Our dialer sets up TCP options

lib/connections/connections.go

@@ -20,7 +20,6 @@ import (
 	"github.com/syncthing/syncthing/lib/discover"
 	"github.com/syncthing/syncthing/lib/events"
 	"github.com/syncthing/syncthing/lib/model"
-	"github.com/syncthing/syncthing/lib/osutil"
 	"github.com/syncthing/syncthing/lib/protocol"
 	"github.com/syncthing/syncthing/lib/relay"
 	"github.com/syncthing/syncthing/lib/relay/client"
@@ -368,11 +367,6 @@ func (s *connectionSvc) connect() {
 					l.Debugln("Sucessfully joined relay session", inv)
 				}
 
-				err = osutil.SetTCPOptions(conn.(*net.TCPConn))
-				if err != nil {
-					l.Infoln(err)
-				}
-
 				var tc *tls.Conn
 
 				if inv.ServerSocket {

lib/connections/connections_tcp.go

@@ -44,11 +44,6 @@ func tcpDialer(uri *url.URL, tlsCfg *tls.Config) (*tls.Conn, error) {
 		return nil, err
 	}
 
-	err = osutil.SetTCPOptions(conn.(*net.TCPConn))
-	if err != nil {
-		l.Infoln(err)
-	}
-
 	tc := tls.Client(conn, tlsCfg)
 	err = tc.Handshake()
 	if err != nil {

lib/dialer/dialer.go

@@ -16,6 +16,7 @@ import (
 	"golang.org/x/net/proxy"
 
 	"github.com/syncthing/syncthing/lib/logger"
+	"github.com/syncthing/syncthing/lib/osutil"
 )
 
 var (
@@ -48,6 +49,9 @@ func Dial(network, addr string) (net.Conn, error) {
 		conn, err := dialer.Dial(network, addr)
 		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)
+			}
 			return dialerConn{
 				conn, newDialerAddr(network, addr),
 			}, nil
@@ -58,6 +62,9 @@ func Dial(network, addr string) (net.Conn, error) {
 	conn, err := proxy.Direct.Dial(network, addr)
 	if err == nil {
 		l.Debugf("Dialing %s address %s directly - success, %s -> %s", network, addr, conn.LocalAddr(), conn.RemoteAddr())
+		if tcpconn, ok := conn.(*net.TCPConn); ok {
+			osutil.SetTCPOptions(tcpconn)
+		}
 	} else {
 		l.Debugf("Dialing %s address %s directly - error %s", network, addr, err)
 	}

lib/relay/relay.go

@@ -9,7 +9,6 @@ package relay
 import (
 	"crypto/tls"
 	"encoding/json"
-	"net"
 	"net/http"
 	"net/url"
 	"sort"
@@ -249,11 +248,6 @@ func (r *invitationReceiver) Serve() {
 				continue
 			}
 
-			err = osutil.SetTCPOptions(conn.(*net.TCPConn))
-			if err != nil {
-				l.Infoln(err)
-			}
-
 			var tc *tls.Conn
 
 			if inv.ServerSocket {