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Re: Making Implicit C-E work.

From: Roland Zink <roland@zinks.de>
Date: Wed, 30 Apr 2014 11:35:04 +0200
Message-ID: <5360C3C8.8080003@zinks.de>
To: ietf-http-wg@w3.org
On 30.04.2014 08:44, Roberto Peon wrote:
> >>> As I described it, its use by the originator of an entity is not 
> mandated, instead behaviors are mandated of recipients when it IS used.​
>     >>>​
>     >>​
>     >> Yeah, mandating it. Which I'm not happy about.
>     >
>     > Mandates support, not use.
>     >
>     Kind of the same thing, from the client's POV. Server's choice.
For C-E this means for example the server decides if the client can do a 
seek. Some interactive clients would prefer to do seeks over getting the 
content compressed. Whereas downloaders would prefer the content to be 
compressed. T-E would allow to have both seek and compression.

> And today it is often neither the server nor the client's choice, 
> which is what is causing the pain. The client expresses that it wants 
> gzip. The intermediary doesn't do it because it makes numbers better, 
> increases throughput, or because they're too lazy to implement it., 
> all at the cost of the decreased user experience.
>     <snip>
>     >
>     > The combination of intermediaries stripping a-e plus the
>     competitive driver to deliver good experience/latency is causing
>     interop failures today where servers will send gzip'd data whether
>     or not the client declares support in a-e.
>     >
>     Wait, you're saying the whole motivator here is that servers don't
>     comply with the protocol? So you're changing the protocol to
>     accommodate them? That does not feel right to me, at all; it's not
>     just blessing a potential misuse of C-E, it's wallpapering over a
>     flat out abuse.
> Partially.
> I'm saying that intermediaries are doing things which are incenting 
> implementors to break compatibility with the spec, and that 
> implementors are doing so because it makes the users happy.
> In the end, making the users happy is what matters, both commercially 
> and privately. The users really don't care about purity, and will 
> migrate to implementations that give them good/better user experience.
>     But even so, why do you have to fix it in HTTP/2? And why does it
>     hurt h2 to *not* fix it?
> Compression is an important part of making latency 
> decrease/performance increase, and, frankly, there is little practical 
> motivation to deploy HTTP/2 if it doesn't succeed in reducing 
> latency/increase performance.
> Success isn't (or shouldn't be) defined as completing a protocol spec, 
> but rather, getting an interoperable protocol deployed. If it doesn't 
> get deployed, the effort is wasted. If it doesn't solve real problems, 
> the effort is wasted.
> In any case, I cannot reliably deploy a T-e based compression solution.
> T-e based compression costs too much CPU, especially as compared with 
> c-e where one simply compresses any static entity once and 
> decompresses (which is cheap) as necessary at the gateway.
If it is really T-E you can do the same compression of static entities 
when the whole file is delivered, it would be different for range 
requests or the frame based approach.
> T-e based compression isn't as performant in terms of 
> compression/deflation ratios.
Don't think this is true, the same bytes can be sent as either T-E or 
C-E. For the frame based approach some numbers were given.
> Many deployed clients/servers wouldn't correctly support it.
There are no deployed HTTP2 clients or servers, or are there some?
> T-e would require that any gateway acting as a loadbalancer/reverse 
> proxy would either need to know which resources it could compress,  or 
> forces us to not use compression.
The gateway can forward the compressed content unmodified. The gateway 
is only forced to do something if either the server or the client 
doesn't support compression.
> Knowing what resources to compress either requires an oracle, or 
> requires content authors to change how they author content (*really* 
> not likely to happen),
Not sure that authors want to know about compression. If it is automatic 
then this would be fine. Currently there is server configuration, for 
example zlib.output_compression in php.ini, and the possibility to do 
this in the content, for example in PHP something like 
ob_start('ob_gzhandler'). I guess there is a lot more authors are not 
aware off.
>     <snip>
>     > The proxy, when forwarding the server's response to the HTTP/1
>     client, must ensure that the data is uncompressed when forwarding
>     to the HTTP/1 client since the client didn't ask for c-e gzip.
>     >
>     Cache-Control:no-transform explicitly forbids the proxy from
>     altering the representation. It's not allowed to decompress it.
> In fact what we're doing is offering two representations simultaneously.
Don't think this will really work. Only one can delivered and 
translating between them (for example range) seems to be difficult.

> <snip>
> -=R
Received on Wednesday, 30 April 2014 09:35:32 UTC

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