Zstandard Compression and the application/zstd Media Type
RFC 8478
| Document | Type |
RFC - Informational
(October 2018; Errata)
Was draft-kucherawy-dispatch-zstd (individual in art area)
|
|
|---|---|---|---|
| Last updated | 2019-07-18 | ||
| Stream | IETF | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | No shepherd assigned | ||
| Shepherd write-up | Show (last changed 2018-05-21) | ||
| IESG | IESG state | RFC 8478 (Informational) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Alexey Melnikov | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) Y. Collet
Request for Comments: 8478 M. Kucherawy, Ed.
Category: Informational Facebook
ISSN: 2070-1721 October 2018
Zstandard Compression and the application/zstd Media Type
Abstract
Zstandard, or "zstd" (pronounced "zee standard"), is a data
compression mechanism. This document describes the mechanism and
registers a media type and content encoding to be used when
transporting zstd-compressed content via Multipurpose Internet Mail
Extensions (MIME).
Despite use of the word "standard" as part of its name, readers are
advised that this document is not an Internet Standards Track
specification; it is being published for informational purposes only.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
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.
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/rfc8478.
Collet & Kucherawy Informational [Page 1]
RFC 8478 application/zstd October 2018
Copyright Notice
Copyright (c) 2018 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/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Collet & Kucherawy Informational [Page 2]
RFC 8478 application/zstd October 2018
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Compression Algorithm . . . . . . . . . . . . . . . . . . . . 5
3.1. Frames . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. Zstandard Frames . . . . . . . . . . . . . . . . . . 6
3.1.1.1. Frame Header . . . . . . . . . . . . . . . . . . 7
3.1.1.2. Blocks . . . . . . . . . . . . . . . . . . . . . 12
3.1.1.3. Compressed Blocks . . . . . . . . . . . . . . . . 14
3.1.1.4. Sequence Execution . . . . . . . . . . . . . . . 28
3.1.1.5. Repeat Offsets . . . . . . . . . . . . . . . . . 29
3.1.2. Skippable Frames . . . . . . . . . . . . . . . . . . 30
4. Entropy Encoding . . . . . . . . . . . . . . . . . . . . . . 30
4.1. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.1.1. FSE Table Description . . . . . . . . . . . . . . . . 31
4.2. Huffman Coding . . . . . . . . . . . . . . . . . . . . . 34
4.2.1. Huffman Tree Description . . . . . . . . . . . . . . 35
4.2.1.1. Huffman Tree Header . . . . . . . . . . . . . . . 36
4.2.1.2. FSE Compression of Huffman Weights . . . . . . . 37
4.2.1.3. Conversion from Weights to Huffman Prefix Codes . 38
4.2.2. Huffman-Coded Streams . . . . . . . . . . . . . . . . 39
5. Dictionary Format . . . . . . . . . . . . . . . . . . . . . . 40
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
6.1. The 'application/zstd' Media Type . . . . . . . . . . . . 42
6.2. Content Encoding . . . . . . . . . . . . . . . . . . . . 43
6.3. Dictionaries . . . . . . . . . . . . . . . . . . . . . . 43
7. Security Considerations . . . . . . . . . . . . . . . . . . . 43
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 44
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
9.1. Normative References . . . . . . . . . . . . . . . . . . 45
9.2. Informative References . . . . . . . . . . . . . . . . . 45
Appendix A. Decoding Tables for Predefined Codes . . . . . . . . 46
A.1. Literal Length Code Table . . . . . . . . . . . . . . . . 46
A.2. Match Length Code Table . . . . . . . . . . . . . . . . . 49
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