fix: Set reuse flags to allow multiple binds on same port on Linux/Mac

Author: g3force

go.mod

@@ -10,4 +10,7 @@ require (
 	google.golang.org/protobuf v1.36.10
 )
 
-require golang.org/x/sys v0.37.0 // indirect
+require (
+	github.com/libp2p/go-reuseport v0.4.0 // indirect
+	golang.org/x/sys v0.37.0 // indirect
+)

go.sum

@@ -1,5 +1,7 @@
 github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/libp2p/go-reuseport v0.4.0 h1:nR5KU7hD0WxXCJbmw7r2rhRYruNRl2koHw8fQscQm2s=
+github.com/libp2p/go-reuseport v0.4.0/go.mod h1:ZtI03j/wO5hZVDFo2jKywN6bYKWLOy8Se6DrI2E1cLU=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 golang.org/x/net v0.23.0 h1:7EYJ93RZ9vYSZAIb2x3lnuvqO5zneoD6IvWjuhfxjTs=

pkg/sslnet/multicast_server.go

@@ -6,6 +6,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/libp2p/go-reuseport"
 	"golang.org/x/net/ipv4"
 )
 
@@ -84,22 +85,31 @@ func (r *MulticastServer) connectToInterface(ifi net.Interface) bool {
 		return false
 	}
 
-	r.connection, err = net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4zero, Port: addr.Port})
+	// Listen using go-reuseport which sets SO_REUSEADDR and SO_REUSEPORT
+	listenAddr := &net.UDPAddr{IP: net.IPv4zero, Port: addr.Port}
+	packetConn, err := reuseport.ListenPacket("udp4", listenAddr.String())
 	if err != nil {
 		log.Printf("Could not listen at %v on %v: %v", r.multicastAddress, ifi.Name, err)
 		return false
 	}
 
+	var ok bool
+	r.connection, ok = packetConn.(*net.UDPConn)
+	if !ok {
+		log.Printf("Could not cast to UDPConn")
+		return false
+	}
+
 	if err := r.connection.SetReadBuffer(maxDatagramSize); err != nil {
 		log.Println("Could not set read buffer: ", err)
 	}
 
-	packetConn := ipv4.NewPacketConn(r.connection)
-	if err := packetConn.JoinGroup(&ifi, addr); err != nil {
+	ipv4PacketConn := ipv4.NewPacketConn(r.connection)
+	if err := ipv4PacketConn.JoinGroup(&ifi, addr); err != nil {
 		log.Printf("Could not join group %v: %v", ifi.Name, err)
 		return false
 	}
-	if err := packetConn.SetMulticastLoopback(true); err != nil {
+	if err := ipv4PacketConn.SetMulticastLoopback(true); err != nil {
 		log.Printf("Could not set multicast loopback %v: %v", ifi.Name, err)
 		return false
 	}