java - 通过 SocketChannel 传输文件时丢失字节

Question

我正在使用 nio ServerSocketChannel 和 SocketChannel 在客户端和服务器之间传输大文件。问题是当我将大小为 6060064 字节的文件从发送方传输到接收方时，接收方仅收到 6059040 字节，缺少一些字节。由于文件大小变得更大，丢失字节的差异差距增加。我找不到为什么这些字节丢失。

发件人代码:

public boolean send(SelectionKey selectionKey) {

    File file = new File("/media/data1/sample.mp4");
    try {
        SocketChannel socketChannel = (SocketChannel) selectionKey
                .channel();
        FileInputStream fileInputStream = new FileInputStream(file);
        System.out.println("File Length :: " + file.length());
        System.out.println("File lastModified :: " + file.lastModified());

        FileChannel fileChannel = fileInputStream.getChannel();

        transfer(fileChannel, socketChannel, file.length(), 1024 * 50);

        fileInputStream.close();

        System.out.println("File Send Completely Done 100%....");
        System.out.println("Closing Connection 100%....");

        return true;

    } catch (Exception e) {
        System.out.println(e);
        System.out.println("Connection Failed. Connectiontimeout.");
        return false;
    }
}

public static void transfer(FileChannel fileChannel,
        SocketChannel socketChannel, long lengthInBytes,
        long chunckSizeInBytes)
        throws IOException {

    long overallBytesTransfered = 0L;
    long time = -System.currentTimeMillis();
    
    while (overallBytesTransfered < lengthInBytes) {

        long bytesTransfered = 0L;

        bytesTransfered = fileChannel.transferTo(
                overallBytesTransfered,
                Math.min(chunckSizeInBytes, lengthInBytes
                        - overallBytesTransfered), socketChannel);

        System.out.println("bytesTransfered :: " + bytesTransfered);

        overallBytesTransfered += bytesTransfered;

        System.out.printf(
                "overall bytes transfered: %s progress %s%%\n",
                overallBytesTransfered, Math.round(overallBytesTransfered / ((double) lengthInBytes) * 100.0));
    }

    time += System.currentTimeMillis();

    System.out.printf("Transfered: %s bytes in: %s s -> %s kbytes/s\n",
                overallBytesTransfered, time / 1000,
                (overallBytesTransfered / 1024.0) / (time / 1000.0));
    System.out.println("------- File transfer completed ------");

}

接收者代码:

public boolean recieve(SelectionKey key) {
    SocketChannel socketChannel = null;
    Socket socket = null;

    try {
        socketChannel = (SocketChannel) key.channel();
        socket = socketChannel.socket();
        System.out.println(socketChannel.getRemoteAddress());

        // Save file destination
        String FileKey = "/media/data1/Test/sample1.mp4";
        // File size
        long sizeInBytes = 6060064;
        
        long timeStap = 1402301850000l;

        File file = new File(FileKey);
        FileOutputStream fileOutputStream = new FileOutputStream(file);
        FileChannel fileChannel = fileOutputStream.getChannel();

        transfer(fileChannel, socketChannel, sizeInBytes, 1024 * 100);

        fileOutputStream.close();

        file.setLastModified(timeStap);
        socket.close();
        return true;

    } catch (Exception e) {
        System.out.println("Connection Failed. Connectiontimeout.");
        e.printStackTrace();
        return false;
    }
}

public static void transfer(FileChannel fileChannel,
        SocketChannel socketChannel, long lengthInBytes, long chunckSizeInBytes)
        throws IOException {

    long overallBytesTransfered = 0L;
    long time = -System.currentTimeMillis();
    while (overallBytesTransfered < lengthInBytes) {
        
        long bytesTransfered = 0L;

        bytesTransfered = fileChannel.transferFrom(
                socketChannel,
                overallBytesTransfered,
                Math.min(chunckSizeInBytes, lengthInBytes
                        - overallBytesTransfered));

        System.out.println("bytesTransfered :: " + bytesTransfered);

        overallBytesTransfered += bytesTransfered;

        System.out.printf(
                "overall bytes transfered: %s progress %s%%\n", overallBytesTransfered,
                Math.round(overallBytesTransfered / ((double) lengthInBytes) * 100.0));

    }
    
    time += System.currentTimeMillis();

        System.out.printf("Transfered: %s bytes in: %s s -> %s kbytes/s\n",
                overallBytesTransfered, time / 1000,
                (overallBytesTransfered / 1024.0) / (time / 1000.0));
        System.out.println("-------Dateiübertragung fertig------");

}

发送者的输出:

bytesTransfered :: 18464

overall bytes transfered: 6060064 progress 100%

Transfered: 6060064 bytes in: 119 s -> 49.67708595651809 kbytes/s

接收器输出:

bytesTransfered :: 0

overall bytes transfered: 6059040 progress 100%

接收器的 while 循环一直持续到我手动停止该进程，并且 bytesTransfered 在接收器端始终返回零，而文件大小增加到 6059040 字节。

请谁能告诉我为什么这些字节丢失了。

Answer 1

我们在 JDK7u60 上看到了同样的情况(我们之前没有看到)

我们注意到，如果缓冲区大于约 200KB，则 SocketChannel 在接收方有时间读取套接字之前关闭。

到目前为止，我们唯一的建议是通过暂停来限制写入

int bytes = socketChannel.write(currentWriteBuffer);
if (bytes > 200000) {
    try {
        Thread.sleep(100 * (bytes / 200000));
    }
    catch (InterruptedException e) {
      // ignore 
    }
}

我还没有研究实际的限制或实际的延迟，但这对我们有用。请注意，我在研究更好的答案时发现了您的问题。