bug#47157: “Bad Read-Header-Line header: #<eof>” while substituting

[Ludovic Courtès]

As reported by a few people on IRC, ‘guix substitute’ sometimes fails in
a way that I just experienced (from
8154beffd8c121e953a7c4cd75c3eebfcc073a9a):

--8<---------------cut here---------------start------------->8---
downloading from 
https://ci.guix.gnu.org/nar/gzip/0bji0q5n59595xaqkqrp2gv52lbz55xz-libpng-1.6.37 
.
 libpng-1.6.37  275KiB                                 11.0MiB/s 00:00 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/h3a5ygxxh4gakhnl53mq7z9b43l8z05g-python-minimal.
 python-minimal-wrapper-3.8.2  351B                     293KiB/s 00:00 
[##################] 100.0%

downloading from 
https://ci.guix.gnu.org/nar/lzip/h8j09yb5d8dh3jffvpzawxslig9bwhdr-freetype-2.10..
 freetype-2.10.4  600KiB                                3.0MiB/s 00:00 
[##################] 100.0%

building /gnu/store/2wfzazqz9g5xizi4vq4pv75nkh1m24bp-perl-5.30.2.drv...
Backtrace:
In guix/ui.scm:
  2164:12 19 (run-guix-command _ . _)
In guix/scripts/substitute.scm:
    691:2 18 (guix-substitute . _)
In unknown file:
          17 (with-continuation-barrier #<procedure thunk ()>)
In ice-9/boot-9.scm:
  1736:10 16 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
In unknown file:
          15 (apply-smob/0 #<thunk 7fcb3b3594a0>)
In ice-9/boot-9.scm:
  1736:10 14 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
  1736:10 13 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
  1731:15 12 (with-exception-handler #<procedure 7fcb3a7c4150 at 
ice-9/boot-9.scm:1815:7 (exn)> _)
In guix/scripts/substitute.scm:
   740:17 11 (_)
    434:7 10 (process-substitution _ 
"/gnu/store/ns00dyapjbq9037dwrxa7hc31dvir00n-grub-minimal-2.)
In ice-9/boot-9.scm:
  1736:10  9 (with-exception-handler _ _ #:unwind? _ #:unwind-for-type _)
In guix/scripts/substitute.scm:
    443:9  8 (_)
In ice-9/boot-9.scm:
  1731:15  7 (with-exception-handler #<procedure 7fcb3a7d37b0 at 
ice-9/boot-9.scm:1815:7 (exn)> _)
  1669:16  6 (raise-exception _ #:continuable? _)
  1667:16  5 (raise-exception _ #:continuable? _)
  1669:16  4 (raise-exception _ #:continuable? _)
  1764:13  3 (_ #<&compound-exception components: (#<&error> #<&irritants 
irritants: (read-header)
  1669:16  2 (raise-exception _ #:continuable? _)
  1667:16  1 (raise-exception _ #:continuable? _)
  1669:16  0 (raise-exception _ #:continuable? _)

ice-9/boot-9.scm:1669:16: In procedure raise-exception:
Bad Read-Header-Line header: #<eof>
--8<---------------cut here---------------end--------------->8---

This is the kind of issue that ‘with-cached-connection’ as it can be
seen in 9158020d7853b6e7925802e0d0a082801c680e8f avoided:

--8<---------------cut here---------------start------------->8---
(define* (call-with-cached-connection uri proc
                                      #:optional
                                      (open-connection
                                       open-connection-for-uri/cached))
  (let ((port (open-connection uri)))
    (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)))
            (proc (open-connection uri #:fresh? #t))
            (apply throw key args))))))
--8<---------------cut here---------------end--------------->8---

I think 7b812f7c84c43455cdd68a0e51b6ded018afcc8e and subsequent commits
may have caused this regression.  In particular, in
20c08a8a45d0f137ead7c05e720456b2aea44402,
‘call-with-connection-error-handling’ is now used, but that one doesn’t
catch the exceptions mentioned above, in this case ‘bad-header’.

Ludo’.