godns_soreuseport.diff

diff --git a/server.go b/server.go
index 685753f..8cf4038 100644
--- a/server.go
+++ b/server.go
@@ -10,6 +10,8 @@ import (
 	"net"
 	"sync"
 	"time"
+
+	"github.com/libp2p/go-reuseport"
 )
 
 // Maximum number of TCP queries before we close the socket.
@@ -300,10 +302,16 @@ type Server struct {
 	// Shutdown handling
 	lock    sync.RWMutex
 	started bool
+	// Should we use SO_REUSE_PORT
+	Soreuseport bool
 }
 
 // ListenAndServe starts a nameserver on the configured address in *Server.
 func (srv *Server) ListenAndServe() error {
+	var l net.Listener
+	var p *net.UDPConn
+	var err error
+
 	srv.lock.Lock()
 	defer srv.lock.Unlock()
 	if srv.started {
@@ -319,12 +327,19 @@ func (srv *Server) ListenAndServe() error {
 	switch srv.Net {
 	case "tcp", "tcp4", "tcp6":
 		a, err := net.ResolveTCPAddr(srv.Net, addr)
-		if err != nil {
-			return err
-		}
-		l, err := net.ListenTCP(srv.Net, a)
-		if err != nil {
-			return err
+		if srv.Soreuseport {
+			l, err = reuseport.Listen(srv.Net, a.String())
+			if err != nil {
+				return err
+			}
+		} else {
+			if err != nil {
+				return err
+			}
+			l, err = net.ListenTCP(srv.Net, a)
+			if err != nil {
+				return err
+			}
 		}
 		srv.Listener = l
 		srv.started = true
@@ -340,9 +355,17 @@ func (srv *Server) ListenAndServe() error {
 			network = "tcp6"
 		}
 
-		l, err := tls.Listen(network, addr, srv.TLSConfig)
-		if err != nil {
-			return err
+		if srv.Soreuseport {
+			l, err = reuseport.Listen(srv.Net, addr)
+			if err != nil {
+				return err
+			}
+			l = tls.NewListener(l, srv.TLSConfig)
+		} else {
+			l, err = tls.Listen(network, addr, srv.TLSConfig)
+			if err != nil {
+				return err
+			}
 		}
 		srv.Listener = l
 		srv.started = true
@@ -351,21 +374,32 @@ func (srv *Server) ListenAndServe() error {
 		srv.lock.Lock() // to satisfy the defer at the top
 		return err
 	case "udp", "udp4", "udp6":
-		a, err := net.ResolveUDPAddr(srv.Net, addr)
-		if err != nil {
-			return err
-		}
-		l, err := net.ListenUDP(srv.Net, a)
-		if err != nil {
-			return err
+		var ok bool
+		if srv.Soreuseport {
+			pConn, err := reuseport.ListenPacket(srv.Net, addr)
+			if err != nil {
+				return err
+			}
+			if p, ok = pConn.(*net.UDPConn); !ok {
+				return &Error{err: "Cannot cast PacketConn to *net.UDPConn"}
+			}
+		} else {
+			a, err := net.ResolveUDPAddr(srv.Net, addr)
+			if err != nil {
+				return err
+			}
+			p, err = net.ListenUDP(srv.Net, a)
+			if err != nil {
+				return err
+			}
 		}
-		if e := setUDPSocketOptions(l); e != nil {
+		if e := setUDPSocketOptions(p); e != nil {
 			return e
 		}
-		srv.PacketConn = l
+		srv.PacketConn = p
 		srv.started = true
 		srv.lock.Unlock()
-		err = srv.serveUDP(l)
+		err = srv.serveUDP(p)
 		srv.lock.Lock() // to satisfy the defer at the top
 		return err
 	}