Question

In my .NET 2.0 application, I need to check if sufficient permissions exist to create and write to files to a directory. To this end, I have the following function that attempts to create a file and write a single byte to it, deleting itself afterwards to test that permissions do exist.

I figured the best way to check was to actually try and do it, catching any exceptions that occur. I’m not particularly happy about the general Exception catch though, so is there a better or perhaps a more accepted way of doing this?

private const string TEMP_FILE = "\\tempFile.tmp";

/// <summary>
/// Checks the ability to create and write to a file in the supplied directory.
/// </summary>
/// <param name="directory">String representing the directory path to check.</param>
/// <returns>True if successful; otherwise false.</returns>
private static bool CheckDirectoryAccess(string directory)
{
    bool success = false;
    string fullPath = directory + TEMP_FILE;

    if (Directory.Exists(directory))
    {
        try
        {
            using (FileStream fs = new FileStream(fullPath, FileMode.CreateNew, 
                                                            FileAccess.Write))
            {
                fs.WriteByte(0xff);
            }

            if (File.Exists(fullPath))
            {
                File.Delete(fullPath);
                success = true;
            }
        }
        catch (Exception)
        {
            success = false;
        }
    }

Answer 1

The answers by Richard and Jason are sort of in the right direction. However what you should be doing is computing the effective permissions for the user identity running your code. None of the examples above correctly account for group membership for example.

I’m pretty sure Keith Brown had some code to do this in his wiki version (offline at this time) of The .NET Developers Guide to Windows Security. This is also discussed in reasonable detail in his Programming Windows Security book.

Computing effective permissions is not for the faint hearted and your code to attempt creating a file and catching the security exception thrown is probably the path of least resistance.