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RE: #445: Transfer-codings

From: <K.Morgan@iaea.org>
Date: Wed, 9 Apr 2014 17:53:57 +0000
To: <matthew@kerwin.net.au>, <ietf-http-wg@w3.org>
Message-ID: <0356EBBE092D394F9291DA01E8D28EC20100F499C2@sem002pd.sg.iaea.org>
See my comments in-line below...

On Friday,04 April 2014 04:39, Matthew Kerwin wrote:
>
> Encoding: A 16 bit identifier which describes the encoding ...

I agree with what others have said - 16 bits is overkill.  I suggest one byte.

>
> SETTINGS_ACCEPT_DATA_ENCODING (5): ...
>
> The Value field is further divided into two sub-fields, an unsigned 16 bit encoding
> identifier and an unsigned 16-bit rank.
>


> On Friday,04 April 2014 06:34, Martin Thomson wrote (emphasis added):

>>  Settings have a single value. ... you will need to explain how values are processed,

>>  and how an implementation is able to limit the storage it dedicates to storage of this new setting.

I still think you didn't catch Martin's point. Theoretically a client has to store 64K x 4B of SETTINGS_ACCEPT_DATA_ENCODING values.

I suggest a simpler approach.  Only allow a single value sub-divided into 4 bytes to announce support for up to 4 distinct encodings.  A new value received for this setting replaces the current setting.  This would allow the setting to remain a single 32-bit value. I also suggest you ditch the rank. The endpoint generating the compression should be allowed to decide the best compression scheme, if any, given the context.

In other words, I would suggest something like...

<<<<<<<
 The Value field is further divided into four sub-fields, each representing
 an unsigned 8 bit encoding identifier.

  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | Encoding1 (8) | Encoding2 (8) | Encoding3 (8) | Encoding4 (8) |
  +-------------------------------+-------------------------------+

An endpoint may advertise support for up to four encodings at any
given time. Sending a new value for SETTINGS_ACCEPT_DATA_ENCODING
replaces the previous value. An encoding value of 0 means "unused".
>>>>>>>

(If you really wanted to keep the concept of rank, you could use the ordering of the four bytes as the rank.)

If an endpoint decides mid-connection they don't want to support compression any more for whatever reason (e.g. under heavy CPU load), it simply has to send a NULL value for this setting.


-keith


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Received on Wednesday, 9 April 2014 17:54:48 UTC

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