Add "zone" multiaddr (IPv6 zone)

See [rfc4007].

Can be prefixed to "ip6" like so:

    /zone/eth0/ip6/fe80::1

This corresponds to the rfc4007 address `fe80::1%eth0`

[rfc4007] https://tools.ietf.org/html/rfc4007

multiaddr_test.go

@@ -23,6 +23,9 @@ func TestConstructFails(t *testing.T) {
 		"/ip4/::1",
 		"/ip4/fdpsofodsajfdoisa",
 		"/ip6",
+		"/ip6zone",
+		"/ip6zone/",
+		"/ip6zone//ip6/fe80::1",
 		"/udp",
 		"/tcp",
 		"/sctp",
@@ -65,6 +68,10 @@ func TestConstructSucceeds(t *testing.T) {
 		"/ip6/::1",
 		"/ip6/2601:9:4f81:9700:803e:ca65:66e8:c21",
 		"/ip6/2601:9:4f81:9700:803e:ca65:66e8:c21/udp/1234/quic",
+		"/ip6zone/x/ip6/fe80::1",
+		"/ip6zone/x%y/ip6/fe80::1",
+		"/ip6zone/x%y/ip6/::",
+		"/ip6zone/x/ip6/fe80::1/udp/1234/quic",
 		"/onion/timaq4ygg2iegci7:1234",
 		"/onion/timaq4ygg2iegci7:80/http",
 		"/udp/0",
@@ -492,3 +499,32 @@ func TestInvalidP2PAddr(t *testing.T) {
 		_ = ma.String()
 	}
 }
+
+func TestZone(t *testing.T) {
+	ip6String := "/ip6zone/eth0/ip6/::1"
+	ip6Bytes := []byte{
+		0x2a, 4,
+		'e', 't', 'h', '0',
+		0x29,
+		0, 0, 0, 0,
+		0, 0, 0, 0,
+		0, 0, 0, 0,
+		0, 0, 0, 1,
+	}
+
+	ma, err := NewMultiaddr(ip6String)
+	if err != nil {
+		t.Error(err)
+	}
+	if !bytes.Equal(ma.Bytes(), ip6Bytes) {
+		t.Errorf("expected %x, got %x", ip6Bytes, ma.Bytes())
+	}
+
+	ma2, err2 := NewMultiaddrBytes(ip6Bytes)
+	if err2 != nil {
+		t.Error(err)
+	}
+	if ma2.String() != ip6String {
+		t.Errorf("expected %s, got %s", ip6String, ma2.String())
+	}
+}

protocols.go

@@ -6,21 +6,22 @@ package multiaddr
 // TODO: Use a single source of truth for all multicodecs instead of
 // distributing them like this...
 const (
-	P_IP4   = 0x0004
-	P_TCP   = 0x0006
-	P_UDP   = 0x0111
-	P_DCCP  = 0x0021
-	P_IP6   = 0x0029
-	P_QUIC  = 0x01CC
-	P_SCTP  = 0x0084
-	P_UDT   = 0x012D
-	P_UTP   = 0x012E
-	P_UNIX  = 0x0190
-	P_P2P   = 0x01A5
-	P_IPFS  = 0x01A5 // alias for backwards compatability
-	P_HTTP  = 0x01E0
-	P_HTTPS = 0x01BB
-	P_ONION = 0x01BC
+	P_IP4     = 0x0004
+	P_TCP     = 0x0006
+	P_UDP     = 0x0111
+	P_DCCP    = 0x0021
+	P_IP6     = 0x0029
+	P_IP6ZONE = 0x002A
+	P_QUIC    = 0x01CC
+	P_SCTP    = 0x0084
+	P_UDT     = 0x012D
+	P_UTP     = 0x012E
+	P_UNIX    = 0x0190
+	P_P2P     = 0x01A5
+	P_IPFS    = 0x01A5 // alias for backwards compatability
+	P_HTTP    = 0x01E0
+	P_HTTPS   = 0x01BB
+	P_ONION   = 0x01BC
 )
 
 var (
@@ -64,6 +65,14 @@ var (
 		Transcoder: TranscoderIP6,
 	}
 	// these require varint
+	protoIP6ZONE = Protocol{
+		Name:       "ip6zone",
+		Code:       P_IP6ZONE,
+		VCode:      CodeToVarint(P_IP6ZONE),
+		Size:       LengthPrefixedVarSize,
+		Path:       false,
+		Transcoder: TranscoderIP6Zone,
+	}
 	protoSCTP = Protocol{
 		Name:       "sctp",
 		Code:       P_SCTP,
@@ -127,6 +136,7 @@ func init() {
 		protoUDP,
 		protoDCCP,
 		protoIP6,
+		protoIP6ZONE,
 		protoSCTP,
 		protoONION,
 		protoUTP,

transcoders.go

@@ -47,6 +47,7 @@ func (t twrp) ValidateBytes(b []byte) error {
 
 var TranscoderIP4 = NewTranscoderFromFunctions(ip4StB, ipBtS, nil)
 var TranscoderIP6 = NewTranscoderFromFunctions(ip6StB, ipBtS, nil)
+var TranscoderIP6Zone = NewTranscoderFromFunctions(ip6zoneStB, ip6zoneBtS, nil)
 
 func ip4StB(s string) ([]byte, error) {
 	i := net.ParseIP(s).To4()
@@ -56,6 +57,20 @@ func ip4StB(s string) ([]byte, error) {
 	return i, nil
 }
 
+func ip6zoneStB(s string) ([]byte, error) {
+	if len(s) == 0 {
+		return nil, fmt.Errorf("empty ip6zone")
+	}
+	return []byte(s), nil
+}
+
+func ip6zoneBtS(b []byte) (string, error) {
+	if len(b) == 0 {
+		return "", fmt.Errorf("invalid length (should be > 0)")
+	}
+	return string(b), nil
+}
+
 func ip6StB(s string) ([]byte, error) {
 	i := net.ParseIP(s).To16()
 	if i == nil {