fix(proxy): drop every invalid metadata field before raising so failure hooks never see them

litellm/proxy/litellm_pre_call_utils.py

@@ -1604,10 +1604,13 @@ async def add_litellm_data_to_request(
             continue
         data.pop(_internal_key, None)
     _reject_url_valued_destinations(data)
-    for _metadata_field in ("metadata", "litellm_metadata"):
-        if (_raw_metadata := data.get(_metadata_field)) is not None:
-            data.pop(_metadata_field)
-            data[_metadata_field] = _normalized_metadata_object(_metadata_field, _raw_metadata)
+    _raw_metadata_by_field: Final = {
+        _metadata_field: data.pop(_metadata_field)
+        for _metadata_field in ("metadata", "litellm_metadata")
+        if data.get(_metadata_field) is not None
+    }
+    for _metadata_field, _raw_metadata in _raw_metadata_by_field.items():
+        data[_metadata_field] = _normalized_metadata_object(_metadata_field, _raw_metadata)
     # Strip spoofable auth metadata from user-supplied metadata dict
     _user_metadata = data.get("metadata")
     if isinstance(_user_metadata, dict):

tests/test_litellm/proxy/test_litellm_pre_call_utils.py

@@ -464,6 +464,28 @@ async def test_add_litellm_data_to_request_rejects_non_object_metadata(field, va
     assert field not in data
 
 
+@pytest.mark.asyncio
+async def test_add_litellm_data_to_request_removes_every_invalid_metadata_field_before_raising():
+    """When both fields are invalid, the raise for the first must not leave the
+    second invalid value in data, or failure-logging hooks that inspect the body
+    can crash on it and mask the 400 as a 500."""
+    data = {"input_file_id": "file-abc", "metadata": "abc", "litellm_metadata": "xyz"}
+
+    with pytest.raises(ProxyException) as exc_info:
+        await add_litellm_data_to_request(
+            data=data,
+            request=_batches_request_mock(),
+            user_api_key_dict=UserAPIKeyAuth(api_key="hashed-key"),
+            proxy_config=MagicMock(),
+            general_settings={},
+            version="test-version",
+        )
+
+    assert exc_info.value.param == "metadata"
+    assert "metadata" not in data
+    assert "litellm_metadata" not in data
+
+
 @pytest.mark.asyncio
 async def test_add_litellm_data_to_request_parses_json_object_string_litellm_metadata():
     data = {"input_file_id": "file-abc", "litellm_metadata": json.dumps({"cost_centre": "research"})}