Develop Reference

C# try to connect to the server

I made a server-client program with auto connection.
But the program only works if I first start the server application because the client needs to connect.
My goal is for the client to check with a delay of 2 seconds if the server is already created.
I made a while statement for a trial and error cycle
try
{
int a = 1;
while (a == 1)
{
cliente.Connect(IP_End);
if (cliente.Connected)
{
connectRead();
a = 2;
}
else
{
while (!cliente.Connected)
{
int milliseconds = 2000;
Thread.Sleep(milliseconds);
cliente.Connect(IP_End);
MessageBox.Show(text);
if (cliente.Connected)
{
connectRead();
}
}
}
}
}
catch(SocketException se)
{
MessageBox.Show(se.Message);
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
}
the error is :
No connection can be made because the target computer actively refused them 192.168.254.28:100
the method is here :
private void connectRead()
{
STW = new StreamWriter(cliente.GetStream());
STR = new StreamReader(cliente.GetStream());
STW.AutoFlush = true;
backgroundWorker1.RunWorkerAsync();
backgroundWorker1.WorkerSupportsCancellation = true;
}

Based on the code you almost got it right. I believe the "Connect" extension method should update the value within the client. If it does the way I'd do it would be to introduce a separate method that returns a boolean and it would help to simplify the code. For example:
private bool ConnectClient(SomeClient clientToConnect, IPAddress ipToConnectTo, int delay)
{
System.Threading.Thread.Sleep(delay);
clientToConnect.Connect(ipToConnectTo);
return clientToConnect.Connected;
}
try
{
bool successfulConnection;
while (!successfulConnection)
{
successfulConnection = ConnectClient(yourClient, "10.10.10.10", 2000);
}
}
catch
{
// ...
}

Without knowing more about errors or desired functionality, I can tell you will call connectRead(); twice if you hit the second loop. To fix this replace your second loop with this:
while (!cliente.Connected)
{
int milliseconds = 2000;
Thread.Sleep(milliseconds);
cliente.Connect(IP_End);
if (cliente.Connected)
{
connectRead();
a = 2;
}
}
EDIT:
I also took out the MessageBox because that seems unnecessary and will pause the program until you hit Ok on the MessageBox.
EDIT 2:
Question on actively refused connections
Question on determination of open port

(Apparently) Gracefully Closed UDPClient leaves the socket blocked

The following code, despite apparently closing the UDP Socket, leaves it hanging and unable to reconnect to the same address / port.
These are the class variables I use:
Thread t_listener;
List<string> XSensAvailablePorts;
private volatile bool stopT_listener = false;
volatile UdpClient listener;
IPEndPoint groupEP;
I create and launch a new thread with a method which will handle the Socket connection and listening:
private void startSocketButton_Click(object sender, RoutedEventArgs e)
{
stopT_listener = false;
closeSocketButton.IsEnabled = true;
startSocketButton.IsEnabled = false;
t_listener = new Thread(UDPListener);
t_listener.Name = "UDPListenerThread";
t_listener.Start();
}
The method is the following (I use a time-out on the Receive in order to not leave it blocked if nothing is being sent on the socket and a Stop is being issued):
private void UDPListener()
{
int numberOfPorts = XSensAvailablePorts.Count();
int currAttempt = 0;
int currPort = 0;
bool successfullAttempt = false;
while (!successfullAttempt && currAttempt < numberOfPorts)
{
try
{
currPort = Int32.Parse(XSensAvailablePorts[currAttempt]);
listener = new UdpClient(currPort);
successfullAttempt = true;
}
catch (Exception e)
{
currAttempt++;
}
}
if (successfullAttempt)
{
//timeout = 2000 millis
listener.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 2000);
//Tried with and without, no change: listener.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
statusTB.Dispatcher.BeginInvoke((Action)delegate() { statusTB.Text = "Connected on port:" + currPort; });
groupEP = new IPEndPoint(IPAddress.Parse("143.225.85.130"), currPort);
byte[] receive_byte_array;
try
{
while (!stopT_listener)
{
try
{
receive_byte_array = listener.Receive(ref groupEP);
if (receive_byte_array.Length == 0 || receive_byte_array == null)
continue;
ParseData(receive_byte_array, samplingDatagramCounter);
}
catch (SocketException ex)
{
if (ex.SocketErrorCode == SocketError.TimedOut)
continue;
}
}
}
catch (Exception e)
{
Debug.Print(e.Message);
}
finally
{
if (listener != null)
{
listener.Client.Shutdown(SocketShutdown.Both);
listener.Close();
}
}
}
statusTB.Dispatcher.BeginInvoke((Action)delegate() { statusTB.Text = "Not Connected"; });
return;
}
I order the thread / socket to stop with this method:
private void closeSocketButton_Click(object sender, RoutedEventArgs e)
{
stopT_listener = true;
closeSocketButton.IsEnabled = false;
startSocketButton.IsEnabled = true;
t_listener.Join();
if (listener.Client != null)
{
listener.Client.Shutdown(SocketShutdown.Both);
listener.Close();
}
if (t_listener.IsAlive)
{
t_listener.Abort();
statusTB.Text = "Aborted";
}
else
statusTB.Text = "Not Connected";
}
Despite checking in debug that the socket has been closed, if I retry to connect to the same port, I am unable to do so because it raises a SocketException saying that only one usage of port/address is normally permitted.

I put code you provided in a simple form to run it and... I cannot directly reproduce your problem. I haven't send any data to the client though, but as far as I understand it shouldn't change anything as it's UDP and we're investigating (re)opening socket, not transmitting data.
When clicking Start/Stop buttons the socket is always properly opened and closed, reopening works as intended.
For me the only way to force the SocketException you mentioned was to introduce some obvious misuse of socket logic:
Run two instances of application and click Start in both.
Remove BOTH occurrences of Shutdown and Close (Stop doesn't close socket).
Running app, opening socket, closing the app without closing socket, running app again, trying to open socket.
Only changes I made in your code was removing ParseData(...) line and adding some ports to XSensAvailablePorts list.
Can you check if the port is still open after you apparently close it? You can use netstat -an, or an excellent tool ProcessExplorer. You can also check if the t_listener thread is terminating correctly (standard Task Manager or ProcessExplorer can help you).

Set the listener object to NULL so the resource is released which should also free the connection.

i have same problem, and the problem is in UDPClient.Receive(), she keep the socket in state of used even you call Close/shutdown/... `
try{ // receive loop}
catch{}
finally {
UDP_Listner.Close();
UDP_Listner = null;
}
EDIT :
t_listener = new Thread(UDPListener);//replace by :
t_listener = new Thread(new ThreadStart(UDPListener));
`
to safely close socket & thread ( http://msdn.microsoft.com/en-us/library/system.threading.threadstart(v=vs.110).aspx )

I have the same problem, I am the safest programmer, I always close everything nicely. yet I found that the .net class does not close the socket fast enough. because if I go slow it doesn't happen, but if I open and close(cleanup fully) and open it fast, I get the same error. especially if the user wants to run the same code again and open the port again.

Might be an old answer, but in your attempt to find a usable port, but which failed, i would dispose the listener instance you tested before the next iteration.
try
{
currPort = Int32.Parse(XSensAvailablePorts[currAttempt]);
listener = new UdpClient(currPort);
successfullAttempt = true;
}
catch (Exception e)
{
currAttempt++;
if(listener != null)
{
listener.Close();
}
}

I think Bind or reuse can solve this (even if socket is not closed yet it can be reused and no error is thrown)
Example code:
udpClient = new UdpClient();
udpClient.Client.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
udpClient.Client.Bind(new IPEndPoint(IPAddress.Any, p));

Delay when send string via socket

I make an application in android can send character code to server C# when user input on android keyboard.
This is send method in android side:
public Boolean writeMessage(String message) {
try {
printWriter = new PrintWriter(socket.getOutputStream(), true);
printWriter.println(message);
return true;
} catch (Exception ex) {
Log.e(TAG,"write error: " +ex.getMessage());
return false;
}
}
And server listen the messages (C#):
Thread myThread = new Thread(new ThreadStart(ServeClient));
myThread.Start();
void ServeClient(){
StreamReader reader = new StreamReader(tcpClient.GetStream());
while (true)
{
try
{
String message = reader.ReadLine();
if (message != null)
{
Console.WriteLine(message);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
My code works, but when user input faster, the server delay read message in 1,2 or 3 seconds (I have test the method get character when user input, it works fine, not delay). Where is my problem? Thanks in advance!

Your problem may be caused by Nagle's algorithm reducing TCP traffic. Consider setting TCP_NODELAY on your client (and server - TcpClient.Client.NoDelay - if communication is two-way).
Edit: For java it is Socket.setTcpNoDelay method.

How to sync between a listening/sending tcp client thread and the main execution?

i have a simple windows service which runs and starts a thread which listen/receive heartbeat via tcp/ip. i'm having a hard time finding ways to sync between getting information from the tcp thread and using that value to update something in the main thread.
i try to use a thread.sleep method and keep on looping it for a few times while awaiting the answer back from the thread and then getting the value, but that method seems to be a bit volatile with the method sometimes working and sometimes not.
so what's a good way to sync between these two?
basically what i want to do is to start the listening tcp thread, get specific value and the update the main program.
attached are the receive function and the function which i used to start the thread.
p.s: i'm a totally noobie when it comes to tcp/ip and c# so any comments on any part of the code or the design is more than welcome :)
public virtual void Receive()
{
string eventMessage = string.Empty;
int bytesRcvd = 0;
int totalBytesRcvd = 0;
byte[] byteBuffer = new byte[maxBufferSize];
NetworkStream listenStream;
try
{
if (client.Connected)
{
listenStream = client.GetStream();
}
else
{
return;
}
while (true)
{
//message that is slot in from the object will get sent here.
if (!string.IsNullOrEmpty(MessageToSend))
{
Send(MessageToSend);
MessageToSend = string.Empty;
}
// must convert it back and look for the delimiter, cannot wait for the three heartbeat to pass
string leftoverMsg = string.Empty;
bytesRcvd = listenStream.Read(byteBuffer, totalBytesRcvd, maxBufferSize - totalBytesRcvd);
totalBytesRcvd += bytesRcvd;
//if more than heart beat size, can process to see if it's a heartbeat and proceed to send
if (totalBytesRcvd > msgHeartbeatSize)
{
eventMessage = Encoding.ASCII.GetString(byteBuffer, 0, totalBytesRcvd);
ProcessMessage(eventMessage, ref leftoverMsg, ref totalBytesRcvd, ref byteBuffer);
}
}
}
catch (ThreadAbortException thEx)
{
//do nothing as main thread has aborted and waiting to close
logger.Info(Thread.CurrentThread.Name + " is stopped. ");
}
catch (Exception exce)
{
bIsActive = false;
logger.Error(exce);
CleanUp();
}
finally
{
logger.Info(String.Format("Thread {0} Exiting. ", Thread.CurrentThread.Name));
}
}
public virtual void StartReceivingThread()
{
Thread thrReceive = new Thread(Receive);
try
{
if (!bIsActive && Connect())
{
//NOTE: exception thrown by a thread can only be captured by that thread itself
//start a listen thread
//wait until heartbeat message is accepted
thrReceive.Name = "thr" + serviceType.Name;
thrReceive.Start();
bIsActive = true;
//wait to get the heartbeat message
for (int i = 0; i < maxRetry; i++)
{
Thread.Sleep(maxTimeOutValue);
if (bIsReceivingHeartbeat)
break;
}
//if nothing happens close the connection and try again
if (!bIsReceivingHeartbeat)
{
bIsActive = false;
CleanUp();
logger.Info("Closing receiver thread - " + thrReceive.Name);
}
else
{
logger.Info("Starting receiver thread - " + thrReceive.Name);
}
}
}
catch(Exception ex)
{
logger.Error(ex);
}
//finally
//{
// logger.Info("Exiting receiver thread - " + thrReceive.Name);
//}
}

I assume bIsReceivingHeartbeat is a bool member variable of the class. If the value changed in one thread (receiver) is not visible in the other thread this is most likely due to memory barrier. I am saying this from my Java background but this is most likely true in .net as well.
Try declaring the variables volatile or use a property and make the getter and setter synchronized:
private bool bIsReceivingHeartbeat;
public bool IsReceivingHeartbeat
{
[MethodImpl(MethodImplOptions.Synchronized)]
get { return bIsReceivingHeartbeat; }
[MethodImpl(MethodImplOptions.Synchronized)]
set { bIsReceivingHeartbeat = value; }
}
And in the calling code:
if (!IsReceivingHeartbeat) ....
I am writing from Java background but the situation most likely similar

(Looks like you also posted this code in refactormycode.com.)
Anyway, instead of the loop with a sleep delay, I recommend using an Event object that pulsed by the code that sets IsReceivingHeartbeat. See the ManualResetEvent and AutoResetEvent classes in MSDN.

Server application closes when receiving message

Well I'm making a Client-Server application and I can send messages to my client just fine but when I do it the other way around (Client to server) the server application just closes down, any help on how to fix this?
public void OnDataReceived(IAsyncResult asyn)
{
try
{
SocketPacket socketData = (SocketPacket)asyn.AsyncState;
int iRx = 0;
iRx = socketData.m_currentSocket.EndReceive(asyn);
char[] chars = new char[iRx + 1];
System.Text.Decoder d = System.Text.Encoding.UTF8.GetDecoder();
int charLen = d.GetChars(socketData.dataBuffer,
0, iRx, chars, 0);
System.String szData = new System.String(chars);
area1.AppendText(szData);
WaitForData(socketData.m_currentSocket); // Continue the waiting for data on the Socket
}
catch (ObjectDisposedException)
{
System.Diagnostics.Debugger.Log(0, "1", "\nOnDataReceived: Socket has been closed\n");
}
catch (SocketException se)
{
MessageBox.Show(se.Message);
}
}
After doing some breakpoints I realized it closes after reaching this part when it tries to append it on the textArea it closes without an error.
Any ideas on how to fix this? I guessing something to do with the threads but not sure why it just closes.

Does an exception happen when AppendText is called? If yes, can you include the call stack? Is szData valid data when AppendText is called? Try putting a try/catch around the code to get the exception information:
try
{
... your code...
}
catch (Exception e)
{
... examine 'e' in the debugger or dump it to a log file
}
One thing that might be going wrong is that you are accessing a UI control from the non-UI thread, but it could be other things. It's hard to tell from the code snippet you posted.
Updated:
If the exception was that the control is being invoked from the wrong thread, you can try adding a function like this, then calling that instead of accessing the control directly (untested):
private void AppendText(string text)
{
// InvokeRequired required compares the thread ID of the
// calling thread to the thread ID of the creating thread.
// If these threads are different, it returns true.
if (this.area1.InvokeRequired)
{
SetTextCallback d = new AppendTextCallback(AppendText);
this.Invoke(d, new object[] { text });
}
else
{
this.area1.AppendText(text);
}
}