Add proto fields for IPv6 overlay and compact IP encoding

shared/netiputil/compact.go

@@ -0,0 +1,74 @@
+// Package netiputil provides compact binary encoding for IP prefixes used in
+// the management proto wire format.
+//
+// Format: [IP bytes][1 byte prefix_len]
+//   - IPv4: 5 bytes total (4 IP + 1 prefix_len, 0-32)
+//   - IPv6: 17 bytes total (16 IP + 1 prefix_len, 0-128)
+//
+// Address family is determined by length: 5 = v4, 17 = v6.
+package netiputil
+
+import (
+	"fmt"
+	"net/netip"
+)
+
+// EncodePrefix encodes a netip.Prefix into compact bytes.
+// The address is always unmapped before encoding.
+func EncodePrefix(p netip.Prefix) []byte {
+	addr := p.Addr().Unmap()
+	raw := addr.As16()
+
+	if addr.Is4() {
+		b := make([]byte, 5)
+		copy(b, raw[12:16])
+		b[4] = byte(p.Bits())
+		return b
+	}
+
+	b := make([]byte, 17)
+	copy(b, raw[:])
+	b[16] = byte(p.Bits())
+	return b
+}
+
+// DecodePrefix decodes compact bytes into a netip.Prefix.
+func DecodePrefix(b []byte) (netip.Prefix, error) {
+	switch len(b) {
+	case 5:
+		addr := netip.AddrFrom4([4]byte(b[:4]))
+		return netip.PrefixFrom(addr, int(b[4])), nil
+	case 17:
+		addr := netip.AddrFrom16([16]byte(b[:16])).Unmap()
+		bits := int(b[16])
+		// Clamp prefix length when unmapping v4-mapped v6 to v4
+		if addr.Is4() && bits > 32 {
+			bits = 32
+		}
+		return netip.PrefixFrom(addr, bits), nil
+	default:
+		return netip.Prefix{}, fmt.Errorf("invalid compact prefix length %d (expected 5 or 17)", len(b))
+	}
+}
+
+// EncodeAddr encodes a netip.Addr into compact prefix bytes with a host prefix
+// length (/32 for v4, /128 for v6). The address is always unmapped before encoding.
+func EncodeAddr(a netip.Addr) []byte {
+	a = a.Unmap()
+	bits := 128
+	if a.Is4() {
+		bits = 32
+	}
+	return EncodePrefix(netip.PrefixFrom(a, bits))
+}
+
+// DecodeAddr decodes compact prefix bytes and returns only the address,
+// discarding the prefix length. Useful when the prefix length is implied
+// (e.g. peer overlay IPs are always /32 or /128).
+func DecodeAddr(b []byte) (netip.Addr, error) {
+	p, err := DecodePrefix(b)
+	if err != nil {
+		return netip.Addr{}, err
+	}
+	return p.Addr(), nil
+}