Ignore invalid utf-8 strings (closes #49)

telethon/utils/binary_reader.py

@@ -89,7 +89,19 @@ class BinaryReader:
 
     def tgread_string(self):
         """Reads a Telegram-encoded string"""
-        return str(self.tgread_bytes(), encoding='utf-8')
+        return self._decode_string(self.tgread_bytes())
+
+    @staticmethod
+    def _decode_string(encoded):
+        # Workaround for issues #49 and #67
+        # Sometimes an invalid utf-8 string is received. We can just remove
+        # the offending parts and replace them with a different solution.
+        # There aren't many other options, besides crashing.
+        try:
+            return str(encoded, encoding='utf-8')
+        except UnicodeDecodeError as e:
+            fixed = encoded[:e.start] + encoded[e.end:]
+            return BinaryReader._decode_string(fixed)
 
     def tgread_bool(self):
         """Reads a Telegram boolean value"""