Fix #61 freeze/broken pipe after some idle time

When keeping long-lived websocket connection, after some idle time
the connection will go into a bad state. Calling send() cause no
response at first and then broken pipe error is raised on the
subsequent call. The cause is that there is no designated thread
to keep the socket alive.

samsungctl/remote_websocket.py

@@ -1,8 +1,9 @@
 import base64
 import json
 import logging
-import socket
+import threading
 import time
+import select
 
 from . import exceptions
 
@@ -26,9 +27,12 @@ def __init__(self, config):
                                 self._serialize_string(config["name"]))
 
         self.connection = websocket.create_connection(url, config["timeout"])
-
         self._read_response()
 
+        ## Keep long-lived connection alive by spawning a thread
+        thread = threading.Thread(target=self._keep_alive, daemon=True)
+        thread.start()
+
     def __enter__(self):
         return self
 
@@ -73,6 +77,18 @@ def _read_response(self):
 
         logging.debug("Access granted.")
 
+    def _keep_alive(self):
+        while True:
+            r, w, e = select.select((self.connection.sock, ), (), ())
+            if not (self.connection and self.connection.connected):
+                # stop if connection was already closed
+                # while blocking in select function above
+                logging.debug("keep alive thread terminating.")
+                return
+            if r:
+                _ = self.connection.recv()
+                logging.debug("data received.")
+
     @staticmethod
     def _serialize_string(string):
         if isinstance(string, str):