Add IPv6 overlay address support to client interface and engine

client/iface/wgaddr/address.go

@@ -3,12 +3,18 @@ package wgaddr
 import (
 	"fmt"
 	"net/netip"
+
+	"github.com/netbirdio/netbird/shared/netiputil"
 )
 
 // Address WireGuard parsed address
 type Address struct {
 	IP      netip.Addr
 	Network netip.Prefix
+
+	// IPv6 overlay address, if assigned.
+	IPv6    netip.Addr
+	IPv6Net netip.Prefix
 }
 
 // ParseWGAddress parse a string ("1.2.3.4/24") address to WG Address
@@ -23,6 +29,57 @@ func ParseWGAddress(address string) (Address, error) {
 	}, nil
 }
 
-func (addr Address) String() string {
-	return fmt.Sprintf("%s/%d", addr.IP.String(), addr.Network.Bits())
+// HasIPv6 reports whether a v6 overlay address is assigned.
+func (addr Address) HasIPv6() bool {
+	return addr.IPv6.IsValid()
+}
+
+func (addr Address) String() string {
+	return addr.Prefix().String()
+}
+
+// IPv6String returns the v6 address in CIDR notation, or empty string if none.
+func (addr Address) IPv6String() string {
+	if !addr.HasIPv6() {
+		return ""
+	}
+	return addr.IPv6Prefix().String()
+}
+
+// Prefix returns the v4 host address with its network prefix length (e.g. 100.64.0.1/16).
+func (addr Address) Prefix() netip.Prefix {
+	return netip.PrefixFrom(addr.IP, addr.Network.Bits())
+}
+
+// IPv6Prefix returns the v6 host address with its network prefix length, or a zero prefix if none.
+func (addr Address) IPv6Prefix() netip.Prefix {
+	if !addr.HasIPv6() {
+		return netip.Prefix{}
+	}
+	return netip.PrefixFrom(addr.IPv6, addr.IPv6Net.Bits())
+}
+
+// SetIPv6FromCompact decodes a compact prefix (5 or 17 bytes) and sets the IPv6 fields.
+// Returns an error if the bytes are invalid. A nil or empty input is a no-op.
+//
+//nolint:recvcheck
+func (addr *Address) SetIPv6FromCompact(raw []byte) error {
+	if len(raw) == 0 {
+		return nil
+	}
+	prefix, err := netiputil.DecodePrefix(raw)
+	if err != nil {
+		return fmt.Errorf("decode v6 overlay address: %w", err)
+	}
+	addr.IPv6 = prefix.Addr()
+	addr.IPv6Net = prefix.Masked()
+	return nil
+}
+
+// ClearIPv6 removes the IPv6 overlay address, leaving only v4.
+//
+//nolint:recvcheck // ClearIPv6 is the only mutating method on this otherwise value-type struct.
+func (addr *Address) ClearIPv6() {
+	addr.IPv6 = netip.Addr{}
+	addr.IPv6Net = netip.Prefix{}
 }