support zipped plugins

[Paul Collins]

It seems to be fairly common to distribute Grafana plugins as zip files (e.g. https://github.com/grafana/piechart-panel/releases).

The charm doesn't support zip files:

2020-03-10 20:09:50 INFO config-changed shutil.ReadError: /tmp/grafana-plugin.tar.gz is not a compressed or uncompressed tar file

So we have to repack them first. It would be good to eliminate this step.

[Paul Collins (pjdc)]

Looks like this is because the charm always writes the file to /tmp/grafana-plugin.tar.gz (unsafe usage of /tmp there!) and shutil.unpack_archive guesses based on the filename.

-----

2020-03-10 20:09:50 INFO config-changed File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.4/site-packages/charms/reactive/bus.py", line 181, in invoke
2020-03-10 20:09:50 INFO config-changed self._action(*args)
2020-03-10 20:09:50 INFO config-changed File "/var/lib/juju/agents/unit-grafana-0/charm/reactive/grafana.py", line 183, in install_plugins
2020-03-10 20:09:50 INFO config-changed shutil.unpack_archive(plugin_file, plugins_dir)
2020-03-10 20:09:50 INFO config-changed File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.4/shutil.py", line 961, in unpack_archive
2020-03-10 20:09:50 INFO config-changed func(filename, extract_dir, **kwargs)
2020-03-10 20:09:50 INFO config-changed File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.4/shutil.py", line 904, in _unpack_tarfile
2020-03-10 20:09:50 INFO config-changed "%s is not a compressed or uncompressed tar file" % filename)
2020-03-10 20:09:50 INFO config-changed shutil.ReadError: /tmp/grafana-plugin.tar.gz is not a compressed or uncompressed tar file

-----

Help on function unpack_archive in module shutil:

unpack_archive(filename, extract_dir=None, format=None)
[...]
    `format` is the archive format: one of "zip", "tar", "gztar", "bztar",
    or "xztar". Or any other registered format. If not provided,
    unpack_archive will use the filename extension and see if an unpacker
    was registered for that extension.
[...]