Remove unnecessary use of SO_REUSEPORT

[btrtrc.git] / socket.go

diff --git a/socket.go b/socket.go
index c1fb97fdbcbee17728d530da76a9fe5a6f5ab094..2d4ea863ac292f39e4d97effd297fe2b98afcfa5 100644 (file)
--- a/socket.go
+++ b/socket.go
@@ -37,10 +37,17 @@ func listen(n network, addr string, f firewallCallback, logger log.Logger) (sock
        }
 }
 
+// Dialing TCP from a local port limits us to a single outgoing TCP connection to each remote
+// client. Instead, this should be a last resort if we need to use holepunching, and only then to
+// connect to other clients that actually try to holepunch TCP.
+const dialTcpFromListenPort = false
+
 var tcpListenConfig = net.ListenConfig{
        Control: func(network, address string, c syscall.RawConn) (err error) {
                controlErr := c.Control(func(fd uintptr) {
-                       err = setReusePortSockOpts(fd)
+                       if dialTcpFromListenPort {
+                               err = setReusePortSockOpts(fd)
+                       }
                })
                if err != nil {
                        return
@@ -54,38 +61,49 @@ var tcpListenConfig = net.ListenConfig{
 
 func listenTcp(network, address string) (s socket, err error) {
        l, err := tcpListenConfig.Listen(context.Background(), network, address)
-       return tcpSocket{
+       if err != nil {
+               return
+       }
+       netDialer := net.Dialer{
+               // We don't want fallback, as we explicitly manage the IPv4/IPv6 distinction ourselves,
+               // although it's probably not triggered as I think the network is already constrained to
+               // tcp4 or tcp6 at this point.
+               FallbackDelay: -1,
+               // BitTorrent connections manage their own keepalives.
+               KeepAlive: tcpListenConfig.KeepAlive,
+               Control: func(network, address string, c syscall.RawConn) (err error) {
+                       controlErr := c.Control(func(fd uintptr) {
+                               err = setSockNoLinger(fd)
+                               if err != nil {
+                                       // Failing to disable linger is undesirable, but not fatal.
+                                       log.Levelf(log.Debug, "error setting linger socket option on tcp socket: %v", err)
+                                       err = nil
+                               }
+                               // This is no longer required I think, see
+                               // https://github.com/anacrolix/torrent/discussions/856. I added this originally to
+                               // allow dialling out from the client's listen port, but that doesn't really work. I
+                               // think Linux older than ~2013 doesn't support SO_REUSEPORT.
+                               if dialTcpFromListenPort {
+                                       err = setReusePortSockOpts(fd)
+                               }
+                       })
+                       if err == nil {
+                               err = controlErr
+                       }
+                       return
+               },
+       }
+       if dialTcpFromListenPort {
+               netDialer.LocalAddr = l.Addr()
+       }
+       s = tcpSocket{
                Listener: l,
                NetworkDialer: NetworkDialer{
                        Network: network,
-                       Dialer: &net.Dialer{
-                               // Dialling TCP from a local port limits us to a single outgoing TCP connection to
-                               // each remote client. Instead this should be a last resort if we need to use holepunching, and only then to connect to other clients that actually try to holepunch TCP.
-                               //LocalAddr: l.Addr(),
-
-                               // We don't want fallback, as we explicitly manage the IPv4/IPv6 distinction
-                               // ourselves, although it's probably not triggered as I think the network is already
-                               // constrained to tcp4 or tcp6 at this point.
-                               FallbackDelay: -1,
-                               // BitTorrent connections manage their own keep-alives.
-                               KeepAlive: tcpListenConfig.KeepAlive,
-                               Control: func(network, address string, c syscall.RawConn) (err error) {
-                                       controlErr := c.Control(func(fd uintptr) {
-                                               err = setSockNoLinger(fd)
-                                               if err != nil {
-                                                       // Failing to disable linger is undesirable, but not fatal.
-                                                       log.Printf("error setting linger socket option on tcp socket: %v", err)
-                                               }
-                                               err = setReusePortSockOpts(fd)
-                                       })
-                                       if err == nil {
-                                               err = controlErr
-                                       }
-                                       return
-                               },
-                       },
+                       Dialer:  &netDialer,
                },
-       }, err
+       }
+       return
 }
 
 type tcpSocket struct {