Fix runaway KISS driver on failed connnection

This patch fixes an issue when the KISS connection fails to start
and or goes away during the lifetime of the active connection.
Aprsd would runaway in a tight loop eating 100% cpu.  We now detect
when the underlying asyncio connection has failed and raise, which
induces a sleep in the consumer to try again.

aprsd/client/drivers/kiss.py

@@ -18,12 +18,13 @@ class KISS3Client:
 
     # date for last time we heard from the server
     aprsd_keepalive = datetime.datetime.now()
+    _connected = False
 
     def __init__(self):
         self.setup()
 
     def is_alive(self):
-        return True
+        return self._connected
 
     def setup(self):
         # we can be TCP kiss or Serial kiss
@@ -56,17 +57,33 @@ class KISS3Client:
             self.path = CONF.kiss_tcp.path
 
         LOG.debug('Starting KISS interface connection')
-        self.kiss.start()
+        try:
+            self.kiss.start()
+            if self.kiss.protocol.transport.is_closing():
+                LOG.warning('KISS transport is closing, not setting consumer callback')
+                self._connected = False
+            else:
+                self._connected = True
+        except Exception:
+            LOG.error('Failed to start KISS interface.')
+            self._connected = False
 
     @trace.trace
     def stop(self):
+        if not self._connected:
+            # do nothing since we aren't connected
+            return
+
         try:
             self.kiss.stop()
             self.kiss.loop.call_soon_threadsafe(
                 self.kiss.protocol.transport.close,
             )
-        except Exception as ex:
-            LOG.exception(ex)
+        except Exception:
+            LOG.error('Failed to stop KISS interface.')
+
+    def close(self):
+        self.stop()
 
     def set_filter(self, filter):
         # This does nothing right now.
@@ -86,8 +103,14 @@ class KISS3Client:
             LOG.exception(ex)
 
     def consumer(self, callback):
+        if not self._connected:
+            raise Exception('KISS transport is not connected')
+
         self._parse_callback = callback
-        self.kiss.read(callback=self.parse_frame, min_frames=None)
+        if not self.kiss.protocol.transport.is_closing():
+            self.kiss.read(callback=self.parse_frame, min_frames=1)
+        else:
+            self._connected = False
 
     def send(self, packet):
         """Send an APRS Message object."""

aprsd/client/kiss.py

@@ -140,3 +140,4 @@ class KISSClient(base.APRSClient):
         except Exception as ex:
             LOG.error(f'Consumer failed {ex}')
             LOG.error(ex)
+            raise ex