相当于 C# 异步套接字中的 Peek？

Question

我习惯使用同步套接字。为了处理尚未完全到达的消息，我将前 4 个字节设置为消息的预期长度。然后，我将使用 Socket.Receive(tcpRecv, 1024, SocketFlags.Peek); 来查看消息，而不将其从缓冲区中取出。如果所有这些都在那里，我就会提取数据。如果不是，我会把它留在那里。我设计的协议确保消息不会超过 1024 字节。

在异步套接字中，我看不到查看数据的方法。有办法做到这一点吗？有没有比查看数据更好的方法？

谢谢。

-缺口

Answer 1

您无需查看：.NET 异步套接字允许您无需查看即可实现相同类型的功能。我想您可能正在寻找这样的东西：

private void BeginReceive()
{
    if ( _clientState == EClientState.Receiving)
    {
        if (_asyncTask.BytesReceived != 0 && _asyncTask.TotalBytesReceived <= _maxPageSize)
        {
            SocketAsyncEventArgs e = new SocketAsyncEventArgs();
            e.SetBuffer(_asyncTask.ReceiveBuffer, 0, _asyncTask.ReceiveBuffer.Length);
            e.Completed += new EventHandler<SocketAsyncEventArgs>(ReceiveCallback);
            e.UserToken = _asyncTask.Host;

            bool comletedAsync = false;
            try
            {
                comletedAsync = _socket.ReceiveAsync(e);
            }
            catch (SocketException se)
            {
                Console.WriteLine("Error receiving data from: " + _asyncTask.Host);
                Console.WriteLine("SocketException: {0} Error Code: {1}", se.Message, se.NativeErrorCode);

                ChangeState(EClientState.Failed);
            }

            if (!comletedAsync)
            {
                // The call completed synchronously so invoke the callback ourselves
                ReceiveCallback(this, e);
            }
        }
        else
        {
            //Console.WriteLine("Num bytes received: " + _asyncTask.TotalBytesReceived);
            ChangeState(EClientState.ReceiveDone);
        }
    }
}

当您收到回调时，您可以安排另一个接收：

private void ReceiveCallback(object sender, SocketAsyncEventArgs args)
{
    lock (_sync) // re-entrant lock
    {
        // Fast fail: should not be receiving data if the client
        // is not in a receiving state.
        if (_clientState == EClientState.Receiving)
        {
            String host = (String)args.UserToken;

            if (_asyncTask.Host == host && args.SocketError == SocketError.Success)
            {
                try
                {
                    Encoding encoding = Encoding.ASCII;
                    _asyncTask.BytesReceived = args.BytesTransferred;
                    _asyncTask.TotalBytesReceived += _asyncTask.BytesReceived;
                    _asyncTask.DocSource += encoding.GetString(_asyncTask.ReceiveBuffer, 0, _asyncTask.BytesReceived);

                    BeginReceive();
                }
                catch (SocketException e)
                {
                    Console.WriteLine("Error receiving data from: " + host);
                    Console.WriteLine("SocketException: {0} Error Code: {1}", e.Message, e.NativeErrorCode);

                    ChangeState(EClientState.Failed);
                }
            }
            else if (_asyncTask.Host != host)
            {
                Console.WriteLine("Warning: received a callback for {0}, but the client is currently working on {1}.",
                    host, _asyncTask.Host);
            }
            else
            {
                Console.WriteLine("Socket Error: {0} when receiving from {1}",
                   args.SocketError,
                   _asyncTask.Host);
                ChangeState(EClientState.Failed);
            }
        }
    }
}

您可以在我的博客上看到整个异步客户端：http://codesprout.blogspot.com/2011/04/asynchronous-http-client.html

Answer 2

您的相同数据流无需偷看即可工作：

• 在完成时安排四字节读取
• ，将其保存在缓冲区中并将其解码为长度“n”
• 在完成时安排长度“n”-4的读取
• ，将其附加到四个字节已经在那里
• 解码您的消息

与偷看的唯一区别是您必须在最初读取它们时保存四个字节。