From d3efc8f57d1f49b670e4234cb575bae29eccd098 Mon Sep 17 00:00:00 2001
From: Lonami Exo <totufals@hotmail.com>
Date: Wed, 8 Aug 2018 12:04:20 +0200
Subject: [PATCH] Better logging for packing errors

https://github.com/expectocode/telegram-export/issues/76
---
 telethon/tl/core/tlmessage.py | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/telethon/tl/core/tlmessage.py b/telethon/tl/core/tlmessage.py
index 5d032c7c..e4284eaf 100644
--- a/telethon/tl/core/tlmessage.py
+++ b/telethon/tl/core/tlmessage.py
@@ -1,10 +1,13 @@
 import asyncio
+import logging
 import struct
 
 from .gzippacked import GzipPacked
 from .. import TLObject
 from ..functions import InvokeAfterMsgRequest
 
+__log__ = logging.getLogger(__name__)
+
 
 class TLMessage(TLObject):
     """
@@ -48,11 +51,17 @@ class TLMessage(TLObject):
         if not out:
             self._body = struct.pack('<qi', msg_id, seq_no)
         else:
-            if self.after_id is None:
-                body = GzipPacked.gzip_if_smaller(self.obj)
-            else:
-                body = GzipPacked.gzip_if_smaller(
-                    InvokeAfterMsgRequest(self.after_id, self.obj))
+            try:
+                if self.after_id is None:
+                    body = GzipPacked.gzip_if_smaller(self.obj)
+                else:
+                    body = GzipPacked.gzip_if_smaller(
+                        InvokeAfterMsgRequest(self.after_id, self.obj))
+            except Exception:
+                # struct.pack doesn't give a lot of information about
+                # why it may fail so log the exception AND the object
+                __log__.exception('Failed to pack %s', self.obj)
+                raise
 
             self._body = struct.pack('<qii', msg_id, seq_no, len(body)) + body