IFilter ErrorCode FILTER_E_ACCESS when reading .rtf (Rick Text format) from byte array

Question

I'm using this http://www.codeproject.com/Articles/31944/Implementing-a-TextReader-to-extract-various-files and it's mostly working.

I wrote this test to check if the Filter would read as expected from a byte array.

private const string ExpectedText = "This is a test!";
[Test]
public void FilterReader_RtfBytes_TextMatch()
{
    var bytes = File.ReadAllBytes(@"Test Documents\DocTest.rtf");
    var reader = new FilterReader(bytes, ".rtf");
    reader.Init();
    var actualText = reader.ReadToEnd();
    StringAssert.Contains(ExpectedText, actualText);
}

The test fails with ErrorCode : FILTER_E_ACCESS, it works fine when I give it the filename.

new FilterReader(@"Test Documents\DocTest.rtf", ".rtf"); <-- works

I'm puzzled as to why that is. I looked through the code and it seems it's the rtf filter dll that returns the error. Which is even more puzzling.

It works fine for other file types, like; .doc, .docx, .pdf

Answer 1

under the hood the using of concrete way of work with iFilter is defined by constructor: when you use constructor FilterReader(byte[] bytes, string extension) is used IPersistStream for content loading from memory, when FilterReader(string path, string extension) - IPersistFile for loading from file.

why rtf-ifilter returns error when used with IPersistStream i'm afraid we will not able to know because source code isn't opened

in my case i encapsulate filter's specific in constructor and refactor code next way:

• remove all constructors
• remove public void Init()-method

• implement one custom constructor public FilterReader(string fileName, string extension, uint blockSize = 0x2000):

  #region Contracts
  
  Contract.Requires(!string.IsNullOrEmpty(fileName));
  Contract.Requires(!string.IsNullOrEmpty(extension));
  Contract.Requires(blockSize > 1);
  
  #endregion
  
  const string rtfExtension = ".rtf";
  
  FileName = fileName;
  Extension = extension;
  BufferSize = blockSize;
  
  _buffer = new char[ActBufferSize];
  
  // ! Take into account that Rtf-file can be loaded only using IPersistFile.
  var doUseIPersistFile = string.Compare(rtfExtension, extension, StringComparison.InvariantCultureIgnoreCase) == 0;
  
  // Initialize _filter instance.
  try
  {
      if (doUseIPersistFile)
      {
          // Load content using IPersistFile.
          _filter = FilterLoader.LoadIFilterFromIPersistFile(FileName, Extension);
      }
      else
      {
          // Load content using IPersistStream.
          using (var stream = new FileStream(path: fileName, mode: FileMode.Open, access: FileAccess.Read, share: FileShare.Read))
          {
              var buffer = new byte[stream.Length];
              stream.Read(buffer, 0, buffer.Length);
  
              _filter = FilterLoader.LoadIFilterFromStream(buffer, Extension);
          }
      }
  }
  catch (FileNotFoundException)
  {
      throw;
  }
  catch (Exception e)
  {
      throw new AggregateException(message: string.Format("Filter Not Found or Loaded for extension '{0}'.", Extension), innerException: e);
  }