feat(perfectprivacy): port forwarding support (#2378)

internal/provider/perfectprivacy/portforward.go

@@ -0,0 +1,43 @@
+package perfectprivacy
+
+import (
+	"context"
+	"net/netip"
+
+	"github.com/qdm12/gluetun/internal/provider/utils"
+)
+
+// PortForward calculates and returns the VPN server side ports forwarded.
+func (p *Provider) PortForward(_ context.Context,
+	objects utils.PortForwardObjects) (ports []uint16, err error) {
+	if !objects.InternalIP.IsValid() {
+		panic("internal ip is not set")
+	}
+
+	return internalIPToPorts(objects.InternalIP), nil
+}
+
+func (p *Provider) KeepPortForward(ctx context.Context,
+	_ utils.PortForwardObjects) (err error) {
+	<-ctx.Done()
+	return ctx.Err()
+}
+
+// See https://www.perfect-privacy.com/en/faq section
+// How are the default forwarding ports being calculated?
+func internalIPToPorts(internalIP netip.Addr) (ports []uint16) {
+	internalIPBytes := internalIP.AsSlice()
+	// Convert the internal IP address to a bit string
+	// and keep only the last 12 bits
+	last16Bits := internalIPBytes[len(internalIPBytes)-2:]
+	last12Bits := []byte{
+		last16Bits[0] & 0b00001111, // only keep 4 bits
+		last16Bits[1],
+	}
+	basePort := uint16(last12Bits[0])<<8 + uint16(last12Bits[1]) //nolint:gomnd
+	return []uint16{
+		10000 + basePort,
+		20000 + basePort,
+		30000 + basePort,
+	}
+}