events: add qubesd reconnection support

If connection is interrupted (for example qubesd restart), attempt to
reconnect.

qubesmgmt/config.py

@@ -24,3 +24,4 @@
 QUBESD_SOCKET = '/var/run/qubesd.sock'
 QREXEC_CLIENT = '/usr/lib/qubes/qrexec-client'
 QREXEC_CLIENT_VM = '/usr/bin/qrexec-client-vm'
+QUBESD_RECONNECT_DELAY = 1.0

qubesmgmt/events/__init__.py

@@ -102,7 +102,7 @@ class EventsDispatcher(object):
         return reader, cleanup_func
 
     @asyncio.coroutine
-    def listen_for_events(self, vm=None):
+    def listen_for_events(self, vm=None, reconnect=True):
         '''
         Listen for events and call appropriate handlers.
         This function do not exit until manually terminated.
@@ -111,40 +111,67 @@ class EventsDispatcher(object):
 
         :param vm: Listen for events only for this VM, use None to listen for
         events about all VMs and not related to any particular VM.
-        :return: None
+        :param reconnect: should reconnect to qubesd if connection is
+        interrupted?
+        :rtype: None
+        '''
+        while True:
+            try:
+                yield from self._listen_for_events(vm)
+            except ConnectionRefusedError:
+                pass
+            if not reconnect:
+                break
+            self.app.log.warning(
+                'Connection to qubesd terminated, reconnecting in {} '
+                'seconds'.format(qubesmgmt.config.QUBESD_RECONNECT_DELAY))
+            # avoid busy-loop if qubesd is dead
+            yield from asyncio.sleep(qubesmgmt.config.QUBESD_RECONNECT_DELAY)
+
+    @asyncio.coroutine
+    def _listen_for_events(self, vm=None):
+        '''
+        Listen for events and call appropriate handlers.
+        This function do not exit until manually terminated.
+
+        This is coroutine.
+
+        :param vm: Listen for events only for this VM, use None to listen for
+        events about all VMs and not related to any particular VM.
+        :return: True if any event was received, otherwise False
+        :rtype: bool
         '''
 
+        reader, cleanup_func = yield from self._get_events_reader(vm)
         try:
-            reader, cleanup_func = yield from self._get_events_reader(vm)
-        except asyncio.CancelledError:
-            return
+            some_event_received = False
+            while not reader.at_eof():
+                try:
+                    event_data = yield from reader.readuntil(b'\0\0')
+                    if event_data == b'1\0\0':
+                        # event with non-VM subject contains \0\0 inside of
+                        # event, need to receive rest of the data
+                        event_data += yield from reader.readuntil(b'\0\0')
+                except asyncio.IncompleteReadError as err:
+                    if err.partial == b'':
+                        break
+                    else:
+                        raise
 
-        while not reader.at_eof():
-            try:
-                event_data = yield from reader.readuntil(b'\0\0')
-                if event_data == b'1\0\0':
-                    # event with non-VM subject contains \0\0 inside of
-                    # event, need to receive rest of the data
-                    event_data += yield from reader.readuntil(b'\0\0')
-            except asyncio.CancelledError:
-                break
-            except asyncio.IncompleteReadError as err:
-                if err.partial == b'':
-                    break
-                else:
-                    raise
+                if not event_data.startswith(b'1\0'):
+                    raise qubesmgmt.exc.QubesDaemonCommunicationError(
+                        'Non-event received on events connection: '
+                        + repr(event_data))
+                event_data = event_data.decode('utf-8')
+                _, subject, event, *kwargs = event_data.split('\0')
+                # convert list to dict, remove last empty entry
+                kwargs = dict(zip(kwargs[:-2:2], kwargs[1:-2:2]))
+                self.handle(subject, event, **kwargs)
 
-            if not event_data.startswith(b'1\0'):
-                raise qubesmgmt.exc.QubesDaemonCommunicationError(
-                    'Non-event received on events connection: '
-                    + repr(event_data))
-            event_data = event_data.decode('utf-8')
-            _, subject, event, *kwargs = event_data.split('\0')
-            # convert list to dict, remove last empty entry
-            kwargs = dict(zip(kwargs[:-2:2], kwargs[1:-2:2]))
-            self.handle(subject, event, **kwargs)
-
-        cleanup_func()
+                some_event_received = True
+        finally:
+            cleanup_func()
+        return some_event_received
 
     def handle(self, subject, event, **kwargs):
         '''Call handlers for given event'''

qubesmgmt/tests/events.py

@@ -111,7 +111,8 @@ class TC_00_Events(qubesmgmt.tests.QubesTestCase):
             b'1\0some-vm\0other-event\0\0',
         ]
         asyncio.ensure_future(self.send_events(stream, events))
-        loop.run_until_complete(self.dispatcher.listen_for_events())
+        loop.run_until_complete(self.dispatcher.listen_for_events(
+            reconnect=False))
         self.assertEqual(handler.mock_calls, [
             unittest.mock.call(None, 'some-event', arg1='value1'),
             unittest.mock.call(

qubesmgmt/tools/qvm_start_gui.py

@@ -209,7 +209,10 @@ def main(args=None):
             loop.add_signal_handler(getattr(signal, signame),
                 events_listener.cancel)  # pylint: disable=no-member
 
-        loop.run_until_complete(events_listener)
+        try:
+            loop.run_until_complete(events_listener)
+        except asyncio.CancelledError:
+            pass
         loop.stop()
         loop.run_forever()
         loop.close()