[Fix] Convert TypeError to BadRequestError for missing/invalid parameters

[hula-la]

Title

Convert TypeError to BadRequestError for missing/invalid parameters

Relevant issues

Fixes #16993

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• I have added a screenshot of my new test passing locally
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🐛 Bug Fix

Changes

Problem

When calling LiteLLM API functions with missing or invalid parameters, error handling is inconsistent:

1. Core Library: TypeError raised instead of BadRequestError when parameters completely omitted
2. Proxy Server: HTTP 500 returned instead of HTTP 400 when wrong parameter names used

Solution

Added TypeError to BadRequestError conversion at two layers:

1. Core Library (litellm/utils.py)

• Added TypeError handling in @client decorator (both sync and async)
• Extracts missing parameter name using regex: r"missing (\d+ )?required positional argument[s]?:? '?([^']+)'?"
• Fixed KeyError when wrong parameter names used (kwargs.get instead of kwargs[])
• Raises BadRequestError with HTTP 400 status code and clear error message

2. Proxy Layer (litellm/proxy/route_llm_request.py)

• Added TypeError handling in route_request function
• Wraps _route_request_impl in try-except block
• Prevents TypeError from bubbling up as HTTP 500 error
• Converts to BadRequestError with HTTP 400 status code

3. Test Coverage

Added comprehensive test suite:

• Core library tests (tests/test_litellm/test_parameter_validation_error.py): 5 test cases

  • Missing required parameters (model, input)
  • Wrong parameter names (messages vs input)
  • HTTP 400 status code validation

• Proxy tests (tests/proxy_unit_tests/test_proxy_parameter_validation.py): 6 test cases

  • End-to-end testing through proxy server
  • Missing model parameter
  • Wrong parameter names causing HTTP 500
  • Error response format validation

Test Results

Core Library Tests - AFTER Implementation:

tests/test_litellm/test_parameter_validation_error.py::test_bad_request_error_has_400_status_code PASSED
tests/test_litellm/test_parameter_validation_error.py::test_missing_required_parameter_aresponses PASSED
tests/test_litellm/test_parameter_validation_error.py::test_missing_required_parameter_async PASSED
tests/test_litellm/test_parameter_validation_error.py::test_missing_required_parameter_sync PASSED
tests/test_litellm/test_parameter_validation_error.py::test_responses_api_wrong_parameter PASSED

======================== 5 passed, 1 warning in 0.09s =========================

Proxy Tests - AFTER Implementation:

tests/proxy_unit_tests/test_proxy_parameter_validation.py::test_proxy_acompletion_missing_model PASSED
tests/proxy_unit_tests/test_proxy_parameter_validation.py::test_proxy_chat_completion_missing_messages PASSED
tests/proxy_unit_tests/test_proxy_parameter_validation.py::test_proxy_chat_completion_missing_model PASSED
tests/proxy_unit_tests/test_proxy_parameter_validation.py::test_proxy_error_response_format PASSED
tests/proxy_unit_tests/test_proxy_parameter_validation.py::test_proxy_responses_api_missing_model PASSED
tests/proxy_unit_tests/test_proxy_parameter_validation.py::test_proxy_responses_api_wrong_parameter PASSED

======================== 6 passed, 3 warnings in 5.48s =========================

Impact

• ✅ API consumers can distinguish between client (4xx) and server (5xx) errors
• ✅ Follows HTTP status code conventions
• ✅ Clear error messages indicating missing parameters
• ✅ Prevents confusing HTTP 500 errors for user mistakes
• ✅ No breaking changes - only improves error handling

Files Changed

• litellm/utils.py: Added TypeError handling in @client decorator
• litellm/proxy/route_llm_request.py: Added TypeError handling in route_request
• tests/test_litellm/test_parameter_validation_error.py: New test file (5 tests)
• tests/proxy_unit_tests/test_proxy_parameter_validation.py: New test file (6 tests)

[vercel]

@hula-la is attempting to deploy a commit to the CLERKIEAI Team on Vercel.

A member of the Team first needs to authorize it.

[krrishdholakia]

if this is already fixed in utils.py why have it again here?

[hula-la]

@krrishdholakia
Due to the code below, certain requests(ex. aresponses), wrap client method (ex. litellm.aresponses), so the @client logic is executed.

# router.py
        self.aresponses = self.factory_function(
            litellm.aresponses, call_type="aresponses"
        )

In contrast, requests like acompletion go directly to methods implemented as shown below, so they do not go through the validation performed by the @client wrapping.

# router.py
    async def acompletion(
        self,
        model: str,
        messages: List[AllMessageValues],
        stream: bool = False,
        **kwargs,
    ):
        try:
         ...