Merge pull request #2798 from nidhijaju/add-zstd-window-size-draft

Add draft-ietf-httpbis-zstd-window-size

draft-ietf-httpbis-zstd-window-size.md

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+---
+title: Window Sizing for Zstandard Content Encoding
+abbrev: Zstd Window Size
+category: info
+
+docname: draft-ietf-httpbis-zstd-window-size-latest
+submissiontype: IETF
+number:
+date:
+consensus: true
+v: 3
+area: Web and Internet Transport
+workgroup: HTTPBIS
+keyword:
+ - zstd
+ - zstandard
+ - compression
+ - content encoding
+ - content coding
+ - application/zstd
+venue:
+  group: HTTP
+  type: Working Group
+  mail: [email protected]
+  arch: https://lists.w3.org/Archives/Public/ietf-http-wg/
+  github: https://github.com/httpwg/http-extensions/labels/zstd-window-size
+  latest: "https://httpwg.org/http-extensions/draft-ietf-httpbis-zstd-window-size.html"
+github-issue-label: zstd-window-size
+
+author:
+ -
+    ins: N. Jaju
+    fullname: Nidhi Jaju
+    role: editor
+    organization: Google
+    street: Shibuya Stream, 3 Chome-21-3 Shibuya
+    region: Shibuya City, Tokyo
+    code: 150-0002
+    country: Japan
+    email: [email protected]
+ -
+    ins: F. Handte
+    fullname: W. Felix P. Handte
+    role: editor
+    organization: Meta Platforms, Inc.
+    street: 380 W 33rd St
+    city: New York
+    region: NY
+    code: 10001
+    country: US
+    email: [email protected]
+
+normative:
+
+informative:
+
+
+--- abstract
+
+Deployments of Zstandard, or "zstd", can use different window sizes to limit
+memory usage during compression and decompression. Some browsers and user
+agents limit window sizes to mitigate memory usage concerns, causing
+interoperability issues. This document updates the window size limit in RFC8878
+from a recommendation to a requirement in HTTP contexts.
+
+
+--- middle
+
+# Introduction
+
+Zstandard, or "zstd", specified in {{?RFC8878}}, is a lossless data compression
+mechanism similar to gzip. When used with HTTP, the "zstd" content coding
+token signals to the decoder that the content is Zstandard-compressed.
+
+An important property of Zstandard-compressed content is its Window_Size
+({{!RFC8878, Section 3.1.1.1.2}}), which describes the maximum distance for
+back-references and therefore how much of the content must be kept in memory
+during decompression.
+
+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
+to improve the compression ratio, but at the cost of increased memory usage.
+
+To protect against unreasonable memory usage, some browsers and user agents
+limit the maximum Window_Size they will handle. This causes failures to decode
+responses when the content is compressed with a larger Window_Size than the
+recipient allows, leading to decreased interoperability.
+
+{{!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 using a Window_Size larger
+than 8 MB. However, it imposes no requirements.
+
+This document updates {{RFC8878}} to enforce Window_Size limits on the encoder
+and decoder for the "zstd" content coding.
+
+
+# Conventions and Definitions
+
+{::boilerplate bcp14-tagged}
+
+# Window Size
+
+To ensure interoperability, when using the "zstd" content coding, decoders MUST
+support a Window_Size of up to and including 8 MB, and encoders MUST NOT
+generate frames requiring a Window_Size larger than 8 MB (see
+{{zstd-iana-token}}).
+
+# Security Considerations
+
+This document introduces no new security considerations beyond those discussed
+in {{RFC8878}}.
+
+# IANA Considerations
+
+## Content Encoding {#zstd-iana-token}
+
+This document updates the entry added in {{RFC8878}} to the "HTTP Content
+Coding Registry" within the "Hypertext Transfer Protocol (HTTP) Parameters"
+registry:
+
+Name:
+
+: zstd
+
+Description:
+
+: A stream of bytes compressed using the Zstandard protocol with a Window_Size
+  of not more than 8 MB.
+
+Reference:
+
+: This document
+
+
+--- back
+
+# Acknowledgments
+{:numbered="false"}
+
+Zstandard was developed by Yann Collet.
+
+The authors would like to thank Yann Collet, Klaus Post, Adam Rice, and members
+of the Web Performance Working Group in the W3C for collaborating on the window
+size issue and helping to formulate a solution. Also, thank you to Nick Terrell
+for providing feedback that went into RFC 8478 and RFC 8878.
+