fix: handle empty tool response (#8118)

* handle empty tool response

* Update src/backend/base/langflow/components/tools/mcp_component.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* DataFrame

* fix test

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/backend/base/langflow/components/tools/mcp_component.py

@@ -17,7 +17,7 @@ from langflow.inputs.inputs import InputTypes
 from langflow.io import MessageTextInput, MultilineInput, Output, TabInput
 from langflow.io.schema import flatten_schema, schema_to_langflow_inputs
 from langflow.logging import logger
-from langflow.schema import Message
+from langflow.schema import DataFrame
 
 
 def maybe_unflatten_dict(flat: dict[str, Any]) -> dict[str, Any]:
@@ -409,7 +409,7 @@ class MCPToolsComponent(Component):
             logger.exception(msg)
             raise ValueError(msg) from e
 
-    async def build_output(self) -> Message:
+    async def build_output(self) -> DataFrame:
         """Build output with improved error handling and validation."""
         try:
             await self.update_tools()
@@ -426,8 +426,12 @@ class MCPToolsComponent(Component):
 
                 output = await exec_tool.coroutine(**unflattened_kwargs)
 
-                return Message(text=output.content[len(output.content) - 1].text)
+                tool_content = []
-            return Message(text="You must select a tool", error=True)
+                for item in output.content:
+                    item_dict = item.model_dump()
+                    tool_content.append(item_dict)
+                return DataFrame(data=tool_content)
+            return DataFrame(data=[{"error": "You must select a tool"}])
         except Exception as e:
             msg = f"Error in build_output: {e!s}"
             logger.exception(msg)

src/backend/tests/unit/components/tools/test_mcp_component.py

@@ -108,7 +108,10 @@ class TestMCPToolsComponent(ComponentTestBaseWithoutClient):
 
         # Mock the coroutine response
         mock_response = AsyncMock()
-        mock_response.content = [MagicMock(text="Test response")]
+        mock_content_item = MagicMock()
+        mock_content_item.text = "Test response"
+        mock_content_item.model_dump.return_value = {"text": "Test response"}
+        mock_response.content = [mock_content_item]
         mock_create_coroutine.return_value = AsyncMock(return_value=mock_response)
 
         # Create a mock tool and add it to the cache
@@ -126,7 +129,8 @@ class TestMCPToolsComponent(ComponentTestBaseWithoutClient):
             mock_get_inputs.return_value = {"test_tool": [mock_input]}
             output = await component.build_output()
 
-            assert output.text == "Test response"
+            # Use iloc to access the first row's 'text' column value
+            assert output.iloc[0]["text"] == "Test response"
             # Verify the mocks were called correctly
             mock_get_inputs.assert_called_once_with(component.tools)
             mock_structured_tool.coroutine.assert_called_once_with(test_param="test value")