Lzip Compressed Format and the application/lzip Media Type
draft-diaz-lzip-01

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Internet Engineering Task Force (IETF)                           A. Diaz
INTERNET-DRAFT  draft-diaz-lzip-01                           GNU Project
Category: Informational                                       April 2020
Expiration date: 2020-10-26

       Lzip Compressed Format and the application/lzip Media Type

Abstract

   Lzip is a lossless compressed data format designed for data sharing,
   long-term archiving, and parallel (de)compression.  Lzip uses a
   simplified form of the Lempel-Ziv-Markov chain-Algorithm (LZMA)
   stream format, chosen to maximize safety and interoperability.  Lzip
   can achieve higher compression ratios than gzip.  This document
   describes the lzip format and registers a media type and content
   encoding to be used when transporting lzip-compressed content via
   Multipurpose Internet Mail Extensions (MIME).

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
   http://www.rfc-editor.org/info/rfc<rfc-no>.

Comments are solicited and should be addressed to the lzip's mailing
list at lzip-bug@nongnu.org and/or the author.

Diaz                          Informational                     [Page 1]
draft-diaz-lzip-01          application/lzip                  April 2020

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
      1.1.  Purpose  . . . . . . . . . . . . . . . . . . . . . . . .   3
      1.2.  Compliance . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  File Format . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Format of the LZMA stream in lzip files . . . . . . . . . . .   5
      3.1.  What is coded  . . . . . . . . . . . . . . . . . . . . .   6
      3.2.  The coding contexts  . . . . . . . . . . . . . . . . . .   8
      3.3.  The range decoder  . . . . . . . . . . . . . . . . . . .  10
      3.4.  Decoding and verifying the LZMA stream . . . . . . . . .  10
      3.5.  Compression  . . . . . . . . . . . . . . . . . . . . . .  10
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
      4.1.  The 'application/lzip' Media Type  . . . . . . . . . . .  11
      4.2.  Content Encoding . . . . . . . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
      6.1.  Normative References . . . . . . . . . . . . . . . . . .  13
      6.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Appendix A.  Reference Source Code  . . . . . . . . . . . . . . .  13
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  23
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  23

Diaz                          Informational                     [Page 2]
draft-diaz-lzip-01          application/lzip                  April 2020

1.  Introduction

   Lzip is a lossless compressed data format similar to gzip [RFC1952].
   Lzip is designed for data sharing, long-term archiving, parallel
   (de)compression, and limited random access to the data.  Lzip can