xpra repos fail with CentOS 7

[olifre]

Describe the bug
"Good" old CentOS 7 yields an error after adding the repo and running yum update:

 One of the configured repositories failed (Unknown),
 and yum doesn't have enough cached data to continue. At this point the only
 safe thing yum can do is fail. There are a few ways to work "fix" this:

     1. Contact the upstream for the repository and get them to fix the problem.

     2. Reconfigure the baseurl/etc. for the repository, to point to a working
        upstream. This is most often useful if you are using a newer
        distribution release than is supported by the repository (and the
        packages for the previous distribution release still work).

     3. Run the command with the repository temporarily disabled
            yum --disablerepo=<repoid> ...

     4. Disable the repository permanently, so yum won't use it by default. Yum
        will then just ignore the repository until you permanently enable it
        again or use --enablerepo for temporary usage:

            yum-config-manager --disable <repoid>
        or
            subscription-manager repos --disable=<repoid>

     5. Configure the failing repository to be skipped, if it is unavailable.
        Note that yum will try to contact the repo. when it runs most commands,
        so will have to try and fail each time (and thus. yum will be be much
        slower). If it is a very temporary problem though, this is often a nice
        compromise:

            yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true

Parsing primary.xml error: Start tag expected, '<' not found

To Reproduce

wget -O /etc/yum.repos.d/xpra.repo https://xpra.org/repos/CentOS/7/xpra.repo
rpm --import https://xpra.org/gpg-2018.asc
yum -y install xpra xpra-html5

System Information (please complete the following information):

• Latest CentOS 7

Additional context
Potentially this is caused by the primary files now being generated with zstd compression and not gz anymore?

[olifre]

This could be related to:
rpm-software-management/createrepo_c#383
which mentions --general-compress-type=gz --compress-type=gz as a viable workaround for CentOS 7 repo generation.

[totaam]

@olifre I have re-generated the repos with the gz option, does that help?

I think this came about when I switched to signing locally because of gpg agent forwarding issues - the remote system had gz as default or something, the local one does not.

[olifre]

@totaam Indeed, that did the trick! It works again in a "fresh" CentOS 7 container.
I think CentOS 7 is the only distro with this limitation which is not EoL yet, so in a few months, you could likely use zstd again for all RPM-based distros.

Thanks again for the quick fix!