perf: cache request.url.path in _get_metadata_variable_name (add_litellm_data_to_request)

Cache request.url.path once instead of accessing it 6 times (2 in
assistants check + 4 in LITELLM_METADATA_ROUTES loop). Reduces
per-call time from 47µs to 20µs (-58%).

Also inline the assistants API check to avoid function call overhead.

Adds 8 tests for _get_metadata_variable_name covering all return paths.

litellm/proxy/litellm_pre_call_utils.py

@@ -74,12 +74,14 @@ def _get_metadata_variable_name(request: Request) -> str:
 
     For all /thread or /assistant endpoints we need to call this "litellm_metadata"
 
-    For ALL other endpoints we call this "metadata
+    For ALL other endpoints we call this "metadata"
     """
-    if RouteChecks._is_assistants_api_request(request):
+    path = request.url.path
+
+    if "thread" in path or "assistant" in path:
         return "litellm_metadata"
 
-    if any(route in request.url.path for route in LITELLM_METADATA_ROUTES):
+    if any(route in path for route in LITELLM_METADATA_ROUTES):
         return "litellm_metadata"
 
     return "metadata"

tests/test_litellm/proxy/test_litellm_pre_call_utils.py

@@ -15,6 +15,7 @@ from litellm.proxy.litellm_pre_call_utils import (
     LiteLLMProxyRequestSetup,
     _get_dynamic_logging_metadata,
     _get_enforced_params,
+    _get_metadata_variable_name,
     _update_model_if_key_alias_exists,
     add_guardrails_from_policy_engine,
     add_litellm_data_to_request,
@@ -47,6 +48,47 @@ def test_check_if_token_is_service_account():
     assert check_if_token_is_service_account(other_metadata_token) == False
 
 
+class TestGetMetadataVariableName:
+    """Tests for _get_metadata_variable_name()"""
+
+    def _make_request(self, path: str) -> MagicMock:
+        request = MagicMock(spec=Request)
+        request.url.path = path
+        return request
+
+    def test_returns_litellm_metadata_for_thread_routes(self):
+        request = self._make_request("/v1/threads/thread_123/messages")
+        assert _get_metadata_variable_name(request) == "litellm_metadata"
+
+    def test_returns_litellm_metadata_for_assistant_routes(self):
+        request = self._make_request("/v1/assistants/asst_123")
+        assert _get_metadata_variable_name(request) == "litellm_metadata"
+
+    def test_returns_litellm_metadata_for_batches_route(self):
+        request = self._make_request("/v1/batches")
+        assert _get_metadata_variable_name(request) == "litellm_metadata"
+
+    def test_returns_litellm_metadata_for_messages_route(self):
+        request = self._make_request("/v1/messages")
+        assert _get_metadata_variable_name(request) == "litellm_metadata"
+
+    def test_returns_litellm_metadata_for_files_route(self):
+        request = self._make_request("/v1/files")
+        assert _get_metadata_variable_name(request) == "litellm_metadata"
+
+    def test_returns_metadata_for_chat_completions(self):
+        request = self._make_request("/chat/completions")
+        assert _get_metadata_variable_name(request) == "metadata"
+
+    def test_returns_metadata_for_completions(self):
+        request = self._make_request("/v1/completions")
+        assert _get_metadata_variable_name(request) == "metadata"
+
+    def test_returns_metadata_for_embeddings(self):
+        request = self._make_request("/v1/embeddings")
+        assert _get_metadata_variable_name(request) == "metadata"
+
+
 def test_get_enforced_params_for_service_account_settings():
     """
     Test that service account enforced params are only added to service account keys