Question

我正在用Java编写一个小型UDP服务器。当服务器收到命令（'GET_VIDEO'）时，他会读取一个文件（'video.raw'），然后将其发送给客户端。我的问题是从服务器发送的字节数不等于客户端收到的字节数，我的测试失败。这是服务器代码：

public class ServerMock {

public static void main(String[] args) throws Exception {

    byte[] buff = new byte[64];
    DatagramPacket packet = new DatagramPacket(buff, buff.length);
    DatagramSocket socket = new DatagramSocket(8080);

    System.out.println("Server started at 8080 ...");

    while (true) {
        socket.receive(packet);
        new ServerMock.ThreadVideo(socket, packet).run();

    }
}

public static class ThreadVideo implements Runnable {

    private DatagramPacket packet;
    private DatagramSocket socket;

    public ThreadVideo(DatagramSocket socket, DatagramPacket packet) {
        this.packet = packet;
        this.socket = socket;
    }

    public void run() {
        String cmd = new String(packet.getData(), 0, packet.getLength());
        if (cmd.equals("GET_VIDEO")) {
            try {
                read_and_send_video(this.packet.getAddress());
            } catch (IOException e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("S:Exiting ....");
            System.exit(0);
        }
    }


    private void read_and_send_video(InetAddress address)
            throws IOException {

        File file = new File("./video/video.raw");
        FileInputStream fis = new FileInputStream(file);
        DatagramPacket pack;

        int size = 0;
        byte[] buffer = new byte[64000];
        ByteBuffer bb = ByteBuffer.allocate(4);
        bb.order(ByteOrder.BIG_ENDIAN);

        while (true) {
            size = fis.read(buffer);
            System.out.println("Size = " + size);

            // Envoi du contenu du fichier
            pack = new DatagramPacket(buffer, buffer.length, address,
                    packet.getPort());
            socket.send(pack);
            if (size == -1) {
                break;
            }
        }

        String cmd = "END_VIDEO";
        pack = new DatagramPacket(cmd.getBytes(), cmd.getBytes().length,
                address, packet.getPort());
        socket.send(pack);

    }

}

}

这是我的客户代码：

public void client(int timeout, String message)
        throws SocketTimeoutException, SocketException {

    try {

        File file = new File("./video/tmp.raw");
        FileOutputStream fos = new FileOutputStream(file);
        File filein = new File("./video/video.raw");

        InetAddress address = InetAddress.getByName(host);
        byte[] data = message.getBytes();
        byte[] buffer = new byte[64000];

        DatagramSocket socket = new DatagramSocket();
        socket.setSoTimeout(timeout);

        DatagramPacket packet = new DatagramPacket(data, data.length,
                address, port);
        socket.send(packet);

        DatagramPacket rpacket = new DatagramPacket(buffer, buffer.length);

        while (true) {
            socket.receive(rpacket);
            if (rpacket.getLength() <= 9) {
                String cmd = new String(rpacket.getData(), 0,
                        rpacket.getLength());
                if (cmd.equals("END_VIDEO")) {
                    System.out.println("C:Fin de transmission");
                    break;
                }
            }
            fos.write(rpacket.getData());
        }

        System.out.println("video.raw ->" + filein.length());
        System.out.println("tmp.raw -> " + file.length());
        Assert.assertTrue(file.length() == filein.length());

    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (UnknownHostException e) {

        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

}

任何人都可以帮我解决这个问题。有些朋友建议我使用类ByteBuffer，ByteOrder，但我不知道如何使用它们，因为我不知道当服务器读取文件时真正读取了多少字节。什么是实现这一目标的最佳方式

谢谢

Answer 1

UDP不可靠，无法保证您将收到所有已发送的UDP数据包，或者您将按照发送的顺序接收它们。您需要使用序列号标记每个数据包，您需要在客户端重新排序它们，您需要告诉服务器何时减速（或实现确认机制），您将需要能够请求重新传输

简而言之，除非客户对丢失和无序数据包感到满意（因为大多数流客户端都是如此），否则您需要重新实现TCP over UDP，或者只使用TCP。

Answer 2

我正在搜索从udp服务器发送文件的示例，我找到了您的问题。您必须修改以下行：

在服务器中：

    int size = 0;
    byte[] buffer = new byte[(int) file.length()];
    ByteBuffer bb = ByteBuffer.allocate(4);
    bb.order(ByteOrder.BIG_ENDIAN);

而且，你必须移动“socket.send（数据包）”：

while (true) {
size = fis.read(buffer);
System.out.println("Size = " + size);

// Envoi du contenu du fichier
pack = new DatagramPacket(buffer, buffer.length, address, packet.getPort());

if (size == -1) {
   break;
}

    socket.send(pack);
 }

在客户端中，使用fos.write(rpacket.getData());

修改fos.write(rpacket.getData(), 0, rpacket.getLength());

从UDP服务器发送文件时出现问题

2 个答案: