dial: use OS defaults for TCP keepalive params

Fixes #605

dial.go

@@ -21,20 +21,15 @@ type DialConfig struct {
 	// often around 3 minutes.
 	DialTimeout time.Duration
 
-	// KeepAlive specifies the interval between keep-alive
-	// probes for an active network connection.
-	// If zero, keep-alive probes are sent with a default value
-	// (currently 15 seconds), if supported by the protocol and operating
-	// system. Network protocols or operating systems that do
-	// not support keep-alives ignore this field.
-	// If negative, keep-alive probes are disabled.
-	KeepAlive time.Duration
+	// KeepAlive enables TCP keep-alive probes for an active network connection.
+	// The keep-alive probes are sent with OS specific intervals.
+	KeepAlive bool
 }
 
 func DefaultDialConfig() *DialConfig {
 	return &DialConfig{
 		DialTimeout: 10 * time.Second,
-		KeepAlive:   30 * time.Second,
+		KeepAlive:   true,
 	}
 }
 
@@ -43,15 +38,21 @@ type Dialer struct {
 }
 
 func NewDialer(cfg *DialConfig) *Dialer {
-	return &Dialer{
-		net.Dialer{
-			Timeout:   cfg.DialTimeout,
-			KeepAlive: cfg.KeepAlive,
-			Resolver: &net.Resolver{
-				PreferGo: true,
-			},
+	nd := net.Dialer{
+		Timeout:   cfg.DialTimeout,
+		KeepAlive: -1,
+		Resolver: &net.Resolver{
+			PreferGo: true,
 		},
 	}
+
+	if cfg.KeepAlive {
+		enableTCPKeepAlive(&nd)
+	}
+
+	return &Dialer{
+		nd: nd,
+	}
 }
 
 func (d *Dialer) DialContext(ctx context.Context, network, address string) (net.Conn, error) {

dial_unix.go

@@ -0,0 +1,27 @@
+// Copyright 2023 Sauce Labs Inc., all rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//go:build unix
+
+package forwarder
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+)
+
+func enableTCPKeepAlive(d *net.Dialer) {
+	d.KeepAlive = -1
+	d.Control = func(network, address string, c syscall.RawConn) error {
+		return c.Control(func(fd uintptr) {
+			if err := syscall.SetsockoptInt(int(fd), syscall.SOL_SOCKET, syscall.SO_KEEPALIVE, 1); err != nil {
+				fmt.Fprintf(os.Stderr, "failed to set SO_KEEPALIVE: %v\n", err)
+			}
+		})
+	}
+}

dial_windows.go

@@ -0,0 +1,31 @@
+// Copyright 2023 Sauce Labs Inc., all rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//go:build windows
+
+package forwarder
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+func enableTCPKeepAlive(d *net.Dialer) {
+	d.KeepAlive = -1
+	d.Control = func(network, address string, c syscall.RawConn) error {
+		return c.Control(func(fd uintptr) {
+			optval := (*byte)(unsafe.Pointer(&[4]byte{1}))
+			if err := windows.Setsockopt(windows.Handle(fd), windows.SOL_SOCKET, windows.SO_KEEPALIVE, optval, 1); err != nil {
+				fmt.Fprintf(os.Stderr, "failed to set SO_KEEPALIVE: %v\n", err)
+			}
+		})
+	}
+}