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions
3. Window Size . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Window Size
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 5. IANA Considerations
5.1. Content Encoding . . . . . . . . . . . . . . . . . . . . 4 5.1. Content Encoding
6. Normative References . . . . . . . . . . . . . . . . . . . . 4 6. Normative References
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4 Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 Authors' Addresses
1. Introduction 1. Introduction
Zstandard, or "zstd", specified in [RFC8878], is a lossless data Zstandard, or "zstd", specified in [RFC8878], is a lossless data
compression mechanism similar to gzip. When used with HTTP, the compression mechanism similar to gzip. When used with HTTP, the
"zstd" content coding token signals to the decoder that the content "zstd" content coding token signals to the decoder that the content
is Zstandard-compressed. is Zstandard-compressed.
An important property of Zstandard-compressed content is its An important property of Zstandard-compressed content is its
Window_Size ([RFC8878], Section 3.1.1.1.2), which describes the Window_Size ([RFC8878], Section 3.1.1.1.2), which describes the
maximum distance for back-references and therefore how much of the maximum distance for back-references and therefore how much of the
content must be kept in memory during decompression. content must be kept in memory during decompression.
The minimum Window_Size is 1 KB. The maximum Window_Size is (1<<41) The minimum Window_Size is 1 KB. The maximum Window_Size is (1<<41)
+ 7*(1<<38) bytes, which is 3.75 TB. Larger Window_Size values tend + 7*(1<<38) bytes, where "<<" denotes a bitwise left shift, which is
to improve the compression ratio, but at the cost of increased memory 3.75 TB. Larger Window_Size values tend to improve the compression
usage. ratio but at the cost of increased memory usage.
To protect against unreasonable memory usage, some browsers and user To protect against unreasonable memory usage, some browsers and user
agents limit the maximum Window_Size they will handle. This causes agents limit the maximum Window_Size they will handle. This causes
failures to decode responses when the content is compressed with a failures to decode responses when the content is compressed with a
larger Window_Size than the recipient allows, leading to decreased larger Window_Size than the recipient allows, leading to decreased
interoperability. interoperability.
[RFC8878], Section 3.1.1.1.2 recommends that decoders support a [RFC8878], Section 3.1.1.1.2 recommends that decoders support a
Window_Size of up to 8 MB, and that encoders not generate frames Window_Size of up to 8 MB, and that encoders not generate frames
using a Window_Size larger than 8 MB. However, it imposes no using a Window_Size larger than 8 MB. However, it imposes no
skipping to change at page 4, line 4 skipping to change at line 119
This document introduces no new security considerations beyond those This document introduces no new security considerations beyond those
discussed in [RFC8878]. discussed in [RFC8878].
Note that decoders still need to take into account that they can Note that decoders still need to take into account that they can
receive oversized frames that do not follow the window size limit receive oversized frames that do not follow the window size limit
specified in this document and fail decoding when such invalid frames specified in this document and fail decoding when such invalid frames
are received. are received.
5. IANA Considerations 5. IANA Considerations
5.1. Content Encoding 5.1. Content Encoding
This document updates the entry added in [RFC8878] to the "HTTP This document updates the following entry in the "HTTP Content Coding
Content Coding Registry" (https://www.iana.org/assignments/http- Registry" in the "Hypertext Transfer Protocol (HTTP) Parameters"
parameters/http-parameters.xhtml#content-coding) within the registry group (https://www.iana.org/assignments/http-parameters):
"Hypertext Transfer Protocol (HTTP) Parameters"
(https://www.iana.org/assignments/http-parameters/http-
parameters.xhtml) registry:
Name: zstd Name: zstd
Description: A stream of bytes compressed using the Zstandard Description: A stream of bytes compressed using the Zstandard
protocol with a Window_Size of not more than 8 MB. protocol with a Window_Size of not more than 8 MB.
Reference: This document and [RFC8878] Reference: This document and [RFC8878]
6. Normative References 6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8878] Collet, Y. and M. Kucherawy, Ed., "Zstandard Compression [RFC8878] Collet, Y. and M. Kucherawy, Ed., "Zstandard Compression
and the 'application/zstd' Media Type", RFC 8878, and the 'application/zstd' Media Type", RFC 8878,
DOI 10.17487/RFC8878, February 2021, DOI 10.17487/RFC8878, February 2021,
<https://www.rfc-editor.org/rfc/rfc8878>. <https://www.rfc-editor.org/info/rfc8878>.
Acknowledgments Acknowledgments
Zstandard was developed by Yann Collet. Zstandard was developed by Yann Collet.
The authors would like to thank Yann Collet, Klaus Post, Adam Rice, The authors would like to thank Yann Collet, Klaus Post, Adam Rice,
and members of the Web Performance Working Group in the W3C for and members of the Web Performance Working Group in the W3C for
collaborating on the window size issue and helping to formulate a collaborating on the window size issue and helping to formulate a
solution. Also, thank you to Nick Terrell for providing feedback solution.
that went into RFC 8478 and RFC 8878.
Authors' Addresses Authors' Addresses
Nidhi Jaju (editor) Nidhi Jaju (editor)
Google Google
Shibuya Stream, 3 Chome-21-3 Shibuya, Shibuya City, Tokyo Shibuya Stream, 3 Chome-21-3 Shibuya, Shibuya City, Tokyo
150-0002 150-0002
Japan Japan
Email: nidhijaju@google.com Email: nidhijaju@google.com
W. Felix P. Handte (editor) W. Felix P. Handte (editor)
Meta Platforms, Inc. Meta Platforms, Inc.
380 W 33rd St 380 W 33rd St
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