用於多個客戶端的異步TCP服務器

Question

我有一個TCP服務器異步偵聽傳入連接。如果只有一個客戶端連接，一切正常。但是，如果有兩個或更多個連接，則服務器不會收到第一條消息。當我調試ReceiveCallback函數，我可以看到服務器獲取消息的長度，但不是數據。即如果我連接兩個客戶端並嘗試發送第一條消息：「hello」，服務器將得到：received = 5;緩衝區=/0/0/0/0/0，因此不顯示任何內容。在同一客戶端的第二條消息中，服務器獲取數據。

這就是我的服務器看起來像：

 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

看到http://msdn.microsoft.com/en-us/library/dxkwh6zw.aspx

比如你想改變你的代碼，以便它分配一個新的每次調用BeginReceive時間緩衝：

 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); 

每個客戶端必須有一個緩衝區。否則，一個客戶端可以覆蓋另一個客戶端使用的緩衝區。