C# Test If User Has Write Access to a Folder

C# Test if user has write access to a folder

That's a perfectly valid way to check for folder access in C#. The only place it might fall down is if you need to call this in a tight loop where the overhead of an exception may be an issue.

There have been other similar questions asked previously.

Checking if a directory has read and write permissions using .Net Core

FileIOPermission is part of .NET's code security - it's meant to allow you to host .NET code that has lower permissions than the host process (i.e. software process isolation). It doesn't have anything to do with the file system's access rights.

For .NET Core, you can read and modify access control to files with the System.IO.FileSystem.AccessControl package. After adding the package, you can do something like this:

using System.IO;

public void Main(string[] args)
{
  var ac = new FileInfo(@"C:\Test.txt").GetAccessControl();

  // ac has the ACL for the file
}

Needless to say, this is Windows specific.

Check if directory exists and Permissions

Well try creating the directory or the file and if you don't have permission an exception would be thrown which you can catch and do as needed.

try
{
 // code to create directory or file
}
catch(Exception ex)
{
  // do something here
}

Checking for directory and file write permissions in .NET

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.

Check that can write to FileShare without actually writing to it

private bool hasWriteAccessToFolder(string folderPath)
{
    try
    {
        // Attempt to get a list of security permissions from the folder. 
        // This will raise an exception if the path is read only or do not have access to view the permissions. 
        System.Security.AccessControl.DirectorySecurity ds = Directory.GetAccessControl(folderPath);
        return true;
    }
    catch (UnauthorizedAccessException)
    {
        return false;
    }
}

Borrowed from : C# Test if user has write access to a folder

In this scenario, I am assuming that a FileShare is going to behave similarly to a typical Windows Directory.
As far as I know - Windows does all the work in the background to treat network shares as directories, and it should use the same permission system etc.

How do you check for permissions to write to a directory or file?

UPDATE:

Modified the code based on this answer to get rid of obsolete methods.

You can use the Security namespace to check this:

public void ExportToFile(string filename)
{
    var permissionSet = new PermissionSet(PermissionState.None);    
    var writePermission = new FileIOPermission(FileIOPermissionAccess.Write, filename);
    permissionSet.AddPermission(writePermission);

    if (permissionSet.IsSubsetOf(AppDomain.CurrentDomain.PermissionSet))
    {
        using (FileStream fstream = new FileStream(filename, FileMode.Create))
        using (TextWriter writer = new StreamWriter(fstream))
        {
            // try catch block for write permissions 
            writer.WriteLine("sometext");


        }
    }
    else
    {
        //perform some recovery action here
    }

}

As far as getting those permission, you are going to have to ask the user to do that for you somehow. If you could programatically do this, then we would all be in trouble ;)

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