py3 returns xmlrpclib.Base64 entity instead of string, which fails in next step of encoding.
xmlrpclib.Base64
Reproduce: click on any task output in web ui
PR #1290
Most task output is a direct link. You need one that uses the getfile handler, e.g. the tail links for task outputs.
Or in the cli: download-logs or watch-logs (or the runroot plugin)
Commit 3a1e9a93 fixes this issue
Commit 4222b097 fixes this issue
This issue has been migrated to Fedora Forge: https://forge.fedoraproject.org/koji/koji/issues/1289
Please continue any further discussion there.