bug#71160: --fallback and (fallback #t) do not apply when receiving a corrupt nar

[Richard Sent]

Richard Sent <richard@freakingpenguin.com> writes:

> Trying to pass --fallback on the command line has no effect, even though
> both the documentation and [1] imply that should work.

This issue might have some spiciness to it. I have two machines with
identical guix commits and --fallback works on one but not the other.

--8<---------------cut here---------------start------------->8---
# Failing machine:
root@lifeline ~# guix describe
Generation 2    May 25 2024 21:03:46    (current)
  guix 94c8cec
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 94c8cec99969fe9f65777637fde1f05e1c576a3f

# Good machine:
Generation 3    May 25 2024 21:58:15    (current)
  guix 94c8cec
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 94c8cec99969fe9f65777637fde1f05e1c576a3f
--8<---------------cut here---------------end--------------->8---

On the failing machine, I get an error like this:

--8<---------------cut here---------------start------------->8---
root@lifeline ~# guix build linux-libre-arm64-generic --system=aarch64-linux 
--fallback
# snip
downloading from 
https://bordeaux.guix.gnu.org/nar/none/y813phs2n9xnb7zbcr07g0j9509bzbsb-linux-libre-6.8.10-guix.tar.xz
 ...
 linux-libre-6.8.10-guix.tar.xz  136.5MiB                                       
                                   19.0MiB/s 00:07 ▕█████████████████▉▏  
99.9%guix substitute: error: corrupt input while restoring 
'/gnu/store/y813phs2n9xnb7zbcr07g0j9509bzbsb-linux-libre-6.8.10-guix.tar.xz' 
from #<input: string 7f558e7233f0>
substitution of 
/gnu/store/y813phs2n9xnb7zbcr07g0j9509bzbsb-linux-libre-6.8.10-guix.tar.xz 
failed
guix build: error: corrupt input while restoring archive from #<closed: file 
7f51c615b380>
root@lifeline ~# logout
--8<---------------cut here---------------end--------------->8---

whereas on the good machine:

--8<---------------cut here---------------start------------->8---
root@gibraltar ~# guix build linux-libre-arm64-generic --system=aarch64-linux 
--fallback
# snip
downloading from 
https://bordeaux.guix.gnu.org/nar/none/y813phs2n9xnb7zbcr07g0j9509bzbsb-linux-libre-6.8.10-guix.tar.xz
 ...
 linux-libre-6.8.10-guix.tar.xz  136.5MiB                                       
                                   19.6MiB/s 00:07 ▕█████████████████▊▏  
98.8%guix substitute: error: corrupt input while restoring 
'/gnu/store/y813phs2n9xnb7zbcr07g0j9509bzbsb-linux-libre-6.8.10-guix.tar.xz' 
from #<input: string 7f7b2a223b60>
substitution of 
/gnu/store/y813phs2n9xnb7zbcr07g0j9509bzbsb-linux-libre-6.8.10-guix.tar.xz 
failed
building 
/gnu/store/ny56fdcig9cd9bd3pssmlraz2c1q10q8-linux-libre-6.8.10-guix.tar.xz.drv...
--8<---------------cut here---------------end--------------->8---

I thought perhaps there was some hyper-odd race condition going on here
(lifeline is consistently at a higher percent than gibraltar when the
error is detected), but I just had a outlier that seems to disprove
that, where lifeline had the same error with a 97.2% download progress
bar.

-- 
Take it easy,
Richard Sent
Making my computer weirder one commit at a time.