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
+}

shared/netiputil/compact_test.go

@@ -0,0 +1,127 @@
+package netiputil
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEncodeDecodePrefix(t *testing.T) {
+	tests := []struct {
+		name   string
+		prefix string
+		size   int
+	}{
+		{
+			name:   "v4 host",
+			prefix: "100.64.0.1/32",
+			size:   5,
+		},
+		{
+			name:   "v4 network",
+			prefix: "10.0.0.0/8",
+			size:   5,
+		},
+		{
+			name:   "v4 default",
+			prefix: "0.0.0.0/0",
+			size:   5,
+		},
+		{
+			name:   "v6 host",
+			prefix: "fd00::1/128",
+			size:   17,
+		},
+		{
+			name:   "v6 network",
+			prefix: "fd00:1234:5678::/48",
+			size:   17,
+		},
+		{
+			name:   "v6 default",
+			prefix: "::/0",
+			size:   17,
+		},
+		{
+			name:   "v4 /16 overlay",
+			prefix: "100.64.0.1/16",
+			size:   5,
+		},
+		{
+			name:   "v6 /64 overlay",
+			prefix: "fd00::abcd:1/64",
+			size:   17,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := netip.MustParsePrefix(tt.prefix)
+			b := EncodePrefix(p)
+			assert.Equal(t, tt.size, len(b), "encoded size")
+
+			decoded, err := DecodePrefix(b)
+			require.NoError(t, err)
+			assert.Equal(t, p, decoded)
+		})
+	}
+}
+
+func TestEncodePrefixUnmaps(t *testing.T) {
+	// v4-mapped v6 address should encode as v4
+	mapped := netip.MustParsePrefix("::ffff:10.1.2.3/32")
+	b := EncodePrefix(mapped)
+	assert.Equal(t, 5, len(b), "v4-mapped should encode as 5 bytes")
+
+	decoded, err := DecodePrefix(b)
+	require.NoError(t, err)
+	assert.Equal(t, netip.MustParsePrefix("10.1.2.3/32"), decoded)
+}
+
+func TestDecodeAddr(t *testing.T) {
+	v4 := netip.MustParseAddr("100.64.0.5")
+	b := EncodeAddr(v4)
+	assert.Equal(t, 5, len(b))
+
+	got, err := DecodeAddr(b)
+	require.NoError(t, err)
+	assert.Equal(t, v4, got)
+
+	v6 := netip.MustParseAddr("fd00::1")
+	b = EncodeAddr(v6)
+	assert.Equal(t, 17, len(b))
+
+	got, err = DecodeAddr(b)
+	require.NoError(t, err)
+	assert.Equal(t, v6, got)
+}
+
+func TestDecodePrefixInvalidLength(t *testing.T) {
+	_, err := DecodePrefix([]byte{1, 2, 3})
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "invalid compact prefix length 3")
+
+	_, err = DecodePrefix(nil)
+	assert.Error(t, err)
+
+	_, err = DecodePrefix([]byte{})
+	assert.Error(t, err)
+}
+
+func TestDecodePrefixUnmapsV6Input(t *testing.T) {
+	// If someone encodes a v4-mapped v6 as 17 bytes, decode should unmap it
+	// and clamp the prefix length to 32 for v4
+	addr := netip.MustParseAddr("::ffff:192.168.1.1")
+
+	raw := addr.As16()
+	b := make([]byte, 17)
+	copy(b, raw[:])
+	b[16] = 128
+
+	decoded, err := DecodePrefix(b)
+	require.NoError(t, err)
+	assert.True(t, decoded.Addr().Is4(), "should be unmapped to v4")
+	assert.Equal(t, netip.MustParsePrefix("192.168.1.1/32"), decoded)
+}