我正在尝试发送一个 DatagramPacket，然后必须等待来自服务器的确认，以便我知道我是否必须重新发送相同的数据包或发送下一个数据包......

我在客户端使用相同的套接字，发送数据包并接收确认 (ack)，在服务器端，另一个套接字用于接收数据包，然后发送致谢客户..

第一个问题是客户端正在发送数据包，服务器正在接收它，然后向客户端发送确认，但客户端在收到确认包时阻塞。

我正在制作一些 System.out.println 来确定问题出在哪里，但我找不到解决这个问题的方法。

第二个问题是服务器仍然总是在接收数据，并且不要等待客户端发送一些东西，我检查了因为我得到了那些行(比如“得到了长度为 xxx 的数据包”“ack sent with ackNr yyy” ...”一直打印在服务器端，尽管客户端在发送第一个数据包后处于阻塞状态，因为它正在等待未收到的确认!

这是客户端的代码:

package blatt7;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketTimeoutException;
import java.net.UnknownHostException;
import java.nio.ByteBuffer;
import java.util.zip.CRC32;




public class FileSender { 


String zielRechner;
String filePath;
InetAddress host;
File file;
FileInputStream fis;
int readLength;
int sequenceNr = 0;
int receivedSeqNr = 1;
static int port = 7777;
int packetNr = 0;
byte[] packet = new byte[1216];
byte[] data = new byte[1200];
byte[] header = new byte[16];
byte[] readLengthByte = new byte[4];
byte[] sequenceNrByte = new byte[4];
byte[] checksumByte = new byte[8];
byte[] ackBuffer = new byte[4];
CRC32 checksumCalculator = new CRC32();
DatagramPacket dp;
DatagramPacket ackPacket;
DatagramSocket sendSocket = null;
//DatagramSocket ackSocket = null;
static boolean ackReceived = true;

public FileSender(String zielRechner, String filePath) throws UnknownHostException, FileNotFoundException {
    this.zielRechner = zielRechner;
    this.filePath = filePath;
    this.host = InetAddress.getByName(zielRechner);
    this.file = new File(filePath);
    fis = new FileInputStream(file);        
}

public void sendFile() throws IOException {

    while((readLength = fis.read(data)) != -1) {
        if (sequenceNr == 1)
            sequenceNr = 0;
        else
            sequenceNr = 1;

        readLengthByte = intToBytes(readLength);
        sequenceNrByte = intToBytes(sequenceNr);

        for(int i=0; i<4; i++) {
            header[8+i] = readLengthByte[i];                
        }

        for(int i=0; i<4; i++) {
            header[12+i] =sequenceNrByte[i];                
        }

        int j=0; 
        for (int i=0; i<packet.length; i++) {
            if (i < header.length) 
                packet[i] = header[i];
            else { 
                packet[i] = data[j];
                j++;
            }
        }

        checksumCalculator.reset();
        checksumCalculator.update(packet,8,8+readLength);
        checksumByte = longToBytes(checksumCalculator.getValue());

        for(int i=0; i < 8; i++) {
            packet[i] = checksumByte[i];
        }

        dp = new DatagramPacket(packet, packet.length, host, port);

        while(receivedSeqNr == sequenceNr && ackReceived) {
            try {
                ackReceived = false;
                sendSocket = new DatagramSocket();
                sendSocket.send(dp);
                sendSocket.setSoTimeout(10000);
                packetNr++;
                System.out.println("Packet sent with seqNr: " + sequenceNr + " and length: " + bytesToInt(readLengthByte, 0) + " - PACKET NR: " + packetNr);
                ackPacket = new DatagramPacket(ackBuffer, ackBuffer.length);
                System.out.println("TEST!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
                sendSocket.receive(ackPacket);
                System.out.println("Receiving ACK!!");
                ackReceived = true;
                ackBuffer = ackPacket.getData();
                receivedSeqNr = bytesToInt(ackBuffer,0);
                System.out.println("got SequenceNr with receivedSeq-Nr: " + receivedSeqNr);
            } catch (SocketTimeoutException e) {
                    e.printStackTrace();
                    break;
            }
        }   
    }

    fis.close();
    System.out.println("Transfer Completed Successfully!");
    sendSocket.close();
}

public static byte[] longToBytes(long value) {
    ByteBuffer buffer = ByteBuffer.allocate(8);
    buffer.putLong(value);
    return buffer.array();
}

public static long bytesToLong(byte[] bytes, int index) {
    ByteBuffer buffer = ByteBuffer.allocate(8);
    buffer.put(bytes);
    buffer.flip();//need flip 
    return buffer.getLong(index);
}

public static byte[] intToBytes(int value) {
    ByteBuffer buffer = ByteBuffer.allocate(4);
    buffer.putInt(value);
    return buffer.array();
}

public static int bytesToInt(byte[] bytes, int index) {
    ByteBuffer buffer = ByteBuffer.allocate(4);
    buffer.put(bytes);
    buffer.flip();//need flip 
    return buffer.getInt(index);
}

public static void main(String[] args) throws IOException,ClassNotFoundException {

    FileSender sender = new FileSender("localhost", "C:/Users/Kb/Desktop/Deepophile - Psychedelic Sessions.wav");
    sender.sendFile();

}

}

这是服务器的代码:

package blatt7;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.util.zip.CRC32;

public class FileReceiver {

byte[] incomingBuffer;
DatagramPacket incomingPacket;
DatagramSocket receiveSocket;
DatagramPacket ackPacket;
int packetCounter = 0;
int dataLength;
int receivedSeqNr;
long calculatedChecksum;
long receivedChecksum;
CRC32 checksumCalculator = new CRC32();
byte[] dataLengthByte = new byte[4];
byte[] receivedSeqNrByte = new byte[4];
byte[] receivedChecksumByte = new byte[8];
byte[] ackArray;


public FileReceiver() throws SocketException {
    incomingBuffer = new byte[1500];
    incomingPacket = new DatagramPacket(incomingBuffer, incomingBuffer.length);
}

public void receive() throws IOException {

    receiveSocket = new DatagramSocket(FileSender.port);
    receiveSocket.setSoTimeout(10000);
    System.out.println("Server socket created. Waiting for incoming data...");

    while(true && FileSender.ackReceived)
    {   
        receiveSocket.receive(incomingPacket);
        packetCounter++;

        for (int i=0; i <4; i++) {
            dataLengthByte[i] = incomingBuffer[8+i];
        }
        dataLength = FileSender.bytesToInt(dataLengthByte,0);

        checksumCalculator.reset();
        checksumCalculator.update(incomingBuffer, 8, dataLength+8);             
        calculatedChecksum = checksumCalculator.getValue();


        for (int i=0; i <4; i++) {
            receivedSeqNrByte[i] = incomingBuffer[12+i];
        }
        receivedSeqNr = FileSender.bytesToInt(receivedSeqNrByte,0);


        for (int i=0; i <8; i++) {
            receivedChecksumByte[i] = incomingBuffer[i];
        }
        long receivedChecksum = FileSender.bytesToLong(receivedChecksumByte,0);

        System.out.println("Got packet with checksum: " + receivedChecksum);
        System.out.println("Server-calculated checksum: " + calculatedChecksum);
        System.out.println("Got packet with seqNr: " + receivedSeqNr + " and length: " + dataLength);

        if (calculatedChecksum != receivedChecksum)  {
            sendACK(receivedSeqNr);
            System.out.println("Packet have erros(s)! It must be sent another time!");
        }
        else if(calculatedChecksum == receivedChecksum && receivedSeqNr == 1) {
            sendACK(0);
            System.out.println("SeqNr '0' sent");
        }
        else if (calculatedChecksum == receivedChecksum && receivedSeqNr == 0) {
            sendACK(1);
            System.out.println("SeqNr '1' sent");
        }
    }
}

public void sendACK(int seqNum) throws IOException {
    byte[] ackArray = FileSender.intToBytes(seqNum);
    ackPacket = new DatagramPacket(ackArray, ackArray.length, InetAddress.getByName("localhost"), FileSender.port);
    receiveSocket.send(ackPacket);      
}

public static void main(String[] args) throws IOException,ClassNotFoundException {
    FileReceiver receiver = new FileReceiver();
    receiver.receive();     
}

}

你可以尝试执行一下看看是哪里出了问题... 所以，如果您有任何关于如何解决这个问题的想法，请告诉我!

非常感谢!

谁能告诉我在哪里可以找到收到的文件？或者我应该如何更改我的代码以便我选择保存它的位置？？

最佳答案

是的，这是可能的。您的问题是发送 ACK 数据报时目标地址:端口错误。您应该从接收到的 DatagramPacket 中获取目标地址:端口，或者更简单的只是重用具有不同数据的数据报作为 ACK 数据报。

关于java - 是否可以仅使用 1 个 UDPSocket 在同一端口上发送/接收？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14085606/