internal: use OS defaults for TCP keepalive params in Windows (#6863)

Author: mmatczuk

internal/tcp_keepalive_nonunix.go renamed to internal/tcp_keepalive_others.go

@@ -1,4 +1,4 @@
-//go:build !unix
+//go:build !unix && !windows
 
 /*
  * Copyright 2023 gRPC authors.

internal/tcp_keepalive_windows.go

@@ -0,0 +1,54 @@
+//go:build windows
+
+/*
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package internal
+
+import (
+	"net"
+	"syscall"
+	"time"
+
+	"golang.org/x/sys/windows"
+)
+
+// NetDialerWithTCPKeepalive returns a net.Dialer that enables TCP keepalives on
+// the underlying connection with OS default values for keepalive parameters.
+//
+// TODO: Once https://github.com/golang/go/issues/62254 lands, and the
+// appropriate Go version becomes less than our least supported Go version, we
+// should look into using the new API to make things more straightforward.
+func NetDialerWithTCPKeepalive() *net.Dialer {
+	return &net.Dialer{
+		// Setting a negative value here prevents the Go stdlib from overriding
+		// the values of TCP keepalive time and interval. It also prevents the
+		// Go stdlib from enabling TCP keepalives by default.
+		KeepAlive: time.Duration(-1),
+		// This method is called after the underlying network socket is created,
+		// but before dialing the socket (or calling its connect() method). The
+		// combination of unconditionally enabling TCP keepalives here, and
+		// disabling the overriding of TCP keepalive parameters by setting the
+		// KeepAlive field to a negative value above, results in OS defaults for
+		// the TCP keealive interval and time parameters.
+		Control: func(_, _ string, c syscall.RawConn) error {
+			return c.Control(func(fd uintptr) {
+				windows.SetsockoptInt(windows.Handle(fd), windows.SOL_SOCKET, windows.SO_KEEPALIVE, 1)
+			})
+		},
+	}
+}