Add DiscordWebSocket.latency to measure discord heartbeat latency.

discord/gateway.py

@@ -63,6 +63,7 @@ class KeepAliveHandler(threading.Thread):
         self.msg = 'Keeping websocket alive with sequence %s.'
         self._stop_ev = threading.Event()
         self._last_ack = time.time()
+        self._last_send = time.time()
 
     def run(self):
         while not self._stop_ev.wait(self.interval):
@@ -88,6 +89,8 @@ class KeepAliveHandler(threading.Thread):
                 f.result()
             except Exception:
                 self.stop()
+            else:
+                self._last_send = time.time()
 
     def get_payload(self):
         return {
@@ -408,6 +411,12 @@ class DiscordWebSocket(websockets.client.WebSocketClientProtocol):
         for index in reversed(removed):
             del self._dispatch_listeners[index]
 
+    @property
+    def latency(self):
+        """float: Measures latency between a HEARTBEAT and a HEARTBEAT_ACK in seconds."""
+        heartbeat = self._keep_alive
+        return float('inf') if heartbeat is None else heartbeat._last_ack - heartbeat._last_send
+
     def _can_handle_close(self, code):
         return code not in (1000, 4004, 4010, 4011)