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RE: Making Implicit C-E work.

From: <K.Morgan@iaea.org>
Date: Thu, 1 May 2014 21:57:43 +0000
To: <grmocg@gmail.com>, <matthew@kerwin.net.au>
CC: <ietf-http-wg@w3.org>
Message-ID: <0356EBBE092D394F9291DA01E8D28EC201129876F9@sem001pd.sg.iaea.org>
In many different e-mails grmocg@gmail.com wrote:

> I have a real honest-to-goodness pragmatic deployment problem (myriad pre-existing servers/clients

> whose deployment I do not and cannot control) here that I cannot wish away ...


> Many of my customers will not be writing custom servers, and as such to be deployable,

> we need solutions that will work with what is out there. ...

> My problem is dealing with the rest of the world, which is mostly HTTP/1.X and is unlikely to rapidly change.

> In other words, I'm concerned mainly with HTTP/1.X clients and especially servers. ...

I  honestly want to understand your problem, but I don't.  It might be really helpful if you could write down the hypothetical network connections between client and server (including as many potential intermediaries as you know about) and denote either HTTP/1.x or HTTP/2 for every hop.

I've been sitting here trying to understand how implicit C-E gzip helps based on what you've already said and I still don't get it.

You said you are concerned especially about HTTP/1.X servers.  But your proposal can't help because the 1.X servers won't know about the implicit gzip and certainly won't know to add the "uncompressed-*" headers.

In the opposite direction, if the server is HTTP/2 and the client is HTTP/1.X, the body will have to be decompressed anyway so you only benefit for the hops that are HTTP/2.  Is that really that beneficial?

Between an HTTP/2 client and an HTTP/2 server, we can already do something about it without breaking things i.e. some sort of transfer coding.

> The same bytes can't be sent in both [C-E and T-E], unless the we're willing to suffer vastly increased DoS surface area and memory usage [for T-E] ...

I don't buy the "vastly increased DoS surface area" argument. The receivers already have this "DoS surface area" for decompressing C-E gzip entities.  If the receiver of a stream has a gzip decompression context for decompressing a C-E gzip entity OR a T-E gzip message, they still just have one context.  If a receiver has N outstanding streams it has N outstanding gzip contexts, even if they're all C-E gzip.  Sure stupid servers could do both C-E and T-E, but it's near impossible to design a protocol that prevents implementors from doing every stupid thing imaginable.

So, yes the same bytes could be sent in both cases (C-E or T-E) and it's actually probably the right way to do T-E (as opposed to the frame-by-frame).

> 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.

You're comparing apples and oranges. Dynamic gzip has the same cpu cost whether it's called C-E or T-E. For static entities, as I pointed out above, you can pre-compress once and send the same bytes as either C-E or T-E.

> T-e based compression isn't as performant in terms of compression/deflation ratios.

LOL. I assume you could only possibly be talking about frame-by-frame T-E. Ironically, in another thread you said the performance difference for frame-by-frame is negligible (and we sent out data to back that up).

> Many deployed clients/servers wouldn't correctly support it.

I know of no clients/servers that *incorrectly* support T-E.  I assume you just mean wouldn't support it at all?

> 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. Knowing what resources to compress either
> requires an oracle, or requires content authors to change how they author content (*really* not likely to happen),

How do they solve the same problem with C-E?  The server decides, right?  Same thing for T-E.

> [With implicit C-E gzip] [a]n HTTP/1 client still receives an uncompressed entity if it didn't request it compressed.

What are _HTTP/2_ clients supposed to do to that really want an uncompressed (identity) entity?

Accept-Encoding: identity

Implicit-Accept-Encoding: pretty please don't use gzip

In addition to everything above, I noticed that you still haven't responded to concerns that Matthew & Julian brought up. It would be good for you to update your proposal to address these concerns...

- Matthew wrote: "[What about] last-modified? And, possibly, other fields from Vary? There's more entity-specific metadata than just ETag."

- Matthew also wrote: "Cache-Control:no-transform explicitly forbids the proxy from altering the representation. It's not allowed to decompress it."

- And elsewhere Julian brought up the issue of entity-specific metadata in the body itself. He used the example of WebDav. Do you expect intermediaries to parse through bodies and patch up that metadata too?

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Received on Thursday, 1 May 2014 21:58:27 UTC

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