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我在使用Java中的CRC32庫計算我的校驗和時遇到問題。校驗和一次計算正確，然後在Java中沒有CRC32之後
所以客戶端計算校驗像這樣....
/**
* Increments current packet message number, selects a
* random destination, and sends the packet.
* @param connection
* @throws InterruptedException
* @throws IOException
*/
private void generateAndSendPackets(Socket connection) throws InterruptedException, IOException
{
byte packet[] = new byte[5];
for (byte messageNumber = 0; messageNumber <= 20; messageNumber++)
{
packet[0] = CLIENT_ID; //SOURCE
packet[1] = randomDestination(); //DESTINATION
packet[3] = messageNumber; //DATA
packet[4] = messageNumber;
//Need more data?
packet[2] = computeCheckSum(packet); //COMPUTE CHECKSUM
send(packet); //SEND PACKET
Thread.sleep(4000); //WAIT TO SEND NEXT PACKET
}
closeConnection(connection); //Closes the connection
}
/**
* Given a packet, it computes the checksum for
* the packet with internal Checksum library
* @param packet
* @return
*/
private byte computeCheckSum(byte[] packet)
{
Checksum checkSum = new CRC32();
checkSum.update(packet, 0, packet.length);
return (byte)checkSum.getValue();
}
然後發送數據包。包括校驗和。
路由器然後計算校驗和是這樣的...
/**
* Given a packet, it computes the checksum for
* the packet with internal Checksum library
* @param p
* @return
*/
private boolean checkCheckSum(byte[] p)
{
byte[] packet = p;
byte[] tempPacket = new byte[5];
tempPacket[0] = packet[0];
tempPacket[1] = packet[1];
tempPacket[3] = packet[3];
tempPacket[4] = packet[4];
Checksum checkSum = new CRC32();
checkSum.update(tempPacket, 0, tempPacket.length);
byte cc = (byte)checkSum.getValue();
System.out.println(packet[0] + " " + packet[1] + " " + packet[2] + " " + packet[3] + " " + packet[4]);
tempPacket[2] = (byte)checkSum.getValue();
System.out.println(tempPacket[0] + " " + tempPacket[1] + " " + tempPacket[2] + " " + tempPacket[3] + " " + tempPacket[4]);
if((byte)checkSum.getValue() == packet[2]){
System.out.println(packet[2] + "," + cc);
return true;
}else{
System.out.println(packet[2] + "," + cc);
return false;
}
}
所以當它計算和輸出，它不糾正它第一次......不過那之後，只不過沒有像這樣..
Waiting for connection....
Connection recieved from /127.0.0.1 on port 9000
Waiting for packet...
Packet recieved: 11 44 -118 00
11 44 -118 0 0
11 44 -118 0 0
-118,-118
<Error here because we weren't done another part yet>
Waiting for packet...
Packet recieved: 11 33 -42 11
11 33 -42 1 1
11 33 -128 1 1
-42,-128
Checksum invalid!!!!
Waiting for packet...
然後每個後無效....
所以它得到正確的校驗一次，那之後搞砸了，再次得到檢驗。我認爲這是我做錯了Java的CRC32庫是我的猜測。這些都是他們自己的線索，但我不認爲這會是一個問題。
這是我們下面的代碼，我試圖強調上述問題的部分，因爲有一些地方有這樣完成了一半....
Client.java
package runner;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.*;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
/**
* Client side for our client
* server project. Sends a request
* with a string to reverse.
* @author xxxxx
*
*/
public class Client
{
private static final int PORT = 9000;
private static final String HOST = "localhost";
private static final byte CLIENT_ID = (byte)11;
private Random rand;
//For reciving packets
private ServerSocket clientRecieverSocket = null;
//Output to server
private PrintWriter out;
//Input from server
private Scanner conIn;
//Input from user
private Scanner in;
//Data Output Stream
private DataOutputStream dos;
/**
* Creates a new instance of the client
* @param args
* @throws UnknownHostException
* @throws IOException
* @throws InterruptedException
*/
public static void main(String[] args) throws IOException, InterruptedException
{
Client c = new Client();
c.run();
}
/**
* Runs the client
*
* @throws UnknownHostException
* @throws IOException
* @throws InterruptedException
*/
private void run() throws IOException, InterruptedException
{
String msg; //Recieve messages from server
//Opens connection
Socket connection = openConnection();
//Gets I/O streams from server
System.out.println("Getting output stream...");
out = new PrintWriter(connection.getOutputStream());
System.out.println("Getting input stream...");
conIn = new Scanner(connection.getInputStream());
System.out.println();
dos = new DataOutputStream(connection.getOutputStream());
msg = conIn.nextLine();
System.out.println(msg);
in = new Scanner(System.in);
generateAndSendPackets(connection);
}
/**
* Increments current packet message number, selects a
* random destination, and sends the packet.
* @param connection
* @throws InterruptedException
* @throws IOException
*/
private void generateAndSendPackets(Socket connection) throws InterruptedException, IOException
{
byte packet[] = new byte[5];
for (byte messageNumber = 0; messageNumber <= 20; messageNumber++)
{
packet[0] = CLIENT_ID; //SOURCE
packet[1] = randomDestination(); //DESTINATION
packet[3] = messageNumber; //DATA
packet[4] = messageNumber;
//Need more data?
packet[2] = computeCheckSum(packet); //COMPUTE CHECKSUM
send(packet); //SEND PACKET
Thread.sleep(4000); //WAIT TO SEND NEXT PACKET
}
closeConnection(connection); //Closes the connection
}
/**
* Given a packet, it computes the checksum for
* the packet with internal Checksum library
* @param packet
* @return
*/
private byte computeCheckSum(byte[] packet)
{
Checksum checkSum = new CRC32();
checkSum.update(packet, 0, packet.length);
return (byte)checkSum.getValue();
}
/**
* Select random destination
* to send to.
*/
private byte randomDestination()
{
List<Byte> destinations = Arrays.asList((byte)22,(byte)33,(byte)44);
//destinations.remove(CLIENT_ID); //Do not send it to itself...
rand = new Random();
return destinations.get(rand.nextInt(destinations.size())); //converts string to byte
}
/**
* Open the connection
* @return
* @throws UnknownHostException
* @throws IOException
*/
private Socket openConnection() throws IOException
{
System.out.println("Connecting to server...");
Socket connection = new Socket(HOST, PORT); //Connects to server
System.out.println("Connection made!");
return connection;
}
/**
* Closes the connection
* @param connection
* @throws IOException
*/
private void closeConnection(Socket connection) throws IOException
{
System.out.println("Closing connection...");
connection.close();
}
/**
* Sends a message to the server
* with the string to reverse.
* @param packet
*/
private void send(byte[] packet) throws IOException
{
System.out.println("You sent " + packet + ", sending message...");
System.out.println(packet[0] + " " + packet[1] + " " + packet[2] + " " + packet[3] + " " + packet[4]);
dos.write(packet, 0, packet.length);
dos.flush();
}
}
Router.java
import javax.xml.crypto.Data;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Hashtable;
import java.util.Scanner;
import java.util.zip.CRC32;
import java.util.zip.Checksum;
/**
* Router class routes messages
* around to different routers/clients
*
* @Author Abe and Carson
*/
public class Router{
//Stores routing table
private Hashtable<Byte, String> routingTable;
//Stores socket
private static ServerSocket SERVER;
private static Socket CLIENT;
//Stores router ID (CHANGE THIS IS HARDCODED!!!!!!)
private static final int ROUTER_ID = 1;
public static void main(String args[]) throws IOException
{
Router r = new Router();
System.out.println("Waiting for connection....");
while(true)
{
Socket incomingConnection = SERVER.accept();
System.out.println("Connection recieved from "
+ incomingConnection.getInetAddress()
+ " on port "
+ incomingConnection.getLocalPort());
RouterHandlerThread rht = new RouterHandlerThread(incomingConnection, r);
rht.start();
}
}
/**
* Creates a router object
* with a server socket that opens to listen for packets
* and a routing table
*/
public Router()
{
//Creates routing tables HashTable<Byte, String> for router to use based on its ID
RoutingTableFactory rtf = new RoutingTableFactory();
try{
routingTable = rtf.getRoutingTable(ROUTER_ID);
} catch(RoutingTableFactory.InvalidRouterIDException e){
e.printStackTrace();
}
try {
SERVER = new ServerSocket(9000);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* Getter for the routers
* Routing Table
* @return
*/
public Hashtable<Byte, String> getRoutingTable()
{
return this.routingTable;
}
/**
* Thread for handling router processes for
* forwarding a packet to a different link.
*/
private static class RouterHandlerThread extends Thread
{
private Socket connection;
private Router router;
private Scanner in;
private PrintWriter out;
//Used for sending the packet byte[], can't use Scanner for byte[] :(
private DataInputStream dis;
RouterHandlerThread(Socket c, Router r) throws IOException
{
this.router = r;
this.connection = c;
in = new Scanner(c.getInputStream());
out = new PrintWriter(c.getOutputStream());
dis = new DataInputStream(c.getInputStream());
}
/**
* Given a packet, it computes the checksum for
* the packet with internal Checksum library
* @param p
* @return
*/
private boolean checkCheckSum(byte[] p)
{
byte[] packet = p;
byte[] tempPacket = new byte[5];
tempPacket[0] = packet[0];
tempPacket[1] = packet[1];
tempPacket[3] = packet[3];
tempPacket[4] = packet[4];
Checksum checkSum = new CRC32();
checkSum.update(tempPacket, 0, tempPacket.length);
byte cc = (byte)checkSum.getValue();
System.out.println(packet[0] + " " + packet[1] + " " + packet[2] + " " + packet[3] + " " + packet[4]);
tempPacket[2] = (byte)checkSum.getValue();
System.out.println(tempPacket[0] + " " + tempPacket[1] + " " + tempPacket[2] + " " + tempPacket[3] + " " + tempPacket[4]);
if((byte)checkSum.getValue() == packet[2]){
System.out.println(packet[2] + "," + cc);
return true;
}else{
System.out.println(packet[2] + "," + cc);
return false;
}
}
public void run()
{
out.println("R: Connected to router " + ROUTER_ID + " at " + SERVER.getLocalPort());
out.flush();
while(connection.isConnected())
{
byte[] packet = new byte[5];
System.out.println("Waiting for packet...");
//Reads packet byte[] from the client, stores in packet.
try{
dis.readFully(packet);
}catch(Exception e){
e.printStackTrace();
}
//Print out each byte of packet.
System.out.println("Packet recieved: " + packet[0] + " " + packet[1] + " " + packet[2] + " " + packet[3] + packet[4]);
//Get routing table, look up what link to send packet to.
Hashtable<Byte, String> routingTable = router.getRoutingTable();
if(checkCheckSum(packet)){
String destination = routingTable.get(packet[1]);
try {
Socket targetRouter = new Socket(destination, 9000);
DataOutputStream dos = new DataOutputStream(targetRouter.getOutputStream());
dos.write(packet);
dos.flush();
System.out.println("Forwarding to " + destination);
targetRouter.close();
dos.close();
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}else{
System.out.println("Checksum invalid!!!!");
}
}
}
}
}
/**********
* CODE FIDDLING WITH STRINGS -> BYTES AND VICE VERSA
public static void main(String[] args)
{
byte packet[] = new byte[4];
packet[0] = 'D';
packet[1] = 'B';
packet[3] = 29;
Checksum checkSum = new CRC32();
checkSum.update(packet, 0, packet.length);
packet[2] = (byte)checkSum.getValue();
System.out.println(packet[0] + " " + packet[1] + " " + packet[2] + " " + packet[3]);
String str = new String(packet);
System.out.println(str);
}
*/
爲什麼使用CRC-32並只傳輸一個字節？這根本不符合邏輯。 – EJP