Java nio 通道数据未正确读取

Question

我通过 java nio 通道发送数据流，基本上是这样构建的：

<int:size of packet><int:packet id><packet data>

数据包数据以特定顺序填充不同的数据类型（数据包ID告诉如何解析它）。当我尝试在本地发送一些数据时，它工作得很好，但是当我尝试在 Windows Server 2012 上运行它时，它会读取一个无效的数据包大小值，例如负值或太大的值：

客户端输出：

Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkRequest (size: 24)
2988
-2032198748
java.lang.IllegalArgumentException
    at java.nio.ByteBuffer.allocate(Unknown Source)
    at network.ClientSocket.run(ClientSocket.java:66)
    at java.lang.Thread.run(Unknown Source)

最后的数字是读取的包大小，您可以在其中注意到一个荒谬的数字，它在尝试为其准备缓冲区时会导致异常。

服务器输出：

Sending packet: network.PacketLoginAck (size: 16)
Sending packet: network.PacketPlayerData (size: 951)
Sending packet: network.PacketWorldInfo (size: 33)
Received packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkData (size: 2988)     // This is the first package that still worked
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Received packet: network.PacketChunkRequest (size: 24)
Sending packet: network.PacketChunkData (size: 2518)
Sending packet: network.PacketChunkData (size: 2741)
Sending packet: network.PacketChunkData (size: 2966)
Sending packet: network.PacketChunkData (size: 2449)
Sending packet: network.PacketChunkData (size: 2769)
Sending packet: network.PacketChunkData (size: 1862)
Sending packet: network.PacketChunkData (size: 2526)
Sending packet: network.PacketChunkData (size: 2353)

一个PacketChunkRequest包含两个int，两个坐标，而PacketChunkData也包含这两个int，加上二进制数据，这是一个描述数据长度的int，后面跟着实际数据。

我这样发送数据：

for(Packet p : packets) {
    System.out.println("Sending packet: "+p.getClass().getName()+" (size: "+p.length()+")");

    ByteBuffer b = p.getBuffer();
    while (b.hasRemaining()) {
        clientChannel.write(b);
    }
    b.clear();

    sentPackages.add(p);
}

这是读取数据包的代码：

List<ByteBuffer> packets = new ArrayList<ByteBuffer>();

ByteBuffer bin = null;

int packetLength = 0;

while((bytesRead = channel.read(buffer)) > 0) {
    buffer.flip();
    while(buffer.remaining() > 0) {
        if(packetLength == 0) {
            if(buffer.remaining() < 4) break;

            packetLength = buffer.getInt();
            System.out.println(packetLength);        // This is the output of the length
            bin = ByteBuffer.allocate(packetLength); // This is where the error happens
        }  

        int readSize = Math.min(packetLength, buffer.remaining());

        buffer.limit(buffer.position() + readSize);

        bin.put(buffer);

        buffer.limit(bytesRead);

        packetLength -= readSize;

        if(packetLength == 0) {
            bin.flip();

            packets.add(bin);
        }
    }

    byte[] remaining = new byte[buffer.remaining()];
    for(int i = 0; buffer.remaining() > 0; i++) remaining[i] = buffer.get(); 

    buffer.clear();
    for(byte b : remaining) buffer.put(b);
}

此代码尝试通过将与包大小（包的第一个 int）一样多的字节读入单个缓冲区来重构一起发送的各个包。

此错误并非总是可重现，而是不断出现，但不是在本地（至少我从未遇到过）

Answer 1

您与发件人不同步。我没有详细分析你的接收代码，但显然它不能处理所有可能的情况，也不能正确地将数据包长度读取为整数。您正在阅读部分节奏作为长度词。你需要重新考虑你的逻辑。

我会质疑您为什么要为此使用 NIO。尝试使用DataInputStream，依次使用readInt() 和readFully()，直到抛出EOFException。