rewrite value for protocols and add more tests

multiaddr.go

@@ -117,28 +117,15 @@ func (m *multiaddr) Decapsulate(o Multiaddr) Multiaddr {
 var ErrProtocolNotFound = fmt.Errorf("protocol not found in multiaddr")
 
 func (m *multiaddr) ValueForProtocol(code int) (string, error) {
-	protos := m.Protocols()
-	found := -1
-	index := 2
-
-	for i, p := range protos {
-		if code == p.Code {
+	for _, sub := range Split(m) {
+		p := sub.Protocols()[0]
+		if p.Code == code {
 			if p.Size == 0 {
 				return "", nil
 			}
-			found = i
-			break
-		} else {
-			index += 2
-			if p.Size == 0 {
-				index--
-			}
+			return strings.Split(sub.String(), "/")[2], nil
 		}
 	}
 
-	if found == -1 {
-		return "", ErrProtocolNotFound
-	}
-
-	return strings.Split(m.String(), "/")[index], nil
+	return "", ErrProtocolNotFound
 }

multiaddr_test.go

@@ -330,4 +330,15 @@ func TestGetValue(t *testing.T) {
 	default:
 		t.Fatalf("expected ErrProtocolNotFound but got: %s", err)
 	}
+
+	a = newMultiaddr(t, "/ip4/0.0.0.0") // only one addr
+	assertValueForProto(t, a, P_IP4, "0.0.0.0")
+
+	a = newMultiaddr(t, "/ip4/0.0.0.0/ip4/0.0.0.0/ip4/0.0.0.0") // same sub-addr
+	assertValueForProto(t, a, P_IP4, "0.0.0.0")
+
+	a = newMultiaddr(t, "/ip4/0.0.0.0/udp/12345/utp") // ending in a no-value one.
+	assertValueForProto(t, a, P_IP4, "0.0.0.0")
+	assertValueForProto(t, a, P_UDP, "12345")
+	assertValueForProto(t, a, P_UTP, "")
 }