Intercepting internet download requests using WinInet

[Albert]

WinInet experts

I am in the process of writing a sample application that intercepts file download requests when a user selects to download a file from the Internet (yes another one). I have successfully implemented a custom IE Download Manager by implementing the IDownloadManager COM interface etc. but I suspect that there may be another approach to intercepting HTTP and FTP file requests with WinInet that may be better suited to what I need

Because I’m unfamiliar with WinInet I was hoping that you would be able to
a) Give me an indication if intercepting client file requests is at all possible with WinInet. (Comments on inter-application issues and welcome)

b) Point me at some documentation. Have not been able to get anything from the MSDN documentation so far except a good reference for methods, interfaces etc. but then again I am unfamiliar with the API so I may be missing things in there

c) If you happen to know exactly how to do it and coincidently have some sample code for this, well, that would be just fantastic. :

Thanks
Albert

[Paul Baker [MVP, Windows - SDK]]

WinInet is just an HTTP, FTP, gopher client that Internet Explorer uses. To
intercept an Internet Explorer download, you must write a Custom Download
Manager, just as you are doing. Details are here:

http://msdn.microsoft.com/library/default.asp?url=/workshop/browser/ext/overview/downloadmgr.asp

Are you intending to intercept a download from any application that uses
WinInet? I don't see how this is realstically possible.

What's the problem with using a Custom Download Manager?

Paul

WinInet experts,
I am in the process of writing a sample application that intercepts file

download requests when a user selects to download a file from the Internet
(yes another one). I have successfully implemented a custom IE Download
Manager by implementing the IDownloadManager COM interface etc. but I
suspect that there may be another approach to intercepting HTTP and FTP file
requests with WinInet that may be better suited to what I need.

Because I'm unfamiliar with WinInet I was hoping that you would be able
a) Give me an indication if intercepting client file requests is at all

possible with WinInet. (Comments on inter-application issues and welcome).

b) Point me at some documentation. Have not been able to get anything from

the MSDN documentation so far except a good reference for methods,
interfaces etc. but then again I am unfamiliar with the API so I may be
missing things in there.

c) If you happen to know exactly how to do it and coincidently have some

sample code for this, well, that would be just fantastic. :)

Thanks,
Albert.

[Paul Baker [MVP, Windows - SDK]]

Albert,

I'm sorry, I don't think I know enough about Internet Explorer to help you,
but I'll try. I would recommend working through this problem instead of
looking for an alternative. I assure you it will be the simplest way forward
in the long run!

What does "selects a download link and the URL resolves to the actual file"
mean?

What does "if the link is actually a redirect to the file to download" mean?

What I'm getting at is, are you talking about a link to a file:// URL? A
link to a http:// URL with a redirection response containing a file:// URL?
The file name of cache entry? What?

Paul

Thanks for your response Paul.
Here is a brief summary of my "hurdle" with the IDownloadManager

implementation.

When a user selects a download link and the URL resolves to the actual

file to download I have no problem retrieving the complete URL from the
IMoniker::GetDisplayName method but.if the link is actually a redirect to

- Internet Explorer displays the "Open / Save" dialog that prompts the

user if they wish to open or save the file (not to concerned about this
since I assume I would be able to change a configuration value somewhere to
make this go away)

-Then regardless of if the user selects Open or Save my IDownloadManager

implementation gets called with an URL Moniker that does not seem to point
to the file to be downloaded but rather it only contains part of the URL.

HRESULT Download(
IMoniker *pmk,
IBindCtx *pbc,
DWORD dwBindVerb,
LONG grfBINDF,
BINDINFO *pBindInfo,
LPCOLESTR pszHeaders,
LPCOLESTR pszRedir,
UINT uiCP
);
...the pszRedir value should contain the URL that the Moniker is

redirected to, but this parameter is empty when my implementation gets calle
d by IE for a redirected link.

What I have not mentioned here is that I am doing all of this using .NET

and C# and that I do not intend to make use of the URL Moniker methods to
download the file itself since I want to make use of the System.Net classes
in the .NET Framework to do this, so all that I really need from IE is the
complete URL to the file.

a) Should I be using something other than pszRedir to get the complete

URL? Is there another property that contains the file name?

b) Is there perhaps a marshalling problem between the COM call and my .NET

implementation for the download method that could cause the pszRedir value
to be lost as part of the interoperation for the method call?

public void Download(
UCOMIMoniker pmk,
UCOMIBindCtx pbc,
int dwBindVerb,
int grfBINDF,
int pBindInfo,
[MarshalAs(UnmanagedType.LPStr)] string pszHeaders,
[MarshalAs(UnmanagedType.LPStr)] string pszRedir,
int uiCP
)
c) Is there a bug in IE that it is not populating pszRedir correctly or

not creating the URL Moniker passed to me with the complete URL?

Thanks,
Albert

[Paul Baker [MVP, Windows - SDK]]

Albert,

How does Internet Explorer decide when to call your download manager? Does
it call it for all HTTP responses, or does it only call it for responses
that would ordinarily show the downloading file dialog?

You confused me with your use of the word "file". A web server doesn't
simply serve files. It can execute certain files instead of simply serving
them, like .ASP, and it is the response that we're talking about, not the
"file".

When HTTP makes a redirection, it sends a complete response with a status
code indicating that the resource is available elsewhere and a new URL in
the headers.

In your example, it is getting the response to "GET /someproduct/downloads",
which is a redirection, then making another round trip to the server to get
a response to "GET /someproduct/downloads/somefile.zip". If it is calling
your download manager for the first response, you can ignore it and continue
to the second response (which is why I ask when it is called).

Honestly, I have no clue what pszRedir is. It's not very well documented.

Paul

Much appreciated, lets try and solve this mystery. :)
What does "selects a download link and the URL resolves to the actual

file" mean?

I mean that if the user selects a HTTP URL link on a web page that

directly points to the file that the user wants to download, say
"http://www.microsoft.com/someproduct/urgentpatches/patch101.exe" for
example, then IE calls my Download method and I call the
IMoniker::GetDisplayName method that in turn returns me the complete URL
"http://www.microsoft.com/someproduct/urgentpatches/patch101.exe" that I can
use to retrieve the file from the server.

What does "if the link is actually a redirect to the file to download" mean?
I mean that the user selects a HTTP URL link on a web page that do not

directly point to the file that the user wants to download, say
"http://www.microsoft.com/someproduct/downloads", then the HTTP server that
handles the request redirects the request to say
"http://www.microsoft.com/someproduct/downloads/somefile.zip". In this
scenario, when IE calls my Download method and I call the GetDisplayName
method then I get the incomplete URL
"http://www.microsoft.com/someproduct/downloads" back from the method call
instead of the URL
"http://www.microsoft.com/someproduct/downloads/somefile.zip" that I need to
actually download the file.