Re: Cache control in trailers?

If adding trailers requires the body to be well-formed, then this would
seem to preclude option (c), so this could not be used to indicate an
error.  It would only apply to cases where the body is correct and usable
but less cacheable than expected, which seems like a very narrow use case.

On Tue, Feb 2, 2021 at 7:43 PM Mark Nottingham <mnot@mnot.net> wrote:

> Hi all,
>
> One of the fundamental limitations of HTTP that people often bump into is
> that the status code and headers precede the body,[1] so if something goes
> wrong while the response is being generated, they can get into awkward
> situations.
>
> For example, if server-side script has made the response cacheable and
> encounters an unrecoverable error while generating it, that response will
> get stored and reused by downstream systems.
>
> Right now, the only ways for it to avoid this is (a) buffer the whole
> response, (b) don't ever make the response cacheable, in case an error
> occurs, or (c) purposefully truncate the response (i.e., cause a protocol
> error), hoping that all downstream caches correctly avoid storing
> incomplete responses.
>
> None of these seem like great options.
>
> One better way would be to indicate the error in trailers. This has been
> mused upon before, e.g., allowing the status code to occur in trailers --
> but that is likely unworkable, because all of the potential effects of a
> different status code can't be accounted for when trailers are received.
>
> A more limited approach would be to focus just on the cache's behaviour --
> e.g., to allow Cache-Control: no-cache in trailers,[2] updating the
> semantics of the response to make sure that it's revalidated before it's
> reused.
>
> What do folks think - would this be useful? Obviously it would need to be
> implemented in browsers and other caches.
>
> Cheers,
>
> 1. Or is that 'content' now?
> 2. Note that we don't have to reuse CC: no-cache; it could be that a new
> trailer communicates what's intended more clearly.
>
> --
> Mark Nottingham   https://www.mnot.net/
>
>
>