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;
}
}
}
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