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Using WinInet to Call a Server Script Asynchronously

, 24 Aug 2007
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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

  1. Use INTERNET_FLAG_ASYNC to open the session
  2. Set a status callback using InternetSetStatusCallback
  3. Open the connection using InternetOpenUrl
  4. Read the handle when the callback function receives INTERNET_STATUS_HANDLE_CREATED
  5. 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));
        }
    }
}   

History

  • 24th August, 2007: Initial post

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Sean OConnor
Web Developer
United Kingdom United Kingdom
No Biography provided

Comments and Discussions

 
GeneralMy vote of 3 Pinmemberbadwei22-Aug-10 19:16 
General997 error Pinmemberdelinhabit6-May-08 2:05 
I implemented your code in my application and i'm getting an 997 error code (GetLastError) after calling InternetOpenUrl. I want to implement a progress bar to see the download progress.
 
Have you encountered this behavior?
Thanks!
GeneralRe: 997 error PinmemberShilpi Boosar18-May-08 21:15 
GeneralRe: 997 error Pinmemberdelinhabit18-May-08 23:49 
GeneralRe: 997 error PinmemberShilpi Boosar18-May-08 23:59 
GeneralRe: 997 error Pinmemberdelinhabit19-May-08 0:18 
GeneralRe: 997 error PinmemberShilpi Boosar19-May-08 0:42 
GeneralRe: 997 error Pinmemberdelinhabit19-May-08 0:55 
GeneralRe: 997 error PinmemberShilpi Boosar19-May-08 1:36 
GeneralRe: 997 error PinmemberAnandtv28-May-08 2:31 
GeneralRe: 997 error PinmemberShilpi Boosar28-May-08 2:57 
AnswerRe: 997 error PinmemberAnandtv28-May-08 20:04 
GeneralRe: 997 error PinmemberShilpi Boosar28-May-08 20:44 
GeneralExactly what I was looking for! PinmemberGilad Novik27-Aug-07 7:24 

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