fix(logging): keep partial logging payloads intact when nothing needs truncating

litellm/integrations/custom_logger.py

@@ -833,16 +833,12 @@ class CustomLogger:  # https://docs.litellm.ai/docs/observability/custom_callbac
         the original fields.
         """
         max_str_length: Final = 10_000
-        error_str, messages, response = (
-            self._truncate_field(field_value=standard_logging_object.get(field), max_length=max_str_length)
+        candidates: Final = {
+            field: self._truncate_field(field_value=standard_logging_object.get(field), max_length=max_str_length)
             for field in ("error_str", "messages", "response")
-        )
-        return {
-            **standard_logging_object,
-            "error_str": standard_logging_object["error_str"] if error_str is None else error_str,
-            "messages": standard_logging_object["messages"] if messages is None else messages,
-            "response": standard_logging_object["response"] if response is None else response,
         }
+        truncated_fields: Final = {field: text for field, text in candidates.items() if text is not None}
+        return {**standard_logging_object, **truncated_fields}
 
     def _truncate_field(self, field_value: object, max_length: int) -> str | None:
         """

tests/logging_callback_tests/test_standard_logging_payload.py

@@ -634,6 +634,14 @@ def test_truncate_standard_logging_payload():
     assert len(str(truncated["error_str"])) < 10_500
 
 
+def test_truncate_standard_logging_payload_keeps_a_partial_payload_intact():
+    """A payload built with only some of its fields comes back with exactly those keys and values"""
+    _custom_logger = CustomLogger()
+    partial_payload = StandardLoggingPayload(request_tags=["tag"], metadata=StandardLoggingMetadata())
+
+    assert _custom_logger.truncate_standard_logging_payload_content(partial_payload) == partial_payload
+
+
 def test_strip_trailing_slash():
     common_api_base = "https://api.test.com"
     assert (