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

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

internal/natpmp/externaladdress_test.go

@@ -0,0 +1,71 @@
+package natpmp
+
+import (
+	"context"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Client_ExternalAddress(t *testing.T) {
+	t.Parallel()
+
+	canceledCtx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	testCases := map[string]struct {
+		ctx                       context.Context
+		gateway                   netip.Addr
+		initialRetry              time.Duration
+		exchanges                 []udpExchange
+		durationSinceStartOfEpoch time.Duration
+		externalIPv4Address       netip.Addr
+		err                       error
+		errMessage                string
+	}{
+		"failure": {
+			ctx:          canceledCtx,
+			gateway:      netip.AddrFrom4([4]byte{127, 0, 0, 1}),
+			initialRetry: time.Millisecond,
+			err:          context.Canceled,
+			errMessage:   "executing remote procedure call: reading from udp connection: context canceled",
+		},
+		"success": {
+			ctx:          context.Background(),
+			gateway:      netip.AddrFrom4([4]byte{127, 0, 0, 1}),
+			initialRetry: time.Millisecond,
+			exchanges: []udpExchange{{
+				request:  []byte{0, 0},
+				response: []byte{0x0, 0x80, 0x0, 0x0, 0x0, 0x13, 0xf2, 0x4f, 0x49, 0x8c, 0x36, 0x9a},
+			}},
+			durationSinceStartOfEpoch: time.Duration(0x13f24f) * time.Second,
+			externalIPv4Address:       netip.AddrFrom4([4]byte{0x49, 0x8c, 0x36, 0x9a}),
+		},
+	}
+
+	for name, testCase := range testCases {
+		testCase := testCase
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			remoteAddress := launchUDPServer(t, testCase.exchanges)
+
+			client := Client{
+				serverPort:   uint16(remoteAddress.Port),
+				initialRetry: testCase.initialRetry,
+				maxRetries:   1,
+			}
+
+			durationSinceStartOfEpoch, externalIPv4Address, err :=
+				client.ExternalAddress(testCase.ctx, testCase.gateway)
+			assert.ErrorIs(t, err, testCase.err)
+			if testCase.err != nil {
+				assert.EqualError(t, err, testCase.errMessage)
+			}
+			assert.Equal(t, testCase.durationSinceStartOfEpoch, durationSinceStartOfEpoch)
+			assert.Equal(t, testCase.externalIPv4Address, externalIPv4Address)
+		})
+	}
+}