bug#51593: guix substitute died unexpectedly on unmatched line

[Maxim Cournoyer]

Hello,

One of my substitute servers is currently offline; and it caused the
following (non-deterministic) error:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix build webkitgtk-with-libsoup2
substitute: updating substitutes from 'http://127.0.0.1:8181'...  
90.7%Backtrace:
substitute: In ice-9/boot-9.scm:
substitute:   1752:10 17 (with-exception-handler _ _ #:unwind? _ # _)
substitute: In unknown file:
substitute:           16 (apply-smob/0 #<thunk 7efd2817bf60>)
substitute: In ice-9/boot-9.scm:
substitute:     724:2 15 (call-with-prompt _ _ #<procedure 
default-prompt-handle…>)
substitute: In ice-9/eval.scm:
substitute:     619:8 14 (_ #(#(#<directory (guile-user) 7efd28175c80>)))
substitute: In guix/ui.scm:
substitute:    2185:7 13 (run-guix . _)
substitute:   2148:10 12 (run-guix-command _ . _)
substitute: In ice-9/boot-9.scm:
substitute:   1752:10 11 (with-exception-handler _ _ #:unwind? _ # _)
substitute:   1752:10 10 (with-exception-handler _ _ #:unwind? _ # _)
substitute: In guix/scripts/substitute.scm:
substitute:    757:18  9 (_)
substitute:    348:26  8 (process-query #<output: file 4> _ #:cache-urls _ 
#:acl _)
substitute: In guix/substitutes.scm:
substitute:    361:27  7 (lookup-narinfos/diverse _ _ #<procedure 7efd249d7a80 
…> …)
substitute:    318:31  6 (lookup-narinfos _ _ #:open-connection _ # _)
substitute:    241:26  5 (fetch-narinfos _ _ #:open-connection _ # _)
substitute: In ice-9/boot-9.scm:
substitute:   1685:16  4 (raise-exception _ #:continuable? _)
substitute:   1685:16  3 (raise-exception _ #:continuable? _)
substitute:   1780:13  2 (_ #<&compound-exception components: (#<&error> 
#<&orig…>)
substitute:   1685:16  1 (raise-exception _ #:continuable? _)
substitute:   1685:16  0 (raise-exception _ #:continuable? _)
substitute: 
substitute: ice-9/boot-9.scm:1685:16: In procedure raise-exception:
substitute: unmatched line "1 404 Not Found\r"
guix build: error: 
`/gnu/store/49vfv8l1j96bbd73ssbqanpnjz83arss-guix-1.3.0-11.014f1b6/bin/guix 
substitute' died unexpectedly
--8<---------------cut here---------------end--------------->8---

Thanks,

Maxim