source: trunk/eraser/Eraser.Manager/Plugins.cs @ 2010

/* 
 * $Id$
 * Copyright 2008-2010 The Eraser Project
 * Original Author: Joel Low <lowjoel@users.sourceforge.net>
 * Modified By:
 * 
 * This file is part of Eraser.
 * 
 * Eraser is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software
 * Foundation, either version 3 of the License, or (at your option) any later
 * version.
 * 
 * Eraser is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
 * 
 * A copy of the GNU General Public License can be found at
 * <http://www.gnu.org/licenses/>.
 */

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;

using System.IO;
using System.Reflection;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using Eraser.Util;

namespace Eraser.Manager.Plugin
{
    /// <summary>
    /// The plugins host interface which is used for communicating with the host
    /// program.
    /// </summary>
    /// <remarks>Remember to call Load to load the plugins into memory, otherwise
    /// they will never be loaded.</remarks>
    public abstract class Host : IDisposable
    {
        #region IDisposable members
        protected virtual void Dispose(bool disposing)
        {
        }

        /// <summary>
        /// Cleans up resources used by the host. Also unloads all loaded plugins.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }
        #endregion

        /// <summary>
        /// Getter that retrieves the global plugin host instance.
        /// </summary>
        public static Host Instance
        {
            get { return ManagerLibrary.Instance.Host; }
        }

        /// <summary>
        /// Retrieves the list of currently loaded plugins.
        /// </summary>
        /// <remarks>The returned list is read-only</remarks>
        public abstract IList<PluginInstance> Plugins
        {
            get;
        }

        /// <summary>
        /// Loads all plugins into memory.
        /// </summary>
        public abstract void Load();

        /// <summary>
        /// The plugin loaded event.
        /// </summary>
        public EventHandler<PluginLoadedEventArgs> PluginLoaded { get; set; }

        /// <summary>
        /// Event callback executor for the OnPluginLoad Event
        /// </summary>
        internal void OnPluginLoaded(object sender, PluginLoadedEventArgs e)
        {
            if (PluginLoaded != null)
                PluginLoaded(sender, e);
        }

        /// <summary>
        /// Loads a plugin.
        /// </summary>
        /// <param name="filePath">The absolute or relative file path to the
        /// DLL.</param>
        public abstract void LoadPlugin(string filePath);
    }

    /// <summary>
    /// Event argument for the plugin loaded event.
    /// </summary>
    public class PluginLoadedEventArgs : EventArgs
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="instance">The plugin instance of the recently loaded plugin.</param>
        public PluginLoadedEventArgs(PluginInstance instance)
        {
            Instance = instance;
        }

        /// <summary>
        /// The <see cref="PluginInstance"/> object representing the newly loaded plugin.
        /// </summary>
        public PluginInstance Instance { get; private set; }
    }

    /// <summary>
    /// The default plugins host implementation.
    /// </summary>
    internal class DefaultHost : Host
    {
        /// <summary>
        /// Constructor. Loads all plugins in the Plugins folder.
        /// </summary>
        public DefaultHost()
        {
        }

        public override void Load()
        {
            AppDomain.CurrentDomain.AssemblyResolve += AssemblyResolve;
            AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve += ResolveReflectionDependency;
            string pluginsFolder = Path.Combine(
                Path.GetDirectoryName(Assembly.GetEntryAssembly().Location), //Assembly location
                PLUGINSFOLDER //Plugins folder
            );

            foreach (string fileName in Directory.GetFiles(pluginsFolder))
            {
                FileInfo file = new FileInfo(fileName);
                if (file.Extension.Equals(".dll"))
                    try
                    {
                        LoadPlugin(file.FullName);
                    }
                    catch (BadImageFormatException)
                    {
                    }
                    catch (FileLoadException)
                    {
                    }
            }
        }

        protected override void Dispose(bool disposing)
        {
            if (plugins == null)
                return;

            if (disposing)
            {
                //Unload all the plugins. This will cause all the plugins to execute
                //the cleanup code.
                foreach (PluginInstance plugin in plugins)
                    if (plugin.Plugin != null)
                        plugin.Plugin.Dispose();
            }

            plugins = null;
        }

        /// <summary>
        /// The path to the folder containing the plugins.
        /// </summary>
        public const string PLUGINSFOLDER = "Plugins";

        public override IList<PluginInstance> Plugins
        {
            get { return plugins.AsReadOnly(); }
        }

        public override void LoadPlugin(string filePath)
        {
            //Create the PluginInstance structure
            Assembly reflectAssembly = Assembly.ReflectionOnlyLoadFrom(filePath);
            PluginInstance instance = new PluginInstance(reflectAssembly, null);
            Type typePlugin = null;

            //Iterate over every exported type, checking if it implements IPlugin
            foreach (Type type in instance.Assembly.GetExportedTypes())
            {
                //Check for an implementation of IPlugin
                Type typeInterface = type.GetInterface("Eraser.Manager.Plugin.IPlugin", true);
                if (typeInterface != null)
                {
                    typePlugin = type;
                    break;
                }
            }

            //If the typePlugin type is empty the assembly doesn't implement IPlugin; we
            //aren't interested.
            if (typePlugin == null)
                return;

            //OK this assembly is a plugin
            lock (plugins)
                plugins.Add(instance);

            //If the plugin does not have an approval or denial, check for the presence of
            //a valid signature.
            IDictionary<Guid, bool> approvals = ManagerLibrary.Settings.PluginApprovals;
            if (!approvals.ContainsKey(instance.AssemblyInfo.Guid) &&
                (reflectAssembly.GetName().GetPublicKey().Length == 0 ||
                !Security.VerifyStrongName(filePath) ||
                instance.AssemblyAuthenticode == null))
            {
                return;
            }

            //The plugin either is explicitly allowed or disallowed to load, or
            //it has an Authenticode Signature as well as a Strong Name. Get the
            //loading policy of the plugin.
            instance.Assembly = Assembly.LoadFrom(filePath);
            {
                object[] attr = instance.Assembly.GetCustomAttributes(typeof(LoadingPolicyAttribute), true);
                if (attr.Length != 0)
                {
                    instance.LoadingPolicy = ((LoadingPolicyAttribute)attr[0]).Policy;

                    //If the loading policy is that the plugin is Core, we need to verify
                    //the public key of the assembly.
                    if (instance.LoadingPolicy == LoadingPolicy.Core &&
                        !reflectAssembly.GetName().GetPublicKey().SequenceEqual(
                            Assembly.GetExecutingAssembly().GetName().GetPublicKey()))
                    {
                        instance.LoadingPolicy = LoadingPolicy.None;
                    }
                }
            }

            bool loadPlugin = false;

            //If the loading policy is such that the plugin is a core plugin, ALWAYS load it.
            if (instance.LoadingPolicy == LoadingPolicy.Core)
                loadPlugin = true;

            //The plugin is not a core plugin, is there an approval or denial?
            else if (approvals.ContainsKey(instance.AssemblyInfo.Guid))
                loadPlugin = approvals[instance.AssemblyInfo.Guid];

            //There's no approval or denial, what is the specified loading policy?
            else
                loadPlugin = instance.LoadingPolicy != LoadingPolicy.DefaultOff;


            if (loadPlugin)
            {
                try
                {
                    //Initialize the plugin
                    IPlugin pluginInterface = (IPlugin)Activator.CreateInstance(
                        instance.Assembly.GetType(typePlugin.ToString()));
                    pluginInterface.Initialize(this);
                    instance.Plugin = pluginInterface;

                    //And broadcast the plugin load event
                    OnPluginLoaded(this, new PluginLoadedEventArgs(instance));
                }
                catch (System.Security.SecurityException e)
                {
                    MessageBox.Show(S._("Could not load the plugin {0}.\n\nThe error returned was: {1}",
                        filePath, e.Message), S._("Eraser"), MessageBoxButtons.OK, MessageBoxIcon.Error,
                        MessageBoxDefaultButton.Button1, Localisation.IsRightToLeft(null) ?
                            MessageBoxOptions.RtlReading | MessageBoxOptions.RightAlign : 0);
                }
            }
        }

        private Assembly AssemblyResolve(object sender, ResolveEventArgs args)
        {
            lock (plugins)
                foreach (PluginInstance instance in plugins)
                    if (instance.Assembly.FullName == args.Name)
                        return instance.Assembly;
            return null;
        }

        private Assembly ResolveReflectionDependency(object sender, ResolveEventArgs args)
        {
            return Assembly.ReflectionOnlyLoad(args.Name);
        }

        private List<PluginInstance> plugins = new List<PluginInstance>();
    }

    /// <summary>
    /// Structure holding the instance values of the plugin like handle and path.
    /// </summary>
    public class PluginInstance
    {
        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="assembly">The assembly representing this plugin.</param>
        /// <param name="path">The path to the ass</param>
        /// <param name="plugin"></param>
        internal PluginInstance(Assembly assembly, IPlugin plugin)
        {
            Assembly = assembly;
            Plugin = plugin;

            //Verify the certificate in the assembly.
            if (Security.VerifyAuthenticode(assembly.Location))
            {
                X509Certificate2 cert = new X509Certificate2(
                    X509Certificate.CreateFromSignedFile(assembly.Location));
                AssemblyAuthenticode = cert;
            }
        }

        /// <summary>
        /// Gets the Assembly this plugin instance came from.
        /// </summary>
        public Assembly Assembly
        {
            get
            {
                return assembly;
            }
            internal set
            {
                assembly = value;

                AssemblyInfo info = new AssemblyInfo();
                info.Version = assembly.GetName().Version;
                IList<CustomAttributeData> attributes = CustomAttributeData.GetCustomAttributes(assembly);
                foreach (CustomAttributeData attr in attributes)
                    if (attr.Constructor.DeclaringType == typeof(GuidAttribute))
                        info.Guid = new Guid((string)attr.ConstructorArguments[0].Value);
                    else if (attr.Constructor.DeclaringType == typeof(AssemblyCompanyAttribute))
                        info.Author = (string)attr.ConstructorArguments[0].Value;

                this.AssemblyInfo = info;
            }
        }

        /// <summary>
        /// Gets the attributes of the assembly, loading from reflection-only sources.
        /// </summary>
        public AssemblyInfo AssemblyInfo { get; private set; }

        /// <summary>
        /// The Authenticode signature used for signing the assembly.
        /// </summary>
        public X509Certificate2 AssemblyAuthenticode { get; private set; }

        /// <summary>
        /// Gets whether the plugin is required for the functioning of Eraser (and
        /// therefore cannot be disabled.)
        /// </summary>
        public LoadingPolicy LoadingPolicy { get; internal set; }

        /// <summary>
        /// Gets the IPlugin interface which the plugin exposed. This may be null
        /// if the plugin was not loaded.
        /// </summary>
        public IPlugin Plugin { get; internal set; }

        /// <summary>
        /// Gets whether this particular plugin is currently loaded in memory.
        /// </summary>
        public bool Loaded
        {
            get { return Plugin != null; }
        }

        private Assembly assembly;
    }

    /// <summary>
    /// Reflection-only information retrieved from the assembly.
    /// </summary>
    public struct AssemblyInfo
    {
        /// <summary>
        /// The GUID of the assembly.
        /// </summary>
        public Guid Guid { get; set; }

        /// <summary>
        /// The publisher of the assembly.
        /// </summary>
        public string Author { get; set; }

        /// <summary>
        /// The version of the assembly.
        /// </summary>
        public Version Version { get; set; }

        public override bool Equals(object obj)
        {
            if (!(obj is AssemblyInfo))
                return false;
            return Equals((AssemblyInfo)obj);
        }

        public bool Equals(AssemblyInfo other)
        {
            return Guid == other.Guid;
        }

        public static bool operator ==(AssemblyInfo assembly1, AssemblyInfo assembly2)
        {
            return assembly1.Equals(assembly2);
        }

        public static bool operator !=(AssemblyInfo assembly1, AssemblyInfo assembly2)
        {
            return !assembly1.Equals(assembly2);
        }

        public override int GetHashCode()
        {
            return Guid.GetHashCode();
        }
    }

    /// <summary>
    /// Basic plugin interface which allows for the main program to utilize the
    /// functions in the DLL
    /// </summary>
    public interface IPlugin : IDisposable
    {
        /// <summary>
        /// Initializer.
        /// </summary>
        /// <param name="host">The host object which can be used for two-way
        /// communication with the program.</param>
        void Initialize(Host host);

        /// <summary>
        /// The name of the plug-in, used for descriptive purposes in the UI
        /// </summary>
        string Name
        {
            get;
        }

        /// <summary>
        /// The author of the plug-in, used for display in the UI and for users
        /// to contact the author about bugs. Must be in the format:
        ///     (.+) \<([a-zA-Z0-9_.]+)@([a-zA-Z0-9_.]+)\.([a-zA-Z0-9]+)\>
        /// </summary>
        /// <example>Joel Low <joel@joelsplace.sg></example>
        string Author
        {
            get;
        }

        /// <summary>
        /// Determines whether the plug-in is configurable.
        /// </summary>
        bool Configurable
        {
            get;
        }

        /// <summary>
        /// Fulfil a request to display the settings for this plug-in.
        /// </summary>
        /// <param name="parent">The parent control which the settings dialog should
        /// be parented with.</param>
        void DisplaySettings(Control parent);
    }

    /// <summary>
    /// Loading policies applicable for a given plugin.
    /// </summary>
    public enum LoadingPolicy
    {
        /// <summary>
        /// The host decides the best policy for loading the plugin.
        /// </summary>
        None,

        /// <summary>
        /// The host will enable the plugin by default.
        /// </summary>
        DefaultOn,

        /// <summary>
        /// The host will disable the plugin by default
        /// </summary>
        DefaultOff,

        /// <summary>
        /// The host must always load the plugin.
        /// </summary>
        /// <remarks>For this policy to have an effect, the plugin assembly must
        /// have the same Strong Name as the loading assembly, otherwise it defaults
        /// to None.</remarks>
        Core
    }

    /// <summary>
    /// Declares the loading policy for the assembly containing the plugin. Only
    /// plugins signed with an Authenticode signature will be trusted and have
    /// this attribute checked at initialisation.
    /// </summary>
    [AttributeUsage(AttributeTargets.Assembly, Inherited = false, AllowMultiple = false)]
    public sealed class LoadingPolicyAttribute : Attribute
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="policy">The policy used for loading the plugin.</param>
        public LoadingPolicyAttribute(LoadingPolicy policy)
        {
            Policy = policy;
        }

        /// <summary>
        /// The loading policy to be applied to the assembly.
        /// </summary>
        public LoadingPolicy Policy
        {
            get;
            set;
        }
    }
}