Re: accept extension

S.N.Brodie@ecs.soton.ac.uk
Wed, 28 Jun 1995 11:48:30 +0100 (BST)


Brian Behlendorf wrote:
>
> On Tue, 27 Jun 1995 www-html-request@www10.w3.org wrote:
> > How about extending the Accept header to pass this information.
> ...
> > Accept: image/png; q=0.8; colordepth=8, image/png; q=0.7
> >
> > which would be interpreted as: "if you have an 8 bit colour PNG, send it;
> > otherwise send me any PNG you have".
>
> So by what mechanism should the server determine arbitrary,
> non-meta-informational attributes of the files it has available to serve,
> without have to code up a lot of content-type-specific smarts into the server
> itself? I.e., if a request on the file similar to the unix command "file"
> returned a attribute/value pair listing, then maybe that would work, but
> that's not something every content-type has natively.

That's the major stumbling block, I agree. I was merely suggesting a
method for incorporating the clients wishes in the HTTP protocol.
Maybe one could construct simple scripts for determining such information
and have a mapping in the server's configuration between the types and
the 'file information' scripts.

>
> Also, Accept: doesn't have any way to express the statement "send me a
> PNG of the *lowest* bitdepth you have, please" - we'll need that unless
> we can assume that a given "level" of a document also implies
> compatibility with earlier levels.

You would need to fix this by specifying different q factors for different
bit depths eg.

Accept: image/png; q=0.8; colordepth=1
Accept: image/png; q=0.7; colordepth=8
Accept: image/png; q=0.6; colordepth=24

etc.

>
> In general, though, I think this kind of fine-tune negotiation should
> occur as *close* to the client as possible - so that if three people
> behind the Hensa proxy cache want different bitdepths of the same image,
> hensa can download the canonical version of the image and downconvert
> accordingly if it wants, rather than store three different versions.

This would mean building in the graphics conversion software to the proxy
server. I do not know what the proxy stores, but I presume it needs to
remember most (all?) of the headers which the real machine sent. What if
the server wishes to send different images depending on the available
bitdepth?

-- 
Stewart Brodie
Dept. Electronics & Computer Science, Southampton University, UK.
http://louis.ecs.soton.ac.uk/~snb94r/
http://delenn.ecs.soton.ac.uk/   <-- running on my Risc PC