我用java写了一个服务器，端口是4444。然后我用终端连接到端口4444（我的mysql真实端口是3306）然后用jpcap捕获数据包并将src端口和ip更改为我的服务器端口和ip 并且我将目标端口和 id 更改为 mysql 端口和 ip。我用 jpcapSender 发送新数据包。问题是，当我发送数据包时，它的长度是 74。但是当我捕获该数据包时，它是 60 字节。我猜这是因为 dont_frag 是假的。但改变它并没有帮助。封装连接；
public class Bridge implements PacketReceiver {
NetworkInterface device;
static int DeviceName;
public Bridge(NetworkInterface device,int deviceName) throws IOException {
ServerSocket ss = new ServerSocket(4444);
this.device = device;
this.DeviceName=deviceName;
System.err.println(DeviceName);
JpcapCaptor jpcap;
jpcap = JpcapCaptor.openDevice(device, 2000, false, 20);
// System.err.println(jpcap.isNonBlockinMode());
jpcap.loopPacket(-1, new Bridge());
}
public Bridge() {
}
@Override
public void receivePacket(Packet p) {
if (p instanceof TCPPacket) {
TCPPacket myPacket = (TCPPacket) p;
if(myPacket.dst_port==3306 && myPacket.src_port==4444){
System.err.println("don't frag"+myPacket.len);
}
if (myPacket.dst_port == 4444) {
if(myPacket.syn==true){
System.err.println("connecting"+myPacket.len);
DatalinkPacket dlp=myPacket.datalink;
System.err.println(dlp.toString());
try {
Server.src_ip = myPacket.src_ip;
Server.src_port = myPacket.src_port;
myPacket.src_ip = InetAddress.getByName("127.0.0.1");// TODO
// variable
myPacket.src_port = 4444;
myPacket.dst_ip = InetAddress.getByName("127.0.0.1");// System.err.println("device"+this.DeviceName);
myPacket.dst_port = 3306;
sendPacket(myPacket);
} catch (UnknownHostException e) {
// Auto-generated catch block
e.printStackTrace();
}//
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (myPacket.syn = false ) {//
System.err.println("query request");
MySqlRequestParser parser = new MySqlRequestParser(
myPacket.data);
String query = parser.getQuery();
System.err.println(query);
// TODO get rules from db
// TODO check for rules
try {
Server.src_ip = myPacket.src_ip;
Server.src_port = myPacket.src_port;
// myPacket.src_ip = InetAddress.getByName("127.0.0.1");// TODO
// variable
//myPacket.src_port = 4444;
myPacket.dst_ip = InetAddress.getByName("127.0.0.1");// TODO
myPacket.dst_port = 3306;
sendPacket(myPacket);
} catch (UnknownHostException e) {
// Auto-generated catch block
e.printStackTrace();
}//
catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
if (myPacket.src_port == 3306) {
System.err.println("response"+myPacket.sequence);
if (myPacket.syn == false || myPacket.syn == true) {
System.err.println("response to query");
myPacket.dst_ip = Server.src_ip;
myPacket.dst_port = Server.src_port;
myPacket.src_port = 4444;// TODO about ip it's kinda
// fishiiii
try {
sendPacket(myPacket);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
}
public void sendPacket(TCPPacket packet) throws IOException {
NetworkInterface[] devices = JpcapCaptor.getDeviceList();
System.err.println("dev number"+DeviceName);
NetworkInterface dev=devices[DeviceName];
System.err.println("in sender packet src ip"
+ packet.src_ip.getHostAddress() + " dst ip "
+ packet.dst_ip.getHostAddress() + " src port "
+ packet.src_port + " dst port " + packet.dst_port+" len"+packet.len+" datalink:"+packet.datalink.toString());
JpcapSender sender = JpcapSender.openDevice(dev);
//TCPPacket tp=new TCPPacket(packet.src_port,packet.dst_port, packet.sequence, packet.ack_num, packet.urg, packet.ack, packet.psh, packet.rst, packet.syn, packet.fin, packet.rsv1, packet.rsv2, packet.window, packet.urgent_pointer);
System.err.println("open device"+packet.len);
boolean df=packet.dont_frag;
boolean mf=packet.more_frag;
boolean rf=packet.rsv_frag;
packet.dont_frag=true;
packet.offset=(short)(((packet.offset&0xFF)<<8)|((packet.offset&0xF00)>>8));
packet.offset=(short)((packet.offset|((mf?0x0020:0)|(df?0x0040:0)|(rf?0x0080:0))));
System.err.println("don't frag"+packet.dont_frag);
sender.sendPacket(packet);
System.err.println("packet sent");
sender.close();
}
public static void main(String[] arg) throws IOException {
NetworkInterface[] devices = JpcapCaptor.getDeviceList();
int localIndex = 0;
for (int i = 0; i < devices.length; i++) {
if (devices[i].name.equals("lo")) {
localIndex = i;
}
}
System.err.println("lo:" + localIndex);
Bridge br = new Bridge(devices[localIndex],localIndex);
}
}