Start reconnect if a second ping is sent without a pong for the first

May help with #1564.

telethon/client/updates.py

@@ -348,7 +348,7 @@ async def _update_loop(self: 'TelegramClient'):
             # We also don't really care about their result.
             # Just send them periodically.
             try:
-                self._sender.send(functions.PingRequest(rnd()))
+                self._sender._keepalive_ping(rnd())
             except (ConnectionError, asyncio.CancelledError):
                 return
 
@@ -399,7 +399,7 @@ async def _dispatch_update(self: 'TelegramClient', update, others, channel_id, p
                     pass
                 except ValueError:
                     # There is a chance that GetFullChannelRequest and GetDifferenceRequest
-                    # inside the _get_difference() function will end up with 
+                    # inside the _get_difference() function will end up with
                     # ValueError("Request was unsuccessful N time(s)") for whatever reasons.
                     pass
 

telethon/network/mtprotosender.py

@@ -16,6 +16,7 @@
 from ..extensions import BinaryReader
 from ..tl.core import RpcResult, MessageContainer, GzipPacked
 from ..tl.functions.auth import LogOutRequest
+from ..tl.functions import PingRequest
 from ..tl.types import (
     MsgsAck, Pong, BadServerSalt, BadMsgNotification, FutureSalts,
     MsgNewDetailedInfo, NewSessionCreated, MsgDetailedInfo, MsgsStateReq,
@@ -55,6 +56,7 @@ def __init__(self, auth_key, *, loggers,
         self._update_callback = update_callback
         self._auto_reconnect_callback = auto_reconnect_callback
         self._connect_lock = asyncio.Lock()
+        self._ping = None
 
         # Whether the user has explicitly connected or disconnected.
         #
@@ -217,7 +219,7 @@ async def _connect(self):
         self._log.info('Connecting to %s...', self._connection)
 
         connected = False
-        
+
         for attempt in retry_range(self._retries):
             if not connected:
                 connected = await self._try_connect(attempt)
@@ -358,7 +360,7 @@ async def _reconnect(self, last_error):
         self._state.reset()
 
         retries = self._retries if self._auto_reconnect else 0
-        
+
         attempt = 0
         ok = True
         # We're already "retrying" to connect, so we don't want to force retries
@@ -419,6 +421,18 @@ def _start_reconnect(self, error):
             self._reconnecting = True
             asyncio.get_event_loop().create_task(self._reconnect(error))
 
+    def _keepalive_ping(self, rnd_id):
+        """
+        Send a keep-alive ping. If a pong for the last ping was not received
+        yet, this means we're probably not connected.
+        """
+        # TODO this is ugly, update loop shouldn't worry about this, sender should
+        if self._ping is None:
+            self._ping = rnd_id
+            self.send(PingRequest(rnd_id))
+        else:
+            self._start_reconnect(None)
+
     # Loops
 
     async def _send_loop(self):
@@ -641,6 +655,9 @@ async def _handle_pong(self, message):
         """
         pong = message.obj
         self._log.debug('Handling pong for message %d', pong.msg_id)
+        if self._ping == pong.ping_id:
+            self._ping = None
+
         state = self._pending_state.pop(pong.msg_id, None)
         if state:
             state.future.set_result(pong)