I'm using some example code from
http://www.codeproject.com/csharp/DesktopSearch1.asp?df=100&forumid=190772&exp=0
&select=1153650
to parse PDF files for a DotLucene index.  It uses the query.dll com
object's LoadIFilter method to return the correct IFilter for the file
being parsed (the PDF IFilter must be downloaded from adobe and
installed.

I want my index to be able to parse files from a database (via a Stream
object).  There is a method for this as well, BindIFilterFromStream.  I
am not an interop expert by any means - this is my first real attempt
at using it.  So, I tried adding the method to my class like so:

[DllImport("query.dll", CharSet = CharSet.Unicode, SetLastError =
true)]
private extern static int BindIFilterFromStream (ref UCOMIStream pStm,
ref IUnknown pUnkOuter, [Out] out  IFilter ppIUnk);

With the help of Mattias Sjongren I was able to create the UCOMIStream
and call the method:

private static IFilter loadIFilter(Stream stream)
{
    IUnknown iunk = null;
    IFilter filter = null;

    // copy stream to byte array
    byte[] b = new byte[stream.Length];
    stream.Read(b, 0, b.Length);
    // allocate space on the native heap
    IntPtr nativePtr = Marshal.AllocHGlobal(b.Length);
    // copy byte array to native heap
    Marshal.Copy(b, 0, nativePtr, b.Length);
    // Create a UCOMIStream from the allocated memory
    UCOMIStream comStream;
    CreateStreamOnHGlobal(nativePtr, true, out comStream);

    // Try to load the corresponding IFilter
    int resultLoad = BindIFilterFromStream( ref comStream, ref iunk, out
filter );
    if (resultLoad == (int)IFilterReturnCodes.S_OK)
    {
        return filter;
    }
    else
    {
        throw new Exception("BindIFilterFromStream error: " +
Marshal.GetLastWin32Error());
    }

}

This seems to work except that when the BindIFilterFromStream method is
called, it returns a result of -2147467259, and the
Marshal.GetLastWin32Error() returns 127 - "The specified procedure
could not be found."  I am pretty sure that the method is being called,
because in prior testing I was able to get error messages about the
parameters I was trying to pass before getting help from Mattias.  But
I don't know how to debug this further to see why I am not getting the
IFilter.  I do know that if I serialize the file to the file system,
and use LoadIFilter, it works fine.  So it's not the file, nor the COM
object.

Any ideas??  There is some more background on what I am doing on my
blog at www.refactory.net/blog