BUG: Bytes Read Is Not Set on Asynchronous InternetReadFile (255580)

SYMPTOMS

If you call FtpOpenFile and then InternetReadFile asynchronously, lpdwNumberOfBytesRead is not updated when the operation concludes.

Also, the INTERNET_STATUS_REQUEST_COMPLETE notification for InternetReadFile, dwResult, and dwError in (LPINTERNET_ASYNC_RESULT) lpvStatusInfo contains incorrect values.

The problem only occurs in Internet Explorer 5, not Internet Explorer 4.x.

RESOLUTION

To work around this problem, use the following procedure, which is based on the fact that InternetReadFile yields these values in LPINTERNET_ASYNC_RESULT structure:

SUCCESS: dwResult = 1; dwError = bytes read (IE5) or 0 (IE4)
FAILURE: dwResult = 0; dwError = error code.

Check the Internet Explorer version programmatically as shown in the following Knowledge Base article:
244857 HOWTO: Interpret the Results of InternetQueryOption with the INTERNET_VERSION_INFO Structure

If the version number is Internet Explorer 5, modify the callback function as follows:

void CALLBACK InternetCallback(HINTERNET hInternet,
    DWORD dwContext, DWORD dwInternetStatus, void* lpStatusInfo,
    DWORD dwStatusInfoLength)
{
    strProgress *pProgress;
    switch(dwInternetStatus)
    {
    ...
    case INTERNET_STATUS_REQUEST_COMPLETE:
        INTERNET_ASYNC_RESULT* pResult;
        pResult = (INTERNET_ASYNC_RESULT*)lpStatusInfo;
        pProgress = (strProgress*)dwContext;
        pProgress->dwError = pResult->dwError;
        pProgress->dwResult = pResult->dwResult;
        pProgress->bComplete = true;
        if (pResult->dwResult == 1 && pProgress->type == TYPE_READFILE)
        {
            //pResult->dwError actually stores the bytes read for InternetReadFile in IE5
            pProgress->dwResult = pResult->dwError;
            pProgress->dwError = ERROR_SUCCESS; 
        }
        break;
    }
    ...
}

In the main() function, pProgress->dwError will then contain the number of bytes read if pProgress->dwError is ERROR_SUCCESS.