fix(decisions): log non-UTF-8 bytes as base64 so the request reaches validation and gets a 400 (#47564)

Co-authored-by: devin-ai-integration[bot] <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Backport of #47564 to stable/1.106.x
Cherry-picked from ce63f48ed2 (main)

litellm/decisions/call.py

@@ -418,7 +418,7 @@ def _jsonable_fallback(value: object) -> object:
 
 def _logged_request_message(caller_request: object) -> ChatCompletionUserMessage:
     caller_fields: Final = _LOGGED_FIELDS_ADAPTER.validate_python(
-        to_jsonable_python(caller_request, fallback=_jsonable_fallback)
+        to_jsonable_python(caller_request, fallback=_jsonable_fallback, bytes_mode="base64")
     )
     sent_fields: Final = json.dumps(
         dict((name, value) for name, value in caller_fields.items() if value not in (None, [], {}))

tests/unit/decisions/test_call.py

@@ -1,3 +1,4 @@
+import base64
 import json
 from collections.abc import Mapping
 from datetime import datetime, timezone
@@ -112,3 +113,22 @@ def test_decisions_request_is_logged_even_when_its_questions_fail_validation():
 
     logged: Final = _logged_request(logging_obj)
     assert logged["questions"][0]["instructions"] == QUESTION_TEXT
+
+
+def test_non_utf8_bytes_in_the_request_are_logged_and_rejected_with_a_400():
+    logging_obj: Final = _logging_obj("adecisions")
+    raw_input: Final = b"\xff\xfe not utf-8"
+
+    with pytest.raises(litellm.BadRequestError):
+        _prepare_decisions_call(
+            **CONNECTION,
+            decision_input=raw_input,
+            questions=[{"type": "predicate", "instructions": QUESTION_TEXT}],
+            audio=None,
+            videos=None,
+            kwargs={"litellm_logging_obj": logging_obj},
+        )
+
+    logged: Final = _logged_request(logging_obj)
+    assert base64.urlsafe_b64decode(logged["input"]) == raw_input
+    assert logged["questions"][0]["instructions"] == QUESTION_TEXT