source: branches/RefactorPluginInfrastructure-2522/HeuristicLab.PluginInfrastructure/3.3/PluginValidator.cs @ 13363

Last change on this file since 13363 was 13363, checked in by gkronber, 4 years ago

#2522: improvements to new PluginInformationDialog and removed obsolete classes

File size: 31.4 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2015 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
4 *
5 * This file is part of HeuristicLab.
6 *
7 * HeuristicLab is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
11 *
12 * HeuristicLab is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
19 */
20#endregion
21
22using System;
23using System.Collections.Generic;
24using System.IO;
25using System.Linq;
26using System.Reflection;
27using System.Security;
28using System.Text;
29
30
31namespace HeuristicLab.PluginInfrastructure.Manager {
32  /// <summary>
33  /// Discovers all installed plugins in the plugin directory. Checks correctness of plugin meta-data and if
34  /// all plugin files are available and checks plugin dependencies.
35  /// </summary>
36  internal sealed class PluginValidator : MarshalByRefObject {
37    // private class to store plugin dependency declarations while reflecting over plugins
38    private class PluginDependency {
39      public string Name { get; private set; }
40      public Version Version { get; private set; }
41
42      public PluginDependency(string name, Version version) {
43        this.Name = name;
44        this.Version = version;
45      }
46    }
47
48
49    internal event EventHandler<PluginInfrastructureEventArgs> PluginLoaded;
50
51    private Dictionary<PluginDescription, IEnumerable<PluginDependency>> pluginDependencies;
52
53    private List<ApplicationDescription> applications;
54    internal IEnumerable<ApplicationDescription> Applications {
55      get {
56        if (string.IsNullOrEmpty(PluginDir)) throw new InvalidOperationException("PluginDir is not set.");
57        if (applications == null) DiscoverAndCheckPlugins();
58        return applications;
59      }
60    }
61
62    private IEnumerable<PluginDescription> plugins;
63    internal IEnumerable<PluginDescription> Plugins {
64      get {
65        if (string.IsNullOrEmpty(PluginDir)) throw new InvalidOperationException("PluginDir is not set.");
66        if (plugins == null) DiscoverAndCheckPlugins();
67        return plugins;
68      }
69    }
70
71    internal string PluginDir { get; set; }
72
73    internal PluginValidator() {
74      this.pluginDependencies = new Dictionary<PluginDescription, IEnumerable<PluginDependency>>();
75
76      // ReflectionOnlyAssemblyResolveEvent must be handled because we load assemblies from the plugin path
77      // (which is not listed in the default assembly lookup locations)
78      AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve += ReflectionOnlyAssemblyResolveEventHandler;
79    }
80
81    private Dictionary<string, Assembly> reflectionOnlyAssemblies = new Dictionary<string, Assembly>();
82    private Assembly ReflectionOnlyAssemblyResolveEventHandler(object sender, ResolveEventArgs args) {
83      if (reflectionOnlyAssemblies.ContainsKey(args.Name))
84        return reflectionOnlyAssemblies[args.Name];
85      else
86        return Assembly.ReflectionOnlyLoad(args.Name);
87    }
88
89
90    /// <summary>
91    /// Init first clears all internal datastructures (including plugin lists)
92    /// 1. All assemblies in the plugins directory are loaded into the reflection only context.
93    /// 2. The validator checks if all necessary files for each plugin are available.
94    /// 3. The validator checks if all declared plugin assemblies can be loaded.
95    /// 4. The validator builds the tree of plugin descriptions (dependencies)
96    /// 5. The validator checks if there are any cycles in the plugin dependency graph and disables plugin with circular dependencies
97    /// 6. The validator checks for each plugin if any dependency is disabled.
98    /// 7. All plugins that are not disabled are loaded into the execution context.
99    /// 8. Each loaded plugin (all assemblies) is searched for a types that implement IPlugin
100    ///    then one instance of each IPlugin type is activated and the OnLoad hook is called.
101    /// 9. All types implementing IApplication are discovered
102    /// </summary>
103    internal void DiscoverAndCheckPlugins() {
104      pluginDependencies.Clear();
105
106      IEnumerable<Assembly> reflectionOnlyAssemblies = ReflectionOnlyLoadDlls(PluginDir);
107      IEnumerable<PluginDescription> pluginDescriptions = GatherPluginDescriptions(reflectionOnlyAssemblies);
108      CheckPluginFiles(pluginDescriptions);
109
110      // check if all plugin assemblies can be loaded
111      CheckPluginAssemblies(pluginDescriptions);
112
113      // a full list of plugin descriptions is available now we can build the dependency tree
114      BuildDependencyTree(pluginDescriptions);
115
116      // check for dependency cycles
117      CheckPluginDependencyCycles(pluginDescriptions);
118
119      // 1st time recursively check if all necessary plugins are available and not disabled
120      // disable plugins with missing or disabled dependencies
121      // to prevent that plugins with missing dependencies are loaded into the execution context
122      // in the next step
123      CheckPluginDependencies(pluginDescriptions);
124
125      // test full loading (in contrast to reflection only loading) of plugins
126      // disables plugins that are not loaded correctly
127      CheckExecutionContextLoad(pluginDescriptions);
128
129      // 2nd time recursively check if all necessary plugins have been loaded successfully and not disabled
130      // disable plugins with for which dependencies could not be loaded successfully
131      CheckPluginDependencies(pluginDescriptions);
132
133      // mark all plugins as enabled that were not disabled in CheckPluginFiles, CheckPluginAssemblies,
134      // CheckCircularDependencies, CheckPluginDependencies and CheckExecutionContextLoad
135      foreach (var desc in pluginDescriptions)
136        if (desc.PluginState != PluginState.Disabled)
137          desc.Enable();
138
139      // load the enabled plugins
140      LoadPlugins(pluginDescriptions);
141
142      plugins = pluginDescriptions;
143      DiscoverApplications(pluginDescriptions);
144    }
145
146    private void DiscoverApplications(IEnumerable<PluginDescription> pluginDescriptions) {
147      applications = new List<ApplicationDescription>();
148      foreach (IApplication application in GetApplications(pluginDescriptions)) {
149        Type appType = application.GetType();
150        ApplicationAttribute attr = (from x in appType.GetCustomAttributes(typeof(ApplicationAttribute), false)
151                                     select (ApplicationAttribute)x).Single();
152        ApplicationDescription info = new ApplicationDescription();
153        PluginDescription declaringPlugin = GetDeclaringPlugin(appType, pluginDescriptions);
154        info.Name = application.Name;
155        info.Version = declaringPlugin.Version;
156        info.Description = application.Description;
157        info.DeclaringAssemblyName = appType.Assembly.GetName().Name;
158        info.DeclaringTypeName = appType.Namespace + "." + application.GetType().Name;
159
160        applications.Add(info);
161      }
162    }
163
164    private static IEnumerable<IApplication> GetApplications(IEnumerable<PluginDescription> pluginDescriptions) {
165      return from asm in AppDomain.CurrentDomain.GetAssemblies()
166             from t in asm.GetTypes()
167             where typeof(IApplication).IsAssignableFrom(t) &&
168               !t.IsAbstract && !t.IsInterface && !t.HasElementType
169             where GetDeclaringPlugin(t, pluginDescriptions).PluginState != PluginState.Disabled
170             select (IApplication)Activator.CreateInstance(t);
171    }
172
173    private IEnumerable<Assembly> ReflectionOnlyLoadDlls(string baseDir) {
174      List<Assembly> assemblies = new List<Assembly>();
175      // recursively load .dll files in subdirectories
176      foreach (string dirName in Directory.GetDirectories(baseDir)) {
177        assemblies.AddRange(ReflectionOnlyLoadDlls(dirName));
178      }
179      // try to load each .dll file in the plugin directory into the reflection only context
180      foreach (string filename in Directory.GetFiles(baseDir, "*.dll").Union(Directory.GetFiles(baseDir, "*.exe"))) {
181        try {
182          Assembly asm = Assembly.ReflectionOnlyLoadFrom(filename);
183          RegisterLoadedAssembly(asm);
184          assemblies.Add(asm);
185        } catch (BadImageFormatException) { } // just ignore the case that the .dll file is not a CLR assembly (e.g. a native dll)
186        catch (FileLoadException) { } catch (SecurityException) { } catch (ReflectionTypeLoadException) { } // referenced assemblies are missing
187      }
188      return assemblies;
189    }
190
191    /// <summary>
192    /// Checks if all plugin assemblies can be loaded. If an assembly can't be loaded the plugin is disabled.
193    /// </summary>
194    /// <param name="pluginDescriptions"></param>
195    private void CheckPluginAssemblies(IEnumerable<PluginDescription> pluginDescriptions) {
196      foreach (var desc in pluginDescriptions.Where(x => x.PluginState != PluginState.Disabled)) {
197        try {
198          var missingAssemblies = new List<string>();
199          foreach (var asmLocation in desc.AssemblyLocations) {
200            // the assembly must have been loaded in ReflectionOnlyDlls
201            // so we simply determine the name of the assembly and try to find it in the cache of loaded assemblies
202            var asmName = AssemblyName.GetAssemblyName(asmLocation);
203            if (!reflectionOnlyAssemblies.ContainsKey(asmName.FullName)) {
204              missingAssemblies.Add(asmName.FullName);
205            }
206          }
207          if (missingAssemblies.Count > 0) {
208            StringBuilder errorStrBuiler = new StringBuilder();
209            errorStrBuiler.AppendLine("Missing assemblies:");
210            foreach (string missingAsm in missingAssemblies) {
211              errorStrBuiler.AppendLine(missingAsm);
212            }
213            desc.Disable(errorStrBuiler.ToString());
214          }
215        } catch (BadImageFormatException ex) {
216          // disable the plugin
217          desc.Disable("Problem while loading plugin assemblies:" + Environment.NewLine + "BadImageFormatException: " + ex.Message);
218        } catch (FileNotFoundException ex) {
219          // disable the plugin
220          desc.Disable("Problem while loading plugin assemblies:" + Environment.NewLine + "FileNotFoundException: " + ex.Message);
221        } catch (FileLoadException ex) {
222          // disable the plugin
223          desc.Disable("Problem while loading plugin assemblies:" + Environment.NewLine + "FileLoadException: " + ex.Message);
224        } catch (ArgumentException ex) {
225          // disable the plugin
226          desc.Disable("Problem while loading plugin assemblies:" + Environment.NewLine + "ArgumentException: " + ex.Message);
227        } catch (SecurityException ex) {
228          // disable the plugin
229          desc.Disable("Problem while loading plugin assemblies:" + Environment.NewLine + "SecurityException: " + ex.Message);
230        }
231      }
232    }
233
234
235    // find all types implementing IPlugin in the reflectionOnlyAssemblies and create a list of plugin descriptions
236    // the dependencies in the plugin descriptions are not yet set correctly because we need to create
237    // the full list of all plugin descriptions first
238    private IEnumerable<PluginDescription> GatherPluginDescriptions(IEnumerable<Assembly> assemblies) {
239      List<PluginDescription> pluginDescriptions = new List<PluginDescription>();
240      foreach (Assembly assembly in assemblies) {
241        // GetExportedTypes throws FileNotFoundException when a referenced assembly
242        // of the current assembly is missing.
243        try {
244          // if there is a type that implements IPlugin
245          // use AssemblyQualifiedName to compare the types because we can't directly
246          // compare ReflectionOnly types and execution types
247          var assemblyPluginDescriptions = from t in assembly.GetExportedTypes()
248                                           where !t.IsAbstract && t.GetInterfaces().Any(x => x.AssemblyQualifiedName == typeof(IPlugin).AssemblyQualifiedName)
249                                           select GetPluginDescription(t);
250          pluginDescriptions.AddRange(assemblyPluginDescriptions);
251        }
252          // ignore exceptions. Just don't yield a plugin description when an exception is thrown
253        catch (FileNotFoundException) {
254        } catch (FileLoadException) {
255        } catch (InvalidPluginException) {
256        } catch (TypeLoadException) {
257        } catch (MissingMemberException) {
258        }
259      }
260      return pluginDescriptions;
261    }
262
263    /// <summary>
264    /// Extracts plugin information for this type.
265    /// Reads plugin name, list and type of files and dependencies of the plugin. This information is necessary for
266    /// plugin dependency checking before plugin activation.
267    /// </summary>
268    /// <param name="pluginType"></param>
269    private PluginDescription GetPluginDescription(Type pluginType) {
270
271      string pluginName, pluginDescription, pluginVersion;
272      string contactName, contactAddress;
273      GetPluginMetaData(pluginType, out pluginName, out pluginDescription, out pluginVersion);
274      GetPluginContactMetaData(pluginType, out contactName, out contactAddress);
275      var pluginFiles = GetPluginFilesMetaData(pluginType);
276      var pluginDependencies = GetPluginDependencyMetaData(pluginType);
277
278      // minimal sanity check of the attribute values
279      if (!string.IsNullOrEmpty(pluginName) &&
280          pluginFiles.Count() > 0 &&                                 // at least one file
281          pluginFiles.Any(f => f.Type == PluginFileType.Assembly)) { // at least one assembly
282        // create a temporary PluginDescription that contains the attribute values
283        PluginDescription info = new PluginDescription();
284        info.Name = pluginName;
285        info.Description = pluginDescription;
286        info.Version = new Version(pluginVersion);
287        info.ContactName = contactName;
288        info.ContactEmail = contactAddress;
289        info.LicenseText = ReadLicenseFiles(pluginFiles);
290        info.AddFiles(pluginFiles);
291
292        this.pluginDependencies[info] = pluginDependencies;
293        return info;
294      } else {
295        throw new InvalidPluginException("Invalid metadata in plugin " + pluginType.ToString());
296      }
297    }
298
299    private static string ReadLicenseFiles(IEnumerable<PluginFile> pluginFiles) {
300      // combine the contents of all plugin files
301      var licenseFiles = from file in pluginFiles
302                         where file.Type == PluginFileType.License
303                         select file;
304      if (licenseFiles.Count() == 0) return string.Empty;
305      StringBuilder licenseTextBuilder = new StringBuilder();
306      licenseTextBuilder.AppendLine(File.ReadAllText(licenseFiles.First().Name));
307      foreach (var licenseFile in licenseFiles.Skip(1)) {
308        licenseTextBuilder.AppendLine().AppendLine(); // leave some empty space between multiple license files
309        licenseTextBuilder.AppendLine(File.ReadAllText(licenseFile.Name));
310      }
311      return licenseTextBuilder.ToString();
312    }
313
314    private static IEnumerable<PluginDependency> GetPluginDependencyMetaData(Type pluginType) {
315      // get all attributes of type PluginDependency
316      var dependencyAttributes = from attr in CustomAttributeData.GetCustomAttributes(pluginType)
317                                 where IsAttributeDataForType(attr, typeof(PluginDependencyAttribute))
318                                 select attr;
319
320      foreach (var dependencyAttr in dependencyAttributes) {
321        string name = (string)dependencyAttr.ConstructorArguments[0].Value;
322        Version version = new Version("0.0.0.0"); // default version
323        // check if version is given for now
324        // later when the constructor of PluginDependencyAttribute with only one argument has been removed
325        // this conditional can be removed as well
326        if (dependencyAttr.ConstructorArguments.Count > 1) {
327          try {
328            version = new Version((string)dependencyAttr.ConstructorArguments[1].Value); // might throw FormatException
329          } catch (FormatException ex) {
330            throw new InvalidPluginException("Invalid version format of dependency " + name + " in plugin " + pluginType.ToString(), ex);
331          }
332        }
333        yield return new PluginDependency(name, version);
334      }
335    }
336
337    private static void GetPluginContactMetaData(Type pluginType, out string contactName, out string contactAddress) {
338      // get attribute of type ContactInformation if there is any
339      var contactInfoAttribute = (from attr in CustomAttributeData.GetCustomAttributes(pluginType)
340                                  where IsAttributeDataForType(attr, typeof(ContactInformationAttribute))
341                                  select attr).SingleOrDefault();
342
343      if (contactInfoAttribute != null) {
344        contactName = (string)contactInfoAttribute.ConstructorArguments[0].Value;
345        contactAddress = (string)contactInfoAttribute.ConstructorArguments[1].Value;
346      } else {
347        contactName = string.Empty;
348        contactAddress = string.Empty;
349      }
350    }
351
352    // not static because we need the PluginDir property
353    private IEnumerable<PluginFile> GetPluginFilesMetaData(Type pluginType) {
354      // get all attributes of type PluginFileAttribute
355      var pluginFileAttributes = from attr in CustomAttributeData.GetCustomAttributes(pluginType)
356                                 where IsAttributeDataForType(attr, typeof(PluginFileAttribute))
357                                 select attr;
358      foreach (var pluginFileAttribute in pluginFileAttributes) {
359        string pluginFileName = (string)pluginFileAttribute.ConstructorArguments[0].Value;
360        PluginFileType fileType = (PluginFileType)pluginFileAttribute.ConstructorArguments[1].Value;
361        yield return new PluginFile(Path.GetFullPath(Path.Combine(PluginDir, pluginFileName)), fileType);
362      }
363    }
364
365    private static void GetPluginMetaData(Type pluginType, out string pluginName, out string pluginDescription, out string pluginVersion) {
366      // there must be a single attribute of type PluginAttribute
367      var pluginMetaDataAttr = (from attr in CustomAttributeData.GetCustomAttributes(pluginType)
368                                where IsAttributeDataForType(attr, typeof(PluginAttribute))
369                                select attr).Single();
370
371      pluginName = (string)pluginMetaDataAttr.ConstructorArguments[0].Value;
372
373      // default description and version
374      pluginVersion = "0.0.0.0";
375      pluginDescription = string.Empty;
376      if (pluginMetaDataAttr.ConstructorArguments.Count() == 2) {
377        // if two arguments are given the second argument is the version
378        pluginVersion = (string)pluginMetaDataAttr.ConstructorArguments[1].Value;
379      } else if (pluginMetaDataAttr.ConstructorArguments.Count() == 3) {
380        // if three arguments are given the second argument is the description and the third is the version
381        pluginDescription = (string)pluginMetaDataAttr.ConstructorArguments[1].Value;
382        pluginVersion = (string)pluginMetaDataAttr.ConstructorArguments[2].Value;
383      }
384    }
385
386    private static bool IsAttributeDataForType(CustomAttributeData attributeData, Type attributeType) {
387      return attributeData.Constructor.DeclaringType.AssemblyQualifiedName == attributeType.AssemblyQualifiedName;
388    }
389
390    // builds a dependency tree of all plugin descriptions
391    // searches matching plugin descriptions based on the list of dependency names for each plugin
392    // and sets the dependencies in the plugin descriptions
393    private void BuildDependencyTree(IEnumerable<PluginDescription> pluginDescriptions) {
394      foreach (var desc in pluginDescriptions.Where(x => x.PluginState != PluginState.Disabled)) {
395        var missingDependencies = new List<PluginDependency>();
396        foreach (var dependency in pluginDependencies[desc]) {
397          var matchingDescriptions = from availablePlugin in pluginDescriptions
398                                     where availablePlugin.PluginState != PluginState.Disabled
399                                     where availablePlugin.Name == dependency.Name
400                                     where IsCompatiblePluginVersion(availablePlugin.Version, dependency.Version)
401                                     select availablePlugin;
402          if (matchingDescriptions.Count() > 0) {
403            desc.AddDependency(matchingDescriptions.Single());
404          } else {
405            missingDependencies.Add(dependency);
406          }
407        }
408        // no plugin description that matches the dependencies are available => plugin is disabled
409        if (missingDependencies.Count > 0) {
410          StringBuilder errorStrBuilder = new StringBuilder();
411          errorStrBuilder.AppendLine("Missing dependencies:");
412          foreach (var missingDep in missingDependencies) {
413            errorStrBuilder.AppendLine(missingDep.Name + " " + missingDep.Version);
414          }
415          desc.Disable(errorStrBuilder.ToString());
416        }
417      }
418    }
419
420    /// <summary>
421    /// Checks if version <paramref name="available"/> is compatible to version <paramref name="requested"/>.
422    /// Note: the compatibility relation is not bijective.
423    /// Compatibility rules:
424    ///  * major and minor number must be the same
425    ///  * build and revision number of <paramref name="available"/> must be larger or equal to <paramref name="requested"/>.
426    /// </summary>
427    /// <param name="available">The available version which should be compared to <paramref name="requested"/>.</param>
428    /// <param name="requested">The requested version that must be matched.</param>
429    /// <returns></returns>
430    private static bool IsCompatiblePluginVersion(Version available, Version requested) {
431      // this condition must be removed after all plugins have been updated to declare plugin and dependency versions
432      if (
433        (requested.Major == 0 && requested.Minor == 0) ||
434        (available.Major == 0 && available.Minor == 0)) return true;
435      return
436        available.Major == requested.Major &&
437        available.Minor == requested.Minor &&
438        available.Build >= requested.Build &&
439        available.Revision >= requested.Revision;
440    }
441
442    private void CheckPluginDependencyCycles(IEnumerable<PluginDescription> pluginDescriptions) {
443      foreach (var plugin in pluginDescriptions) {
444        // if the plugin is not disabled check if there are cycles
445        if (plugin.PluginState != PluginState.Disabled && HasCycleInDependencies(plugin, plugin.Dependencies)) {
446          plugin.Disable("Dependency graph has a cycle.");
447        }
448      }
449    }
450
451    private bool HasCycleInDependencies(PluginDescription plugin, IEnumerable<PluginDescription> pluginDependencies) {
452      foreach (var dep in pluginDependencies) {
453        // if one of the dependencies is the original plugin we found a cycle and can return
454        // if the dependency is already disabled we can ignore the cycle detection because we will disable the plugin anyway
455        // if following one of the dependencies recursively leads to a cycle then we also return
456        if (dep == plugin || dep.PluginState == PluginState.Disabled || HasCycleInDependencies(plugin, dep.Dependencies)) return true;
457      }
458      // no cycle found and none of the direct and indirect dependencies is disabled
459      return false;
460    }
461
462    private void CheckPluginDependencies(IEnumerable<PluginDescription> pluginDescriptions) {
463      foreach (PluginDescription pluginDescription in pluginDescriptions.Where(x => x.PluginState != PluginState.Disabled)) {
464        List<PluginDescription> disabledPlugins = new List<PluginDescription>();
465        if (IsAnyDependencyDisabled(pluginDescription, disabledPlugins)) {
466          StringBuilder errorStrBuilder = new StringBuilder();
467          errorStrBuilder.AppendLine("Dependencies are disabled:");
468          foreach (var disabledPlugin in disabledPlugins) {
469            errorStrBuilder.AppendLine(disabledPlugin.Name + " " + disabledPlugin.Version);
470          }
471          pluginDescription.Disable(errorStrBuilder.ToString());
472        }
473      }
474    }
475
476
477    private bool IsAnyDependencyDisabled(PluginDescription descr, List<PluginDescription> disabledPlugins) {
478      if (descr.PluginState == PluginState.Disabled) {
479        disabledPlugins.Add(descr);
480        return true;
481      }
482      foreach (PluginDescription dependency in descr.Dependencies) {
483        IsAnyDependencyDisabled(dependency, disabledPlugins);
484      }
485      return disabledPlugins.Count > 0;
486    }
487
488    // tries to load all plugin assemblies into the execution context
489    // if an assembly of a plugin cannot be loaded the plugin is disabled
490    private void CheckExecutionContextLoad(IEnumerable<PluginDescription> pluginDescriptions) {
491      // load all loadable plugins (all dependencies available) into the execution context
492      foreach (var desc in PluginDescriptionIterator.IterateDependenciesBottomUp(pluginDescriptions
493                                                                                .Where(x => x.PluginState != PluginState.Disabled))) {
494        // store the assembly names so that we can later retrieve the assemblies loaded in the appdomain by name
495        var assemblyNames = new List<string>();
496        foreach (string assemblyLocation in desc.AssemblyLocations) {
497          if (desc.PluginState != PluginState.Disabled) {
498            try {
499              string assemblyName = (from assembly in AppDomain.CurrentDomain.ReflectionOnlyGetAssemblies()
500                                     where string.Equals(Path.GetFullPath(assembly.Location), Path.GetFullPath(assemblyLocation), StringComparison.CurrentCultureIgnoreCase)
501                                     select assembly.FullName).Single();
502              // now load the assemblies into the execution context 
503              // this can still lead to an exception
504              // even when the assemby was successfully loaded into the reflection only context before
505              // when loading the assembly using it's assemblyName it can be loaded from a different location than before (e.g. the GAC)
506              Assembly.Load(assemblyName);
507              assemblyNames.Add(assemblyName);
508            } catch (BadImageFormatException) {
509              desc.Disable(Path.GetFileName(assemblyLocation) + " is not a valid assembly.");
510            } catch (FileLoadException) {
511              desc.Disable("Can't load file " + Path.GetFileName(assemblyLocation));
512            } catch (FileNotFoundException) {
513              desc.Disable("File " + Path.GetFileName(assemblyLocation) + " is missing.");
514            } catch (SecurityException) {
515              desc.Disable("File " + Path.GetFileName(assemblyLocation) + " can't be loaded because of security constraints.");
516            } catch (NotSupportedException ex) {
517              // disable the plugin
518              desc.Disable("Problem while loading plugin assemblies:" + Environment.NewLine + "NotSupportedException: " + ex.Message);
519            }
520          }
521        }
522        desc.AssemblyNames = assemblyNames;
523      }
524    }
525
526    // assumes that all plugin assemblies have been loaded into the execution context via CheckExecutionContextLoad
527    // for each enabled plugin:
528    // calls OnLoad method of the plugin
529    // and raises the PluginLoaded event
530    private void LoadPlugins(IEnumerable<PluginDescription> pluginDescriptions) {
531      List<Assembly> assemblies = new List<Assembly>(AppDomain.CurrentDomain.GetAssemblies());
532      foreach (var desc in pluginDescriptions) {
533        if (desc.PluginState == PluginState.Enabled) {
534          // cannot use ApplicationManager to retrieve types because it is not yet instantiated
535          foreach (string assemblyName in desc.AssemblyNames) {
536            var asm = (from assembly in assemblies
537                       where assembly.FullName == assemblyName
538                       select assembly)
539                      .SingleOrDefault();
540            if (asm == null) throw new InvalidPluginException("Could not load assembly " + assemblyName + " for plugin " + desc.Name);
541            foreach (Type pluginType in asm.GetTypes()) {
542              if (typeof(IPlugin).IsAssignableFrom(pluginType) && !pluginType.IsAbstract && !pluginType.IsInterface && !pluginType.HasElementType) {
543                IPlugin plugin = (IPlugin)Activator.CreateInstance(pluginType);
544                plugin.OnLoad();
545                OnPluginLoaded(new PluginInfrastructureEventArgs(desc));
546              }
547            }
548          } // end foreach assembly in plugin
549          desc.Load();
550        }
551      } // end foreach plugin description
552    }
553
554    // checks if all declared plugin files are actually available and disables plugins with missing files
555    private void CheckPluginFiles(IEnumerable<PluginDescription> pluginDescriptions) {
556      foreach (PluginDescription desc in pluginDescriptions) {
557        IEnumerable<string> missingFiles;
558        if (ArePluginFilesMissing(desc, out missingFiles)) {
559          StringBuilder errorStrBuilder = new StringBuilder();
560          errorStrBuilder.AppendLine("Missing files:");
561          foreach (string fileName in missingFiles) {
562            errorStrBuilder.AppendLine(fileName);
563          }
564          desc.Disable(errorStrBuilder.ToString());
565        }
566      }
567    }
568
569    private bool ArePluginFilesMissing(PluginDescription pluginDescription, out IEnumerable<string> missingFiles) {
570      List<string> missing = new List<string>();
571      foreach (string filename in pluginDescription.Files.Select(x => x.Name)) {
572        if (!FileLiesInDirectory(PluginDir, filename) ||
573          !File.Exists(filename)) {
574          missing.Add(filename);
575        }
576      }
577      missingFiles = missing;
578      return missing.Count > 0;
579    }
580
581    private static bool FileLiesInDirectory(string dir, string fileName) {
582      var basePath = Path.GetFullPath(dir);
583      return Path.GetFullPath(fileName).StartsWith(basePath);
584    }
585
586    private static PluginDescription GetDeclaringPlugin(Type appType, IEnumerable<PluginDescription> plugins) {
587      return (from p in plugins
588              from asmLocation in p.AssemblyLocations
589              where Path.GetFullPath(asmLocation).Equals(Path.GetFullPath(appType.Assembly.Location), StringComparison.CurrentCultureIgnoreCase)
590              select p).Single();
591    }
592
593    // register assembly in the assembly cache for the ReflectionOnlyAssemblyResolveEvent
594    private void RegisterLoadedAssembly(Assembly asm) {
595      if (reflectionOnlyAssemblies.ContainsKey(asm.FullName) || reflectionOnlyAssemblies.ContainsKey(asm.GetName().Name)) {
596        throw new ArgumentException("An assembly with the name " + asm.GetName().Name + " has been registered already.", "asm");
597      }
598      reflectionOnlyAssemblies.Add(asm.FullName, asm);
599      reflectionOnlyAssemblies.Add(asm.GetName().Name, asm); // add short name
600    }
601
602    private void OnPluginLoaded(PluginInfrastructureEventArgs e) {
603      if (PluginLoaded != null)
604        PluginLoaded(this, e);
605    }
606
607    /// <summary>
608    /// Initializes the life time service with an infinite lease time.
609    /// </summary>
610    /// <returns><c>null</c>.</returns>
611    public override object InitializeLifetimeService() {
612      return null;
613    }
614  }
615}
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