feat(portforward): port redirection with VPN_PORT_FORWARDING_LISTENING_PORT

internal/portforward/interfaces.go

@@ -18,6 +18,8 @@ type Routing interface {
 type PortAllower interface {
 	SetAllowedPort(ctx context.Context, port uint16, intf string) (err error)
 	RemoveAllowedPort(ctx context.Context, port uint16) (err error)
+	RedirectPort(ctx context.Context, intf string, sourcePort,
+		destinationPort uint16) (err error)
 }
 
 type Logger interface {

internal/portforward/loop.go

@@ -39,8 +39,9 @@ func NewLoop(settings settings.PortForwarding, routing Routing,
 		settings: Settings{
 			VPNIsUp: ptrTo(false),
 			Service: service.Settings{
-				Enabled:  settings.Enabled,
-				Filepath: *settings.Filepath,
+				Enabled:       settings.Enabled,
+				Filepath:      *settings.Filepath,
+				ListeningPort: *settings.ListeningPort,
 			},
 		},
 		routing:     routing,

internal/portforward/service/interfaces.go

@@ -10,6 +10,8 @@ import (
 type PortAllower interface {
 	SetAllowedPort(ctx context.Context, port uint16, intf string) (err error)
 	RemoveAllowedPort(ctx context.Context, port uint16) (err error)
+	RedirectPort(ctx context.Context, intf string, sourcePort,
+		destinationPort uint16) (err error)
 }
 
 type Routing interface {

internal/portforward/service/settings.go

@@ -14,6 +14,7 @@ type Settings struct {
 	Filepath      string
 	Interface     string // needed for PIA and ProtonVPN, tun0 for example
 	ServerName    string // needed for PIA
+	ListeningPort uint16
 }
 
 func (s Settings) Copy() (copied Settings) {
@@ -22,6 +23,7 @@ func (s Settings) Copy() (copied Settings) {
 	copied.Filepath = s.Filepath
 	copied.Interface = s.Interface
 	copied.ServerName = s.ServerName
+	copied.ListeningPort = s.ListeningPort
 	return copied
 }
 
@@ -31,6 +33,7 @@ func (s *Settings) OverrideWith(update Settings) {
 	s.Filepath = gosettings.OverrideWithString(s.Filepath, update.Filepath)
 	s.Interface = gosettings.OverrideWithString(s.Interface, update.Interface)
 	s.ServerName = gosettings.OverrideWithString(s.ServerName, update.ServerName)
+	s.ListeningPort = gosettings.OverrideWithNumber(s.ListeningPort, update.ListeningPort)
 }
 
 var (

internal/portforward/service/start.go

@@ -40,6 +40,13 @@ func (s *Service) Start(ctx context.Context) (runError <-chan error, err error)
 		return nil, fmt.Errorf("allowing port in firewall: %w", err)
 	}
 
+	if s.settings.ListeningPort != 0 {
+		err = s.portAllower.RedirectPort(ctx, s.settings.Interface, port, s.settings.ListeningPort)
+		if err != nil {
+			return nil, fmt.Errorf("redirecting port in firewall: %w", err)
+		}
+	}
+
 	err = s.writePortForwardedFile(port)
 	if err != nil {
 		_ = s.cleanup()

internal/portforward/service/stop.go

@@ -35,6 +35,15 @@ func (s *Service) cleanup() (err error) {
 		return fmt.Errorf("blocking previous port in firewall: %w", err)
 	}
 
+	if s.settings.ListeningPort != 0 {
+		ctx := context.Background()
+		const listeningPort = 0 // 0 to clear the redirection
+		err = s.portAllower.RedirectPort(ctx, s.settings.Interface, s.port, listeningPort)
+		if err != nil {
+			return fmt.Errorf("removing previous port redirection in firewall: %w", err)
+		}
+	}
+
 	s.port = 0
 
 	filepath := s.settings.Filepath