fix(pia): support port forwarding using Wireguard (#2420)

- Build API IP address using the first 2 bytes of the gateway IP and adding `128.1` to it
- API IP address is valid for both OpenVPN and Wireguard
- Fix #2320

internal/configuration/settings/serverselection.go

@@ -191,11 +191,19 @@ func validateServerFilters(settings ServerSelection, filterChoices models.Filter
 		return fmt.Errorf("%w: %w", ErrHostnameNotValid, err)
 	}
 
-	if vpnServiceProvider == providers.Custom && len(settings.Names) == 1 {
-		// Allow a single name to be specified for the custom provider in case
-		// the user wants to use VPN server side port forwarding with PIA
-		// which requires a server name for TLS verification.
-		filterChoices.Names = settings.Names
+	if vpnServiceProvider == providers.Custom {
+		switch len(settings.Names) {
+		case 0:
+		case 1:
+			// Allow a single name to be specified for the custom provider in case
+			// the user wants to use VPN server side port forwarding with PIA
+			// which requires a server name for TLS verification.
+			filterChoices.Names = settings.Names
+		default:
+			return fmt.Errorf("%w: %d names specified instead of "+
+				"0 or 1 for the custom provider",
+				ErrNameNotValid, len(settings.Names))
+		}
 	}
 	err = atLeastOneIsOneOfCaseInsensitive(settings.Names, filterChoices.Names, warner)
 	if err != nil {

internal/provider/privateinternetaccess/portforward.go

@@ -39,7 +39,7 @@ func (p *Provider) PortForward(ctx context.Context,
 	}
 
 	serverName := objects.ServerName
-
+	apiIP := buildAPIIPAddress(objects.Gateway)
 	logger := objects.Logger
 
 	if !objects.CanPortForward {
@@ -70,7 +70,7 @@ func (p *Provider) PortForward(ctx context.Context,
 
 	if !dataFound || expired {
 		client := objects.Client
-		data, err = refreshPIAPortForwardData(ctx, client, privateIPClient, objects.Gateway,
+		data, err = refreshPIAPortForwardData(ctx, client, privateIPClient, apiIP,
 			p.portForwardPath, objects.Username, objects.Password)
 		if err != nil {
 			return nil, fmt.Errorf("refreshing port forward data: %w", err)
@@ -80,7 +80,7 @@ func (p *Provider) PortForward(ctx context.Context,
 	logger.Info("Port forwarded data expires in " + format.FriendlyDuration(durationToExpiration))
 
 	// First time binding
-	if err := bindPort(ctx, privateIPClient, objects.Gateway, data); err != nil {
+	if err := bindPort(ctx, privateIPClient, apiIP, data); err != nil {
 		return nil, fmt.Errorf("binding port: %w", err)
 	}
 
@@ -100,6 +100,8 @@ func (p *Provider) KeepPortForward(ctx context.Context,
 		panic("gateway is not set")
 	}
 
+	apiIP := buildAPIIPAddress(objects.Gateway)
+
 	privateIPClient, err := newHTTPClient(objects.ServerName)
 	if err != nil {
 		return fmt.Errorf("creating custom HTTP client: %w", err)
@@ -127,7 +129,7 @@ func (p *Provider) KeepPortForward(ctx context.Context,
 			}
 			return ctx.Err()
 		case <-keepAliveTimer.C:
-			err = bindPort(ctx, privateIPClient, objects.Gateway, data)
+			err = bindPort(ctx, privateIPClient, apiIP, data)
 			if err != nil {
 				return fmt.Errorf("binding port: %w", err)
 			}
@@ -139,14 +141,25 @@ func (p *Provider) KeepPortForward(ctx context.Context,
 	}
 }
 
+func buildAPIIPAddress(gateway netip.Addr) (api netip.Addr) {
+	if gateway.Is6() {
+		panic("IPv6 gateway not supported")
+	}
+
+	gatewayBytes := gateway.As4()
+	gatewayBytes[2] = 128
+	gatewayBytes[3] = 1
+	return netip.AddrFrom4(gatewayBytes)
+}
+
 func refreshPIAPortForwardData(ctx context.Context, client, privateIPClient *http.Client,
-	gateway netip.Addr, portForwardPath, username, password string) (data piaPortForwardData, err error) {
+	apiIP netip.Addr, portForwardPath, username, password string) (data piaPortForwardData, err error) {
 	data.Token, err = fetchToken(ctx, client, username, password)
 	if err != nil {
 		return data, fmt.Errorf("fetching token: %w", err)
 	}
 
-	data.Port, data.Signature, data.Expiration, err = fetchPortForwardData(ctx, privateIPClient, gateway, data.Token)
+	data.Port, data.Signature, data.Expiration, err = fetchPortForwardData(ctx, privateIPClient, apiIP, data.Token)
 	if err != nil {
 		return data, fmt.Errorf("fetching port forwarding data: %w", err)
 	}
@@ -286,15 +299,15 @@ func fetchToken(ctx context.Context, client *http.Client,
 	return result.Token, nil
 }
 
-func fetchPortForwardData(ctx context.Context, client *http.Client, gateway netip.Addr, token string) (
+func fetchPortForwardData(ctx context.Context, client *http.Client, apiIP netip.Addr, token string) (
 	port uint16, signature string, expiration time.Time, err error) {
 	errSubstitutions := map[string]string{url.QueryEscape(token): "<token>"}
 
 	queryParams := make(url.Values)
 	queryParams.Add("token", token)
 	url := url.URL{
 		Scheme:   "https",
-		Host:     net.JoinHostPort(gateway.String(), "19999"),
+		Host:     net.JoinHostPort(apiIP.String(), "19999"),
 		Path:     "/getSignature",
 		RawQuery: queryParams.Encode(),
 	}
@@ -340,7 +353,7 @@ var (
 	ErrBadResponse = errors.New("bad response received")
 )
 
-func bindPort(ctx context.Context, client *http.Client, gateway netip.Addr, data piaPortForwardData) (err error) {
+func bindPort(ctx context.Context, client *http.Client, apiIPAddress netip.Addr, data piaPortForwardData) (err error) {
 	payload, err := packPayload(data.Port, data.Token, data.Expiration)
 	if err != nil {
 		return fmt.Errorf("serializing payload: %w", err)
@@ -351,7 +364,7 @@ func bindPort(ctx context.Context, client *http.Client, gateway netip.Addr, data
 	queryParams.Add("signature", data.Signature)
 	bindPortURL := url.URL{
 		Scheme:   "https",
-		Host:     net.JoinHostPort(gateway.String(), "19999"),
+		Host:     net.JoinHostPort(apiIPAddress.String(), "19999"),
 		Path:     "/bindPort",
 		RawQuery: queryParams.Encode(),
 	}