Cannot add to received string in UDP Listener C #

Question

I have a form that creates a UDP object, a UDPClient is created in the UDP class, and the received data is executed in the BeginReceive method using EndReceive.

When I print a string of detected data, after converting the byte [], to the console from the beginreceive method, with the added text, only the received data prints the non-attached text.

So, it seems that the data received is incomplete.

When a line is printed, NewLine and the added "done" are not displayed.

Any help would be great!

thanks

class Udp { public EventHandler _dataReceived; public Udp() { int receiverPort = 1248; UdpClient receiver = new UdpClient(receiverPort); string discovery = "<?xml version=\"1.0\"?><ServiceQuery></ServiceQuery>"; receiver.BeginReceive(new AsyncCallback( DataReceived), receiver); IPEndPoint end = new IPEndPoint(IPAddress.Broadcast, 1248); receiver.Send(Encoding.ASCII.GetBytes(discovery + "\0"), discovery.Length + 1, end); } private void DataReceived(IAsyncResult ar) { UdpClient c = (UdpClient)ar.AsyncState; IPEndPoint receivedIpEndPoint = new IPEndPoint(IPAddress.Any, 1248); Byte[] receivedBytes = c.EndReceive(ar, ref receivedIpEndPoint); string receivedText = ASCIIEncoding.ASCII.GetString(receivedBytes); Console.WriteLine("\n"); if(_dataReceived != null) { Console.Write(receivedIpEndPoint + ": " + receivedText + Environment.NewLine + "done"); _dataReceived(receivedText, new EventArgs()); } c.BeginReceive(new AsyncCallback(DataReceived), c); } } 

Answer 1

The simplest play I can come up with for this problem is this code:

  private void button1_Click(object sender, EventArgs e) { Byte[] receivedBytes = new byte[] { 0x48, 0x65, 0x6c, 0x00, 0x6c, 0x6f }; string receivedText = Encoding.ASCII.GetString(receivedBytes); Console.Write(receivedText + ", you won't see this"); } 

Output after pressing the button several times:

  HelHelHelHel 

Undoubtedly, now you recognize the poison tablet in the receivedBytes array, this is the presence of byte 0x00, which leads to a reduction in the output string. None of this byte falls into the Visual Studio output window.

Explaining this behavior requires a pretty deep dive into how Console.Write () works in a Winforms application and how it can generate output even if your program does not have a console. This is a long story that can hardly entertain anyone, so I will sing for the short version. If the debugging option of the Visual Studio hosting process is enabled, Console.Write () is equivalent to Debug.Write (). The debug output is intercepted by the DefaultTraceListener class, it throws OutputDebugString () to get the text in the debugger trace window. These winapi functions accept C strings, the C string ends with zero to indicate the end of the string.

There are several ways to fix this; the programmer's way is to convert the contents of the byte [] array to hex:

  Byte[] receivedBytes = new byte[] { 0x48, 0x65, 0x6c, 0x00, 0x6c, 0x6f }; string receivedText = BitConverter.ToString(receivedBytes); Console.WriteLine(receivedText + ", you see this"); 

Output:

  48-65-6C-00-6C-6F, you see this 48-65-6C-00-6C-6F, you see this 48-65-6C-00-6C-6F, you see this 

Or you can take a better look at the data you are transmitting, ensuring that it is actually printed text that can be correctly converted using Encoding.ASCII