UDP Async Server/Client Problem

[Ryman]

Hello, I've just recently began network programming for c# (bought the book C# Network Programming) and I've ran into a few problems. Whenever I click the submit button on the client (to send the UDP packet to the UDP server), it doesn't work the first time (so it seems) and I must click it again to get the server to receive the packet and display it in a List Box. I was wondering if somone could help me track this problem down, I'm sure it's just something simple because I'm still very new to Network Programming. Here is my code:

UDP Server

 
public partial class Form1 : Form
    {       
        private byte[] data = new byte[1024];
        private int size = 1024;
        private Socket server;          
        public static IPEndPoint iep = new IPEndPoint(IPAddress.Any, 9050);
        public static IPEndPoint sender2 = new IPEndPoint(IPAddress.Any, 0);
        public static EndPoint sender3 = (EndPoint)sender2;
 
        public Form1()
        {
            CheckForIllegalCrossThreadCalls = false;
            InitializeComponent();  
            server = new Socket(AddressFamily.InterNetwork,
            SocketType.Dgram, ProtocolType.Udp);     
            server.Bind(iep);           
            server.BeginReceive(data, 0, data.Length, SocketFlags.None, new AsyncCallback(connTest), server);
        }
 
 
        void connTest(IAsyncResult iar)
        {
            Socket client = (Socket)iar.AsyncState;
 
 
            //Receive Data from Client
 
            string dataString;           
            client.ReceiveFrom(data, ref sender3);
            dataString = Encoding.ASCII.GetString(data);
            results.Items.Add(dataString);         
 
 
            data = new byte[1024];
            int sent = client.EndReceive(iar);
            server.BeginReceive(data, 0, data.Length, SocketFlags.None, new AsyncCallback(connTest), client);
        }      
 
 
    }
 

UDP Client (Code was cut down a bit)

 
  public partial class Form1 : Form
    {
        public static byte[] data = new byte[1024];
        public static string stringData;
        public static UdpClient server = new UdpClient("127.0.0.1", 9050);
        public static IPEndPoint sender2 = new IPEndPoint(IPAddress.Any, 0);
        public static Socket newSock = new Socket(AddressFamily.InterNetwork,
                SocketType.Dgram, ProtocolType.Udp);
 
 
void sentData(IAsyncResult iar)
        {
            label5.Text = "Data Sent";
        }
 
 
private void submitText_Click(object sender, EventArgs e)
        {
            //data
            data = new byte[1024];
            data = Encoding.ASCII.GetBytes(input.Text);
 
            //Send message to server
            server.BeginSend(data, data.Length, sentData, server);            
        }
}
 
 
 

Any help would be appreciated!

Thanks.

[DMenT]

Hello, I've just recently began network programming for c# (bought the book C# Network Programming) and I've ran into a few problems. Whenever I click the submit button on the client (to send the UDP packet to the UDP server), it doesn't work the first time (so it seems) and I must click it again to get the server to receive the packet and display it in a List Box. I was wondering if somone could help me track this problem down, I'm sure it's just something simple because I'm still very new to Network Programming. Here is my code:

UDP Server

 
public partial class Form1 : Form
    {       
        private byte[] data = new byte[1024];
        private int size = 1024;
        private Socket server;          
        public static IPEndPoint iep = new IPEndPoint(IPAddress.Any, 9050);
        public static IPEndPoint sender2 = new IPEndPoint(IPAddress.Any, 0);
        public static EndPoint sender3 = (EndPoint)sender2;
 
        public Form1()
        {
            CheckForIllegalCrossThreadCalls = false;
            InitializeComponent();  
            server = new Socket(AddressFamily.InterNetwork,
            SocketType.Dgram, ProtocolType.Udp);     
            server.Bind(iep);           
            server.BeginReceive(data, 0, data.Length, SocketFlags.None, new AsyncCallback(connTest), server);
        }
 
 
        void connTest(IAsyncResult iar)
        {
            Socket client = (Socket)iar.AsyncState;
 
 
            //Receive Data from Client
 
            string dataString;           
            client.ReceiveFrom(data, ref sender3);
            dataString = Encoding.ASCII.GetString(data);
            results.Items.Add(dataString);         
 
 
            data = new byte[1024];
            int sent = client.EndReceive(iar);
            server.BeginReceive(data, 0, data.Length, SocketFlags.None, new AsyncCallback(connTest), client);
        }      
 
 
    }
 

UDP Client (Code was cut down a bit)

 
  public partial class Form1 : Form
    {
        public static byte[] data = new byte[1024];
        public static string stringData;
        public static UdpClient server = new UdpClient("127.0.0.1", 9050);
        public static IPEndPoint sender2 = new IPEndPoint(IPAddress.Any, 0);
        public static Socket newSock = new Socket(AddressFamily.InterNetwork,
                SocketType.Dgram, ProtocolType.Udp);
 
 
void sentData(IAsyncResult iar)
        {
            label5.Text = "Data Sent";
        }
 
 
private void submitText_Click(object sender, EventArgs e)
        {
            //data
            data = new byte[1024];
            data = Encoding.ASCII.GetBytes(input.Text);
 
            //Send message to server
            server.BeginSend(data, data.Length, sentData, server);            
        }
}
 
 
 

Any help would be appreciated!

Thanks.

The problem I've seen in your code is the following:

client.ReceiveFrom(data, ref sender3);

In this line you are attemping to read from the client socket, but at this point you already have a message in the data Byte array.

You could put a breakpoint at this line and watch the value for the data variable to se the behavior I am trying to explain.

Sorry for my bad english, I hope my comments let you some help.

Kind Regards,
DMenT.