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POWhy do I receive twice the data sent over UDP broadcast?
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copied!<p>I have a problem with the code below. What it does is send the current date/time using UDP broadcast and listens to this message. My current use of this code is local, I use the Send and Receive in the same application, on the same computer. I didn't try it between 2 computers yet.</p> <pre><code>public class Agent { public static int Port = 33333; public delegate void OnMessageHandler(string message); Socket socketSend; Socket socketReceive; bool receiving = false; Thread receiveThread; public event OnMessageHandler OnMessage; public Agent() { socketSend = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp); socketSend.EnableBroadcast = true; socketSend.Connect(new IPEndPoint(IPAddress.Broadcast, Port)); socketReceive = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp); socketReceive.EnableBroadcast = true; socketReceive.Bind(new IPEndPoint(IPAddress.Any, Port)); } public void Start() { Console.WriteLine("Agent started!"); receiving = true; receiveThread = new Thread(new ThreadStart(Receive)); receiveThread.IsBackground = true; receiveThread.Start(); } public void Stop() { receiving = false; socketSend.Close(); socketReceive.Close(); receiveThread.Join(); Console.WriteLine("Agent ended."); } public void Send(string message) { Console.WriteLine("Sending : {0}", message); byte[] bytes = Encoding.Convert(Encoding.Unicode, Encoding.UTF8, Encoding.Unicode.GetBytes(message)); socketSend.Send(bytes); Console.WriteLine("Message sent."); } protected void Receive() { Console.WriteLine("Thread started!"); while (receiving) { try { if (socketReceive.Available > 0) { byte[] bytes = new byte[socketReceive.Available]; Console.WriteLine("Waiting for receive..."); int bytesReceived = socketReceive.Receive(bytes, SocketFlags.None); Console.WriteLine("Bytes received : {0}", bytesReceived); string message = Encoding.UTF8.GetString(bytes); Console.WriteLine("Received message : {0}", message); OnMessage(message); } else { Console.Write("."); Thread.Sleep(200); } } catch (SocketException ex) { if (ex.SocketErrorCode == SocketError.Interrupted) { break; } else { throw; } } } Console.WriteLine("Thread ended."); } } </code></pre> <p>The problem I have is that it sends the data once (when I click on a button) but it receives twice the amount expected. For example, a normal date/time is 19 bytes long but the first time Available is > 0, its value is 38. The Receive call following only grabs 19 bytes and the loop continues with the next 19 bytes. That means I receive my message and twice and I want it only once of course.</p> <p>Example of an output :</p> <pre><code>Agent started! Thread started! ..........Sending : 29/07/2009 12:05:04 Message sent. Waiting for receive... Bytes received : 19 Received message : 29/07/2009 12:05:04 Waiting for receive... Bytes received : 19 Received message : 29/07/2009 12:05:04 ......Thread ended. Agent ended. </code></pre>

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