fix(stdio): suppress BrokenResourceError in stdout_reader (#1960)

src/mcp/client/stdio.py

@@ -158,7 +158,7 @@ async def stdout_reader():
 
                         session_message = SessionMessage(message)
                         await read_stream_writer.send(session_message)
-        except anyio.ClosedResourceError:  # pragma: lax no cover
+        except (anyio.ClosedResourceError, anyio.BrokenResourceError):
             await anyio.lowlevel.checkpoint()
 
     async def stdin_writer():

tests/client/test_stdio.py

@@ -7,6 +7,7 @@
 
 import anyio
 import anyio.abc
+import anyio.lowlevel
 import pytest
 
 from mcp.client.session import ClientSession
@@ -67,7 +68,29 @@ async def test_stdio_client():
 
         assert len(read_messages) == 2
         assert read_messages[0] == JSONRPCRequest(jsonrpc="2.0", id=1, method="ping")
-        assert read_messages[1] == JSONRPCResponse(jsonrpc="2.0", id=2, result={})
+    assert read_messages[1] == JSONRPCResponse(jsonrpc="2.0", id=2, result={})
+
+
+@pytest.mark.anyio
+async def test_stdio_client_exits_cleanly_while_stdout_reader_is_blocked_in_send():
+    server_script = textwrap.dedent(
+        r"""
+        import sys
+
+        sys.stdout.write('{"jsonrpc":"2.0","id":1,"result":{}}\n')
+        sys.stdout.flush()
+
+        # Wait for stdin to close so the parent can exercise the shutdown path.
+        for _line in sys.stdin:
+            pass
+        """
+    )
+    server_params = StdioServerParameters(command=sys.executable, args=["-c", server_script])
+
+    async with stdio_client(server_params) as (read_stream, _write_stream):
+        with anyio.fail_after(5.0):
+            while read_stream.statistics().tasks_waiting_send == 0:
+                await anyio.lowlevel.checkpoint()
 
 
 @pytest.mark.anyio