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How to close a socket in C#?

Posted on 2008-06-18
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Last Modified: 2013-12-16
Is there any way to close a socket if you know the port number?
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Question by:Tharo_Systems
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Expert Comment

by:jcoehoorn
ID: 21815598
Not if you don't own it.
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Author Comment

by:Tharo_Systems
ID: 21815616
I have a program that opens a socket for listening. I need to be able to close it from a different function.
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Expert Comment

by:jcoehoorn
ID: 21816173
And do you have the source for that program?  Can we see it?
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Author Comment

by:Tharo_Systems
ID: 21816315
Here's the function that creates the socket. I would like to have another function that closes the socket.
private void CreateListenerSocket(int PortToListenOn)
	{
		// Determine the IP address of the machine
		IPAddress [] aryLocalAddr = null;
		try
		{
			IPHostEntry ipEntry = Dns.GetHostEntry( Dns.GetHostName() );
			aryLocalAddr = ipEntry.AddressList;
		}
		catch( Exception ex )
		{
			theLog.WriteEntry("Error trying to get local address {0}: " + ex.Message, EventLogEntryType.Error);
		}
		// Verify that an address was obtained. Write to the log if not.
		if( aryLocalAddr == null || aryLocalAddr.Length < 1 )
		{
			theLog.WriteEntry("Unable to get local address", EventLogEntryType.Error);
			return;
		}
                listener = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp );
		listener.Blocking = false;
		for (int i = 0; i < aryLocalAddr.Length; i++)
                {
                  if (aryLocalAddr[i].AddressFamily == AddressFamily.InterNetwork)
                  {
                    listener.Bind(new IPEndPoint(aryLocalAddr[i], PortToListenOn));
                    break;
                }
            }
	listener.Listen( 10 );
	listener.BeginAccept( new AsyncCallback( OnConnectRequest ), listener );
	}

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Expert Comment

by:jcoehoorn
ID: 21816399
If you keep a reference to your listener variable handy it's as simple as calling listener.Close();
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Author Comment

by:Tharo_Systems
ID: 21816486
I was hoping it would be a simple answer. I'm very new to this. Can you elaborate on how to do that? Thanks!
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Expert Comment

by:jcoehoorn
ID: 21816555
Well, the method you posted doesn't declare listener anywhere, so I'm assuming it's a class-level variable.  With that in mind, you can just say this in any non-static method in your class and the socket will close:

if (listener!= null) listener.Close();

That's it.
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Author Comment

by:Tharo_Systems
ID: 21821125
Can it be done from another class?
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Author Comment

by:Tharo_Systems
ID: 21821250
OK, I tried adding that code before the line that creates the socket. I want to prevent the program from opening more than one. The first time through, it's fine because listener is null. The second time it's called, it does close listener, but when it hits the "listener = new socket..." line, it crashes. Am i doing something wrong? Thanks!
private void CreateListenerSocket(int PortToListenOn)
	{
		// Determine the IP address of the machine
		IPAddress [] aryLocalAddr = null;
		try
		{
			IPHostEntry ipEntry = Dns.GetHostEntry( Dns.GetHostName() );
			aryLocalAddr = ipEntry.AddressList;
		}
		catch( Exception ex )
		{
			theLog.WriteEntry("Error trying to get local address {0}: " + ex.Message, EventLogEntryType.Error);
		}
		// Verify that an address was obtained. Write to the log if not.
		if( aryLocalAddr == null || aryLocalAddr.Length < 1 )
		{
			theLog.WriteEntry("Unable to get local address", EventLogEntryType.Error);
			return;
		}
 
            try
            {
                if (listener != null)
                {
                    listener.Close();
                }
            }
            catch (Exception ex)
            {
                theLog.WriteEntry(ex.Message, EventLogEntryType.Error);
            }  
 
                listener = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp );
		listener.Blocking = false;
		for (int i = 0; i < aryLocalAddr.Length; i++)
                {
                  if (aryLocalAddr[i].AddressFamily == AddressFamily.InterNetwork)
                  {
                    listener.Bind(new IPEndPoint(aryLocalAddr[i], PortToListenOn));
                    break;
                }
            }
	listener.Listen( 10 );
	listener.BeginAccept( new AsyncCallback( OnConnectRequest ), listener );
	}
 

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Author Comment

by:Tharo_Systems
ID: 21821525
Upon further inspection, it seems it's crashing when it tries to access aryLocalAddr. Not sure why, but I'm getting "system.objectdisposedexception" errors. Any ideas? I also want to be able to close the socket completely by a button/checkbox/whatever in a separate configuration window in a different class, but I don't know how to access listener from there. Thanks!
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Accepted Solution

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jcoehoorn earned 500 total points
ID: 21821890
Any other class that needs to use the listener member will then need a reference to the correct instance of this class, and listener will need to be public- preferably exposed as a property.

Not sure what's going on with aryLocalAddr.  Calling listener.Close() is the exact same thing as disposing (calling listener.Dispose()) - the two are interchangeable, if that helps.  Is seems that two are intertwined there somehow.  The error puzzles me because if closing the socket also disposed the the IPEndPoint then I would expect it to dispose of the individual items in the array and not the array itself.  That would leave with an error message complaining about aryLocalAddr[n] rather than aryLocalAddr itself.
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