bug#48468: substitute server connection timeout

[Mathieu Othacehe]

Hello,

> It means that upstream (i.e., ‘guix publish’) closed the connection,
> right?
>
> And it means that it closed it prematurely I guess?

Looks like it yes.

>> However, like suggested in your hypothesis number 1, it seems instead
>> that we are replying 404 to the worker which resets the connection. As
>> we have put aside the baking thing, the question is now why are those
>> derivations not available?
>
> In that case we’re not replying at all, are we?

Well could be, I'm not 100% sure how to understand those nginx logs. If
we are replying anything, it will be visible with the new traces. If on
the other hand the publish server is hanging up then they won't help
much I guess.

> Drop ‘G_’ (we don’t translate debugging messages) and use ASCII, to be
> on the safe side…

Done.

> Instead of an env. var., maybe add a ‘--debug’ command-line option and
> parameterize ‘%debug?’ accordingly?

The --debug command-line feels better but it involves a guix-daemon
modification so I kept the environment variable,

> You can also have something like:
>
>   (define-syntax (debug fmt args ...)
>     (when (%debug?)
>       (format #t fmt args ...)))
>

and used that macro :)

Thanks for having a look!

Mathieu