bug#56005: exception while downloading substitutes

[Thiago Jung Bauermann]

Hello,

I just ran “guix pull && guix package -u” and after downloading many
substitutes, guix package aborted with the following error:

--8<---------------cut here---------------start------------->8---
    ⋮
substitute: atualizando substitutos de "https://ci.guix.gnu.org";...   
0.0%Backtrace:
substitute:           14 (primitive-load 
"/gnu/store/yxh9kr0150494jf8phrf1x28mhw…")
substitute: In guix/ui.scm:
substitute:    2230:7 13 (run-guix . _)
substitute:   2193:10 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:    365:27  7 (lookup-narinfos/diverse _ _ #<procedure 7f22cf4534a0 
…> …)
substitute:    322:31  6 (lookup-narinfos "https://ci.guix.gnu.org"; _ # _ # _)
substitute:    245:26  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: In procedure write_wait_fd: unimplemented
guix package: erro: `/gnu/store/yxh9kr0150494jf8phrf1x28mhwnnv7f-guix-command 
substitute' died unexpectedly
popigai: (1) guix describe
Geração 144     15 jun 2022 22:55:58    (atual)
  guix 128697d
    URL do repositório: https://git.savannah.gnu.org/git/guix.git
    ramo: master
    commit: 128697d43c21eb229ff5413f1c4cf79ae1a9dcd4
--8<---------------cut here---------------end--------------->8---

I immediately ran “guix package -u” again, and this time the command
completed successfully.

I had a quick look at ‘fetch-narinfos’ but I couldn't figure out what
could be calling into this unimplemented function ‘write_wait_fd’…

-- 
Thanks
Thiago