fritzcollectd: Recover from XMLSyntaxError in read callback

In rare cases reading from the FRITZ!Box can trigger XMLSyntaxError
exceptions (for example: 'Opening and ending tag mismatch: HR line 1
and BODY, line 1, column 180 (line 1)'. If this happens the connection
seems to be unusable and the error would happen also on subsequent
calls. Reinitialize the connection if this happens.

This has been reported for a FRITZ!Box 6490 (6.52) when the device is
remotely reset by Unitymedia.

See #12.

fritzcollectd.py

@@ -29,7 +29,7 @@
 
 import collectd  # pylint: disable=import-error
 
-__version__ = '0.5.0'
+__version__ = '0.5.1'
 
 
 CONFIGS = []
@@ -261,7 +261,12 @@ def callback_init():
 def callback_read():
     """ Read callback """
     for config in CONFIGS:
-        config.read()
+        try:
+            config.read()
+        except XMLSyntaxError:
+            collectd.warning('fritzcollectd: Invalid data received, '
+                             'attempting to reconnect')
+            config.init()
 
 
 def callback_shutdown():

test_fritzcollectd.py

@@ -281,6 +281,16 @@ def test_incorrect_password(fc_class_mock):
     MOCK.process(CollectdConfig({'Password': 'incorrect'}))
 
 
+@mock.patch('fritzconnection.FritzConnection', autospec=True)
+@with_setup(teardown=MOCK.reset_mock)
+def test_xmlsyntaxerror_in_read(fc_class_mock):
+    """ Simulate an XMLSyntaxError exception when reading data. """
+    fc_mock = FritzConnectionMock()
+    fc_class_mock.return_value = fc_mock
+    fc_mock.call_action.side_effect = [{0}, XMLSyntaxError(0, 0, 0, 0), {0}]
+    MOCK.process()
+
+
 # System tests that try to interact with a real hardware device.
 
 @nottest