[bug#47160,v2,1/2] scripts: substitute: Add back some error handling.

In f50f5751fff4cfc6d5abba9681054569694b7a5c, the way fetch was called within
process-substitution was changed.  As with-cached-connection actually includes
important error handling for the opening of a HTTP request (when using a
cached connection), this change removed some error handling.

This commit adds that error handling back,
(call-)with-cached-connection is back, rebranded as
call-with-cached-connection-and-error-handling.

* guix/scripts/substitute.scm (process-substitution): Retry once for some
errors when making HTTP requests to fetch substitutes.
---
 guix/scripts/substitute.scm | 38 ++++++++++++++++++++++++++++++++-----
 1 file changed, 33 insertions(+), 5 deletions(-)

Christopher Baines <mail@cbaines.net> skribis:

> In f50f5751fff4cfc6d5abba9681054569694b7a5c, the way fetch was called within
> process-substitution was changed.  As with-cached-connection actually includes
> important error handling for the opening of a HTTP request (when using a
> cached connection), this change removed some error handling.
>
> This commit adds that error handling back,
> (call-)with-cached-connection is back, rebranded as
> call-with-cached-connection-and-error-handling.
>
> * guix/scripts/substitute.scm (process-substitution): Retry once for some
> errors when making HTTP requests to fetch substitutes.

Please mention also the new procedure, and a
“Fixes <https://bugs.gnu.org/47157>.” line

> +(define (call-with-cached-connection-and-error-handling uri proc)
> +  (define (get-port)
> +    (open-connection-for-uri/cached uri
> +                                    #:verify-certificate? #f))
> +
> +  (let ((port (get-port)))
> +    (catch #t
> +      (lambda ()
> +        (proc port))
> +      (lambda (key . args)
> +        ;; If PORT was cached and the server closed the connection in the
> +        ;; meantime, we get EPIPE.  In that case, open a fresh connection
> +        ;; and retry.  We might also get 'bad-response or a similar
> +        ;; exception from (web response) later on, once we've sent the
> +        ;; request, or a ERROR/INVALID-SESSION from GnuTLS.
> +        (if (or (and (eq? key 'system-error)
> +                     (= EPIPE (system-error-errno `(,key ,@args))))
> +                (and (eq? key 'gnutls-error)
> +                     (eq? (first args) error/invalid-session))
> +                (memq key '(bad-response bad-header bad-header-component)))
> +            (begin
> +              (close-port port)       ; close the port to get a fresh one
> +              (proc (get-port)))

I find it marginally clearer to pass #:fresh? #t (as was done in
the code removed in 7c85877fdf964694061e3192eac35723ebc047bf) than to
rely on the closed-port side effect.

I think it’s OK to remove ‘-and-error-handling’ because that doesn’t
really tell much and because too many words obscure the message IMO, but
that’s a detail.  I also like the helper macro as was removed in
7c85877fdf964694061e3192eac35723ebc047bf.

Apart from that LGTM.

My limited testing suggests it’s working as intended.

Thank you!

Ludo’.

Ludovic Courtès <ludo@gnu.org> writes:

> Christopher Baines <mail@cbaines.net> skribis:
>
>> In f50f5751fff4cfc6d5abba9681054569694b7a5c, the way fetch was called within
>> process-substitution was changed.  As with-cached-connection actually includes
>> important error handling for the opening of a HTTP request (when using a
>> cached connection), this change removed some error handling.
>>
>> This commit adds that error handling back,
>> (call-)with-cached-connection is back, rebranded as
>> call-with-cached-connection-and-error-handling.
>>
>> * guix/scripts/substitute.scm (process-substitution): Retry once for some
>> errors when making HTTP requests to fetch substitutes.
>
> Please mention also the new procedure, and a
> “Fixes <https://bugs.gnu.org/47157>.” line
>
>> +(define (call-with-cached-connection-and-error-handling uri proc)
>> +  (define (get-port)
>> +    (open-connection-for-uri/cached uri
>> +                                    #:verify-certificate? #f))
>> +
>> +  (let ((port (get-port)))
>> +    (catch #t
>> +      (lambda ()
>> +        (proc port))
>> +      (lambda (key . args)
>> +        ;; If PORT was cached and the server closed the connection in the
>> +        ;; meantime, we get EPIPE.  In that case, open a fresh connection
>> +        ;; and retry.  We might also get 'bad-response or a similar
>> +        ;; exception from (web response) later on, once we've sent the
>> +        ;; request, or a ERROR/INVALID-SESSION from GnuTLS.
>> +        (if (or (and (eq? key 'system-error)
>> +                     (= EPIPE (system-error-errno `(,key ,@args))))
>> +                (and (eq? key 'gnutls-error)
>> +                     (eq? (first args) error/invalid-session))
>> +                (memq key '(bad-response bad-header bad-header-component)))
>> +            (begin
>> +              (close-port port)       ; close the port to get a fresh one
>> +              (proc (get-port)))
>
> I find it marginally clearer to pass #:fresh? #t (as was done in
> the code removed in 7c85877fdf964694061e3192eac35723ebc047bf) than to
> rely on the closed-port side effect.
>
> I think it’s OK to remove ‘-and-error-handling’ because that doesn’t
> really tell much and because too many words obscure the message IMO, but
> that’s a detail.  I also like the helper macro as was removed in
> 7c85877fdf964694061e3192eac35723ebc047bf.

Sure, I'll send a v3 set of patches shortly.