Using WinInet to Call a Server Script Asynchronously

Introduction

I wanted to find a simple way of running a script (e.g. Perl, PHP, etc.) on a webserver but it needed to be asynchronous as I didn't want the application to hang while waiting for the webserver's response. I didn't need to read any output from the script so all the solutions I could find were overly complicated for my needs.

Theory

Use INTERNET_FLAG_ASYNC to open the session
Set a status callback using InternetSetStatusCallback
Open the connection using InternetOpenUrl
Read the handle when the callback function receives INTERNET_STATUS_HANDLE_CREATED
Free up everything when the call has finished and the callback function receives INTERNET_STATUS_REQUEST_COMPLETE

Using the Code

The complete code is:

HINTERNET    hInternetSession = NULL;   
HINTERNET    hURL = NULL;

typedef struct
{
    HWND        hWindow;     // window handle
    HINTERNET   hResource;   // HINTERNET handle created by InternetOpenUrl
} REQUEST_CONTEXT;

REQUEST_CONTEXT    request_context;

void __stdcall InternetCallbackFunction(HINTERNET hInternet,
                        DWORD dwContext,
                        DWORD dwInternetStatus,
                        LPVOID lpvStatusInformation,
                        DWORD dwStatusInformationLength)
{
    REQUEST_CONTEXT* cpContext;
    INTERNET_ASYNC_RESULT* res;

    cpContext = (REQUEST_CONTEXT*)dwContext;

    // what has this callback function been told has happened?
    switch (dwInternetStatus)
    {
        case INTERNET_STATUS_HANDLE_CREATED:
            // get the handle now that it has been created so it can be freed up later
            res = (INTERNET_ASYNC_RESULT*)lpvStatusInformation;
            hURL = (HINTERNET)(res->dwResult);

            break;

        case INTERNET_STATUS_REQUEST_COMPLETE:
            // script has been called so close handles now and 
	   // cancel the callback function
            InternetCloseHandle(hURL);
            InternetSetStatusCallback(hInternetSession, NULL);
            InternetCloseHandle(hInternetSession);

            // flag as having been completed now
            hURL = NULL;
            hInternetSession = NULL;

            break;
    }
}

void RunScript(char* szURL)
{
    // only run this script if finished all others
    if (hInternetSession == NULL)
    {
        hInternetSession = InternetOpen("Microsoft Internet Explorer",
                        INTERNET_OPEN_TYPE_PRECONFIG,
                        NULL,
                        NULL,
                        INTERNET_FLAG_ASYNC);
        
        if (hInternetSession != NULL)
        {
            // set the callback function
            InternetSetStatusCallback(hInternetSession,
                        (INTERNET_STATUS_CALLBACK)InternetCallbackFunction);

            // run the script
            hURL = InternetOpenUrl(hInternetSession,
                        szURL,
                        NULL,
                        0,
                        INTERNET_FLAG_RELOAD |
                        INTERNET_FLAG_PRAGMA_NOCACHE |
                        INTERNET_FLAG_NO_CACHE_WRITE,
                        (unsigned long)(&request_context));
        }
    }
}