用于多个客户端的异步 TCP 服务器

Question

我有一个异步侦听传入连接的 TCP 服务器。如果只连接一个客户端，一切正常。但是如果有两个或多个连接，服务器就不会收到第一条消息。当我调试 ReceiveCallback 函数时，我可以看到服务器获取消息的长度，而不是数据。 IE。如果我连接两个客户端并尝试发送第一条消息：“hello”，服务器会得到：received = 5; buffer= /0/0/0/0/0，所以什么都不显示。在同一客户端的第二条消息中，服务器获取数据。

这就是我的服务器的样子：

        private void StartServer()
    {
        try
        {
            serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            serverSocket.Bind(new IPEndPoint(IPAddress.Any, 3333));
            serverSocket.Listen(100);
            serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);   

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }


     private void AcceptCallback(IAsyncResult ar)
    {
        try
        {
            Socket clientSocket = serverSocket.EndAccept(ar); 
            clientSocketList.Add(clientSocket);
            AppendToTextBox("ClientConnected");
            clientSocket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), clientSocket);
            serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }


        private void ReceiveCallback(IAsyncResult ar)
    {
        try
        {
            int received = 0;
            Socket current = (Socket)ar.AsyncState;
            received = current.EndReceive(ar);
            byte[] data = new byte[received];

            if (received == 0)
            {
                return;
            }

            Array.Copy(buffer, data, received);
            string text = Encoding.ASCII.GetString(data);

            AppendToTextBox(text);
            buffer = null;
            Array.Resize(ref buffer, current.ReceiveBufferSize);

            current.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), current);
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }

Answer 1

查看http://msdn.microsoft.com/en-us/library/dxkwh6zw.aspx的示例

您想更改您的代码，以便在您每次调用 BeginReceive 时分配一个新缓冲区：

        Socket clientSocket = serverSocket.EndAccept(ar); 
        clientSocketList.Add(clientSocket);
        AppendToTextBox("ClientConnected");
        var buffer = new byte[BUFFER_LENGTH];  // <---
        clientSocket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(ReceiveCallback), clientSocket);
        serverSocket.BeginAccept(new AsyncCallback(AcceptCallback), null);

每个客户端必须有一个缓冲区。否则，一个客户端可以覆盖另一个客户端使用的缓冲区。