System.NotSupportedException：不允许在未连接的套接字上执行该操作

Question

I am creating a C# application in which I send files over a LAN connection via sockets, but I encounter an "System.NotSupportedException" when I call the Send function

This is the function of the receiver of the file.

    Socket _newSocket;
    List<byte> endBuffer;

    // Used to connect to the server
    private void button1_Click(object sender, EventArgs e)
    {
        _newSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        _newSocket.Connect(IPAddress.Parse("127.0.0.1"), _PORT);
    }

    // Used to Receive the file
    private void button3_Click(object sender, EventArgs e)
    {
        _newSocket.Receive(endBuffer.ToArray(), SocketFlags.None);
        MessageBox
            .Show(Encoding.ASCII.GetString(endBuffer.ToArray(), 0, endBuffer.Count));
    }

This is the function I used to start the server.

void SetupServer(object sender)
    {
        Button temp = (Button)sender;
        temp.Enabled = false;
        _serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        _serverSocket.Bind(new IPEndPoint(IPAddress.Parse(txtConnectToIP.Text), _PORT));
        _serverSocket.Listen(5);
        _serverSocket.BeginAccept(AcceptCallback, null);
    }

    void AcceptCallback(IAsyncResult AR)
    {
        Socket socket;

        try
        {
            socket = _serverSocket.EndAccept(AR);
        }
        catch
        {
            MessageBox.Show("Not Working!");
            return;
        }

        _clientSockets.Add(socket);
        int id = _clientSockets.Count - 1;
        IPAddress ip = IPAddress.Parse(_serverSocket.LocalEndPoint.ToString().Split(':')[0]);
        string HostName = Dns.GetHostEntry(ip).HostName.Split('.')[0];
        string finalName = HostName + " (" + ip.ToString() + ")";
        AddClientForSelectionCallback(finalName);
    }

This is the send function.

byte[] postBuffer = Encoding.ASCII.GetBytes("Sending Complete!");

    void Send(string filePath)
    {
        try
        {
            _serverSocket.SendFile(filePath, null, postBuffer, TransmitFileOptions.ReuseSocket);
        }
        catch (Exception ec)
        {
            MessageBox.Show("Failed with error message:\n   "+ ec);
        }
    }

Lastly, how would Receive the file sent because _newSocket.Receive() does not seem to work. I have looked at storing its result in a var, but Receive returns nothing and I will try using ConnectAsync.

Help would really be appreciated.

Answer 1

In your program, _serverSocket is the socket that accepts incoming connections, you cannot send data to it.

As soon as a connection is accepted, you get the socket for that connection:

socket = _serverSocket.EndAccept(AR);

You can use this socket instance to communicate with that specific client.