asynchronous downloads

John Drum -- drum@best.com
Wednesday, October 30, 1996

Environment:  VC++ 4.2b, NT 4.0

I'm having trouble getting asynchronous downloads from
the net to work.

The first approach I tried was to derive a class from
CInternetSession with the following constructor:

	CDownloader::CDownloader()
		: CInternetSession(
			_T("Downloader"),
			1,
			PRE_CONFIG_INTERNET_ACCESS,
			NULL,
			NULL,
			INTERNET_FLAG_ASYNC)
	{
		try
		{
			EnableStatusCallback();
		}
		catch (CInternetException* pEx)
		{
			// snip
			pEx->Delete();
		}
	
		m_dwCurrentContext = 2; // incremented for each new request
	}


Then for each download request I did the following in a CDownloader
member function:

	AfxParseURL(url, dwServiceType, strServerName, strObject, nPort))
	// snip
	pHttpConnection = GetHttpConnection(strServerName, nPort);
	// snip
	pHttpFile = pHttpConnection->OpenRequest(
			CHttpConnection::HTTP_VERB_GET,
			strObject,
			NULL,
			fContext,
			NULL,
			NULL,
			INTERNET_FLAG_EXISTING_CONNECT);
	//snip
	pHttpFile->SendRequest();


Now when my overloaded OnStatusCallback() function is finally
called with a INTERNET_STATUS_REQUEST_COMPLETE status, I try
to Read() from the above pHttpFile.  The problem is that
every Read() results in a CInternetException of type
ERROR_IO_PENDING being thrown.



Yesterday afternoon I tried using a CAsyncMonikerFile derivative
(again called CDownloader)
with the OnDataAvailable() member function overidden to detect
completion.  However, I didn't get far with this since my
call to Open() failed every time.

	CString strUrl;

	CDownloader* pDown = new CDownloader();
	CFileException ex;
	if (!pDown->Open(strUrl, &ex))
	{
		CString string;
		string.Format("URL could not be opened, error %d", ex.m_cause);
		AfxMessageBox(string, MB_OK);
		// ex.m_cause was always 1 here
	}


So I would welcome any suggestions for fixing these approaches or
any new and better ideas for asynchronously downloading arbitrary urls.

Thanks,
John

---

Mike Blaszczak -- mikeblas@nwlink.com
Sunday, November 03, 1996

At 15:25 10/30/96 -0800, John Drum  wrote:
>Environment:  VC++ 4.2b, NT 4.0

>I'm having trouble getting asynchronous downloads from
>the net to work.

Doesn't the README for the 4.2b patch explain that INTERNET_FLAG_ASYNC
isn't supported by MFC?  I thought it did, but I don't have a copy
handy.

.B ekiM
http://www.nwlink.com/~mikeblas/
I'm afraid I've become some sort of speed freak.
These words are my own. I do not speak on behalf of Microsoft.

---

Mario Contestabile -- Mario_Contestabile.UOS__MTL@UOSMTL2.universal.com
Tuesday, November 05, 1996

>Doesn't the README for the 4.2b patch explain that INTERNET_FLAG_ASYNC
>isn't supported by MFC?  I thought it did, but I don't have a copy
>handy.
>
>.B ekiM

Why would inet.cpp have a AfxInternetStatusCallbackDebug() function which 
requires
the flag then? I don't have a copy of the readme either...

mcontest@universal.com

---

Slh1995@aol.com
Wednesday, November 06, 1996

In a message dated 96-11-06 22:10:03 EST, you write:

<< >Doesn't the README for the 4.2b patch explain that INTERNET_FLAG_ASYNC
 >isn't supported by MFC?  I thought it did, but I don't have a copy
 >handy.
 >
 >.B ekiM
 
 Why would inet.cpp have a AfxInternetStatusCallbackDebug() function which 
 requires
 the flag then? I don't have a copy of the readme either... >>

I do have a copy of the readme.txt file for 4.2b and it does not have any
reference to INTERNET_FLAG_ASYNC at all...

---

Mike Blaszczak -- mikeblas@nwlink.com
Saturday, November 09, 1996

At 22:28 11/6/96 -0500, Slh1995@aol.com wrote:
>In a message dated 96-11-06 22:10:03 EST, you write:

><< >Doesn't the README for the 4.2b patch explain that INTERNET_FLAG_ASYNC
> >isn't supported by MFC?  I thought it did, but I don't have a copy
> >handy.

> >.B ekiM
 
> Why would inet.cpp have a AfxInternetStatusCallbackDebug() function which 
> requires
> the flag then? I don't have a copy of the readme either... >>

Neither status callbacks in general nor the specific implementation of
AfxInternetStatusCallbackDebug() require INTERNET_FLAG_ASYNC.

.B ekiM
http://www.nwlink.com/~mikeblas/
I'm afraid I've become some sort of speed freak.
These words are my own. I do not speak on behalf of Microsoft.

---

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