anchor.diff:  //Port Restricted Cone
   //Symmetric
   
  +class StunClientSendHeaderResult {
  +  String address;
  +  int port;
  +  StunHeader header;
  +  StunClientSendHeaderResult(this.address, this.port, this.header) {}
  +}
  +
   class StunClient {
     net.TetSocketBuilder builder;
     String address;
  
positive.code:     cash[header.transactionID] = new Completer();
      _udp.send(header.encode(), stunServer, stunServerPort);
      cash[header.transactionID].future.timeout(timeout, onTimeout: () {
        cash.remove(header.transactionID).completeError({"mes":"timeout"});
      });
      return cash[header.transactionID].future;
    }
  
negative.code:   String stunServer;
    int stunServerPort;
  
    Map<StunTransactionID, Completer<StunClientSendHeaderResult>> cash = {};
    net.TetUdpSocket _udp = null;
  
    StunClient(this.builder, this.stunServer, this.stunServerPort, {this.address: "0.0.0.0", this.port: 0}) {
  