Firefox and IE read file names differently

In a recent web project I suddenly got an unexpected exception when I was uploading a file using a standard <asp:FileUpload /> control in ASP.NET 2.0. I’ve only been testing the website in Firefox at that point and everything worked great. The error only occurred in IE 6 and 7.

Here is a little dummy code that I’ll use to demonstrate the difference.

<asp:FileUpload runat="server" ID="txtUpload" />

private void Upload()

{

  string fileName = txtUpload.PostedFile.FileName;

  Response.Write(fileName);

}

If I try to upload the file C:\test.txt then the fileName variable will be set to test.txt in Firefox, but C:\test.txt in IE. The reason for the exception was that I used that filename to name the file on the server when it was uploaded and saved to disk. In Firefox that was no problem because I just added the filename to a folder path on the server like “C:\\uploads\\” + fileName. But in IE that would result in this file path C:\uploads\C:\test.txt which clearly is wrong.

I found the solution within the ASP.NET object model. It is very simple, but gave me a lot of gray hairs before figuring it out.

// Wrong! work only in Firefox

string fileName = txtUpload.PostedFile.FileName;

// Correct! Works on all browsers

string fileName = txtUpload.FileName;

Strange little quirk, but as long as you know your way around it, it’s not a big deal.