Avoid another MemoryError

telethon/tl/tlobject.py

@@ -186,6 +186,19 @@ class TLObject:
             return json.dumps(d, default=default, **kwargs)
 
     def __bytes__(self):
+        try:
+            return self._bytes()
+        except AttributeError:
+            # If a type is wrong (e.g. expected `TLObject` but `int` was
+            # provided) it will try to access `._bytes()`, which will fail
+            # with `AttributeError`. This occurs in fact because the type
+            # was wrong, so raise the correct error type.
+            raise TypeError('a TLObject was expected but found something else')
+
+    # Custom objects will call `(...)._bytes()` and not `bytes(...)` so that
+    # if the wrong type is used (e.g. `int`) we won't try allocating a huge
+    # amount of data, which would cause a `MemoryError`.
+    def _bytes(self):
         raise NotImplementedError
 
     @classmethod

telethon_generator/generators/tlobject.py

@@ -330,7 +330,7 @@ def _write_to_dict(tlobject, builder):
 
 
 def _write_to_bytes(tlobject, builder):
-    builder.writeln('def __bytes__(self):')
+    builder.writeln('def _bytes(self):')
 
     # Some objects require more than one flag parameter to be set
     # at the same time. In this case, add an assertion.
@@ -509,7 +509,7 @@ def _write_arg_to_bytes(builder, arg, args, name=None):
 
     else:
         # Else it may be a custom type
-        builder.write('bytes({})', name)
+        builder.write('{}._bytes()', name)
 
         # If the type is not boxed (i.e. starts with lowercase) we should
         # not serialize the constructor ID (so remove its first 4 bytes).

tests/telethon/test_utils.py

@@ -1,6 +1,8 @@
 import io
 import pathlib
 
+import pytest
+
 from telethon import utils
 from telethon.tl.types import (
     MessageMediaGame, Game, PhotoEmpty

tests/telethon/tl/test_serialization.py

@@ -0,0 +1,13 @@
+import pytest
+
+from telethon.tl import types, functions
+
+
+def test_nested_invalid_serialization():
+    large_long = 2**62
+    request = functions.account.SetPrivacyRequest(
+        key=types.InputPrivacyKeyChatInvite(),
+        rules=[types.InputPrivacyValueDisallowUsers(users=[large_long])]
+    )
+    with pytest.raises(TypeError):
+        bytes(request)