Returning string from class library using Nuget package "NetCoreServer"

Question

I am writing a Windows Form application (TCP Client) using the Nuget package "NetCoreServer". I have implemented the methods specified in the example "TcpChatClient", see: TcpChatClient . This works just fine, and I am able to pass messages back and forth to and from a server and display the messages in the Windows Form.

However, due to reusability (the next TCP Client application might be a console application), I would like to limit the code in the form class to just GUI stuff and move all networking logic to a class library. Basically, I would like the form class to just pass and receive strings to methods in the class library (from what I gather, this is best practice, for reusability).

I have successfully moved the code to a class library and debugging shows that the messages are sent back and forth the same as when I had all the code in the form class. But I am stuck on how to actually get the response from the class library to the form class.

In the class library the relevant code is:

protected override void OnReceived(byte[] buffer, long offset, long size)
{
    string message = Encoding.UTF8.GetString(buffer, (int)offset, (int)size);
}

Since the "OnReceived" method is inherited from a class in the Nuget package, I am unable to change the signature, so I cannot get the method to return a string. This was my initial thought. I feel like I am missing an obvious way to pass the string to the form class, but I just cant figure this out.

I have intentionally not posted much code in this question, but I can of course provide my code if elaboration is necessary. Any help would be greatly appreciated.