Internet explorer changes xsl extension to xlt

FLX TMS FlexCel Studio for .NET
1

When I download an Excel file in xls format from our server I get the warning below in Internet Explorer.

The Excel file is generated using Flexcel for .Net using the save method of the XlsFile class:
excel.Save(stream, TFileFormats.Xls);

The download link ends with the .xls extension but is changed when you click the link. Also when you do a save as from the link Internet Explorer changes the extension to .xlt and thinks it is an Excel template.

I am using Internet Explorer 9 on Windows 7. It makes no difference when I use IE9 in IE7 or IE8 compatibility mode.

Other browsers like FireFox and Google Chrome do not change the extension and do not give this warning below:

Web sites that use the "application/x-msexcel" or "application/vnd.ms-excel" MIME type to open web page content inside of Microsoft Excel may encounter the following warning prompt when the file attempts to open in Excel 2007:

"The file you are trying to open, '[filename]', is in a different format than specified by the file extension. Verify that the file is not corrupted and is from a trusted source before opening the file. Do you want to open the file now?"  (Yes | No | Help)

If the user clicks Yes, the file will open as expected.  If the user clicks No, the file may open anyway, or may prompt a second time, and then not open if the user selects No again.  

2

Correction: also FireFox thinks my Flexcel generated xls file is a template.

3

See the following blog page from Microsoft that explains the problem:


http://blogs.msdn.com/b/vsofficedeveloper/archive/2008/03/11/excel-2007-extension-warning.aspx
4

Hi,

this is weird, I 've tried it here in a clean virtual machine, (Excel 2007, win7, ie9) and it works correctly. I am using the code:
           Response.AddHeader("Content-Disposition", "attachment; filename=Test.xls");
            Response.AddHeader("Content-Length", ms.Length.ToString());
            Response.ContentType = "application/excel"; //octet-stream";
            Response.BinaryWrite(ms.ToArray());

And it looks the filename has priority over the mime type.
If you have the line:
           Response.AddHeader("Content-Disposition", "attachment; filename=Test.xls");

Then the file must be xls, an xlsx will how the warning

If you change this line to be
 Response.AddHeader("Content-Disposition", "attachment; filename=Test.xlsx");

Then the file must be xlsx, and xls will show the warning.

But I haven't seen in any case an "xlt" file saved. I wonder what do you write in the "filename" part?
By the way, you can control if the file is a template or not with FlexCel by reading or writing to 
xls.IsXltTemplate

property. But as said, a standard xls file with an xls filename should work fine, I haven't seen any issues here.

A semi-related note: One known issue that happened with ie is that it might rename files to be "file[2].xls" when the file exists, and file[2].xls is not a valid Excel filename.  (xls filenames can't containt [ ] because it would confuse the formulas like =[file2.xls]!A1.
I am not sure if this know issue still applies in ie9 and actually I haven't seen for some time so it might be fixed, but it is the only ranaming issue I have seen. I haven't seen a file renamed to xlt.

5

I am not streaming directly from the server to the browser. I save the generated Excel file to the hard disk on the server and the user is presented with a direct download link to that file.

An example file name is: MngRpt-C-hd3yiv0pf1v.xls

Also I do not use the content type "application//excel" but in our IIS 7 mime mapping we use the microsoft recommended "application/vnd.ms-excel" for the "xls" extension. This is the IIS 7 default.

The download link in the browser does show the "MngRpt-C-hd3yiv0pf1v.xls" file name with the correct extension. As soon as I click the link Internet Explorer shows the given message. In the title bar of the dialog the filename is displayed as:  "MngRpt-C-hd3yiv0pf1v.xlt"

I will try if changing the mime-type to "application/excel" and setting the IsXltTemplate explicitly to false, makes any difference. All our server show this behaviour. Both the ones using IIS6 and IIS7.
6

Explicitly setting IsXltTemplate to false did not make any difference. This is as expected because it is false by default when creating a new file.


Changing the mime-type for "xls" from "application/vnd.ms-excel" to "application/excel" solved the problem!
7

At least it did for IIS7. Not for IIS 6 but that may be a IIS6 issue.

8
It is a little hard to diagnose this without being able to see how servers are configured, but some ideas:
1)
application/vnd.ms-excel should work, actually application/excel is older and probably the "correct" one today to use should be vnd.ms-excel.
What do you have in your client machine on this registry key?
HKEY_CLASSES_ROOT\MIME\Database\Content Type\application/vnd.ms-excel

I have .xls (and it works fine here). Can you verify you don't have .xlt here?  This could be causing the problem.

What do you have in the "Content-Disposition" ? on the iis server?

2)
According to
http://msdn.microsoft.com/en-us/library/ms775148.aspx
<quote>
If the file is marked as "content-disposition=attachment" in the HTTP header, Internet Explorer treats the file name from the URL as final and does not rename it before placing it in the cache.
</quote>

So, can you try to conifgure IIS to send a "content-distribution=attachment" for the xls files, and this way ensure no renaming is done on the client?