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Versions: 00 01

Network Working Group                                             Y. Nir
Internet-Draft                                               Check Point
Intended status: Informational                           October 9, 2012
Expires: April 12, 2013


              HTTP/2.0 Discussion: Compact Header Encoding
                        draft-nir-httpbis-che-00

Abstract

   This document proposes an alternative encoding for HTTP headers.
   This encoding is considerably more compact than the uncompressed
   textual encoding in HTTP/1.1 and current HTTP/2.0 draft.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 12, 2013.

Copyright Notice

   Copyright (c) 2012 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.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Conventions Used in This Document . . . . . . . . . . . . . 3
   2.  The Binary Encoding . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Flags . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     2.2.  Short Type-Value  . . . . . . . . . . . . . . . . . . . . . 4
     2.3.  Long Type-Value . . . . . . . . . . . . . . . . . . . . . . 4
     2.4.  Type-Length-Value . . . . . . . . . . . . . . . . . . . . . 4
   3.  Header Encoding . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Custom Headers and Custom Enumerations  . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   7.  Changes from Previous Versions  . . . . . . . . . . . . . . . . 6
   8.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Additional Examples  . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 9


































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1.  Introduction

   HTTP/1.x and the current draft of HTTP/2.0 encode headers using text
   labels and text values.  HTTP/2.0 attempts to make this more
   efficient by compressing the textual headers.  This proposes a
   binary-only alternative.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2.  The Binary Encoding

   The header block is formatted as follows:

   +------------------------------------+
   |1|   version     |          8       |
   +------------------------------------+
   | Flags (8)  |   Length (24 bits)    |
   +------------------------------------+
   |X|          Stream-ID (31bits)      |
   +------------------------------------+
   |      Sequence of headers           |
   |                                    |
   +------------------------------------+

   The sequence of headers is just a list of the headers in one of 5
   formats:
   o  Flags - These are headers with no associated data.  The only
      information they convey is by their mere presence.
   o  Short Type-Value - where the header is associated with a 16-bit
      value.
   o  Long Type-Value - where the header is associated with a 32-bit
      value.
   o  Type-Length-Value - where the length is specified in the header.

   All formats include a 16-bit header identifier (see below), and those
   identifiers will be allocated through a new IANA registry (see
   Section 5).  The header identifier specifies which format applies.









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2.1.  Flags

   These headers are 16-bit numbers containing the header identifier.

   +-----------------+
   |header identifier|
   +-----------------+

2.2.  Short Type-Value

   These headers have the 16-bit identifier, and also the 16-bit value.

   +------------------------------------+
   |header identifier|  Value           |
   +------------------------------------+

2.3.  Long Type-Value

   These headers have the 16-bit identifier, and also a 32-bit value.

   +------------------------------------+
   |header identifier|    Value         |
   +-----------------+------------------+
   |  Value (cont)   |
   +-----------------+

2.4.  Type-Length-Value

   These headers have the 16-bit identifier, and also a 24-bit length
   field, and a value of variable length.

   +------------------------------------+
   |header identifier|    Length        |
   +---------+-------+------------------+
   | Length  | Value...                 |
   +---------+--------------------------+


3.  Header Encoding

   The encoding of each header is specified in the specification that
   describes it.  For convenience, this document describes some common
   encodings.  Specification writers SHOULD use these formats whenever
   they are appropriate.

   Unsigned integer numbers can be represented by either the short or
   long type-value, depending on their range.  Cache ages measured in
   seconds, such as in HSTS should use the long type-value, whereas a



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   header specifying an age in days should probably use a short type-
   value.  Either way, the encoding can be called "INT".

   Headers that hold an enumeration (such as Method) SHOULD use a short
   type-value, and SHOULD reserve one value (0xffff) for custom values.

   Time values should be encoded as strings using the RFC3339 format.

   Strings such as names should use the TLV format, and SHOULD be
   encoded as UTF-8.  String headers should be specified by their
   encoding, so "UTF8", or "ASCII".

   For headers with multiple values, the general format is always TLV,
   and the specification should list their type as either of three
   things:
   o  Short values - a list of 16-bit values
   o  Short strings - a sequence of strings, each prefixed by a 1-octet
      length field.
   o  Long strings - a sequence of strings, each prefixed by 1 2-octet
      length field.


4.  Custom Headers and Custom Enumerations

   For each type of header, a range will be allocated for experimental
   and custom headers.  To avoid collisions, we define here a special
   header to denote what kind of header this is.  The header is has
   identifier 49160 (0xC008), so it is TLV-formatted, and its value is
   formatted as follows:

   Custom header format

   +------------------------------------+
   |header identifier| Flags  | Name... |
   +---------+-------+------------------+

   For example, suppose draft-nir-httpbis-copyright-notice defines a
   header that contains a copyright notice for the content.  I will
   65530 (0xFFFA).  Note that the two headers don't have to be
   consecutive.  If the sender knows that the receiver recognizes this
   header with this identifier, the Custom header MAY be omitted.










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   Custom and Copyright Headers

     C0 08 00 00 0C FF FA 00 4C 4F 50 59 52 49 47 48 |........COPYRIGH|
     54 FF FA 00 00 43 6f 70 79 72 69 67 68 74 20 28 |T....Copyright (|
     63 29 20 32 30 31 32 20 49 45 54 46 20 54 72 75 |c) 2012 IETF Tru|
     73 74 20 61 6e 64 20 74 68 65 20 70 65 72 73 6f |st and the perso|
     6e 73 20 69 64 65 6e 74 69 66 69 65 64 20 61 73 |ns identified as|
     20 74 68 65 20 64 6f 63 75 6d 65 6e 74 20 61 75 | the document au|
     74 68 6f 72 73 2e 20 41 6c 6c 20 72 69 67 68 74 |thors. All right|
     73 20 72 65 73 65 72 76 65 64 2e                |s reserved.     |

   For custom values in enumerations we define the Custom-Value header
   with identifier 49161 (0vC009), where the content is the string name
   of the custom value.  This header MUST follow the enumeration header.


5.  IANA Considerations

   IANA is requested to set up a new registry of header identifiers.
   The value is 16-bit, and the range is partitioned as follows:
   o  0-16383 - these values are allocated to flag headers, where the
      format is as in Section 2.1
   o  16384-32767 - these values are allocated to short type-value
      headers, where the format is as in Section 2.2
   o  32768-49151 - these values are allocated to long type-value
      headers, where the format is as in Section 2.3
   o  49152-65535 - these values are allocated to type-length-value
      headers, where the format is as in Section 2.4

   The ending quarter of each range shall be reserved for experimental
   and custom usage, and shall not be allocated by standards action.
   For example, the range 45056-49151 will be reserved for experimental
   and custom long type-value headers.


6.  Security Considerations

   There are no security considerations for this draft.


7.  Changes from Previous Versions

   First version


8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate



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              Requirement Levels", BCP 14, RFC 2119, March 1997.


Appendix A.  Additional Examples

   NOTE: Most of the below examples were shamelessly copied from
   draft-snell-httpbis-bohe-01.

   Assuming the following (intentionally incomplete) header
   registrations:

     +--------------------+-------+------+---------------------------+
     | HTTP Header        | ID    | Hex  | Format                    |
     +--------------------+-------+------+---------------------------+
     | Version            | 16384 | 4000 | Major.Minor in 16-bit     |
     | Method             | 16385 | 4001 | Enumeration               |
     | Host               | 49152 | c000 | UTF8                      |
     | Path (Request URI) | 49153 | c001 | UTF8                      |
     | Status             | 16386 | 4002 | uint16                    |
     | Status-Text        | 49386 | c0ea | UTF8                      |
     | Content-Length     | 32768 | 8000 | uint32                    |
     | Content-Type       | 49154 | c002 | ASCII                     |
     | Expect             | 16387 | 4003 | uint16                    |
     | Last-Modified      | 49155 | c003 | RFC3339                   |
     | ETag               | 49156 | c004 | sequence of short strings |
     | If-None-Match      | 49157 | c005 | sequence of short strings |
     | Allow              | 49158 | c006 | sequence of uint16        |
     | Do-Not-Track       | 58    | 003a | flag                      |
     +--------------------+-------+------+---------------------------+

   And the following values representing known HTTP Methods:

                            +---------+-------+
                            | Method  | Value |
                            +---------+-------+
                            | GET     | 1     |
                            | POST    | 2     |
                            | PUT     | 3     |
                            | DELETE  | 4     |
                            | PATCH   | 5     |
                            | HEAD    | 6     |
                            | OPTIONS | 7     |
                            | CONNECT | 8     |
                            +---------+-------+

   Here is what the encoding looks like:





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   Version Header:

     40 00 02 00             |@...|

   Method Header (GET Request)

     40 01 00 01             |@...|

   Method Header (PATCH Request)

     40 01 00 05             |@...|

   Method Header (Custom "FOO" Method)

     40 01 FF FF C0 09 00 03 46 4F 4F                |@.......FOO     |

   Do Not Track

     00 3A                   |.:|

   Host Header:

     C0 00 00 00 0F 77 77 77 2e 65 78 61 6d 70 6c 65 |.....www.example|
     2e 6f 72 67                                     |.org            |

   HTTP Response Status ("200 OK") as two separate headers, one
   containing the status code, the other containing the status text:

     40 02 00 C8 C0 EA 00 00 02 4F 4B                |@........OK     |

   Content-Length Header (value encoded as uint32):

     80 00 00 00 00 C8       |......|

   Content-Type Header (although maybe it should become an enum:

     C0 02 00 00 0A 69 6d 61 67 65 2f 6a 70 65 67    |.....image/jpeg |

   Expect Header (Expect: 100):

     40 03 00 64             |...d|

   Last-Modified (Using RFC3339 Format):

     C0 03 00 00 19 32 30 31 32 2d 30 38 2d 30 31 54 |.....2012-08-01T|
     30 34 3a 32 33 3a 31 32 2e 31 32 33 34 5a       |04:23:12.1234Z  |





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   ETag (Strong Entity-Tag, String-format):

     C0 04 00 00 06 05 61 62 63 64 65                |......abcde     |

   If-None-Match (Multiple values)

     C0 05 00 00 0C 05 61 62 63 64 65 05 61 62 63 64 |......abcde.abcd|
     66                                              |f               |

   Allow (GET, POST, FOO):

     C0 06 00 00 06 00 01 00 02 FF FF C0 09 00 00 04 |................|
     03 46 4f 4f                                     |.FOO             |


Author's Address

   Yoav Nir
   Check Point Software Technologies Ltd.
   5 Hasolelim st.
   Tel Aviv  67897
   Israel

   Email: ynir@checkpoint.com



























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