HPACK: Header Compression for HTTP/2
RFC 7541

Document Type RFC - Proposed Standard (May 2015; Errata)
Last updated 2015-12-31
Replaces draft-rpeon-httpbis-header-compression, draft-ruellan-headerdiff, draft-ruellan-http-header-compression
Stream IETF
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Stream WG state Submitted to IESG for Publication Jun 2014
Document shepherd Mark Nottingham
Shepherd write-up Show (last changed 2014-12-17)
IESG IESG state RFC 7541 (Proposed Standard)
Consensus Boilerplate Yes
Telechat date
Responsible AD Barry Leiba
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state No IC
Internet Engineering Task Force (IETF)                           R. Peon
Request for Comments: 7541                                   Google, Inc
Category: Standards Track                                     H. Ruellan
ISSN: 2070-1721                                                Canon CRF
                                                                May 2015

                  HPACK: Header Compression for HTTP/2

Abstract

   This specification defines HPACK, a compression format for
   efficiently representing HTTP header fields, to be used in HTTP/2.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   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/rfc7541.

Copyright Notice

   Copyright (c) 2015 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.

Peon & Ruellan               Standards Track                    [Page 1]
RFC 7541                          HPACK                         May 2015

Table of Contents

   1. Introduction ....................................................4
      1.1. Overview ...................................................4
      1.2. Conventions ................................................5
      1.3. Terminology ................................................5
   2. Compression Process Overview ....................................6
      2.1. Header List Ordering .......................................6
      2.2. Encoding and Decoding Contexts .............................6
      2.3. Indexing Tables ............................................6
           2.3.1. Static Table ........................................6
           2.3.2. Dynamic Table .......................................6
           2.3.3. Index Address Space .................................7
      2.4. Header Field Representation ................................8
   3. Header Block Decoding ...........................................8
      3.1. Header Block Processing ....................................8
      3.2. Header Field Representation Processing .....................9
   4. Dynamic Table Management ........................................9
      4.1. Calculating Table Size ....................................10
      4.2. Maximum Table Size ........................................10
      4.3. Entry Eviction When Dynamic Table Size Changes ............11
      4.4. Entry Eviction When Adding New Entries ....................11
   5. Primitive Type Representations .................................11
      5.1. Integer Representation ....................................11
      5.2. String Literal Representation .............................13
   6. Binary Format ..................................................14
      6.1. Indexed Header Field Representation .......................14
      6.2. Literal Header Field Representation .......................15
           6.2.1. Literal Header Field with Incremental Indexing .....15
           6.2.2. Literal Header Field without Indexing ..............16
           6.2.3. Literal Header Field Never Indexed .................17
      6.3. Dynamic Table Size Update .................................18
   7. Security Considerations ........................................19
      7.1. Probing Dynamic Table State ...............................19
           7.1.1. Applicability to HPACK and HTTP ....................20
           7.1.2. Mitigation .........................................20
           7.1.3. Never-Indexed Literals .............................21
      7.2. Static Huffman Encoding ...................................22
      7.3. Memory Consumption ........................................22
      7.4. Implementation Limits .....................................23
   8. References .....................................................23
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