BUG: Bytes Read Is Not Set on Asynchronous InternetReadFile

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This article was previously published under Q255580

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.

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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.

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