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Network Working Group                                           J. Snell
Internet-Draft                                            August 2, 2012
Intended status: Informational
Expires: February 3, 2013


         HTTP/2.0 Discussion: Binary Optimized Header Encoding
                      draft-snell-httpbis-bohe-00

Abstract

   This memo describes a proposed alternative encoding for headers
   within SPDY SYN_STREAM, SYN_REPLY and HEADERS frames.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on February 3, 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
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   described in the Simplified BSD License.






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Table of Contents

   1.  Binary Optimized Header Encoding . . . . . . . . . . . . . . .  3
     1.1.  Registered Headers . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Extension Headers  . . . . . . . . . . . . . . . . . . . .  5
     1.3.  Binary vs. Character Values  . . . . . . . . . . . . . . .  5
     1.4.  Example Headers  . . . . . . . . . . . . . . . . . . . . .  7
   2.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   3.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Additional Examples . . . . . . . . . . . . . . . . .  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12








































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1.  Binary Optimized Header Encoding

   Binary Optimized Header Encoding is a proposed alternative
   serialization for headers within SPDY SYN_STREAM, SYN_REPLY and
   HEADERS frames that is designed to optimize generation, consumption
   and processing of the most commonly used HTTP headers.

   Alternate Header Block Serialization:

      +------------------------------------+
      |      Number of Headers (8bit)      |
      +------------------------------------+
      |T|            Header                |
      +------------------------------------+
      | ...                                |

   Within the existing SPDY Header Block, a 32-bit value is used to
   identify the number of headers within the block.  For all practical
   purposes, it is exceedingly unlikely that a single block of headers
   will contain anywhere near 4,294,967,295 distinct headers.  Obviously
   a 32-bit integer is significant overkill for this purpose.  As an
   alternative, an 8-bit value suggested.

   The header block consists of zero or more distinct headers, each of
   which begin with a single Type-bit whose value indicates the type of
   header.  There are two header types: Registered and Extension.  The
   specific structure of the remaining header depends on the header
   type.

   The header block MAY be compressed as described within
   [draft-montenegro-httpbis-speed-mobility-02].

1.1.  Registered Headers

   Registered Headers are well-known and well-defined headers for which
   there is a published RFC and IANA registration.  Each is assigned an
   unsigned 12-bit integer identifier and an unsigned 3-bit integer
   codepage.  If the codepage is 0, the implication is that the header
   MUST be understood in order for the request or response message to be
   handled properly.  Codepages 1-5 represent "MUST-IGNORE" headers;
   that is, such headers MUST be ignored by processors if they are
   unrecognized by the processing application.  Codepages 6 and 7 are
   reserved for "Private Use", with Codepage 6 being used for "MUST
   UNDERSTAND PRIVATE USE" headers.







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   The structure of Registered Headers:

     +------------------------------+
     |0| cp(3-bit) |   id (12-bit)  |
     +------------------------------+
     | flags(8-bit) |  len (16-bit) |
     +------------------------------+
     |          value...            |
     +------------------------------+

   The first single bit within the structure is the Type-bit.  When this
   bit is off, the header is a Registered Header.

   The next three bits identify the headers codepage.  The value is
   interpreted as an unsigned integer in the range 0-7.

   The next twelve bits specify the header's specific numeric identifier
   within the codepage.

   Following the identifier are 8 reserved flag bits.
   o  Bit 0x1 indicates that the header value contains UTF-8 encoded
      character content.  If the bit is not set, the value is assumed to
      contain non-character-based binary data.
   o  Bit 0x2 indicates that the header specifies multiple NUL (0)
      separated values.  When set, processors MUST treat NUL (0) octets
      within the value as a delimiter and not as part of the value
      itself.

   The remaining content of the structure consists of a 16-bit unsigned
   integer specifying the remaining length of the header value.  The
   value MAY be zero length.

   The minimum length of a registered header is 5-octets (40-bits).

   When Flag 0x2 is set, the header may contain multiple values
   separated by a single NUL (0) byte.  Each distinct value MUST NOT be
   zero-length.  When Flag 0x2 is not set, and Flag 0x1 is also not set,
   NUL bytes contained within the value are to be considered part of the
   value.  The use of NUL bytes within character-based values is not
   permitted except when used as a delimiter separating multiple values.

   When multiple values are included, the value length field MUST
   specify the total length, in octets, of all values plus the number of
   NUL (0) byte separators.  For example, for a header value consisting
   of the two strings "foo" and "bar", the total value length would be
   7.





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1.2.  Extension Headers

   Extension Headers are simple name+value pairs essentially as they
   exist today, but with a number of important modifications.

   The structure of Extension Headers

     +------------------------------+
     |1| flags(7-bit) | namelen (8) |
     +------------------------------+
     | name | val len (16) | value  |
     +------------------------------+

   The first single bit is the Type-bit.  When this bit is on, the
   header is an Extension Header.

   The next seven bits are reserved flags.
   o  Bit 0x1 indicates that the header value contains UTF-8 encoded
      character content.  If the bit is not set, the value is assumed to
      contain non-character-based binary data.
   o  Bit 0x2 indicates that the header specifies multiple NUL (0)
      separated values.  When set, processors MUST treat NUL (0) octets
      within the value as a value-separated and not as part of the value
      itself.

   The next 8-bits specify the length in octets of the ASCII-encoded
   header name as unsigned integer, followed by the name itself.  The
   name MUST conform to the field-name construction as defined in
   [draft-ietf-httpbis-p1-messaging-2].

   The length of the remaining value is specified as an unsigned 16-bit
   integer, followed by the value itself.  Zero length values are
   permitted.

   When Flag 0x2 is set, the header may contain multiple values
   separated by a single NUL (0) byte.  Each distinct value MUST be
   zero-length.

   When multiple values are included, the value length field MUST
   specify the total length, in octets, of all values plus the number of
   NUL (0) byte separators.  For example, for a header value consisting
   of the two strings "foo" and "bar", the total value length would be
   7.

1.3.  Binary vs. Character Values

   Specific header values can be encoded as either a stream of binary
   octets or as UTF-8 encoded character data.



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   For example, within the existing SPDY specification, the HTTP Version
   is represented as a header using the field-name ":version" with the
   version number represented as an ASCII string, consuming 19-bytes in
   all.

   Version Header using the existing SPDY encoding:

     00 00 00 08 3a 76 65 72  |....:ver|
     73 69 6f 6e 00 00 00 03  |sion....|
     31 2e 31                 |2.0|

   Using the Binary Optimized Header Encoding, this can be reduced to a
   compact 7 or 8 bytes using either binary or character data:

   Version Header using Character Data:

     00 01 01 00 03 31 2e 31  |.....2.0|

   Version Header using Binary Data:

     00 01 00 00 02 02 00     |.......|

   Likewise, SPDY uses a ":method" header to specify the HTTP Method
   used for a particular request, with the value represented as an ASCII
   string, consuming 18 bytes for GET requests.

   Method Header using the existing SPDY encoding:

     00 00 00 07 3a 6d 65 74  |....:met|
     68 6f 64 00 00 00 03 47  |hod....G|
     45 54                    |GET|

   Using optimized encoding, this can be reduced to a compact 6 or 8
   bytes using either binary or character data:

   Method Header using Character Data:

     00 02 01 00 03 47 45 54  |.....GET|

   Method Header using Binary Data, assuming the value 0x1 is defined to
   represent the GET method:

     00 02 00 00 01 01       |......|

   There are many headers used within HTTP applications for which binary
   encodings would be difficult or unnecessary.  For those, utilizing
   the character encoding option would be appropriate.  With some work
   it should be possible to define optimized binary encodings for many



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   of the existing complex headers.

1.4.  Example Headers

   Assume the following registered headers:

                  +--------------------+----------+----+
                  | HTTP Header        | Codepage | ID |
                  +--------------------+----------+----+
                  | Version            | 0        | 1  |
                  | Method             | 0        | 2  |
                  | Host               | 0        | 3  |
                  | Path (Request URI) | 0        | 4  |
                  | Accept-Language    | 1        | 1  |
                  +--------------------+----------+----+

   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     |
                            +---------+-------+

   The Version header can be encoded as (7-bytes):

     00 01 00 00 02 02 00    |.......|

   The GET Method header can be encoded as (6-bytes):

     00 02 00 00 01 01       |......|

   The Host Header can be encoded as (20-bytes):

     00 03 01 00 0f 77 77 77 |.....www|
     2e 65 78 61 6d 70 6c 65 |.example|
     2e 6f 72 67             |.org|







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   A simple Accept-Lang header would be encoded as (10-bytes):

     10 01 01 00 05 65 6e 2d |.....en-|
     55 53                   |US|

   A Path header encoding the request URI (45-bytes):

     00 04 01 00 28 2f 74 68  |...../th|
     69 73 2f 69 73 2f 74 68  |is/is/th|
     65 2f 72 65 71 75 65 73  |e/reques|
     74 3f 69 73 3d 69 74 26  |t?is=it&|
     6e 6f 74 3d 62 65 61 75  |not=beau|
     74 69 66 75 6c           |tiful|

   The combined serialization of the five headers into a single block
   requires a total of 89 bytes.  By comparison, the equivalent
   serialization using the existing SPDY encoding requires 150 bytes
   sans compression (28 bytes of which are wasted by the unnecessary use
   of int32).

   The equivalent SPDY encoding:

     00 00 00 05 00 00 00 08  |........|
     3a 76 65 72 73 69 6f 6e  |:version|
     00 00 00 03 31 2e 31 00  |....1.1.|
     00 00 07 3a 6d 65 74 68  |...:meth|
     6f 64 00 00 00 03 47 45  |od....GE|
     54 00 00 00 05 3a 68 6f  |T....:ho|
     73 74 00 00 00 0f 77 77  |st....ww|
     77 2e 65 78 61 6d 70 6c  |w.exampl|
     65 2e 6f 72 67 00 00 00  |e.org...|
     0f 41 63 63 65 70 74 2d  |.Accept-|
     4c 61 6e 67 75 61 67 65  |Language|
     00 00 00 05 65 6e 2d 55  |....en-U|
     53 00 00 00 05 3a 70 61  |S....:pa|
     74 68 00 00 00 28 2f 74  |th..../t|
     68 69 73 2f 69 73 2f 74  |his/is/t|
     68 65 2f 72 65 71 75 65  |he/reque|
     73 74 3f 69 73 3d 69 74  |st?is=it|
     26 6e 6f 74 3d 62 65 61  |&not=bea|
     75 74 69 66 75 6c        |utiful|

   Note that the equivalent information encoded within an HTTP/1.1
   request message requires 102 bytes.







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2.  Security Considerations

   TBD


3.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.


Appendix A.  Additional Examples

   Assuming the following (intentionally incomplete) header
   registrations adapted from the existing http-bis specifications.




































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                  +---------------------+----------+----+
                  | HTTP Header         | Codepage | ID |
                  +---------------------+----------+----+
                  | Version             | 0        | 1  |
                  | Method              | 0        | 2  |
                  | Host                | 0        | 3  |
                  | Path (Request URI)  | 0        | 4  |
                  | Status              | 0        | 5  |
                  | Status-Text         | 0        | 6  |
                  | Content-Length      | 0        | 7  |
                  | Content-Type        | 0        | 8  |
                  | Content-Encoding    | 0        | 9  |
                  | Expect              | 0        | 10 |
                  | Location            | 0        | 11 |
                  | Last-Modified       | 0        | 12 |
                  | ETag                | 0        | 13 |
                  | If-Match            | 0        | 14 |
                  | If-None-Match       | 0        | 15 |
                  | If-Modified-Since   | 0        | 16 |
                  | If-Unmodified-Since | 0        | 17 |
                  | Age                 | 0        | 18 |
                  | Cache-Control       | 0        | 19 |
                  | Expires             | 0        | 20 |
                  | Vary                | 0        | 21 |
                  | Accept              | 1        | 1  |
                  | Accept-Language     | 1        | 2  |
                  | Accept-Charset      | 1        | 3  |
                  | Accept-Encoding     | 1        | 4  |
                  | Allow               | 1        | 5  |
                  | Content-Language    | 1        | 6  |
                  | Content-Location    | 1        | 7  |
                  | Date                | 1        | 8  |
                  | From                | 1        | 9  |
                  | Warning             | 1        | 10 |
                  +---------------------+----------+----+

   And the following values representing known HTTP Methods:














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

   We can derive the following optimized encodings:

   Version Header:

     00 01 00 00 02 02 00    |.......|

   Method Header (GET Request)

     00 02 00 00 01 01       |......|

   Method Header (PATCH Request)

     00 02 00 00 01 05       |......|

   Method Header (Custom "FOO" Method)

     00 02 01 00 03 46 4F 4F |.....FOO|

   Host Header:

     00 03 01 00 0f 77 77 77 |.....www|
     2e 65 78 61 6d 70 6c 65 |.example|
     2e 6f 72 67             |.org|

   Representation of HTTP Response Status ("200 OK"):

     00 05 00 00 01 C8 00 06 |........|
     01 00 02 4F 4B          |...OK|

   The status above is represented as two separate headers, one
   containing the status code, the other containing the status text.







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   Content-Length Header (value encoded as uint32):

     00 07 00 00 04 00 00 00 |........|
     C8                      |.|

   Content-Type Header:

     00 08 01 00 0A 69 6d 61 |.....ima|
     67 65 2f 6a 70 65 67    |ge/jpeg|

   Expect Header (Expect: 100):

     00 0A 00 00 01 64       |......|

   Last-Modified (Using RFC3339 Format):

     00 0C 01 00 19 32 30 31 |.....201|
     32 2d 30 38 2d 30 31 54 |2-08-01T|
     30 34 3a 32 33 3a 31 32 |04:23:12|
     2e 31 32 33 34 5a       |.1234Z|

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

     00 0D 01 00 07 22 61 62 |....."ab|
     63 64 65 22             |cde"|

   If-None-Match:

     00 0F 01 00 07 22 61 62 |....."ab|
     63 64 65 22             |cde"|

   If-None-Match (Multiple values)

     00 0F 03 00 0F 22 61 62 |....."ab|
     63 64 65 22 00 22 61 62 |cde"."ab|
     63 64 66 22             |cdf"|

   Allow (GET, POST, FOO):

     10 05 02 00 07 01 00 02 |........|
     00 46 4f 4f             |.FOO|










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Author's Address

   James M Snell

   Email: jasnell@gmail.com














































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