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RE: Making Implicit C-E work.

From: <K.Morgan@iaea.org>
Date: Thu, 15 May 2014 11:42:06 +0000
To: <mnot@mnot.net>, <martin.thomson@gmail.com>
CC: <grmocg@gmail.com>, <jgraettinger@chromium.org>, <matthew@kerwin.net.au>, <C.Brunhuber@iaea.org>, <ietf-http-wg@w3.org>
Message-ID: <0356EBBE092D394F9291DA01E8D28EC20112D9D9CE@sem002pd.sg.iaea.org>
On Thursday,15 May 2014 12:53, Mark Nottingham wrote:
> On 15 May 2014, at 11:48 am, Martin Thomson <martin.thomson@gmail.com<mailto:martin.thomson@gmail.com>> wrote:

>> I am down with Matthew's suggestion here to lift the MUST. Though I note that there

>> are cases where this places an intermediary between a rock and a hard place in terms

>> of conflicting requirements. Maybe we can note that an intermediary /could/

>> decompress and leave the normative text out of it.


> That makes sense to me...

Let's be more clear.  That only makes sense _if_ you are assuming acceptance of Roberto's proposed "uncompressed-*" headers solution. Otherwise this doesn't solve any of the problems brought up by Matthew, Julian, myself and others with respect to etag, no-transform, metadata within the entity body, etc...

On Tuesday,29 April 2014 22:29, Roberto Peon Wrote:

> [SNIP]

> Servers seeing an implicit gzip a-e and sending a compressed entity MAY include an

> additional header field, ":uncompressed-etag" ...

> [SNIP]

I take issue with the MAY.  IMO, if the server wants to use implicit gzip it MUST include the "uncompressed-*" header fields, if such a header would have been sent with the corresponding entity with c-e: identity. Otherwise it forces the intermediary into a position where it has to either 1) decompress and break the metadata, or, 2) forward the response as-is and possibly cause inter-op issues (on second thought, maybe this a desirable feature for Roberto and others?).

Finally, I also would like to see text added to Roberto's proposal about how servers should deal with range requests with respect to implicit c-e gzip.  As I've pointed out many times, the range n-m of a c-e gzip entity is NOT equal to the range n-m of the entity's c-e identity encoding. Example text:


If a server elects to service a range request, it MUST NOT use implicit gzip content encoding.


As I pointed out earlier though, this opens up loop-holes for intermediaries to work around implicit gzip...

On Wednesday,14 May 2014 09:28, MORGAN, Keith Shearl wrote:

> This introduces loop-holes for all of those intermediaries you're trying to combat which strip a-e gzip.


> For example, an intermediary could...

> + Strip a-e gzip and inject a range request for the entire content:

>    "Accept-Encoding: identity"

>    "Range: bytes=0-"

> + Or, if the server is too smart for that, strip a-e gzip and inject a multi-part range for the entire content:

>    "Accept-Encoding: identity"

>   "Range: bytes=0-0,1-"

> + Or, if the server is really smart, strip a-e gzip and split the request into two separate range requests for the entire content:

>    "Accept-Encoding: identity"

>    "Range: bytes=0-0"

>    ...

>    "Accept-Encoding: identity"

>    "Range: bytes=1-"


> Of course the server could simply disable Range requests (i.e. always send the full c-e gzip response - which is legal).

> I would argue that this will also degrade the user experience as there are more and more users browsing on spotty

> networks (e.g. Safari doesn't use range requests [1] and it drives me crazy every time I'm loading a page and there

> is a break in network connectivity on the subway, because then it has to start all over).


> [1] http://lists.w3.org/Archives/Public/ietf-http-wg/2014AprJun/0112.html

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Received on Thursday, 15 May 2014 11:43:11 UTC

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