我正在尝试使用 TCP 协议进行一些原始套接字编程,但是我遇到了 PacketDotNet 和 TCP 校验和的问题。
我在 PacketDotNet.TCPPacket 中遇到空指针异常。我得到的例外如下:
ValidTCPChecksum = 'tcpPacket.ValidTCPChecksum' threw an exception of type 'System.NullReferenceException'
和
System.NullReferenceException: Object reference not set to an instance of an object.
at PacketDotNet.TransportPacket.CalculateChecksum(TransportChecksumOption option)
at PacketDotNet.TcpPacket.CalculateTCPChecksum()
at ProjectServer.MainWindow.packetstuff(String toIp, String fromIp, Byte[] payload) in c:\\Users\\MyUser\\Documents\\Visual Studio 2012\\Projects\\ProjectServer\\ProjectServer\\MainWindow.xaml.cs:line 131
at ProjectServer.MainWindow.Project_Click(Object sender, RoutedEventArgs e) in c:\\Users\\MyUser\\Documents\\Visual Studio 2012\\Projects\\ProjectServer\\ProjectServer\\MainWindow.xaml.cs:line 68
第 131 行是tcpPacket.Checksum = (ushort)tcpPacket.CalculateTCPChecksum();
似乎它可能与HelpLink
null 有关,但我不是 100% 确定。
我试图自己做校验和,但到目前为止我还不能实现一个有效的校验和算法。
这是基本构建我的数据包的packetstuff方法。也许它有什么问题。
public void packetstuff(string toIp, string fromIp, byte[] payload)
{
ushort tcpSourcePort = 123;
ushort tcpDestinationPort = 321;
var tcpPacket = new TcpPacket(tcpSourcePort, tcpDestinationPort);
var ipSourceAddress = System.Net.IPAddress.Parse(fromIp);
var ipDestinationAddress = System.Net.IPAddress.Parse(toIp);
var ipPacket = new IPv4Packet(ipSourceAddress, ipDestinationAddress);
var sourceHwAddress = "MY-MA-CA-DD-RE-SS";//?actually a bit unsure what this should be
var ethernetSourceHwAddress = System.Net.NetworkInformation.PhysicalAddress.Parse(sourceHwAddress);
var destinationHwAddress = "MY-MA-CA-DD-RE-SS";
var ethernetDestinationHwAddress = System.Net.NetworkInformation.PhysicalAddress.Parse(destinationHwAddress);
var ethernetPacket = new EthernetPacket(ethernetSourceHwAddress,
ethernetDestinationHwAddress,
EthernetPacketType.None);
if (tcpPacket != null)
{
tcpPacket.Checksum = 0;
tcpPacket.Checksum = (ushort)tcpPacket.CalculateTCPChecksum(); //This is where the error occurs.
}
ipPacket.PayloadPacket = tcpPacket;
ipPacket.UpdateIPChecksum();
ethernetPacket.PayloadPacket = ipPacket;
ethernetPacket.UpdateCalculatedValues();
packetBytes = ethernetPacket.Bytes;
Thread producer = new Thread(new ThreadStart(ThreadRun));
device.Open();
producer.Start();
}
Windows7、VS2012