Question

I am developing a plugin host. The plugins should have as little trust as they need, however I want to have the possibility for a plugin to read and write files.

Can the AppDomain where the assembly will be loaded be restricted to have access to only one directory for reading and writing?

Other options and ways to go about this are also appreciated like for example easy ways to stream file data from the host to the plugin (reading) and from the plugin to the host (writing).

If its relevant: I am using the MAF infrastructure for the plugins.
http://msdn.microsoft.com/en-us/library/bb384200.aspx

Answer 1

namespace ConsoleApplication
{
    #region Imports

    using System;
    using System.IO;
    using System.Security;
    using System.Security.Permissions;

    #endregion

    public class Plugin : MarshalByRefObject
    {        
        public string TestRead(string path)
        {
            try
            {
                File.ReadAllBytes(path);
                return "Done";
            }
            catch (SecurityException)
            {
                return "Access Denied";
            }
        }
    }

    public class Program
    {
        static void Main(string[] args)
        {
            var setup = new AppDomainSetup();

            setup.ApplicationBase = 
                AppDomain.CurrentDomain.SetupInformation.ApplicationBase;

            var perm = new PermissionSet(PermissionState.None);

            perm.AddPermission(
                new SecurityPermission(
                    SecurityPermissionFlag.Execution));

            perm.AddPermission(
                new FileIOPermission(
                    FileIOPermissionAccess.Read, "c:\\public\\"));

            var pluginDomain = 
                AppDomain.CreateDomain("PluginDomain", null, setup, perm);

            var plugin = 
                pluginDomain.CreateInstanceAndUnwrap(
                    typeof(Plugin).Assembly.FullName,
                    typeof(Plugin).FullName) as Plugin;

            Console.WriteLine(plugin.TestRead("c:\\public\\test.txt"));
            Console.WriteLine(plugin.TestRead("c:\\secret\\test.txt"));
            Console.ReadKey();
        }
    }
}