How to retrieve XML file stream from unmanaged DLL file in C#

Question

I've received an unmanaged DLL file from a client. This DLL file has an important method that returns an XML stream. I am not sure how to 'catch' this XML stream because the DLL file is pretty much undocumented. This is what I know:

1. I know how to call an unmanaged DLL function, however I am unfamiliar with structs and how to retrieve data from the function using a struct.
2. The 'documentation' says: You can obtain an XML stream handle from the function OpenXmlBridge

This is where I am stuck at right now:

[DllImport("UnmanagedDllFile.DLL")]
public static extern void OpenXmlBridge();

I know that this returns void when executed but I am at a loss right here. I also know that this function exeists because when I replace OpenXmlBridge with some random stuff, I get errors. So until now, I guess I've been on the right track. I haven't been able to find out what to do exactly from here.

I anyone could be able to point me into the right direction so I can retrieve the XML stream handle from this function. Any help or tips are greatly appreciated.

Answer 1

You can use UnmanagedMemoryStream class. In that case your wrapper whould look like:

[DllImport("UnmanagedDllFile.DLL")]
public static extern IntPtr OpenXmlBridge();

And the code to access it would be something like:

var length = 0 //stream length here
var pointer = NativeWrapper.OpenXmlBridge();
using(var ms = new UnmanagedMemoryStream((Byte*)pointer, length){
  var xDocument = new XmlDocument();
  xDocument.Load(ms); 
  //process document
}