bug#45828: guix build: error: got unexpected path `Backtrace:' from substituter

[Ludovic Courtès]

Hi Chris,

Christopher Baines <mail@cbaines.net> skribis:

> I might have managed to reproduce the error happening on the daemon
> side:
>
> → /gnu/store/4j8vn0gbqz5adj1y02nnwcfwmqsjgj8s-guix-1.2.0-6.799f066/bin/guix 
> substitute --query
> info /gnu/store/3c01q1f16kljfry70qjg6cs6k8winfzg-guix-package-cache 
> /gnu/store/6lk8anal4s62gk3d30vgxppykbd5jcfj-guix-85e97c969 
> /gnu/store/9zl2zbh3q2jnbfvxgnhw8j3f637ni7z4-guix-cli 
> /gnu/store/ihricijvy16zwkd2n671xlyrn02sqhf9-guix-manual 
> /gnu/store/m3j427qnlp81vsdj3x9ds7s4i051r1vz-guix-system-tests 
> /gnu/store/mbv9j7wwqvwnr5awzbi126jdsj3h64h5-guix-packages 
> /gnu/store/n2m1ay7kpa5f4fls4vvcy46ar1fdl0wk-guix-system 
> /gnu/store/p4q9ajlb3l7x8xglqs6fflch2iwjqwaj-guix-module-union 
> /gnu/store/snhx33fgjj2xnc5vy96sr3c8jqw9c7s0-guix-85e97c969-modules 
> /gnu/store/vnrlvz9pxl5qrpy5x8y51v6awz7yzn8q-guix-packages-base 
> /gnu/store/z4wj18vyzaas2yqb0577cc3japy4fi7z-guix-config 
> /gnu/store/zdjfbsj1a94vdbbg9r0cx4jcqnwxazxs-guix-translated-texinfo
> Backtrace:
> In ice-9/boot-9.scm:
>   1736:10  5 (with-exception-handler _ _ #:unwind? _ # _)
> In unknown file:
>            4 (apply-smob/0 #<thunk 7f23d4f2e380>)
> In ice-9/boot-9.scm:
>     718:2  3 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
> In ice-9/eval.scm:
>     619:8  2 (_ #(#(#<directory (guile-user) 7f23d4b70f00>)))
> In guix/ui.scm:
>   2127:12  1 (run-guix-command _ . _)
> In guix/scripts/substitute.scm:
>    1256:4  0 (guix-substitute . _)
>
> guix/scripts/substitute.scm:1256:4: In procedure guix-substitute:
> Throw to key `bad-response' with args `("Bad Response-Line: ~s" (""))'.

It’s interesting that we’re not seeing 500 here, but a bad response.

I tried reproducing it locally (running “sudo killall guix-daemon” after
I had started “guix publish”, and then running a command similar to the
one above) but I failed: I get a proper 500 response, which ‘guix
substitute’ gracefully interprets as a transient error.

We could be defensive and catch 'bad-response.  The problem is that
there are other exceptions thrown by (web http) et al. and they’re not
quite documented so it’s not clear to me how to do it nicely.

Thoughts?

Ludo’.