From c5e969d5854bbb44d895fcf19563606aaecab07e Mon Sep 17 00:00:00 2001
From: Lonami Exo <totufals@hotmail.com>
Date: Sat, 13 Jan 2018 19:26:45 +0100
Subject: [PATCH] Add more useful logging on invalid packet length received

---
 telethon/network/connection.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/telethon/network/connection.py b/telethon/network/connection.py
index ff255d00..0adaf98a 100644
--- a/telethon/network/connection.py
+++ b/telethon/network/connection.py
@@ -2,6 +2,7 @@
 This module holds both the Connection class and the ConnectionMode enum,
 which specifies the protocol to be used by the Connection.
 """
+import logging
 import os
 import struct
 from datetime import timedelta
@@ -14,6 +15,8 @@ from ..crypto import AESModeCTR
 from ..extensions import TcpClient
 from ..errors import InvalidChecksumError
 
+__log__ = logging.getLogger(__name__)
+
 
 class ConnectionMode(Enum):
     """Represents which mode should be used to stabilise a connection.
@@ -181,6 +184,21 @@ class Connection:
         packet_len_seq = self.read(8)  # 4 and 4
         packet_len, seq = struct.unpack('<ii', packet_len_seq)
 
+        # Sometimes Telegram seems to send a packet length of 0 (12)
+        # and after that, just a single byte. Not sure what this is.
+        # TODO Figure out what this is, and if there's a better fix.
+        if packet_len <= 12:
+            __log__.error('Read invalid packet length %d, '
+                          'reading data left:', packet_len)
+            while True:
+                try:
+                    __log__.error(repr(self.read(1)))
+                except TimeoutError:
+                    break
+            # Connection reset and hope it's fixed after
+            self.conn.close()
+            raise ConnectionResetError()
+
         body = self.read(packet_len - 12)
         checksum = struct.unpack('<I', self.read(4))[0]