From e24dd3ad751b32eddbea7b8ea6e15083f385a18e Mon Sep 17 00:00:00 2001
From: Lonami Exo <totufals@hotmail.com>
Date: Wed, 7 Aug 2019 23:43:31 +0200
Subject: [PATCH] Prevent double-connect causing double-reads later

Which leads to "RuntimeError: readexactly() called while another
coroutine is already waiting for incoming data" being raised,
and causing everything to break or halt.
---
 telethon/client/telegrambaseclient.py |  7 +++++--
 telethon/network/mtprotosender.py     | 15 +++++++++------
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/telethon/client/telegrambaseclient.py b/telethon/client/telegrambaseclient.py
index 1d09f3ad..6d09344d 100644
--- a/telethon/client/telegrambaseclient.py
+++ b/telethon/client/telegrambaseclient.py
@@ -405,14 +405,17 @@ class TelegramBaseClient(abc.ABC):
                 except OSError:
                     print('Failed to connect')
         """
-        await self._sender.connect(self._connection(
+        if not await self._sender.connect(self._connection(
             self.session.server_address,
             self.session.port,
             self.session.dc_id,
             loop=self._loop,
             loggers=self._log,
             proxy=self._proxy
-        ))
+        )):
+            # We don't want to init or modify anything if we were already connected
+            return
+
         self.session.auth_key = self._sender.auth_key
         self.session.save()
 
diff --git a/telethon/network/mtprotosender.py b/telethon/network/mtprotosender.py
index 0da0ad69..c83240c0 100644
--- a/telethon/network/mtprotosender.py
+++ b/telethon/network/mtprotosender.py
@@ -54,6 +54,7 @@ class MTProtoSender:
         self._auth_key_callback = auth_key_callback
         self._update_callback = update_callback
         self._auto_reconnect_callback = auto_reconnect_callback
+        self._connect_lock = asyncio.Lock(loop=loop)
 
         # Whether the user has explicitly connected or disconnected.
         #
@@ -114,13 +115,15 @@ class MTProtoSender:
         """
         Connects to the specified given connection using the given auth key.
         """
-        if self._user_connected:
-            self._log.info('User is already connected!')
-            return
+        async with self._connect_lock:
+            if self._user_connected:
+                self._log.info('User is already connected!')
+                return False
 
-        self._connection = connection
-        await self._connect()
-        self._user_connected = True
+            self._connection = connection
+            await self._connect()
+            self._user_connected = True
+            return True
 
     def is_connected(self):
         return self._user_connected