Reading a Bitmap from a TIF file - Works in WinForms not in ASP.NET

Question

EDIT Solution Found: See my post below.

We are writing a library that reads in a TIF file from a scanner. Basically, its a scantron. We are examining the form and reading values from it.

Currently we have a windows test app, and we give it a filepath as a string ("c:\testing\image.tif"). It loads up the tif, reads the document correctly and parses the values.

We also have an ASP.NET web application. We have a test page that does exactly what the windows app does, we hand it an identical string, and i calls the same function on the same class from the same library. It however does NOT read the form correctly. We have verified that it does it fact load up the tif file, and it is actually filled with data (pixels we expect to be white/black are white/black when we examine the Bitmap obect in the immediate window of Visual Studio).

The specific problem is in a library called DataMatrix we use to scan a bar-code off the document. This function is supposed to return a List<string>, each of which is a barcode the library found on the document. In the windows app, this function (DataMatrixDecoder.DecodeBarcode(bitmap)) correctly returns with a Count=1. When using the asp.net app, this returns with Count=0.

Because its the exact same image file, I cannot imagine the problem is in DataMatrix. I can only assume its something with ASP.NET or something.

This isn't even my project, but another guy and I are helping our coworker figure this out, and we are just pulling our hair out. All signs indicate that ASP.NET is correctly loading and handing the image off disk to the "processor" class (which is a class library that uses the DataMatrix stuff, we are not doing ANY code in ASP.NET except for opening/handing the file to the function.).

Does anyone have any ideas as to what it might be, or different things we can check?

I'm not even sure what kind of information to give so I tried to say it all, if you have any questions please ask I'd be more than happy to elaborate on anything. Thanks.

edit: this is the code on the ascx.cs code-behind, in a button-click event:

if (formReader.ReadTIFF(@"c:\testing\image.tif"))
{
    messages.Controls.Add(HtmlHelper.DivSuccess("Read successful."));
}

The formReader class then open the file with a FileStream, and uses that to create a Bitmap. The ASP.NET application is not actually opening the file at all (we were uploading it through a FormUpload control, but after experiencing problems we dummied it down to this). This is the most perplexing thing, that it works in the windows app but not from this web site. ASP.NET has full permissions on that folder to do whatever it wants. It can open the image fine, and the bitmap it creates from the FileStream is the actual image.

edit: Also, the ReadTIFF function right now copies the FileStream into a MemoryStream, ensuring its a not a problem streaming from disk (the entire file is in memory).

Answer 1

How are you passing the filepath to the web application?
It is possible that the function which Decodes might be swallowing some exception.

Use reflector to examine the library (if you have not written it).

Answer 2

I agree. It seems your problem is most probably related to User rights on the directory where you're trying to access the files from. Try giving your Web users the Full access rights on the source directory.

Answer 3

EDIT Solution Found: The problem was that the open file dialog was changing the CurrentWorkingDirectory. The reason the website never worked, was because the Environment.CurrentDirectory was set incorrectly. When I manually set the CurrentDirectory to the websites' bin folder, parsing works correctly.

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Small update. Using the Windows App, and selecting the file via OpenFileDialog, will cause the barcode decoder to fail. Technically, I am using the exact same string to hand to the parser ("c:\testing\image.tif"), yet when I use the OpenFileDialog to get the string, the decoder fails. Is there a clue in this?

update: In fact, even if I don't use the string the OpenFileDialog gives me, if I just open the file dialog at all, it will fail. I don't get this. It's something simple. I need to debug the C++ DataMatrix library, really.