Fix hanging on streams when stdio_client exiting (#559)

src/mcp/client/stdio/__init__.py

@@ -181,6 +181,8 @@ async def stdio_client(server: StdioServerParameters, errlog: TextIO = sys.stder
                 await terminate_windows_process(process)
             else:
                 process.terminate()
+            await read_stream.aclose()
+            await write_stream.aclose()
 
 
 def _get_executable_command(command: str) -> str:

tests/client/test_stdio.py

@@ -9,6 +9,13 @@ from mcp.types import JSONRPCMessage, JSONRPCRequest, JSONRPCResponse
 tee: str = shutil.which("tee")  # type: ignore
 
 
+@pytest.mark.anyio
+@pytest.mark.skipif(tee is None, reason="could not find tee command")
+async def test_stdio_context_manager_exiting():
+    async with stdio_client(StdioServerParameters(command=tee)) as (_, _):
+        pass
+
+
 @pytest.mark.anyio
 @pytest.mark.skipif(tee is None, reason="could not find tee command")
 async def test_stdio_client():