桥接非托管C dll并管理C＃dll

Question

I have a third-party Windows app that supports a C plugin/driver (see spec below) to be a passive data receiver once initialized. Now I found a C# package that does the data gathering and Pushing. The only missing piece here is a bridge between the C dll and the C# dll.

The data flow is like this: When the app is launched, it loads and calls the C dll which contains several exported functions including an init function. In this init function, I like to establish a call to the C# to setup some network connection and prepare for incoming data. Once that done, according to the driver spec, the C# dll will gather data and stream it to the receiving driver. To accommodate this, I have two thoughts (you may come up with more):

1) to wrap the C# with C++/Cli and call the expose C#-like methods from the driver. Declare an object with gcroot, then instantiate it with gcnew then call the method(s). Tried that and I got stackoverflowexception. I am new to this mix-mode programming and can't figure out why that happened.

2) to wrap the C dll in some way (like using C++/Cli to import the C functions then interact with the C# data streamer) to be callable from C#. What is the best way to do this?

I have done some reading and it seems C++/Cli is the easy route but I am open to other not so complicated options as well. What are the project settings I have to add/modify to make it work should I choose C++/Cli or any way you suggest?

As I am new to tackle this kind of problem, any samples or related links are helpful. So I appreciate if you could demonstrate how things work one way or the other.

Here is piece of the skeletal C# dll referenced (other methods are omitted):

public class Client {

    public Client()
    {
        //reset();
    }

    public void test()
    {

        Console.WriteLine("test");
    }

    /// <summary>
    /// Connect connects the Client to the server.
    /// Address string has the form host:port.
    /// </summary>
    public void Connect(string address)
    {
        Disconnect();
        // validate address
        int sep = address.IndexOf(':');
        if (sep < 0)
        {
            throw new ArgumentException("Invalid network address");
        }
        // set host and port
        host = address.Substring(0, sep);
        toPort(ref port, address.Substring(sep + 1));
        // connect
        Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        socket.Connect(host, port);
        rw.Set(socket, CLIENT_DEFAULT_BUFFER_SIZE); 
    }

    /// <summary>
    /// Disconnect disconnects the Client from the server.
    /// </summary>
    public void Disconnect()
    {
        backlog.Clear();
        try
        {
            if (Connected)
            {
                write("close");
            }
        }
        catch (Exception e)
        {

        }
        //reset();
        //rw.Close();
    }

}

Here is the skeletal spec of the C dll:

//APIs
#ifdef __cplusplus
extern "C"{
#endif

#define DLL __declspec(dllexport)

////////////////////////////////////////////////////////////////////////////
// Initialization: do some prep for receiving data from C#
// params:
//      hWnd            handle
//      Msg             message
//      nWorkMode       work mode
// return:
//       1              true    
//      -1              false
DLL int Init(HWND hWnd, UINT Msg, int nWorkMode);


// Quitting and closing
// Param:
//      hWnd            same handle as Init
//  return:
//       1              true    
//      -1              fals
DLL int Quit(HWND hWnd);

#ifdef __cplusplus
}
#endif

Answer 1

To call C functions in an external DLL, you can use C++/CLI as you've already mentioned, or use P/Invoke (Platform Invoke).

With P/Invoke, you define a static extern method in your C# assembly then decorate it with appropriate attributes. After that, you can call the method as per any other C# method, and the .NET Framework plumbing will handle the loading of the DLL and marshalling the method parameters back and forth.

For example:

[DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool SystemParametersInfo(uint uiAction, uint uiParam, uint pvParam, uint fWinIni);

The method is declared with the static and extern keywords, and decorated with the DllImport attribute which identifies the DLL that contains the C function. That's generally the minimum you will need.

The hardest part is determining which C types map to which .NET types for the method parameters and return type: this is a bit of a black art! If you visit pinvoke.net you can see how the Windows APIs have been translated, which may help. Searching the web for "pinvoke" should also turn up a number of useful resources.