Zstandard Compression and The application/zstd Media Type
draft-kucherawy-dispatch-zstd-02

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Last updated 2018-07-11
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Network Working Group                                          Y. Collet
Internet-Draft                                         M. Kucherawy, Ed.
Intended status: Informational                                  Facebook
Expires: January 12, 2019                                  July 11, 2018

       Zstandard Compression and The application/zstd Media Type
                    draft-kucherawy-dispatch-zstd-02

Abstract

   Zstandard, or "zstd" (pronounced "zee standard"), is a data
   compression mechanism.  This document describes the mechanism, and
   registers a media type to be used when transporting zstd-compressed
   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, and is being published for informational purposes
   only.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 12, 2019.

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
   (http://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

Collet & Kucherawy      Expires January 12, 2019                [Page 1]
Internet-Draft              application/zstd                   July 2018

   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Compression Algorithm  . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Frames . . . . . . . . . . . . . . . . . . . . . . . . . .  5
       3.1.1.  Zstandard Frames . . . . . . . . . . . . . . . . . . .  5
         3.1.1.1.  Frame Header . . . . . . . . . . . . . . . . . . .  6
         3.1.1.2.  Blocks . . . . . . . . . . . . . . . . . . . . . . 11
         3.1.1.3.  Compressed Blocks  . . . . . . . . . . . . . . . . 12
         3.1.1.4.  Sequence Execution . . . . . . . . . . . . . . . . 26
         3.1.1.5.  Repeat Offsets . . . . . . . . . . . . . . . . . . 27
       3.1.2.  Skippable Frames . . . . . . . . . . . . . . . . . . . 27
   4.  Entropy Encoding . . . . . . . . . . . . . . . . . . . . . . . 28
     4.1.  FSE  . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
       4.1.1.  FSE Table Description  . . . . . . . . . . . . . . . . 29
     4.2.  Huffman Coding . . . . . . . . . . . . . . . . . . . . . . 32
       4.2.1.  Huffman Tree Description . . . . . . . . . . . . . . . 32
         4.2.1.1.  Huffman Tree Header  . . . . . . . . . . . . . . . 34
         4.2.1.2.  FSE Compression of Huffman Weights . . . . . . . . 35
         4.2.1.3.  Conversion from Weights to Huffman Prefix Codes  . 35
       4.2.2.  Huffman-coded Streams  . . . . . . . . . . . . . . . . 36
   5.  Dictionary Format  . . . . . . . . . . . . . . . . . . . . . . 37
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 39
     6.1.  The 'application/zstd' Media Type  . . . . . . . . . . . . 39
     6.2.  Content Encoding . . . . . . . . . . . . . . . . . . . . . 40
     6.3.  Dictionaries . . . . . . . . . . . . . . . . . . . . . . . 40
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 40
   8.  Implementation Status  . . . . . . . . . . . . . . . . . . . . 41
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 42
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 42
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 43
   Appendix B.  Decoding Tables for Predefined Codes  . . . . . . . . 43
     B.1.  Literal Length Code Table  . . . . . . . . . . . . . . . . 44
     B.2.  Match Length Code Table  . . . . . . . . . . . . . . . . . 46
     B.3.  Offset Code Table  . . . . . . . . . . . . . . . . . . . . 49
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