1//go:build windows
 2
 3/*
 4 * Copyright 2023 gRPC authors.
 5 *
 6 * Licensed under the Apache License, Version 2.0 (the "License");
 7 * you may not use this file except in compliance with the License.
 8 * You may obtain a copy of the License at
 9 *
10 *     http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 *
18 */
19
20package internal
21
22import (
23	"net"
24	"syscall"
25	"time"
26
27	"golang.org/x/sys/windows"
28)
29
30// NetDialerWithTCPKeepalive returns a net.Dialer that enables TCP keepalives on
31// the underlying connection with OS default values for keepalive parameters.
32//
33// TODO: Once https://github.com/golang/go/issues/62254 lands, and the
34// appropriate Go version becomes less than our least supported Go version, we
35// should look into using the new API to make things more straightforward.
36func NetDialerWithTCPKeepalive() *net.Dialer {
37	return &net.Dialer{
38		// Setting a negative value here prevents the Go stdlib from overriding
39		// the values of TCP keepalive time and interval. It also prevents the
40		// Go stdlib from enabling TCP keepalives by default.
41		KeepAlive: time.Duration(-1),
42		// This method is called after the underlying network socket is created,
43		// but before dialing the socket (or calling its connect() method). The
44		// combination of unconditionally enabling TCP keepalives here, and
45		// disabling the overriding of TCP keepalive parameters by setting the
46		// KeepAlive field to a negative value above, results in OS defaults for
47		// the TCP keepalive interval and time parameters.
48		Control: func(_, _ string, c syscall.RawConn) error {
49			return c.Control(func(fd uintptr) {
50				windows.SetsockoptInt(windows.Handle(fd), windows.SOL_SOCKET, windows.SO_KEEPALIVE, 1)
51			})
52		},
53	}
54}