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SPDY and the HTTP Binding

From: James M Snell <jasnell@gmail.com>
Date: Thu, 11 Oct 2012 10:13:33 -0700
Message-ID: <CABP7RbcP8rXG6ArMCMCzoEEKS-aH5aHUbinFqQB-zV7vjr--Rg@mail.gmail.com>
To: ietf-http-wg@w3.org
I've been going back through the HTTP binding described in the initial SPDY
draft [1] and going through a variety of options for the header encoding
and the thought struck me.. if headers such as :version, :method and
:scheme are always going to be included in the SYN_STREAM, and these are
always going to have fairly static and well defined values, there's really
no reason at all why those should be encoded as headers in the first place
-- let's just give them fixed positions within the SYN_STREAM block..

[1] http://tools.ietf.org/html/draft-mbelshe-httpbis-spdy-00#section-2.6.1

+------------------------------------+
|1|    version    |         1        |
+------------------------------------+
|  Flags (8)  |  Length (24 bits)    |
+------------------------------------+
|X|           Stream-ID (31bits)     |
+------------------------------------+
|X| Associated-To-Stream-ID (31bits) |
+------------------------------------+
| Pri|S|Unused| Slot |M|             |
+----------------------+             |
| Number of Name/Value pairs (int32) |
+------------------------------------+
|     Length of name (int32)         |
+------------------------------------+
|           Name (string)            |
+------------------------------------+
|     Length of value  (int32)       |
+------------------------------------+
|          Value   (string)          |
+------------------------------------+
|           (repeats)                |

For one, we already have the version field in the SYN_STREAM... we
shouldn't need two separate protocol version identifiers within a single
SYN_STREAM..

This would add one single-bit flag following the priority and one
single-byte fields following the Slot.

The single-bit field following the Priority would indicate whether or not
the SYN_STREAM is secure... this is equivalent to sending
":scheme"="https". This would use up one fo the currently-unused 5-bits
that exist after the priority. (I'm not even yet convinced that this flag
is necessary at all. We might be able to drop the :scheme indicator
completely).

The one-byte field following Slot identifies the HTTP Method. Each method
would be assigned a numeric identifier (GET=0x1, PUT=0x2, etc). New methods
would be registered to get a new identifier (if a server gets a SYN_STREAM
with an unknown method identifier it's no different than if they get a
HTTP/1.1 request with an unknown method name).

Using this approach, we eliminate three special case headers (":version",
":method" and ":scheme") and save at least around 31-bytes per SYN_STREAM.

- James
Received on Thursday, 11 October 2012 17:14:26 GMT

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