One document matched: draft-nir-httpbis-che-00.xml
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<rfc ipr="trust200902" docName="draft-nir-httpbis-che-00" category="info">
<front>
<title abbrev="compact-header">HTTP/2.0 Discussion: Compact Header Encoding</title>
<author initials="Y." surname="Nir" fullname="Yoav Nir">
<organization abbrev="Check Point">Check Point Software Technologies Ltd.</organization>
<address>
<postal>
<street>5 Hasolelim st.</street>
<city>Tel Aviv</city>
<code>67897</code>
<country>Israel</country>
</postal>
<email>ynir@checkpoint.com</email>
</address>
</author>
<date year="2012"/>
<area>Applications Area</area>
<keyword>Internet-Draft</keyword>
<abstract>
<t> 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.</t>
</abstract>
</front>
<middle>
<!-- ====================================================================== -->
<section anchor="introduction" title="Introduction">
<t> 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.</t>
<section anchor="mustshouldmay" title="Conventions Used in This Document">
<t>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 <xref target="RFC2119"/>.</t>
</section>
</section>
<section anchor="encoding" title="The Binary Encoding">
<figure><preamble>The header block is formatted as follows:</preamble><artwork>
+------------------------------------+
|1| version | 8 |
+------------------------------------+
| Flags (8) | Length (24 bits) |
+------------------------------------+
|X| Stream-ID (31bits) |
+------------------------------------+
| Sequence of headers |
| |
+------------------------------------+
</artwork></figure>
<t> The sequence of headers is just a list of the headers in one of 5 formats: <list
style="symbols">
<t> Flags - These are headers with no associated data. The only information they convey is
by their mere presence.</t>
<t> Short Type-Value - where the header is associated with a 16-bit value.</t>
<t> Long Type-Value - where the header is associated with a 32-bit value.</t>
<t> Type-Length-Value - where the length is specified in the header.</t>
</list></t>
<t> All formats include a 16-bit header identifier (see below), and those identifiers will be
allocated through a new IANA registry (see <xref target="iana" />). The header identifier
specifies which format applies.</t>
<section anchor="format1" title="Flags">
<figure><preamble>These headers are 16-bit numbers containing the header identifier.
</preamble><artwork>
+-----------------+
|header identifier|
+-----------------+
</artwork></figure>
</section>
<section anchor="format2" title="Short Type-Value">
<figure><preamble>These headers have the 16-bit identifier, and also the 16-bit value.
</preamble><artwork>
+------------------------------------+
|header identifier| Value |
+------------------------------------+
</artwork></figure>
</section>
<section anchor="format3" title="Long Type-Value">
<figure><preamble>These headers have the 16-bit identifier, and also a 32-bit value.
</preamble><artwork>
+------------------------------------+
|header identifier| Value |
+-----------------+------------------+
| Value (cont) |
+-----------------+
</artwork></figure>
</section>
<section anchor="format4" title="Type-Length-Value">
<figure><preamble>These headers have the 16-bit identifier, and also a 24-bit length
field, and a value of variable length.</preamble><artwork>
+------------------------------------+
|header identifier| Length |
+---------+-------+------------------+
| Length | Value... |
+---------+--------------------------+
</artwork></figure>
</section>
</section>
<section anchor="headerenc" title="Header Encoding">
<t> 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.</t>
<t> 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 header specifying an age in days should probably use a short
type-value. Either way, the encoding can be called "INT".</t>
<t> Headers that hold an enumeration (such as Method) SHOULD use a short type-value, and
SHOULD reserve one value (0xffff) for custom values.</t>
<t> Time values should be encoded as strings using the RFC3339 format.</t>
<t> 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".</t>
<t> For headers with multiple values, the general format is always TLV, and the specification
should list their type as either of three things: <list style="symbols">
<t> Short values - a list of 16-bit values</t>
<t> Short strings - a sequence of strings, each prefixed by a 1-octet length field.</t>
<t> Long strings - a sequence of strings, each prefixed by 1 2-octet length field.</t></list></t>
</section>
<section anchor="custom" title="Custom Headers and Custom Enumerations">
<t> 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:</t>
<figure><preamble>Custom header format</preamble><artwork>
+------------------------------------+
|header identifier| Flags | Name... |
+---------+-------+------------------+
</artwork></figure>
<t> 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.</t>
<figure><preamble>Custom and Copyright Headers</preamble><artwork>
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. |
</artwork></figure>
<t> 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.</t>
</section>
<!-- ====================================================================== -->
<section anchor="iana" title="IANA Considerations">
<t> IANA is requested to set up a new registry of header identifiers. The value is 16-bit,
and the range is partitioned as follows:<list style="symbols">
<t> 0-16383 - these values are allocated to flag headers, where the format is as in
<xref target="format1" /></t>
<t> 16384-32767 - these values are allocated to short type-value headers, where the
format is as in <xref target="format2" /></t>
<t> 32768-49151 - these values are allocated to long type-value headers, where the format
is as in <xref target="format3" /></t>
<t> 49152-65535 - these values are allocated to type-length-value headers, where the format
is as in <xref target="format4" /></t></list></t>
<t> 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.</t>
</section>
<section anchor="security" title="Security Considerations">
<t> There are no security considerations for this draft. </t>
</section>
<section anchor="delta" title="Changes from Previous Versions">
<t> First version </t>
</section>
</middle>
<!-- ====================================================================== -->
<back>
<references title="Normative References">
<reference anchor='RFC2119'>
<front>
<title abbrev='RFC Key Words'>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='Scott Bradner'>
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street>
</postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email>
</address>
</author>
<date year='1997' month='March' />
<area>General</area>
<keyword>keyword</keyword>
</front>
<seriesInfo name='BCP' value='14' />
<seriesInfo name='RFC' value='2119' />
<format type='TXT' octets='4723' target='ftp://ftp.isi.edu/in-notes/rfc2119.txt' />
<format type='HTML' octets='16553' target='http://xml.resource.org/public/rfc/html/rfc2119.html' />
<format type='XML' octets='5703' target='http://xml.resource.org/public/rfc/xml/rfc2119.xml' />
</reference>
</references>
<!-- ====================================================================== -->
<section title="Additional Examples">
<t> NOTE: Most of the below examples were shamelessly copied from draft-snell-httpbis-bohe-01.</t>
<t>Assuming the following (intentionally incomplete) header registrations:</t>
<texttable>
<ttcol>HTTP Header</ttcol>
<ttcol>ID</ttcol>
<ttcol>Hex</ttcol>
<ttcol>Format</ttcol>
<c>Version </c> <c>16384</c> <c>4000</c> <c>Major.Minor in 16-bit</c>
<c>Method </c> <c>16385</c> <c>4001</c> <c>Enumeration</c>
<c>Host </c> <c>49152</c> <c>c000</c> <c>UTF8</c>
<c>Path (Request URI) </c> <c>49153</c> <c>c001</c> <c>UTF8</c>
<c>Status </c> <c>16386</c> <c>4002</c> <c>uint16</c>
<c>Status-Text </c> <c>49386</c> <c>c0ea</c> <c>UTF8</c>
<c>Content-Length </c> <c>32768</c> <c>8000</c> <c>uint32</c>
<c>Content-Type </c> <c>49154</c> <c>c002</c> <c>ASCII</c>
<c>Expect </c> <c>16387</c> <c>4003</c> <c>uint16</c>
<c>Last-Modified </c> <c>49155</c> <c>c003</c> <c>RFC3339</c>
<c>ETag </c> <c>49156</c> <c>c004</c> <c>sequence of short strings</c>
<c>If-None-Match </c> <c>49157</c> <c>c005</c> <c>sequence of short strings</c>
<c>Allow </c> <c>49158</c> <c>c006</c> <c>sequence of uint16</c>
<c>Do-Not-Track </c> <c> 58</c> <c>003a</c> <c>flag</c>
</texttable>
<t>And the following values representing known HTTP Methods:</t>
<texttable>
<ttcol>Method</ttcol>
<ttcol>Value</ttcol>
<c>GET </c> <c>1</c>
<c>POST </c> <c>2</c>
<c>PUT </c> <c>3</c>
<c>DELETE </c> <c>4</c>
<c>PATCH </c> <c>5</c>
<c>HEAD </c> <c>6</c>
<c>OPTIONS</c> <c>7</c>
<c>CONNECT</c> <c>8</c>
</texttable>
<t>Here is what the encoding looks like:</t>
<figure><preamble>Version Header:</preamble><artwork>
40 00 02 00 |@...|
</artwork></figure>
<figure><preamble>Method Header (GET Request)</preamble><artwork>
40 01 00 01 |@...|
</artwork></figure>
<figure><preamble>Method Header (PATCH Request)</preamble><artwork>
40 01 00 05 |@...|
</artwork></figure>
<figure><preamble>Method Header (Custom "FOO" Method)</preamble><artwork>
40 01 FF FF C0 09 00 03 46 4F 4F |@.......FOO |
</artwork></figure>
<figure><preamble>Do Not Track</preamble><artwork>
00 3A |.:|
</artwork></figure>
<figure><preamble>Host Header:</preamble><artwork>
C0 00 00 00 0F 77 77 77 2e 65 78 61 6d 70 6c 65 |.....www.example|
2e 6f 72 67 |.org |
</artwork></figure>
<figure><preamble>HTTP Response Status ("200 OK") as two separate headers, one containing the
status code, the other containing the status text:</preamble><artwork>
40 02 00 C8 C0 EA 00 00 02 4F 4B |@........OK |
</artwork></figure>
<figure><preamble>Content-Length Header (value encoded as uint32):</preamble><artwork>
80 00 00 00 00 C8 |......|
</artwork></figure>
<figure><preamble>Content-Type Header (although maybe it should become an enum:</preamble><artwork>
C0 02 00 00 0A 69 6d 61 67 65 2f 6a 70 65 67 |.....image/jpeg |
</artwork></figure>
<figure><preamble>Expect Header (Expect: 100):</preamble><artwork>
40 03 00 64 |...d|
</artwork></figure>
<figure><preamble>Last-Modified (Using RFC3339 Format):</preamble><artwork>
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 |
</artwork></figure>
<figure><preamble>ETag (Strong Entity-Tag, String-format):</preamble><artwork>
C0 04 00 00 06 05 61 62 63 64 65 |......abcde |
</artwork></figure>
<figure><preamble>If-None-Match (Multiple values)</preamble><artwork>
C0 05 00 00 0C 05 61 62 63 64 65 05 61 62 63 64 |......abcde.abcd|
66 |f |
</artwork></figure>
<figure><preamble>Allow (GET, POST, FOO):</preamble><artwork>
C0 06 00 00 06 00 01 00 02 FF FF C0 09 00 00 04 |................|
03 46 4f 4f |.FOO |
</artwork></figure>
</section>
</back>
</rfc>
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