relation-get permission denied

[Linda Guo]

when grafana has multiple dashboards relations, relation-get would return 'permission denied' if it's running against the wrong relation ID.

$ juju run -u grafana/0 "relation-ids dashboards"
dashboards:197
dashboards:198
dashboards:206

$ juju run -u grafana/0 'relation-get --format=json -r dashboards:197 dashboard rabbitmq-server/0'
ERROR permission denied

----------------------------------

2021-07-15 01:02:58 INFO juju-log dashboards:201: Invoking reactive handler: reactive/grafana.py:1187:dashboards_joined
2021-07-15 01:02:58 INFO juju-log dashboards:201: hook dashboards-relation-joined triggered
2021-07-15 01:02:58 WARNING dashboards-relation-joined ERROR permission denied
2021-07-15 01:02:58 ERROR juju-log dashboards:201: Hook error:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.8/site-packages/charms/reactive/__init__.py", line 74, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.8/site-packages/charms/reactive/bus.py", line 379, in dispatch
    _invoke(hook_handlers)
  File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.8/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.8/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-grafana-0/charm/reactive/grafana.py", line 1198, in dashboards_joined
    dashboard_str = hookenv.relation_get(
  File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.8/site-packages/charmhelpers/core/hookenv.py", line 93, in wrapper
    res = func(*args, **kwargs)
  File "/var/lib/juju/agents/unit-grafana-0/.venv/lib/python3.8/site-packages/charmhelpers/core/hookenv.py", line 486, in relation_get
    return json.loads(subprocess.check_output(_args).decode('UTF-8'))
  File "/usr/lib/python3.8/subprocess.py", line 411, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/usr/lib/python3.8/subprocess.py", line 512, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['relation-get', '--format=json', '-r', 'dashboards:197', 'dashboard', 'remote-6190afcfdf1541ae89ca692b0e1b57ba/4']' returned non-zero exit status 1.

[Linda Guo (lihuiguo)]

In dashboards_joined, it should get relation ID from hookenv.relation_id instead of loop through all relations.