fix(mdns): macos: handle address reuse and fallback for no interfaces

Author: skrashevich

pkg/mdns/client.go

@@ -185,13 +185,21 @@ func (b *Browser) ListenMulticastUDP() error {
 	for _, ip4 := range ip4s {
 		conn, err := lc1.ListenPacket(ctx, "udp4", ip4.String()+":5353") // same port important
 		if err != nil {
+			if strings.Contains(err.Error(), "address already in use") {
+				continue
+			}
 			continue
 		}
 		b.Sends = append(b.Sends, conn)
 	}
 
 	if b.Sends == nil {
-		return errors.New("no interfaces for listen")
+		// Fall back to the system's default interface if no specific interfaces are available
+		conn, err := net.ListenMulticastUDP("udp4", nil, MulticastAddr)
+		if err != nil {
+			return errors.New("no interfaces for listen and fallback failed: " + err.Error())
+		}
+		b.Sends = append(b.Sends, conn)
 	}
 
 	// 3. Create receiver
@@ -388,12 +396,19 @@ loop:
 			switch v := addr.(type) {
 			case *net.IPNet:
 				if ip := v.IP.To4(); ip != nil {
+					if ip.IsLinkLocalUnicast() {
+						continue
+					}
 					ips = append(ips, ip)
 					continue loop
 				}
 			}
 		}
 	}
 
+	if len(ips) == 0 {
+		return nil, errors.New("no IPv4 addresses found")
+	}
+
 	return ips, nil
 }