#552

tests/issues/test_552_windows_hang.py

@@ -0,0 +1,64 @@
+"""Test for issue #552: stdio_client hangs on Windows."""
+
+import sys
+from textwrap import dedent
+
+import anyio
+import pytest
+
+from mcp import ClientSession, StdioServerParameters
+from mcp.client.stdio import stdio_client
+
+
+@pytest.mark.skipif(sys.platform != "win32", reason="Windows-specific test")
+@pytest.mark.anyio
+async def test_windows_stdio_client_with_session():
+    """
+    Test the exact scenario from issue #552: Using ClientSession with stdio_client.
+
+    This reproduces the original bug report where stdio_client hangs on Windows 11
+    when used with ClientSession.
+    """
+    # Create a minimal MCP server that responds to initialization
+    server_script = dedent("""
+        import json
+        import sys
+
+        # Read initialization request
+        line = sys.stdin.readline()
+
+        # Send initialization response
+        response = {
+            "jsonrpc": "2.0",
+            "id": 1,
+            "result": {
+                "protocolVersion": "1.0",
+                "capabilities": {},
+                "serverInfo": {"name": "test-server", "version": "1.0"}
+            }
+        }
+        print(json.dumps(response))
+        sys.stdout.flush()
+
+        # Exit after a short delay
+        import time
+        time.sleep(0.1)
+        sys.exit(0)
+    """).strip()
+
+    params = StdioServerParameters(
+        command=sys.executable,
+        args=["-c", server_script],
+    )
+
+    # This is the exact pattern from the bug report
+    with anyio.fail_after(10):
+        try:
+            async with stdio_client(params) as (read, write):
+                async with ClientSession(read, write) as session:
+                    await session.initialize()
+                # Should exit ClientSession without hanging
+            # Should exit stdio_client without hanging
+        except Exception:
+            # Connection errors are expected when process exits
+            pass