PROMS/EPocalipse.IFilter/FilterLoader.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.Win32;
+using System.IO;
+using System.Runtime.InteropServices.ComTypes;
+using System.Runtime.InteropServices;
+
+namespace EPocalipse.IFilter
+{
+  /// <summary>
+  /// FilterLoader finds the dll and ClassID of the COM object responsible  
+  /// for filtering a specific file extension. 
+  /// It then loads that dll, creates the appropriate COM object and returns 
+  /// a pointer to an IFilter instance
+  /// </summary>
+  static class FilterLoader
+  {
+    #region CacheEntry
+    private class CacheEntry
+    {
+      public string DllName;
+      public string ClassName;
+
+      public CacheEntry(string dllName, string className)
+      {
+        DllName=dllName;
+        ClassName=className;
+      }
+    }
+    #endregion
+
+    static Dictionary<string, CacheEntry> _cache=new Dictionary<string, CacheEntry>();
+
+    #region Registry Read String helper
+    static string ReadStrFromHKLM(string key)
+    {
+      return ReadStrFromHKLM(key,null);
+    }
+    static string ReadStrFromHKLM(string key, string value)
+    {
+      RegistryKey rk=Registry.LocalMachine.OpenSubKey(key);
+      if (rk==null)
+        return null;
+
+      using (rk)
+      {
+        return (string)rk.GetValue(value);
+      }
+    }
+    #endregion
+
+    /// <summary>
+    /// finds an IFilter implementation for a file type
+    /// </summary>
+    /// <param name="ext">The extension of the file</param>
+    /// <returns>an IFilter instance used to retreive text from that file type</returns>
+    private static IFilter LoadIFilter(string ext)
+    {
+      string dllName, filterPersistClass;
+
+      //Find the dll and ClassID
+      if (GetFilterDllAndClass(ext, out dllName, out filterPersistClass))
+      {
+        //load the dll and return an IFilter instance.
+        return LoadFilterFromDll(dllName, filterPersistClass);
+      }
+      return null;
+    }
+
+    internal static IFilter LoadAndInitIFilter(string fileName)
+    {
+      return LoadAndInitIFilter(fileName,Path.GetExtension(fileName));
+    }
+
+    internal static IFilter LoadAndInitIFilter(string fileName, string extension)
+    {
+      IFilter filter=LoadIFilter(extension);
+      if (filter==null)
+        return null;
+      IPersistFile persistFile=(filter as IPersistFile);
+      if (persistFile!=null)
+      {
+        persistFile.Load(fileName, 0);
+        IFILTER_FLAGS flags;
+        IFILTER_INIT iflags =
+					IFILTER_INIT.CANON_HYPHENS |
+					IFILTER_INIT.CANON_PARAGRAPHS |
+					IFILTER_INIT.CANON_SPACES |
+					IFILTER_INIT.APPLY_INDEX_ATTRIBUTES |
+					IFILTER_INIT.HARD_LINE_BREAKS |
+					IFILTER_INIT.FILTER_OWNED_VALUE_OK;
+
+        if (filter.Init(iflags, 0, IntPtr.Zero, out flags)==IFilterReturnCode.S_OK)
+          return filter;
+      }
+      //If we failed to retreive an IPersistFile interface or to initialize 
+      //the filter, we release it and return null.
+      Marshal.ReleaseComObject(filter);
+      return null;
+    }
+
+    private static IFilter LoadFilterFromDll(string dllName, string filterPersistClass)
+    {
+      //Get a classFactory for our classID
+      IClassFactory classFactory=ComHelper.GetClassFactory(dllName, filterPersistClass);
+      if (classFactory==null)
+        return null;
+
+      //And create an IFilter instance using that class factory
+      Guid IFilterGUID=new Guid("89BCB740-6119-101A-BCB7-00DD010655AF");
+      Object obj;
+      classFactory.CreateInstance(null, ref IFilterGUID, out obj);
+      return (obj as IFilter);
+    }
+
+    private static bool GetFilterDllAndClass(string ext, out string dllName, out string filterPersistClass)
+    {
+      if (!GetFilterDllAndClassFromCache(ext, out dllName, out filterPersistClass))
+      {
+        string persistentHandlerClass;
+
+        persistentHandlerClass=GetPersistentHandlerClass(ext,true);
+        if (persistentHandlerClass!=null)
+        {
+          GetFilterDllAndClassFromPersistentHandler(persistentHandlerClass,
+            out dllName, out filterPersistClass);
+        }
+        AddExtensionToCache(ext, dllName, filterPersistClass);
+      }
+      return (dllName!=null && filterPersistClass!=null); 
+    }
+
+    private static void AddExtensionToCache(string ext, string dllName, string filterPersistClass)
+    {
+      lock (_cache)
+      {
+        _cache.Add(ext.ToLower(), new CacheEntry(dllName, filterPersistClass));
+      }
+    }
+
+    private static bool GetFilterDllAndClassFromPersistentHandler(string persistentHandlerClass, out string dllName, out string filterPersistClass)
+    {
+      dllName=null;
+      filterPersistClass=null;
+
+      //Read the CLASS ID of the IFilter persistent handler
+      filterPersistClass=ReadStrFromHKLM(@"Software\Classes\CLSID\" + persistentHandlerClass + 
+        @"\PersistentAddinsRegistered\{89BCB740-6119-101A-BCB7-00DD010655AF}");
+      if (String.IsNullOrEmpty(filterPersistClass))
+          return false;
+
+      //Read the dll name 
+      dllName=ReadStrFromHKLM(@"Software\Classes\CLSID\" + filterPersistClass + 
+        @"\InprocServer32");
+      return (!String.IsNullOrEmpty(dllName));
+    }
+
+    private static string GetPersistentHandlerClass(string ext, bool searchContentType)
+    {
+      //Try getting the info from the file extension
+      string persistentHandlerClass=GetPersistentHandlerClassFromExtension(ext);
+      if (String.IsNullOrEmpty(persistentHandlerClass))
+        //try getting the info from the document type 
+        persistentHandlerClass=GetPersistentHandlerClassFromDocumentType(ext);
+      if (searchContentType && String.IsNullOrEmpty(persistentHandlerClass))
+        //Try getting the info from the Content Type
+        persistentHandlerClass=GetPersistentHandlerClassFromContentType(ext);
+      return persistentHandlerClass;
+    }
+
+    private static string GetPersistentHandlerClassFromContentType(string ext)
+    {
+      string contentType=ReadStrFromHKLM(@"Software\Classes\"+ext,"Content Type");
+      if (String.IsNullOrEmpty(contentType))
+        return null;
+      
+      string contentTypeExtension=ReadStrFromHKLM(@"Software\Classes\MIME\Database\Content Type\"+contentType,
+          "Extension");
+      if (ext.Equals(contentTypeExtension, StringComparison.CurrentCultureIgnoreCase))
+        return null; //No need to look further. This extension does not have any persistent handler
+    
+      //We know the extension that is assciated with that content type. Simply try again with the new extension
+      return GetPersistentHandlerClass(contentTypeExtension, false); //Don't search content type this time.
+    }
+
+    private static string GetPersistentHandlerClassFromDocumentType(string ext)
+    {
+      //Get the DocumentType of this file extension
+      string docType=ReadStrFromHKLM(@"Software\Classes\"+ext);
+      if (String.IsNullOrEmpty(docType))
+        return null;
+      
+      //Get the Class ID for this document type
+      string docClass=ReadStrFromHKLM(@"Software\Classes\" + docType + @"\CLSID");
+      if (String.IsNullOrEmpty(docType))
+        return null;
+
+      //Now get the PersistentHandler for that Class ID
+      return ReadStrFromHKLM(@"Software\Classes\CLSID\" + docClass + @"\PersistentHandler");
+    }
+
+    private static string GetPersistentHandlerClassFromExtension(string ext)
+    {
+      return ReadStrFromHKLM(@"Software\Classes\"+ext+@"\PersistentHandler");
+    }
+
+    private static bool GetFilterDllAndClassFromCache(string ext, out string dllName, out string filterPersistClass)
+    {
+      string lowerExt=ext.ToLower();
+      lock (_cache)
+      {
+        CacheEntry cacheEntry;
+        if (_cache.TryGetValue(lowerExt, out cacheEntry))
+        {
+          dllName=cacheEntry.DllName;
+          filterPersistClass=cacheEntry.ClassName;
+          return true;
+        }
+      }
+      dllName=null;
+      filterPersistClass=null;
+      return false;
+    }
+  }
+}