IntPtr, Unmanaged DLL, and File IO???? Need Network Understanding

[Uriel88]

Hello, I am working with developing an application that uses the Netmon 3.2 API. Currently they have a PInvoke wrapper to access unmanaged C++ DLL functions.

Basically what I am attempting to do is rewrite an example application (written in C++ and provided in their documentation) in C#. Everything compiles fine and executes, but I have no .cap file at the end of the run. Some things that may be wrong: the ADAPTER_INDEX is not correct OR the IntPtr associated with the capture file is not getting passed correctly. Interesting note: when I set a breakpoint in the callback function the program never enters this block (which it should leading me to suspect the ADAPTER_INDEX)

Here is my code:

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Protocols.TestTools.Netmon.API;
using System.Windows.Forms;
using System.Threading;
using System.Runtime.InteropServices;
using System.IO;
 
 
namespace Network_Monitor_Demo
{
    public struct Constants
    {
        public static UInt32 ADAPTER_INDEX = 0;
    }
 
    public class Netmon
    {
 
        public Netmon()
        {
 
           uint ret;
 
 
            //Open a capture file for saving frames.
           string path = @"C:\\Capture\\10sec.cap";
 
            IntPtr myCapFile;
            uint CapSize;
            ret = NetmonAPI.NmCreateCaptureFile(path, 20000000, NmCaptureFileFlag.WrapAround, out myCapFile, out CapSize);
            if (ret != 0)
            {
                MessageBox.Show("Error Opening Capture File" + "10sec.cap");
                return;
            }
 
            //Open the capture engine
            IntPtr myCaptureEngine;
            ret = NetmonAPI.NmOpenCaptureEngine(out myCaptureEngine);
 
            if (ret != 0)
            {
                MessageBox.Show("Error opening capture engine.");
                NetmonAPI.NmCloseHandle(myCapFile);
                return;
 
            }
 
            ret = NetmonAPI.NmConfigAdapter(myCaptureEngine, Constants.ADAPTER_INDEX, new CaptureCallbackDelegate(FrameIndicationCallback), myCapFile, NmCaptureCallbackExitMode.ReturnRemainFrames);
 
            if (ret != 0)
            {
                MessageBox.Show("Error configuration adapter.");
                NetmonAPI.NmCloseHandle(myCaptureEngine);
                NetmonAPI.NmCloseHandle(myCapFile);
 
                return;
            }
 
            MessageBox.Show("Capturing for 10 seconds.");
            NetmonAPI.NmStartCapture(myCaptureEngine, Constants.ADAPTER_INDEX, NmCaptureMode.Promiscuous);
 
 
 
            Thread.Sleep(10000);
 
 
            MessageBox.Show("Stopping Capture.");
            NetmonAPI.NmStopCapture(myCaptureEngine, Constants.ADAPTER_INDEX);
            NetmonAPI.NmCloseHandle(myCaptureEngine);
            NetmonAPI.NmCloseHandle(myCapFile);
 
            return;
 
        }
 
 
        public void FrameIndicationCallback(IntPtr hCapEng, UInt32 ulAdatIdx, IntPtr pContext, IntPtr hRawFrame)
        {
            IntPtr capFile = pContext;
            NetmonAPI.NmAddFrame(capFile, hRawFrame);
        }
 
    }
}
 
 

And here is the code provided in the Network Monitor API documentation, doing the same thing in C++. Network Monitor 3.2 is a free download from Microsoft Downloads.

#include "windows.h"
#include "stdio.h"
#include "stdlib.h"
#include "objbase.h"
#include "ntddndis.h"
#include "NMApi.h"
 
#define ADAPTER_INDEX    0
 
void __stdcall 
MyFrameIndication(HANDLE hCapEng, ULONG ulAdaptIdx, PVOID pContext, HANDLE hRawFrame)
{
    HANDLE capFile = (HANDLE)pContext;
    NmAddFrame(capFile, hRawFrame);
}
 
int __cdecl wmain(int argc, WCHAR* argv[])
{
    ULONG ret;
 
    // Open a capture file for saving frames.
    HANDLE myCapFile;
    ULONG CapSize;
    ret = NmCreateCaptureFile(L"20sec.cap", 20000000, NmCaptureFileWrapAround, &myCapFile, &CapSize);
    if(ret != ERROR_SUCCESS)
    {
        wprintf(L"Error opening capture file, 0x%X\n", ret);
        return ret;
    }
 
    // Open the capture engine.
    HANDLE myCaptureEngine;
    ret = NmOpenCaptureEngine(&myCaptureEngine);
    if(ret != ERROR_SUCCESS)
    {
        wprintf(L"Error opening capture engine, 0x%X\n", ret);
        NmCloseHandle(myCapFile);
        return ret;
    }
 
    ret = NmConfigAdapter(myCaptureEngine, ADAPTER_INDEX, MyFrameIndication, myCapFile);
    if(ret != ERROR_SUCCESS)
    {
        wprintf(L"Error configuration adapter, 0x%X\n", ret);
        NmCloseHandle(myCaptureEngine);
        NmCloseHandle(myCapFile);
        return ret;
    }
 
    wprintf(L"Capturing for 20 seconds\n");
    NmStartCapture(myCaptureEngine, ADAPTER_INDEX, NmLocalOnly);
 
    Sleep(20000);
 
    wprintf(L"Stopping capture\n");
    NmStopCapture(myCaptureEngine, ADAPTER_INDEX);
    NmCloseHandle(myCaptureEngine);
    NmCloseHandle(myCapFile);
 
    return 0;
}
 
 
 

[Plater]

I can't say for sure if it matters or not, but have you considered moving the code out of the constructor and into a function?
It might behave a little nicer.

Also, your adapter index is always 0, are you sure that is not the loopback adapter?

[nukefusion]

Additionally, have you installed WDK? According to the NetMon documentation this is a prerequisite to successfully use the code sample you've posted.

I'd also double check the following line from your code that differs from the NetMon sample:

NetmonAPI.NmStartCapture(myCaptureEngine, Constants.ADAPTER_INDEX, NmCaptureMode.Promiscuous);
 

I imagine you'd need to make sure your network card supports promiscuous mode (many do not) and, if it does, put it into promiscuous mode somehow before starting the capture.

[Plater]

promiscuous mode really only matters if you have an older network structure.
A newer-switch will not route traffic down your port if it shouldn't go to you, so promiscuous mode doesn't buy you much.
Hubs will. And I *believe* older switches might.

I had a wireless card that supported promiscuous mode (they corrected it later) so I could watch every other wireless card's traffic. It was especially fun when I disconnected from an endpoint and was able to pick up multiple endpoint's traffic.

[Uriel88]

Thanks guys for your help. It was the Adapter Index, my wireless card was adapter 3. So I had to implement a method for enumerating and finding the active internet connections adapter and using that index.

The sad thing was I only tested adapters 0 1 and 2 before I posted.... hahhah.

Well thanks again!