fix: Fix McpToolset hanging indefinitely

This fixes McpToolset from hanging indefinitely during a list_tools call (#3084) by adding a timeout.

Co-authored-by: Kathy Wu <wukathy@google.com>
PiperOrigin-RevId: 829499276

Author: wukath

src/google/adk/tools/mcp_tool/mcp_toolset.py

@@ -14,6 +14,7 @@
 
 from __future__ import annotations
 
+import asyncio
 import logging
 import sys
 from typing import Callable
@@ -177,7 +178,17 @@ async def get_tools(
     session = await self._mcp_session_manager.create_session(headers=headers)
 
     # Fetch available tools from the MCP server
-    tools_response: ListToolsResult = await session.list_tools()
+    timeout_in_seconds = (
+        self._connection_params.timeout
+        if hasattr(self._connection_params, "timeout")
+        else None
+    )
+    try:
+      tools_response: ListToolsResult = await asyncio.wait_for(
+          session.list_tools(), timeout=timeout_in_seconds
+      )
+    except Exception as e:
+      raise ConnectionError("Failed to get tools from MCP server.") from e
 
     # Apply filtering based on context and tool_filter
     tools = []

tests/unittests/tools/mcp_tool/test_mcp_toolset.py

@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import asyncio
 from io import StringIO
 import sys
 import unittest
@@ -304,6 +305,26 @@ async def test_close_with_exception(self):
     assert "Warning: Error during McpToolset cleanup" in error_output
     assert "Cleanup error" in error_output
 
+  @pytest.mark.asyncio
+  async def test_get_tools_with_timeout(self):
+    """Test get_tools with timeout."""
+    stdio_params = StdioConnectionParams(
+        server_params=self.mock_stdio_params, timeout=0.01
+    )
+    toolset = MCPToolset(connection_params=stdio_params)
+    toolset._mcp_session_manager = self.mock_session_manager
+
+    async def long_running_list_tools():
+      await asyncio.sleep(0.1)
+      return MockListToolsResult([])
+
+    self.mock_session.list_tools = long_running_list_tools
+
+    with pytest.raises(
+        ConnectionError, match="Failed to get tools from MCP server."
+    ):
+      await toolset.get_tools()
+
   @pytest.mark.asyncio
   async def test_get_tools_retry_decorator(self):
     """Test that get_tools has retry decorator applied."""

tests/unittests/tools/test_mcp_toolset.py

@@ -45,6 +45,7 @@ async def test_mcp_toolset_with_prefix():
   """Test that McpToolset correctly applies the tool_name_prefix."""
   # Mock the connection parameters
   mock_connection_params = MagicMock()
+  mock_connection_params.timeout = None
 
   # Mock the MCPSessionManager and its create_session method
   mock_session_manager = MagicMock()