Prevent reconnection race after disconnect.

Don't print on error, emit an event instead to users can opt in (the
plugs can run out of TCP buffer space on occasion, resulting in
truncated JSON objects).

Author: jmattsson

src/powersensor_local/plug_listener.py

@@ -19,8 +19,11 @@ class PlugListener(AsyncEventEmitter):
       - ("disconnected") When a connection is dropped, be it intentional or not.
       - ("message",{...}) For each event message received from the plug. The
       plug's JSON message is decoded into a dict which is passed as the second
-      argument to the registered event handler(s). The event handlers must be
-      async.
+      argument to the registered event handler(s).
+      - ("malformed",line) If JSON decoding of a message fails. The raw line
+      is included (as a byte string).
+
+      The event handlers must be async.
     """
 
     def __init__(self, ip, port=49476):
@@ -67,6 +70,8 @@ async def _close_connection(self):
             await self.emit('disconnected')
 
     async def _do_connection(self, backoff = 0):
+        if self._disconnecting:
+            return
         if backoff < 9:
             backoff += 1
         try:
@@ -106,7 +111,7 @@ async def _process_line(self, reader, writer):
                 else:
                     await self.emit('message', message)
             except (json.decoder.JSONDecodeError) as ex:
-                print(f"JSON error {ex} from {data}")
+                await self.emit('malformed', data)
 
     async def _send_subscribe(self, writer):
         writer.write(b'subscribe(60)\n')