Set TCP_NODELAY on pydevd client connections

src/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_comm.py

@@ -525,6 +525,10 @@ def start_client(host, port):
         s.setsockopt(socket_module.IPPROTO_TCP, socket_module.TCP_KEEPCNT, 5)
     except (AttributeError, OSError):
         pass  # May not be available everywhere.
+    try:
+        s.setsockopt(socket_module.IPPROTO_TCP, socket_module.TCP_NODELAY, 1)
+    except (AttributeError, OSError):
+        pass  # May not be available everywhere.
 
     try:
         # 10 seconds default timeout

src/debugpy/_vendored/pydevd/tests_python/test_pydevd_comm.py

@@ -0,0 +1,43 @@
+from unittest import mock
+
+from _pydevd_bundle import pydevd_comm
+
+
+def start_client(monkeypatch, sock):
+    monkeypatch.setattr(pydevd_comm, "socket", lambda *_: sock)
+    monkeypatch.setattr(pydevd_comm.socket_module, "getaddrinfo", lambda *_: [])
+    return pydevd_comm.start_client("localhost", 5678)
+
+
+def test_start_client_sets_tcp_nodelay(monkeypatch):
+    sock = mock.Mock()
+    tcp_nodelay = mock.sentinel.tcp_nodelay
+    monkeypatch.setattr(pydevd_comm.socket_module, "TCP_NODELAY", tcp_nodelay)
+
+    assert start_client(monkeypatch, sock) is sock
+    sock.setsockopt.assert_any_call(
+        pydevd_comm.socket_module.IPPROTO_TCP,
+        tcp_nodelay,
+        1,
+    )
+
+
+def test_start_client_without_tcp_nodelay(monkeypatch):
+    sock = mock.Mock()
+    monkeypatch.delattr(pydevd_comm.socket_module, "TCP_NODELAY", raising=False)
+
+    assert start_client(monkeypatch, sock) is sock
+
+
+def test_start_client_ignores_tcp_nodelay_error(monkeypatch):
+    sock = mock.Mock()
+    tcp_nodelay = mock.sentinel.tcp_nodelay
+    monkeypatch.setattr(pydevd_comm.socket_module, "TCP_NODELAY", tcp_nodelay)
+
+    def set_option(_level, option, _value):
+        if option is tcp_nodelay:
+            raise OSError
+
+    sock.setsockopt.side_effect = set_option
+
+    assert start_client(monkeypatch, sock) is sock