How to properly and completely close/reset a TcpClient connection?


What is the correct way to close or reset a TcpClient connection? We have software that communicates with hardware but sometimes something goes wrong and we are no longer to communicate with it, until we restart the software.

I have tried forcing TcpClient.Close() and even setting it to null but that doesn't work. Only a complete restart of the software works.


I can't use the using keyword because TpcClient is only defined in one location, but used throughout the library. (And there is only one connection at any given time)

It's a library that handles communication. The software itself can call the ResetConnection() method of the Controller class (which represents the hardware).

It currently looks like

if (tcpClient != null)
    tcpClient = null;

Now from what I've read here I should use tcpClient.Dispose() instead of " = null"

I'll give that a try and see if it makes a difference.

7/29/2013 5:14:53 PM

Accepted Answer

You have to close the stream before closing the connection:


Closing the client does not close the stream.

12/30/2009 2:44:49 PM

Given that the accepted answer is outdated and I see nothing in the other answers regarding this I am creating a new one. In .Net 2, and earlier, you had to manually close the stream before closing the connection. That bug is fixed in all later versions of TcpClient in C# and as stated in the doc of the Close method a call to the method Close closes both the connection and the stream

EDIT according to Microsoft Docs

The Close method marks the instance as disposed and requests that the associated Socket close the TCP connection. Based on the LingerState property, the TCP connection may stay open for some time after the Close method is called when data remains to be sent. There is no notification provided when the underlying connection has completed closing.

Calling this method will eventually result in the close of the associated Socket and will also close the associated NetworkStream that is used to send and receive data if one was created.

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