Subject: [bug#47174] [PATCH 0/2] substitute: Handle closing connections to substitute servers.

From: Ludovic Courtès <[email-masked]>
Date: Sat, 29 May 2021 23:46:26 +0200

Christopher Baines <[email-masked]> skribis:

> When reusing a HTTP connection to fetch multiple nars, and the remote server
> signals that the connection should be closed.

Incomplete sentence?

> * guix/scripts/substitute.scm (process-substitution): Close connections to
> substitute servers when a Connection: close header is specified in the
> response.
> ---
>  guix/scripts/substitute.scm | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
> index 96f425eaa0..208b8f1273 100755
> --- a/guix/scripts/substitute.scm
> +++ b/guix/scripts/substitute.scm
> @@ -464,7 +464,9 @@ PORT."
>      (case (uri-scheme uri)
>        ((file)
>         (let ((port (open-file (uri-path uri) "r0b")))
> -         (values port (stat:size (stat port)))))
> +         (values port
> +                 (stat:size (stat port))
> +                 (const #t))))          ; no cleanup to do
>        ((http https)
>         (guard (c ((http-get-error? c)
>                    (leave (G_ "download from '~a' failed: ~a, ~s~%")
> @@ -487,7 +489,12 @@ PORT."
>                                         #:keep-alive? #t
>                                         #:buffered? #f)))
>                 (values raw
> -                       (response-content-length response)))))))
> +                       (response-content-length response)
> +                       (match (assq 'connection (response-headers response))
> +                         (('connection 'close)
> +                          (lambda ()
> +                            (close-port port)))
> +                         (_ (const #t)))))))))
>        (else
>         (leave (G_ "unsupported substitute URI scheme: ~a~%")
>                (uri->string uri)))))
> @@ -504,7 +511,7 @@ PORT."
>        (format (current-error-port)
>                (G_ "Downloading ~a...~%") (uri->string uri)))
>  
> -    (let*-values (((raw download-size)
> +    (let*-values (((raw download-size post-fetch-cleanup)
>                     ;; 'guix publish' without '--cache' doesn't specify a
>                     ;; Content-Length, so DOWNLOAD-SIZE is #f in this case.
>                     (fetch uri))
> @@ -565,6 +572,10 @@ PORT."
>        ;; Wait for the reporter to finish.
>        (every (compose zero? cdr waitpid) pids)
>  
> +      ;; Do post-fetch cleanup, maybe closing the HTTP connection if HTTP is
> +      ;; being used, and the connection should be closed
> +      (post-fetch-cleanup)

How about returning a Boolean as the third value, ‘close?’, indicating
whether the port should be closed upon completion?  That seems
marginally clearer to me that the post-cleanup thunk.

Otherwise LGTM, thanks!

Ludo’.