Tim Mackey's Weblog

In a web application i'm working on, i needed to get write access to a folder, and preferably not the temp folder because the data should be kept reasonably safe from being deleted accidentally.  If it was a windows-forms application this would be easy, i would just use Application.UserAppDataPath.  So i thought for asp.net, i could use Environment.SpecialFolder.ApplicationData but this maps to the folder for the current user logged on to Windows, not the process running the web site, or the authenticated web site user.  So i just skip up 2 parent directories from that, and use the current Principal.WindowsIdentity to find the actual process running ASP.NET, and then deduce the correct folder, which by default will have write permissions for Asp.Net.

Here is the code:

string Username = Path.GetFileName(System.Security.Principal.WindowsIdentity.GetCurrent().Name).Replace(" ", "");
string UserAppFolder = String.Format(@"{0}\{1}\Application Data", Directory.GetParent(Directory.GetParent(Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)).FullName).FullName, Username);

By the way, the use of Path.GetFileName is entirely intentional, it solves the case where the current user is "NT Authority\Network Service" by yielding "Network Service", which is what we are interested in.  

This will hopefully come in handy for my 'zero configuration' idea for the application.  Next time you need a write folder, it may be a good idea to use this instead of making users specify write permissions for a custom folder.