Nautilus thumbnailer for XPS/Office 11 files

Thanks to the gnome isv guide I managed to muck my way through a thumbnailer for the new XPS and Office formats. They work the same as they both use the same container format.

While doing so I had the following questions:

1. Does performance matter much on these things?
   
2. Is there a way to fall back to the default icon without failing?
   
3. Why can't I install a thumbnailer for a list of types at once?
   (e.g. both XPS and the new office formats)
   
4. What image formats are supported/preferred?
   

The frustrating parts:

• installing a gconf schema to register the thumbnailer
  (copy the evince one and replace PDF with XPS and the mimetype with application/vnd.ms-xpsdocument)
  
• registering the new mimetype as always (fdo spec)
  
• playing guess the style uri nautilus will use
  

Code below, feel free to use it.

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Xml;

using ICSharpCode.SharpZipLib.Zip;

// A thumbnailer for XPS, and Office 11 Docs
// (anything that uses Open Packaging Conventions)
namespace Opc.Thumbnailer
{
    class Thumbnailer
    {
 static ZipFile zip;

        static int Main (string[] args)
        {
  if (args.Length != 2) {
   PrintUsage ();
   return -1;
  }

  // strip file://
  string file;
  if (args[0].StartsWith ("file://"))
   file = args[0].Substring (7);
  else
   file = args[0];

  if (!File.Exists (file)) {
   Console.Out.WriteLine ("file not found");
   return -1;
  }

  zip = new ZipFile (file);

  string t = FindThumbnail ();
  if (t == null) {
   Console.Out.WriteLine ("no thumbnail found");
   return -1;
  }

  int index = zip.FindEntry (t, false);
  Image image = Image.FromStream (zip.GetInputStream (index));
  // FIXME: convert to a .png?
  image.Save (args[1]);

  return 0;
        }

 static string FindThumbnail ()
 {
  XmlDocument doc = new XmlDocument ();
  int index = zip.FindEntry ("_rels/.rels", false);
  doc.Load (zip.GetInputStream (index));

  foreach (XmlNode n in doc.GetElementsByTagName ("Relationship"))
  {
   if (n.Attributes["Type"].Value == "http://schemas.openxmlformats.org/package/2006/relationships/metadata/thumbnail")
    return n.Attributes["Target"].Value;
  }

  return null;
 }

 static void PrintUsage ()
 {
  Console.Out.WriteLine ("usage: opc-thumbnailer <input> <output>");
 }
    }
}