adds tests for shutdown bind port (#400)

* adds tests for shutdown bind port

* closes file descriptors in for udp on linux

* adds sleep after shutdown in test

* minimizes defer usages

* reduces sleep time

* replaces sleep with notify channel

after starting DNS server

server_test.go

@@ -677,3 +677,43 @@ zDCJkckCgYEAndqM5KXGk5xYo+MAA1paZcbTUXwaWwjLU+XSRSSoyBEi5xMtfvUb
 kFsxKCqxAnBVGEWAvVZAiiTOxleQFjz5RnL0BQp9Lg2cQe+dvuUmIAA=
 -----END RSA PRIVATE KEY-----`)
 )
+
+func testShutdownBindPort(t *testing.T, protocol string, port string) {
+	handler := NewServeMux()
+	handler.HandleFunc(".", func(w ResponseWriter, r *Msg) {})
+	startedCh := make(chan struct{})
+	s := &Server{
+		Addr:    net.JoinHostPort("127.0.0.1", port),
+		Net:     protocol,
+		Handler: handler,
+		NotifyStartedFunc: func() {
+			startedCh <- struct{}{}
+		},
+	}
+	go func() {
+		if err := s.ListenAndServe(); err != nil {
+			t.Log(err)
+		}
+	}()
+	<-startedCh
+	t.Logf("DNS server is started on: %s", s.Addr)
+	if err := s.Shutdown(); err != nil {
+		t.Fatal(err)
+	}
+	time.Sleep(100 * time.Millisecond)
+	go func() {
+		if err := s.ListenAndServe(); err != nil {
+			t.Fatal(err)
+		}
+	}()
+	<-startedCh
+	t.Logf("DNS server is started on: %s", s.Addr)
+}
+
+func TestShutdownBindPortUDP(t *testing.T) {
+	testShutdownBindPort(t, "udp", "1153")
+}
+
+func TestShutdownBindPortTCP(t *testing.T) {
+	testShutdownBindPort(t, "tcp", "1154")
+}

udp_linux.go

@@ -22,14 +22,17 @@ func setUDPSocketOptions4(conn *net.UDPConn) error {
 		return err
 	}
 	if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IP, syscall.IP_PKTINFO, 1); err != nil {
+		file.Close()
 		return err
 	}
 	// Calling File() above results in the connection becoming blocking, we must fix that.
 	// See https://github.com/miekg/dns/issues/279
 	err = syscall.SetNonblock(int(file.Fd()), true)
 	if err != nil {
+		file.Close()
 		return err
 	}
+	file.Close()
 	return nil
 }
 
@@ -40,12 +43,15 @@ func setUDPSocketOptions6(conn *net.UDPConn) error {
 		return err
 	}
 	if err := syscall.SetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_RECVPKTINFO, 1); err != nil {
+		file.Close()
 		return err
 	}
 	err = syscall.SetNonblock(int(file.Fd()), true)
 	if err != nil {
+		file.Close()
 		return err
 	}
+	file.Close()
 	return nil
 }
 
@@ -59,8 +65,10 @@ func getUDPSocketOptions6Only(conn *net.UDPConn) (bool, error) {
 	// dual stack. See http://stackoverflow.com/questions/1618240/how-to-support-both-ipv4-and-ipv6-connections
 	v6only, err := syscall.GetsockoptInt(int(file.Fd()), syscall.IPPROTO_IPV6, syscall.IPV6_V6ONLY)
 	if err != nil {
+		file.Close()
 		return false, err
 	}
+	file.Close()
 	return v6only == 1, nil
 }
 
@@ -69,5 +77,6 @@ func getUDPSocketName(conn *net.UDPConn) (syscall.Sockaddr, error) {
 	if err != nil {
 		return nil, err
 	}
+	defer file.Close()
 	return syscall.Getsockname(int(file.Fd()))
 }