fix: add custom_body parameter to endpoint_func in create_pass_through_route

litellm/proxy/pass_through_endpoints/pass_through_endpoints.py

@@ -1099,6 +1099,7 @@ async def endpoint_func(  # type: ignore
             fastapi_response: Response,
             user_api_key_dict: UserAPIKeyAuth = Depends(user_api_key_auth),
             subpath: str = "",  # captures sub-paths when include_subpath=True
+            custom_body: Optional[dict] = None,  # accepted for signature compatibility with URL-based path; not forwarded because chat_completion_pass_through_endpoint does not support it
         ):
             return await chat_completion_pass_through_endpoint(
                 fastapi_response=fastapi_response,
@@ -1115,6 +1116,7 @@ async def endpoint_func(  # type: ignore
             fastapi_response: Response,
             user_api_key_dict: UserAPIKeyAuth = Depends(user_api_key_auth),
             subpath: str = "",  # captures sub-paths when include_subpath=True
+            custom_body: Optional[dict] = None,
         ):
             from litellm.proxy.pass_through_endpoints.pass_through_endpoints import (
                 InitPassThroughEndpointHelpers,
@@ -1189,11 +1191,16 @@ async def endpoint_func(  # type: ignore
             )
             if query_params:
                 final_query_params.update(query_params)
-            final_custom_body = (
-                custom_body_data
-                if isinstance(custom_body_data, dict) or custom_body_data is None
-                else None
-            )
+            # When a caller (e.g. bedrock_proxy_route) supplies a pre-built
+            # body, use it instead of the body parsed from the raw request.
+            if custom_body is not None:
+                final_custom_body = custom_body
+            else:
+                final_custom_body = (
+                    custom_body_data
+                    if isinstance(custom_body_data, dict) or custom_body_data is None
+                    else None
+                )
 
             return await pass_through_request(  # type: ignore
                 request=request,

tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py

@@ -1960,6 +1960,143 @@ async def test_add_litellm_data_to_request_adds_headers_to_metadata():
     assert "headers" in result["proxy_server_request"]
 
 
+@pytest.mark.asyncio
+async def test_create_pass_through_route_custom_body_url_target():
+    """
+    Test that the URL-based endpoint_func created by create_pass_through_route
+    accepts a custom_body parameter and forwards it to pass_through_request,
+    taking precedence over the request-parsed body.
+
+    This verifies the fix for issue #16999 where bedrock_proxy_route passes
+    custom_body=data to the endpoint function, which previously crashed with:
+    TypeError: endpoint_func() got an unexpected keyword argument 'custom_body'
+    """
+    from litellm.proxy.pass_through_endpoints.pass_through_endpoints import (
+        create_pass_through_route,
+    )
+
+    unique_path = "/test/path/unique/custom_body_url"
+    endpoint_func = create_pass_through_route(
+        endpoint=unique_path,
+        target="https://bedrock-agent-runtime.us-east-1.amazonaws.com",
+        custom_headers={"Content-Type": "application/json"},
+        _forward_headers=True,
+    )
+
+    with patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints.pass_through_request"
+    ) as mock_pass_through, patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints.InitPassThroughEndpointHelpers.is_registered_pass_through_route"
+    ) as mock_is_registered, patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints.InitPassThroughEndpointHelpers.get_registered_pass_through_route"
+    ) as mock_get_registered, patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints._parse_request_data_by_content_type"
+    ) as mock_parse_request:
+        mock_pass_through.return_value = MagicMock()
+        mock_is_registered.return_value = True
+        mock_get_registered.return_value = None
+        # Simulate the request parser returning a different body
+        mock_parse_request.return_value = (
+            {},  # query_params_data
+            {"parsed_from_request": True},  # custom_body_data (from request)
+            None,  # file_data
+            False,  # stream
+        )
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.url = MagicMock()
+        mock_request.url.path = unique_path
+        mock_request.path_params = {}
+        mock_request.query_params = QueryParams({})
+
+        mock_user_api_key_dict = MagicMock()
+        mock_user_api_key_dict.api_key = "test-key"
+
+        # The caller-supplied body (e.g. from bedrock_proxy_route)
+        bedrock_body = {
+            "retrievalQuery": {"text": "What is in the knowledge base?"},
+        }
+
+        # Call endpoint_func with custom_body — this is the call that
+        # used to crash with TypeError before the fix
+        await endpoint_func(
+            request=mock_request,
+            fastapi_response=MagicMock(),
+            user_api_key_dict=mock_user_api_key_dict,
+            custom_body=bedrock_body,
+        )
+
+        mock_pass_through.assert_called_once()
+        call_kwargs = mock_pass_through.call_args[1]
+
+        # The critical assertion: custom_body takes precedence over
+        # the body parsed from the raw request
+        assert call_kwargs["custom_body"] == bedrock_body
+
+
+@pytest.mark.asyncio
+async def test_create_pass_through_route_no_custom_body_falls_back():
+    """
+    Test that the URL-based endpoint_func falls back to the request-parsed body
+    when custom_body is not provided.
+
+    This ensures the default pass-through behavior is preserved — only the
+    Bedrock proxy route (and similar callers) supply a pre-built body.
+    """
+    from litellm.proxy.pass_through_endpoints.pass_through_endpoints import (
+        create_pass_through_route,
+    )
+
+    unique_path = "/test/path/unique/no_custom_body"
+    endpoint_func = create_pass_through_route(
+        endpoint=unique_path,
+        target="http://example.com/api",
+        custom_headers={},
+    )
+
+    with patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints.pass_through_request"
+    ) as mock_pass_through, patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints.InitPassThroughEndpointHelpers.is_registered_pass_through_route"
+    ) as mock_is_registered, patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints.InitPassThroughEndpointHelpers.get_registered_pass_through_route"
+    ) as mock_get_registered, patch(
+        "litellm.proxy.pass_through_endpoints.pass_through_endpoints._parse_request_data_by_content_type"
+    ) as mock_parse_request:
+        mock_pass_through.return_value = MagicMock()
+        mock_is_registered.return_value = True
+        mock_get_registered.return_value = None
+        request_parsed_body = {"key": "from_request"}
+        mock_parse_request.return_value = (
+            {},  # query_params_data
+            request_parsed_body,  # custom_body_data
+            None,  # file_data
+            False,  # stream
+        )
+
+        mock_request = MagicMock(spec=Request)
+        mock_request.url = MagicMock()
+        mock_request.url.path = unique_path
+        mock_request.path_params = {}
+        mock_request.query_params = QueryParams({})
+
+        mock_user_api_key_dict = MagicMock()
+        mock_user_api_key_dict.api_key = "test-key"
+
+        # Call without custom_body — should use the request-parsed body
+        await endpoint_func(
+            request=mock_request,
+            fastapi_response=MagicMock(),
+            user_api_key_dict=mock_user_api_key_dict,
+        )
+
+        mock_pass_through.assert_called_once()
+        call_kwargs = mock_pass_through.call_args[1]
+
+        # Should fall back to the body parsed from the request
+        assert call_kwargs["custom_body"] == request_parsed_body
+
+
 def test_build_full_path_with_root_default():
     """
     Test _build_full_path_with_root with default root path (/)