Address reviewer comments

Author: Mofef

integrations/mcp/src/haystack_integrations/tools/mcp/mcp_tool.py

@@ -63,15 +63,15 @@ def _resolve_headers(headers: dict[str, str | Secret] | None) -> dict[str, str]
     return resolved_headers
 
 
-def extract_first_text_element(result: str) -> str | dict[str, Any]:
+def _extract_first_text_element(tool_call_result: str) -> str | dict[str, Any]:
     """
-    Return the first text content block from an MCP tool response.
+    Return the first text content block from an MCP tool call result.
 
-    MCP tool responses may include mixed content types such as text, image, or
+    MCP tool call results may include mixed content types such as text, image, or
     audio blocks. This helper extracts the first text block because the tool
     invoker expects a single parsed payload rather than the full content list.
     """
-    parsed: dict = json.loads(result)
+    parsed: dict = json.loads(tool_call_result)
     content: list = parsed.get("content", [])
     for block in content:
         if isinstance(block, dict) and block.get("type") == "text":
@@ -1109,7 +1109,7 @@ async def invoke() -> Any:
             # Parse JSON to dict only when outputs_to_state is configured.
             # ToolInvoker requires dict for _merge_tool_outputs(); ToolCallResult.result expects str otherwise.
             if self.outputs_to_state:
-                return extract_first_text_element(result)
+                return _extract_first_text_element(result)
 
             return result
         except (MCPError, TimeoutError) as e:
@@ -1140,7 +1140,7 @@ async def ainvoke(self, **kwargs: Any) -> str | dict[str, Any]:
             # Parse JSON to dict only when outputs_to_state is configured.
             # ToolInvoker requires dict for _merge_tool_outputs(); ToolCallResult.result expects str otherwise.
             if self.outputs_to_state:
-                return extract_first_text_element(result)
+                return _extract_first_text_element(result)
 
             return result
         except asyncio.TimeoutError as e:

integrations/mcp/tests/test_mcp_tool.py

@@ -15,7 +15,7 @@
     MCPTool,
     StdioServerInfo,
 )
-from haystack_integrations.tools.mcp.mcp_tool import StdioClient, extract_first_text_element
+from haystack_integrations.tools.mcp.mcp_tool import StdioClient, _extract_first_text_element
 
 from .mcp_memory_transport import InMemoryServerInfo
 from .mcp_servers_fixtures import calculator_mcp, echo_mcp
@@ -27,19 +27,21 @@ def simple_haystack_tool(name: str) -> str:
     return f"Hello, {name}!"
 
 
+# from https://modelcontextprotocol.io/specification/draft/server/tools#output-schema
+EXAMPLE_MCP_TOOL_CALL_RESULT = {
+    "content": [{"type": "text", "text": '{"temperature": 22.5, "conditions": "Partly cloudy", "humidity": 65}'}],
+    "structuredContent": {"temperature": 22.5, "conditions": "Partly cloudy", "humidity": 65},
+}
+
+
 def test_extract_first_text_element():
     """Test that extract_first_text skips non-text blocks and parses the first text block."""
-    result = json.dumps(
-        {
-            "content": [
-                {"type": "image", "data": "ignored"},
-                {"type": "text", "text": '{"answer": 42}'},
-                {"type": "text", "text": '{"answer": 7}'},
-            ]
-        }
-    )
+    tool_call_result = EXAMPLE_MCP_TOOL_CALL_RESULT
+    tool_call_result["content"].insert(0, {"type": "image", "data": "ignored"})
+    tool_call_result["content"].insert(1, {"type": "text", "text": '{"answer": 42}'})  # target
+    tool_call_result = json.dumps(tool_call_result)
 
-    extracted = extract_first_text_element(result)
+    extracted = _extract_first_text_element(tool_call_result)
 
     assert extracted == {"answer": 42}