bug#61722: (guix cpio) produces corrupted archives when there are non-ASCII filenames

[Maxim Cournoyer <maxim.cournoyer@gmail.com>]

Hi,

It appears that the code we have to generate CPIO archives doesn't
handle the presence of non-ASCII characters in the file names of files
to be archived well:

First, to make rpm usable on a Guix System:

--8<---------------cut here---------------start------------->8---
# mkdir /var/lib/rpm
# chown root:users /var/lib/rpm
# chmod g+rw /var/lib/rpm
--8<---------------cut here---------------end--------------->8---

Then, produce a problematic CPIO via 'guix pack -f rpm', which uses
(guix cpio):

--8<---------------cut here---------------start------------->8---
$ rpm_archive=$(guix pack -R -C none -f rpm nss-certs)
--8<---------------cut here---------------end--------------->8---

Notice that it cannot be installed:
--8<---------------cut here---------------start------------->8---
$ mkdir /tmp/nss-certs
# rpm --prefix=/tmp/nss-certs -i $rpm_archive
error: unpacking of archive failed: cpio: Bad magic
error: nss-certs-3.81-0.x86_64: install failed
--8<---------------cut here---------------end--------------->8---

Let's now inspect the cpio itself.

--8<---------------cut here---------------start------------->8---
$ guix shell rpm cpio
[env]$ rpm2cpio $rpm_archive > nss-certs.cpio
[env]$ cpio -t < nss-certs.cpio |& grep -B3 junk
./gnu/store/1klwvqm3njp070h982ydcix1gzf2zmdl-nss-certs-3.81/etc/ssl/certs/9482e63a.0
./gnu/store/1klwvqm3njp070h982ydcix1gzf2zmdl-nss-certs-3.81/etc/ssl/certs/9846683b.0
./gnu/store/1klwvqm3njp070h982ydcix1gzf2zmdl-nss-certs-3.81/etc/ssl/certs/988a38cb.0
cpio: warning: skipped 248 bytes of junk
--
./gnu/store/1klwvqm3njp070h982ydcix1gzf2zmdl-nss-certs-3.81/etc/ssl/certs/Microsoft_RSA_Root_Certificate_Authority_2017.pem
./gnu/store/1klwvqm3njp070h982ydcix1gzf2zmdl-nss-certs-3.81/etc/ssl/certs/NAVER_Global_Root_Certification_Authority.pem
./gnu/store/1klwvqm3njp070h982ydcix1gzf2zmdl-nss-certs-3.81/etc/ssl/certs/NetLock_Arany_=Class_Gold=_Főtanúsítvány.
cpio: warning: skipped 4 bytes of junk
--8<---------------cut here---------------end--------------->8---

I haven't yet pin-pointed what the problem is.

I could do with extra eyes :-).

-- 
Thanks,
Maxim