HTTP/2.0 Discussion: Binary Optimized Header Encoding
draft-snell-httpbis-bohe-03
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| Author | James M. Snell | ||
| Last updated | 2013-02-18 | ||
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draft-snell-httpbis-bohe-03
Network Working Group J. Snell
Internet-Draft February 18, 2013
Intended status: Informational
Expires: August 22, 2013
HTTP/2.0 Discussion: Binary Optimized Header Encoding
draft-snell-httpbis-bohe-03
Abstract
This memo describes a proposed alternative encoding for headers
within SPDY SYN_STREAM, SYN_REPLY and HEADERS frames.
Status of this Memo
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This Internet-Draft will expire on August 22, 2013.
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Table of Contents
1. Binary Optimized Header Encoding . . . . . . . . . . . . . . . 3
2. Value Encoding . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Example Headers . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
5. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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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:
+-------+---------+
| NUM | Headers |
+-------+---------+
'NUM' is a single unsigned 8-bit value indicating the total number of
distinct headers contained in the encoded block.
'Headers' consists of the complete set of encoded headers. The
format for each header is determined by whether the header name (the
key) and the header value are included in the static "default
dictionary" defined by this specification. The first two bits of
each encoded header record identify the specific header format used.
Registered Key + Registered Value Pair
+--+---+--+
|00|CNT|ID|
+--+---+--+
If the header name and value are both included in the default
dictionary, the associated index of the header as provided by the
dictionary is encoded as a variable-length, unsigned integer in lists
of no more than 63 items. For example, the headers ":path=/",
":method=GET" and ":scheme=https" would be compactly encoded as: 03
03 0F 06
Registered Key + Unregistered Value
+--+---+--+---+---+
|01|FLG|ID|LEN|VAL|
+--+---+--+---+---+
If the header name is included in the default dictionary, but the
value given is not, the header is encoded using five fields: the two-
bit opcode (01) followed by six flag bits as defined below, followed
by the numerically lowest index of the named header as provided by
the default dictionary encoded as a variable-length, unsigned
integer, followed by another variable-length, unsigned integer
specifying the length of the value, followed by the encoded value.
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Unregistered Key + Value Pair
+--+---+------+---+------+---+
|10|FLG|LENkey|key|LENval|val|
+--+---+------+---+------+---+
If the header name and value are not included in the default
dictionary, the header is encoded using six distinct fields: the two-
bit opcode (10) followed by six flag bits as defined below, followed
by a variable-length, unsigned integer specifying the key length,
followed by the ISO-8859-1 encoded key name, followed by a variable-
length, unsigned integer specifying the value length, followed by the
encoded value.
Flags:
FLG = 000000
||||||
|||||Reserved
||||Date (Numeric val represents a date)
|||Numeric (val is one or more uvarints)
||Huffman-encoded
|UTF-8 or ISO8859-1 (1 or 0)
Binary | Text (1 or 0)
When the opcode is either 01 or 10, the six-bit FLG field is used to
specify additional properties about the header value. When the
opcode is 00, the FLG bits are unused and MUST NOT be set.
Moving from the most significant bit to the least, the flags are:
o Binary or Text (0x32) - When set, the value is to be interpreted
as binary data. When unset, the value is to be interpreted as
encoded-text.
o UTF-8 or ISO-8859-1 (0x16) - When set, indicates that the text-
encoded value is UTF-8 encoded. Otherwise, ISO-8859-1 is assumed.
Only used if the Binary bit (0x32) is unset.
o Huffman-encoded (0x08) - When set, indicates that the text-encoded
value has been static huffman encoded. The static dictionary used
for the encoding is dependent on whether the text is UTF-8 or ISO-
8859-1 encoded. Only used if the Binary bit (0x32) is unset.
o Numeric (0x04) - When set, indicates that the value is encoded as
a variable-length unsigned integer. Only used if the Binary bit
(0x32) is set (indicating a binary value).
o Date (0x02) - When set, indicates that the value is a date and
time encoded as a variable-length unsigned integer representing
the total number of seconds that have ellapsed since midnight on
January 1st, 1990, GMT. Only used if the Binary (0x32) and
Numeric (0x04) bits are both set.
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o The final bit (0x01) is reserved.
2. Value Encoding
Header values can be encoded as one of four distinct types: Binary,
Text, Numeric or Date. Each is indicated by the FLG field.
o Binary Header values are encoded as a raw, uninterpreted sequence
of binary octets.
o Numeric values are encoded as variable-length, unsigned integers.
o Date values are encoded as variable-length, unsigned integers
representing the total number of seconds that have ellapsed since
midnight on January 1st, 1990.
o Text values are encoded as a sequence one or more length-prefixed
octet sequences representing ISO-8859-1 or UTF-8 encoded
characters, conforming to the following structure:
string_val = COUNT 1*(LENGTH VAL)
Where COUNT is an unsigned 8-bit value specifying the number of octet
sequences, LENGTH is an unsigned variable-length integer specifying
the length of each sequence, and VAL is the specific sequence of
encoded octets.
3. Example Headers
Assuming the following (incomplete) default dictionary:
+----+-----------------------------+------------+
| ID | Key | Value |
+----+-----------------------------+------------+
| 0 | date | |
| 1 | :scheme | |
| 2 | :scheme | http |
| 3 | :scheme | https |
| 4 | :scheme | ftp |
| 5 | :method | |
| 6 | :method | get |
| 7 | :method | post |
| 8 | :method | put |
| 9 | :method | delete |
| 10 | :method | options |
| 11 | :method | connect |
| 12 | :method | patch |
| 13 | :method | link |
| 14 | :path | |
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| 15 | :path | / |
| 16 | :host | |
| 17 | cookie | |
| 18 | :status | |
| 19 | :status | 200 |
| 20 | :status | 201 |
| 21 | :status | 202 |
| 22 | :status | 204 |
| 23 | :status | 205 |
| 24 | :status-text | |
| 25 | :status-text | OK |
| 26 | :version | |
| 27 | :version | 1.0 |
| 28 | :version | 1.1 |
| 29 | :version | 2.0 |
| 30 | accept | |
| 31 | accept-charset | |
| 32 | accept-encoding | |
| 33 | accept-language | |
| 34 | accept-ranges | |
| 35 | allow | |
| 36 | authorizations | |
| 37 | cache-control | |
| 38 | content-base | |
| 39 | content-encoding | |
| 40 | content-length | |
| 41 | content-location | |
| 42 | content-md5 | |
| 43 | content-range | |
| 44 | content-type | |
| 45 | etag | |
| 46 | expect | |
| 47 | expires | |
| 48 | from | |
| 49 | if-match | |
| 50 | if-modified-since | |
| 51 | if-none-match | |
| 52 | if-range | |
| 53 | if-unmodified-since | |
| 54 | last-modified | |
| 55 | location | |
| 56 | max-forwards | |
| 57 | origin | |
| 58 | pragma | |
| 59 | proxy-authenticate | |
| 60 | proxy-authorization | |
| 61 | range | |
| 62 | referer | |
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| 63 | retry-after | |
| 64 | server | |
| 65 | set-cookie | |
| 66 | status | |
| 67 | te | |
| 68 | trailer | |
| 69 | transfer-encoding | |
| 70 | transfer-encoding | gzip |
| 71 | upgrade | |
| 72 | user-agent | |
| 73 | vary | |
| 74 | via | |
| 75 | warning | |
| 76 | www-authenticate | |
| 77 | access-control-allow-origin | |
| 78 | content-disposition | |
| 79 | get-dictionary | |
| 80 | p3p | |
| 81 | x-content-type-options | |
| 82 | x-frame-options | |
| 83 | x-powered-by | |
| 84 | x-xss-protection | |
| 85 | connection | |
| 86 | connection | keep-alive |
+----+-----------------------------+------------+
The header :version=2.0 would be encoded as:
01 1D |..|
The header :method=GET would be encoded as:
01 06 |..|
The headers :version=2.0 and :method=GET would be encoded as:
02 06 1D |..|
The header :method=foo would be encoded as:
56 05 05 01 03 66 6F 6F |.....foo|
The header foo=bar would be encoded as:
b6 03 66 6f 6f 05 01 |..foo...|
03 62 61 72 |.bar|
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4. Security Considerations
TBD
5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Author's Address
James M Snell
Email: jasnell@gmail.com
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