Use dialer in relay checks (fixes #2732)

lib/dialer/internal.go

@@ -17,7 +17,6 @@ import (
 	"golang.org/x/net/proxy"
 
 	"github.com/syncthing/syncthing/lib/logger"
-	"github.com/syncthing/syncthing/lib/osutil"
 )
 
 var (
@@ -55,7 +54,7 @@ func dialWithFallback(proxyDialFunc dialFunc, fallbackDialFunc dialFunc, network
 	if err == nil {
 		l.Debugf("Dialing %s address %s via proxy - success, %s -> %s", network, addr, conn.LocalAddr(), conn.RemoteAddr())
 		if tcpconn, ok := conn.(*net.TCPConn); ok {
-			osutil.SetTCPOptions(tcpconn)
+			SetTCPOptions(tcpconn)
 		}
 		return dialerConn{
 			conn, newDialerAddr(network, addr),
@@ -67,7 +66,7 @@ func dialWithFallback(proxyDialFunc dialFunc, fallbackDialFunc dialFunc, network
 	if err == nil {
 		l.Debugf("Dialing %s address %s via fallback - success, %s -> %s", network, addr, conn.LocalAddr(), conn.RemoteAddr())
 		if tcpconn, ok := conn.(*net.TCPConn); ok {
-			osutil.SetTCPOptions(tcpconn)
+			SetTCPOptions(tcpconn)
 		}
 	} else {
 		l.Debugf("Dialing %s address %s via fallback - error %s", network, addr, err)

lib/dialer/public.go

@@ -46,3 +46,21 @@ func DialTimeout(network, addr string, timeout time.Duration) (net.Conn, error)
 	}
 	return net.DialTimeout(network, addr, timeout)
 }
+
+// SetTCPOptions sets syncthings default TCP options on a TCP connection
+func SetTCPOptions(conn *net.TCPConn) error {
+	var err error
+	if err = conn.SetLinger(0); err != nil {
+		return err
+	}
+	if err = conn.SetNoDelay(false); err != nil {
+		return err
+	}
+	if err = conn.SetKeepAlivePeriod(60 * time.Second); err != nil {
+		return err
+	}
+	if err = conn.SetKeepAlive(true); err != nil {
+		return err
+	}
+	return nil
+}