Re: Cache control in trailers?

On Mon, Feb 08, 2021 at 08:51:51AM +0000, Poul-Henning Kamp wrote:
> --------
> Roy T. Fielding writes:
> 
> > Please, if there is something specifically wrong with the current definitions
> > of Trailers in the specs currently in WGLC, [...]
> 
> There is, take for instance 6.5.1:
> 
> 	Many fields cannot be processed outside the header section
> 	because their evaluation is necessary prior to receiving
> 	the content, such as those that describe message framing,
> 	routing, authentication, request modifiers, response controls,
> 	or content format.
> 
> The unstated assumption is that the recipient cannot be required to
> spool up the body and wait for the trailers before doing anything
> with it.

... and watch the whole Web collapse because suddenly everyone
needs to buffer every byte in flight before even knowing where to
forward it if at all. This is the e-mail architecture that you're
describing. Far less reliable and fast than the web. Every single
message has to be spooled to disk and some get delivered very late
when not lost. Imagine an HTTP response passing through 10 layers
of intermediaries, you'd divide the effective bandwidth on this
request by 10 because of the store-and-forward approach!

Conversely, announcing upfront who to deal with a message allows to
add controls and to stream it. This is so much important that Expect
was invented to save users from having to upload a whole attachment
for 2 minutes in their webmail before seeing a login pop-up and
figuring they'd have to do it again.

For sure there *are* information that would be useful at the end
(hence the creation of trailer) and possibly even in the middle,
(e.g. timestamping or quality information for streamed contents
maybe). But let's not suddenly declare that everything would be
better at the end because this is utterly wrong.

And it's very fortunate that Authorization and Cookie are sent prior
to any upload, otherwise a number of servers would be forced to store
a lot of crap before figuring if the sender was allowed to upload it
in the first place. This could even have legal implications by the
way.

Regards,
Willy

Received on Monday, 8 February 2021 10:32:50 UTC