更换目的地址、tcp端口，计算ip包、tcp报文字段中的校验和，并写回tun网卡中。下一步研究tun网卡的流量流向，以及如何、从何读出地址修改后的ip包。

app/src/main/java/com/pkusz/min_vpn_client/services/minsocks/MINVpnLBConnection.java

@@ -27,6 +27,7 @@ import java.util.Arrays;
 import java.util.Set;
 
 import common.LoggerHelper;
+import jnr.ffi.annotations.In;
 import util.ByteHelper;
 
 public class MINVpnLBConnection implements MINVpnConnection {
@@ -111,6 +112,7 @@ public class MINVpnLBConnection implements MINVpnConnection {
         builder.setMtu(8000);
         builder.addAddress(allocatedAddress,24);
         builder.addRoute("10.255.0.3",32);
+        builder.addRoute("192.168.0.0",16);
         builder.addDnsServer("114.114.114.114");
         // 1.2创建一个接口
         final ParcelFileDescriptor vpnInterface;
@@ -169,15 +171,67 @@ public class MINVpnLBConnection implements MINVpnConnection {
                 }
                 int[] ip_address_unsignedInt_first=new int[8];
                 if(readLen>0){
-                    System.out.println("A new packet，");
-                    System.out.println("read from tun , readLen ="+readLen);
                     ip_packet_read_from_tun.position(0);
                     ip_packet_read_from_tun.limit(readLen);
 
+                    try {
+                        //System.out.println("after changing, position is"+ip_NAT_packet.position());
+                        System.out.println("直接写入，再读出");
+                        //outputStream.write(ip_NAT_packet.array(), 0, ip_NAT_packet.position());
+                        outputStream.write(ip_packet_read_from_tun.array(), 0, ip_packet_read_from_tun.position());
+                        ByteBuffer temp_buffer = ByteBuffer.allocate(MAX_PACKET_SIZE);
+                        int temp_readLen=inputStream.read(temp_buffer.array(), 0, MAX_PACKET_SIZE);
+                        System.out.println("temp readLen is "+temp_readLen);
+                        byte[] tempData = new byte[temp_readLen];
+                        System.arraycopy(temp_buffer.array(), 0, tempData, 0, temp_readLen);
+                        printHexString("直接从TUN中读：",tempData);
+                    } catch (IOException e) {
+                        e.printStackTrace();
+                        System.out.println("将抓转换后的地址写入tun网卡失败");
+                    }
+
 //                    String binaryString = Integer.toBinaryString(first);
                     byte[] ipPackageData = new byte[readLen];
                     System.arraycopy(ip_packet_read_from_tun.array(), 0, ipPackageData, 0, readLen);
-                    System.out.println("ip packet's content is: " + Arrays.toString(ipPackageData));
+//                    System.out.println("ip packet's content is: " + Arrays.toString(ipPackageData));
+
+                    if(ipPackageData[12]==0 && ipPackageData[13]==0
+                            && ipPackageData[14]==0 && ipPackageData[15]==0){
+                        System.out.println("源地址为0.0.0.0，暂时跳过");
+                        continue;
+                    }
+
+                    System.out.println("A new packet，");
+                    System.out.println("read from tun , readLen ="+readLen);
+                    printHexString("ip packet's content is: ",ipPackageData);
+
+                    //ip包的各种信息
+                    //ip头部长度，tcp报文长度
+                    int ip_head_length=(ipPackageData[0] & 0x0F)*4;
+                    int tcp_length=readLen-ip_head_length;
+                    //源端口、目的端口
+                    byte[] source_port=new byte[2];
+                    source_port[0]=ipPackageData[ip_head_length];
+                    source_port[1]=ipPackageData[ip_head_length+1];
+                    byte[] destination_port=new byte[2];
+                    destination_port[0]=ipPackageData[ip_head_length+2];
+                    destination_port[1]=ipPackageData[ip_head_length+3];
+
+
+                    byte[] test_ipPackageData = new byte[readLen];
+                    System.arraycopy(ip_packet_read_from_tun.array(), 0, test_ipPackageData, 0, readLen);
+                    ByteBuffer test_ip_packet=ByteBuffer.allocate(MAX_PACKET_SIZE);
+                    test_ip_packet.put(test_ipPackageData);
+
+                    //calculate the head checksum
+//                    short ip_checksum=computeChecksum(ipPackageData,20);
+//                    System.out.println("the checksum of ip packet is "+ Integer.toHexString(Short.toUnsignedInt(ip_checksum)));
+//                    System.out.println("the checksum(unsigned int) of ip packet is "+ Short.toUnsignedInt(ip_checksum));
+//                    System.out.println("the checksum(short) of ip packet is "+ ip_checksum);
+//                    将byte数组按16进制输出
+//                    byte[] test=new byte[2];
+//                    test=ByteHelper.uint16ToByteArray(Short.toUnsignedInt(ip_checksum));
+//                    System.out.println("the checksum(hex) of ip packet is "+Integer.toHexString(test[0] & 0xFF)+" "+Integer.toHexString(test[1] & 0xFF));
 
                     //读取源ip: [0]-[3],10.254.0.2 , 目的ip: [4]-[7],10.255.0.3
                     for(int i=12;i<20;i++){
@@ -188,12 +242,14 @@ public class MINVpnLBConnection implements MINVpnConnection {
                             System.out.print("source ip is "+ip_address_unsignedInt_first[i]);
                         else if(i>=1&&i<=3)
                             System.out.print("."+ip_address_unsignedInt_first[i]);
-                        else if(i==4)
+                        else if(i==4){
+                            System.out.print("   source tcp port is "+ByteHelper.new_byteArrayToInt(source_port));
                             System.out.print("\ndestination ip is "+ip_address_unsignedInt_first[i]);
+                        }
                         else
                             System.out.print("."+ip_address_unsignedInt_first[i]);
                     }
-                    System.out.print("\n");
+                    System.out.print("    destination tcp port is "+ByteHelper.new_byteArrayToInt(destination_port)+"\n");
                     
                     // 跳转到第3步
                     //第3.2步，如果目的地址是10.254.0.1，用face发出去【不用实现，打印即可】
@@ -206,22 +262,66 @@ public class MINVpnLBConnection implements MINVpnConnection {
                     else{
                         System.out.println("目的地址不是10.254.0.1，进行地址转换");
                         ip_NAT_packet.clear();
+                        ip_NAT_packet.position(0);
 
                         //更换ip包中目的地址为要转换的地址
                         byte[] address_to_NAT_byte=new byte[4];
-                        int[] address_to_NAT_unsignedINT={192,168,3,2};
+                        int[] address_to_NAT_unsignedINT={192,168,3,12};
                         for(int i=0;i<4;i++){
                             address_to_NAT_byte[i]=ByteHelper.uint8ToByte(address_to_NAT_unsignedINT[i]);
                             //System.out.print(address_to_NAT_byte[i]+" ");
                             ipPackageData[i+16]=address_to_NAT_byte[i];
                         }
+
+                        //calculate the checksum of ip packet, replace the checksum
+                        short ip_checksum=computeChecksum(ipPackageData,ip_head_length,10);
+                        byte[] new_ip_checksum;
+                        new_ip_checksum=ByteHelper.uint16ToByteArray(Short.toUnsignedInt(ip_checksum));
+                        ipPackageData[10]=new_ip_checksum[0];
+                        ipPackageData[11]=new_ip_checksum[1];
+
+                        //calculate the checksum of tcp,replace the checksum
+                        System.out.println("is tcp:"+Byte.toUnsignedInt(ipPackageData[9]));
+                        if(Byte.toUnsignedInt(ipPackageData[9])==6){
+                            byte[] temp_head_to_calculate_checksum;
+                            if((tcp_length+12)%2==0)
+                                temp_head_to_calculate_checksum=new byte[tcp_length+12];
+                            else
+                                temp_head_to_calculate_checksum=new byte[tcp_length+13];
+                            //构造tcp伪头部
+                            for(int i=0;i<8;i++)
+                                temp_head_to_calculate_checksum[i]=ipPackageData[i+12];
+                            temp_head_to_calculate_checksum[8]=ByteHelper.uint8ToByte(0);
+                            temp_head_to_calculate_checksum[9]=ipPackageData[9];
+                            temp_head_to_calculate_checksum[10]=ByteHelper.uint16ToByteArray(tcp_length)[0];
+                            temp_head_to_calculate_checksum[11]=ByteHelper.uint16ToByteArray(tcp_length)[1];
+                            for(int i=0;i<tcp_length;i++){
+                                temp_head_to_calculate_checksum[i+12]=ipPackageData[ip_head_length+i];
+                            }
+                            if((tcp_length+12)%2!=0)
+                                temp_head_to_calculate_checksum[tcp_length+12]=ByteHelper.uint8ToByte(0);
+
+                            //printHexString("content of integrity tcp: ",temp_head_to_calculate_checksum);
+                            short tcp_checksum=computeChecksum(temp_head_to_calculate_checksum,tcp_length+12,28);
+                            //System.out.println("the checksum of tcp datagram is "+ Integer.toHexString(Short.toUnsignedInt(tcp_checksum)));
+                            byte[] new_tcp_checksum;
+                            new_tcp_checksum=ByteHelper.uint16ToByteArray(Short.toUnsignedInt(tcp_checksum));
+                            ipPackageData[ip_head_length+16]=new_tcp_checksum[0];
+                            ipPackageData[ip_head_length+17]=new_tcp_checksum[1];
+                        }
+
+                        System.out.println("before changing, position is"+ip_NAT_packet.position());
                         //搜一下怎么换ip地址，还要更换包里面其他的内容吗
                         ip_NAT_packet.put(ipPackageData);
 
-                        //从buffer中读取转换后的ip包
+
+
+
+
+//                        //从buffer中读取转换后的ip包
 //                        byte[] ipdata_changing= ip_NAT_packet.array();
-//                        System.out.println("the content of ip packet after changing is: " + Arrays.toString(ipdata_changing));
+//                        printHexString("the content of ip packet after changing is: ",ipdata_changing);
-//                        //读取源ip: [12]-[15] , 目的ip: [16]-[19],192.168.3.2
+//                        //读取源ip: [12]-[15] , 目的ip: [16]-[19],192.168.3.12
 //                        int[] ip_address_unsignedInt_changing=new int[8];
 //                        //将ip转化为unsigned int
 //                        for(int i=12;i<20;i++){
@@ -238,13 +338,8 @@ public class MINVpnLBConnection implements MINVpnConnection {
 //                                System.out.print("."+ip_address_unsignedInt_changing[i]);
 //                        }
 //                        System.out.print("\n");
+//                        System.out.println("after changing, position is "+ip_NAT_packet.position());
 
-                        try {
-                            outputStream.write(ip_NAT_packet.array(), 0, ip_NAT_packet.position());
-                        } catch (IOException e) {
-                            e.printStackTrace();
-                            System.out.println("将抓转换后的地址写入tun网卡失败");
-                        }
 
 
                     }
@@ -254,9 +349,19 @@ public class MINVpnLBConnection implements MINVpnConnection {
         readFromTun.start();
 
 
-
+//        Thread writeToTun = new Thread(() -> {
-//        // 第3.1步，如果目的地址不是10.254.0.1，先将IP包的源端口号和目的IP端口号存入表iptables，
+//           while (!this.stop){
-//        //      然后做NAT转换，做完NAT转换的IP包写入tun（通过ParcelFileDescriptor） write()
+//               //System.out.println("ip_NAT_packet position"+ip_NAT_packet.position());
+//
+//               if()
+//
+//
+//               ip_NAT_packet.position(0);
+//           }
+//        });
+//        writeToTun.start();
+        // 第3.1步，如果目的地址不是10.254.0.1，先将IP包的源端口号和目的IP端口号存入表iptables，
+        //      然后做NAT转换，做完NAT转换的IP包写入tun（通过ParcelFileDescriptor） write()
 //        Thread writeToTun = new Thread(() -> {
 //            while(this.stop){
 //                System.out.println("write thread "+temp_buff.position());
@@ -310,13 +415,56 @@ public class MINVpnLBConnection implements MINVpnConnection {
         return MINVpnLBConnection.class.getSimpleName() + "[" + mConnectionId + "]";
     }
 
-    private void transfer_ip_packet_from_thread(ByteBuffer ip_packet,int readLen){
+    /**
-        temp_buff.clear();
+     * 将byte数组以16进制的形式输出
-        byte[] ipPackageData = new byte[readLen];
+     *
-        System.arraycopy(ip_packet.array(), 0, ipPackageData, 0, readLen);
+     * @param b
-        temp_buff.put(ipPackageData);
+     *            byte[]
-        length_of_ip_packet=readLen;
+     * @return void
+     */
+    public static void printHexString(String hint, byte[] b)
+    {
+        System.out.print(hint);
+        for (int i = 0; i < b.length; i++)
+        {
+            String hex = Integer.toHexString(b[i] & 0xFF);
+            if (hex.length() == 1)
+            {
+                hex = '0' + hex;
+            }
+            System.out.print(hex.toUpperCase() + " ");
+        }
+        System.out.println("");
+    }
+    
+
+    /**
+     * Computes the IPv4 head checksum on the passed stream of bytes
+     * representing the packet.
+     *
+     * @param data
+     *            The byte stream
+     * @param length
+     *            The length of the IPv4 packet's head
+     * @return The computed checksum
+     */
+    short computeChecksum(byte[] data,int length,int checksumStart) {
+        short checkSum;
+        int sum = 0;
+        int wordData;
+        for (int i = 0; i <= length - 1; i = i + 2) {
+            // Skip, if the current bytes are checkSum bytes
+            if (i == checksumStart) {
+                continue;
+            }
+            wordData = (data[i] << 8 & 0xFF00) + (data[i + 1] & 0xFF);
+            sum = sum + wordData;
+        }
+        int carry = sum >> 16 & 0xFF;
+        int finalSum = (sum & 0xFFFF) + carry;
+        checkSum = (short) ~((short) finalSum & 0xFFFF);
+
+        return checkSum;
     }
 
-
 }