Brotli Compressed Data Format
RFC 7932
| Document | Type |
RFC - Informational
(July 2016; No errata)
Was draft-alakuijala-brotli (individual in art area)
|
|
|---|---|---|---|
| Last updated | 2016-07-29 | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | Nevil Brownlee | ||
| Shepherd write-up | Show (last changed 2016-03-13) | ||
| IESG | IESG state | RFC 7932 (Informational) | |
| Consensus Boilerplate | No | ||
| Telechat date | |||
| Responsible AD | Alexey Melnikov | ||
| Send notices to | "Nevil Brownlee" <n.brownlee@auckland.ac.nz> | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) J. Alakuijala
Request for Comments: 7932 Z. Szabadka
Category: Informational Google, Inc.
ISSN: 2070-1721 July 2016
Brotli Compressed Data Format
Abstract
This specification defines a lossless compressed data format that
compresses data using a combination of the LZ77 algorithm and Huffman
coding, with efficiency comparable to the best currently available
general-purpose compression methods.
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 has been approved for publication by the Internet
Engineering Steering Group (IESG). Not all documents approved by the
IESG are a candidate 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/rfc7932.
Copyright Notice
Copyright (c) 2016 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
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.
Alakuijala & Szabadka Informational [Page 1]
RFC 7932 Brotli July 2016
Table of Contents
1. Introduction ....................................................3
1.1. Purpose ....................................................3
1.2. Intended Audience ..........................................3
1.3. Scope ......................................................4
1.4. Compliance .................................................4
1.5. Definitions of Terms and Conventions Used ..................4
1.5.1. Packing into Bytes ..................................5
2. Compressed Representation Overview ..............................6
3. Compressed Representation of Prefix Codes ......................10
3.1. Introduction to Prefix Coding .............................10
3.2. Use of Prefix Coding in the Brotli Format .................11
3.3. Alphabet Sizes ............................................13
3.4. Simple Prefix Codes .......................................14
3.5. Complex Prefix Codes ......................................15
4. Encoding of Distances ..........................................17
5. Encoding of Literal Insertion Lengths and Copy Lengths .........19
6. Encoding of Block-Switch Commands ..............................22
7. Context Modeling ...............................................23
7.1. Context Modes and Context ID Lookup for Literals ..........23
7.2. Context ID for Distances ..................................26
7.3. Encoding of the Context Map ...............................26
8. Static Dictionary ..............................................28
9. Compressed Data Format .........................................31
9.1. Format of the Stream Header ...............................31
9.2. Format of the Meta-Block Header ...........................32
9.3. Format of the Meta-Block Data .............................35
10. Decoding Algorithm ............................................36
11. Considerations for Compressor Implementations .................38
11.1. Trivial Compressor .......................................39
11.2. Aligning Compressed Meta-Blocks to Byte Boundaries .......39
11.3. Creating Self-Contained Parts within the
Compressed Data ..........................................40
12. Security Considerations .......................................41
13. IANA Considerations ...........................................42
14. Informative References ........................................43
Appendix A. Static Dictionary Data ................................44
Appendix B. List of Word Transformations .........................124
Appendix C. Computing CRC-32 Check Values ........................127
Appendix D. Source Code ..........................................127
Show full document text