Add support for systemd socket activation

server.go

@@ -97,6 +97,12 @@ func ListenAndServe(addr string, network string, handler Handler) error {
 	return server.ListenAndServe()
 }
 
+// Start a server with these listeners. Invoke handler for incoming queries.
+func StartAndServe(ls []net.Listener, ps []net.PacketConn, handler Handler) error {
+	server := &Server{Listeners: ls, PacketConns: ps, Handler: handler}
+	return server.StartAndServe()
+}
+
 func (mux *ServeMux) match(q string, t uint16) Handler {
 	mux.m.RLock()
 	defer mux.m.RUnlock()
@@ -197,6 +203,10 @@ type Server struct {
 	Addr string
 	// if "tcp" it will invoke a TCP listener, otherwise an UDP one.
 	Net string
+	// TCP Listeners to use, this is to aid in systemd's socket activation.
+	Listeners []net.Listener
+	// UDP "Listeners" to use, this is to aid in systemd's socket activation.
+	PacketConns []net.PacketConn
 	// Handler to invoke, dns.DefaultServeMux if nil.
 	Handler Handler
 	// Default buffer size to use to read incoming UDP messages. If not set
@@ -252,6 +262,28 @@ func (srv *Server) ListenAndServe() error {
 	return &Error{err: "bad network"}
 }
 
+// StartAndServe starts a nameserver with the first listener the or first
+// packetconn configured in *Server.
+func (srv *Server) StartAndServe() error {
+	if len(srv.Listeners) > 0 {
+		if t, ok := srv.Listeners[0].(*net.TCPListener); ok {
+			return srv.serveTCP(t)
+		}
+	}
+	if len(srv.PacketConns) > 0 {
+		if srv.UDPSize == 0 {
+			srv.UDPSize = MinMsgSize
+		}
+		if t, ok := srv.PacketConns[0].(*net.UDPConn); ok {
+			if e := setUDPSocketOptions(t); e != nil {
+				return e
+			}
+			return srv.serveUDP(t)
+		}
+	}
+	return &Error{err: "bad listeners"}
+}
+
 // serveTCP starts a TCP listener for the server.
 // Each request is handled in a seperate goroutine.
 func (srv *Server) serveTCP(l *net.TCPListener) error {

udp_other.go

@@ -15,7 +15,7 @@ import (
 
 // We tried to adhire to some kind of naming scheme.
 
-func setUDPSocketOptions4(conn *net.UDPConn) error                { return nil }
-func setUDPSocketOptions6(conn *net.UDPConn) error                { return nil }
-func getUDPSocketOptions6Only(conn *net.UDPConn) (bool, error)    { return false, nil }
+func setUDPSocketOptions4(conn *net.UDPConn) error                 { return nil }
+func setUDPSocketOptions6(conn *net.UDPConn) error                 { return nil }
+func getUDPSocketOptions6Only(conn *net.UDPConn) (bool, error)     { return false, nil }
 func getUDPSocketName(conn *net.UDPConn) (syscall.Sockaddr, error) { return nil, nil }