feat(protonvpn): port forwarding support with NAT-PMP (#1543)

Co-authored-by: Nicholas Xavier <nicho@nicho.dev>

internal/natpmp/helpers_test.go

@@ -0,0 +1,99 @@
+package natpmp
+
+import (
+	"errors"
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type udpExchange struct {
+	request  []byte
+	response []byte
+	close    bool // to trigger a client error
+}
+
+// launchUDPServer launches an UDP server which will expect
+// the requests precised in each of the given exchanges,
+// and respond the given corresponding response.
+// The server shuts down gracefully at the end of the test.
+// The remote address (127.0.0.1:port) is returned, where
+// port is dynamically assigned by the OS so calling tests
+// can run in parallel.
+func launchUDPServer(t *testing.T, exchanges []udpExchange) (
+	remoteAddress *net.UDPAddr) {
+	t.Helper()
+
+	conn, err := net.ListenUDP("udp", nil)
+	require.NoError(t, err)
+
+	listeningAddress, ok := conn.LocalAddr().(*net.UDPAddr)
+	require.True(t, ok, "listening address is not UDP")
+	remoteAddress = &net.UDPAddr{
+		IP:   net.IPv4(127, 0, 0, 1),
+		Port: listeningAddress.Port,
+	}
+
+	done := make(chan struct{})
+	t.Cleanup(func() {
+		err := conn.Close()
+		if !errors.Is(err, net.ErrClosed) {
+			assert.NoError(t, err)
+		}
+		<-done
+	})
+
+	var maxBufferSize int
+	for _, exchange := range exchanges {
+		if len(exchange.request) > maxBufferSize {
+			maxBufferSize = len(exchange.request)
+		}
+	}
+
+	buffer := make([]byte, maxBufferSize)
+
+	ready := make(chan struct{})
+	go func() {
+		defer close(done)
+		close(ready)
+		for _, exchange := range exchanges {
+			n, clientAddress, err := conn.ReadFromUDP(buffer)
+			if errors.Is(err, net.ErrClosed) {
+				t.Error("at least one exchange is missing")
+				return
+			}
+			require.NoError(t, err)
+
+			assert.Equal(t, len(exchange.request), n,
+				"request message size is unexpected")
+			if n > 0 {
+				assert.Equal(t, exchange.request, buffer[:n],
+					"request message is unexpected")
+			}
+
+			if exchange.close {
+				err = conn.Close()
+				if !errors.Is(err, net.ErrClosed) {
+					// connection might be already closed by client production code
+					assert.NoError(t, err)
+				}
+				return
+			}
+
+			_, err = conn.WriteToUDP(exchange.response, clientAddress)
+			require.NoError(t, err)
+		}
+
+		err := conn.Close()
+		if !errors.Is(err, net.ErrClosed) {
+			// The connection closing can be raced by the test
+			// cleanup function defined above.
+			assert.NoError(t, err)
+		}
+	}()
+	<-ready
+
+	return remoteAddress
+}