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)
|
|
---|---|---|---|
Authors | Yann Collet , Murray Kucherawy | ||
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 . . . . . . . . . . . . . . . . . 49Show full document text