qabro fails to launch and throws `json.decoder.JSONDecodeError` exception

[Pierre Equoy]

Summary
=======

Happens with both QABro 0.12 and 0.13.

Tested on a device with an Intel Atom CPU and 2GB RAM.

Sometimes, qabro fails to launch and throws `json.decoder.JSONDecodeError` exception:

$ qabro
Traceback (most recent call last):
  File "/snap/qabro/119/bin/qabro", line 33, in <module>
    sys.exit(load_entry_point('qabro==0.13', 'console_scripts', 'qabro')())
  File "/snap/qabro/119/lib/python3.6/site-packages/qabro/__init__.py", line 25, in main
    qabro_snap_info = [e for e in ss.get_snaps() if e['name'] == 'qabro'][0]
  File "/snap/qabro/119/lib/python3.6/site-packages/qabro/utils.py", line 54, in get_snaps
    json_resp = self.request(req)
  File "/snap/qabro/119/lib/python3.6/site-packages/qabro/utils.py", line 44, in request
    json_resp = self._get_json_response(raw_resp)
  File "/snap/qabro/119/lib/python3.6/site-packages/qabro/utils.py", line 36, in _get_json_response
    return json.loads(response[begin:end])
  File "/snap/qabro/119/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/snap/qabro/119/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/snap/qabro/119/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Sometimes, qabro can be launched without a problem.

Failure rate: 2/10

Initial investigation
=====================

qabro.utils.snapdsocket.request() seems to not get any raw response from time to time (raw_resp == ''), which leads to the json.decoder.JSONDecodeError exception seen above.

[Pierre Equoy (pieq)]

A better solution to communicate with snapd would be to use, as explained by jamesh on the snapcraft forum a long time ago[1].

It requires python3-gi and gir1.2-snapd-1 packages.

Then (see Snapd Gi doc for more info[2]):

import gi
gi.require_version('Snapd', '1')
from gi.repository import Snapd
c = Snapd.Client()
active_snaps_flag = Snapd.GetSnapsFlags(0)
for snap in c.get_snaps_sync(Snapd.GetSnapsFlags(0), None):
    print(snap.props.name, snap.props.devmode)

[1] https://forum.snapcraft.io/t/how-to-communicate-with-run-snapd-socket-using-python/6432/4
[2] https://lazka.github.io/pgi-docs/#Snapd-1