Internet DRAFT - draft-nir-httpbis-che
draft-nir-httpbis-che
Network Working Group Y. Nir
Internet-Draft Check Point
Intended status: Informational November 9, 2012
Expires: May 13, 2013
HTTP/2.0 Discussion: Compact Header Encoding
draft-nir-httpbis-che-01
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.
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This Internet-Draft will expire on May 13, 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
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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. Default Headers . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Changes from Previous Versions . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Additional Examples . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
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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 6). 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 use
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. Default Headers
Many requests share a lot of their headers. For example, the Cookie,
User-Agents, Host, Connection, and Accept* headers pretty much remain
constant between consecutive requests.
To make the per-stream Headers block even smaller, we allow a default
Headers block. This block is distinguished by having Stream-ID fixed
to all zeros. Additionally a new flag is defined:
0x02 = FLAG_UPD - marks that this frame updates the default headers
Every subsequent request is deemed to include all the default
headers, except where such headers are overridden by that request.
The default headers are persistent for the connection.
A default HEADERS with the FLAG_UPD flag cleared replaces the default
headers for this connection. A default HEADERS block with the
FLAG_UPD set updates the default headers for this connection by
replacing those that had already been set, and adding those that had
not been set. This is useful for example, if a cookie had been set
by the server. The only way to delete a header from the default
headers is by replacement - a default HEADERS block with FLAG_UPD
cleared.
6. 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:
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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.
7. Security Considerations
There are no security considerations for this draft.
8. Changes from Previous Versions
First version
9. 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
NOTE: Most of the below examples were shamelessly copied from
draft-snell-httpbis-bohe-01.
Assuming the following (intentionally incomplete) header
registrations:
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+--------------------+-------+------+---------------------------+
| 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:
Version Header:
40 00 02 00 |@...|
Method Header (GET Request)
40 01 00 01 |@...|
Method Header (PATCH Request)
40 01 00 05 |@...|
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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 |
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 |
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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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