java - 从 UDP 服务器发送文件时出现问题

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，他读取文件('video.raw')，然后将其发送到客户端。我的问题是从服务器发送的字节数不等于客户端接收的字节数，并且我的测试失败。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);

    }

}

}

这是我的客户端代码:

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。一些 friend 建议我使用 ByteBuffer、ByteOrder 类，但我不知道如何使用它们，因为我不知道服务器读取文件时实际读取了多少字节。实现这一目标的最佳方法是什么

谢谢

Answer 1

UDP 是不可靠的，无法保证您会收到所有发送的 UDP 数据包，或者您会按照发送的顺序收到它们。您将需要用序列号标记每个数据包，您将需要在客户端上对它们重新排序，您将需要告诉服务器何时放慢速度(或实现确认机制)，您将需要能够请求重传.

简而言之，除非客户端对丢失和无序的数据包感到满意(就像大多数流媒体客户端一样)，否则您将需要重新实现基于 UDP 的 TCP，或者仅使用 TCP。