java - 环回上的 Pcap4j 数据包捕获不区分传入和传出数据包

Question

我正在使用 pcp4j 为我的项目编写一个简单的数据包捕获和处理引擎。下面是我用来捕获数据包的代码，但是当我使用它只捕获环回地址上的传入数据包时，它会给我传出和传入的数据包。

如何区分环回地址上的传入和传出数据包？

    public class PacketListner {

  int packet_count = 0;
  private static final String READ_TIMEOUT_KEY
      = PacketListner.class.getName() + ".readTimeout";
  private static final int READ_TIMEOUT
      = Integer.getInteger(READ_TIMEOUT_KEY, 10); // [ms]

  private static final String SNAPLEN_KEY
      = PacketListner.class.getName() + ".snaplen";
  private static final int SNAPLEN
      = Integer.getInteger(SNAPLEN_KEY, 65536); // [bytes]

  private static final String TIMESTAMP_PRECISION_NANO_KEY
      = PacketListner.class.getName() + ".timestampPrecision.nano";
  private static final boolean TIMESTAMP_PRECISION_NANO
      = Boolean.getBoolean(TIMESTAMP_PRECISION_NANO_KEY);

  public int sniff() throws PcapNativeException, NotOpenException {

    PcapNetworkInterface nif = null;
    try {
      nif = new NifSelector().selectNetworkInterface();
    } catch (IOException e) {
      e.printStackTrace();
    }

    if (nif == null) {
      return -1;
    }

    System.out.println(nif.getName() + "(" + nif.getDescription() + ")");

    PcapHandle.Builder phb
        = new PcapHandle.Builder(nif.getName())
        .snaplen(SNAPLEN)
        .direction(PcapHandle.PcapDirection.IN)
        .promiscuousMode(PcapNetworkInterface.PromiscuousMode.PROMISCUOUS)
        .timeoutMillis(READ_TIMEOUT);

    if (TIMESTAMP_PRECISION_NANO) {
      phb.timestampPrecision(PcapHandle.TimestampPrecision.NANO);
    }

    PcapHandle handle = phb.build();

    while (true) {
      Packet packet = handle.getNextPacket();
      if (packet != null) {
        if (packet.contains(IpV4Packet.class) &&
            (packet.contains(TcpPacket.class) || packet.contains(UdpPacket.class))) {
          IpV4Packet pkt = packet.get(IpV4Packet.class);
          if (packet.contains (TcpPacket.class)) {
             TcpPacket tcpPkt = packet.get(TcpPacket.class);
             System.out.println(pkt.getHeader().getSrcAddr() + ":" + tcpPkt.getHeader().getDstPort());
          }
          else {
             UDpPacket udpPkt = packet.get(UDpPacket.class);
             System.out.println(pkt.getHeader().getSrcAddr() + ":" + udpPkt.getHeader().getDstPort());
          }

        }
       packet_count++;
      }
    }
  }
}