从 NetworkStream 读取特定数量的字节 [英] read specific number of bytes from NetworkStream

问题描述

我正在尝试从网络流中读取已知长度的消息.我有点期待 NetworkStream.Read() 会等待返回，直到我给它的缓冲区数组已满.如果不是，那么 ReadTimeout 属性的意义何在?

I am trying to read a message of known length from the network stream. I was kinda expecting that NetworkStream.Read() would wait to return until buffer array I gave to it is full. If not, then what is the point of the ReadTimeout property?

我用来测试我的理论的示例代码

Sample code I am using to test my theory

public static void Main(string[] args)
{
    TcpListener listener = new TcpListener(IPAddress.Any, 10001);
    listener.Start();

    Console.WriteLine("Waiting for connection...");

    ThreadPool.QueueUserWorkItem(WriterThread);

    using (TcpClient client = listener.AcceptTcpClient())
    using (NetworkStream stream = client.GetStream())
    {
        Console.WriteLine("Connected. Waiting for data...");

        client.ReceiveTimeout = (int)new TimeSpan(0, 1, 0).TotalMilliseconds;
        stream.ReadTimeout = (int)new TimeSpan(0, 1, 0).TotalMilliseconds;

        byte[] buffer = new byte[1024];
        int bytesRead = stream.Read(buffer, 0, buffer.Length);

        Console.WriteLine("Got {0} bytes.", bytesRead);
    }

    listener.Stop();

    Console.WriteLine("Press any key to exit...");
    Console.ReadKey(true);
}

private static void WriterThread(object state)
{
    using (TcpClient client = new TcpClient())
    {
        client.Connect(new IPEndPoint(IPAddress.Parse("127.0.0.1"), 10001));
        using (NetworkStream stream = client.GetStream())
        {
            byte[] bytes = Encoding.UTF8.GetBytes("obviously less than 1024 bytes");
            Console.WriteLine("Sending {0} bytes...", bytes.Length);
            stream.Write(bytes, 0, bytes.Length);
            Thread.Sleep(new TimeSpan(0, 2, 0));
        }
    }
}

结果是:

Waiting for connection...
Sending 30 bytes...
Connected. Waiting for data...
Got 30 bytes.
Press any key to exit...

是否有一种标准方法可以使同步读取仅在读取指定数量的字节时返回?我确信自己编写一个不会太复杂，但是 TcpClient 和 NetworkStream 上的超时属性的存在有点表明它应该已经这样工作了.>

Is there a standard way of making a sync read that returns only when specified number of bytes was read? I am sure it is not too complicated to write one myself, but presence of the timeout properties on both TcpClient and NetworkStream kinda suggests it should be already working that way.

推荐答案

TCP 是一种不保留应用程序消息边界的字节流协议.它根本无法以这种方式将字节粘合"在一起.读取超时的目的是指定您希望读取阻塞多长时间.但是只要能返回至少一字节的数据，读操作就不会阻塞.

TCP is a byte-stream protocol that does not preserve application message boundaries. It is simply not able to "glue" bytes together in that way. The purpose of the read timeout is to specify how long you would like the read to block. But as long as at least one byte of data can be returned, the read operation will not block.

如果您需要循环调用 read 直到您阅读完整的消息，请执行此操作.TCP 层不关心您认为什么是完整的消息，这不是它的工作.

If you need to call read in a loop until you read a complete message, do that. The TCP layer doesn't care what you consider to be a full message, that's not its job.

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