Update a document's content in .NET

class Demo {
  private DocumentsService service = null;

  public Demo() {
    service = new DocumentsService("google-DocUpdateTip-v1");
    service.setUserCredentials("username@gmail.com", "pa$$word");
    GDataGAuthRequestFactory reqFactory = (GDataGAuthRequestFactory)service.RequestFactory;
    reqFactory.ProtocolMajor = 3;
  }

  static void Main(string[] args) {
    Demo demo = new Demo();

    // Fetch only documents
    DocumentsListQuery query = new DocumentsListQuery("http://docs.google.com/feeds/default/private/full/-/document");
    DocumentsFeed doclistFeed = demo.service.Query(query);

    // Update first document found
    DocumentEntry entry = (DocumentEntry)doclistFeed.Entries[0];
    Console.WriteLine("Updating " + entry.Title.Text + "...");

    DocumentEntry updatedEntry = demo.UpdateDocContents(entry, "C:/Documents and Settings/replacement.doc");
    Console.WriteLine(entry.Title.Text + " Updated!, view at " + entry.AlternateUri.ToString());
  }

  public DocumentEntry UpdateDocContents(DocumentEntry entryToUpdate, String replacementFileName) {
    FileInfo fileInfo = new FileInfo(replacementFileName);
    FileStream stream = fileInfo.Open(FileMode.Open, FileAccess.Read, FileShare.ReadWrite);

    DocumentEntry entry = null;

    try {
      // Convert the extension to caps and strip the "." off the front
      String ext = fileInfo.Extension.ToUpper().Substring(1);

      String contentType = (String)DocumentsService.GDocumentsAllowedTypes[ext];
      if (contentType == null) {
        throw new ArgumentException("File extension '" + ext + "' is not recognized as valid.");
      }
      
      // Set ETag because we're making an update
      GDataRequestFactory factory = (GDataRequestFactory)service.RequestFactory;
      factory.CustomHeaders.Add("If-Match: " + entryToUpdate.Etag);

      Uri mediaUri = new Uri(entryToUpdate.MediaUri.ToString());
      entry = service.Update(mediaUri, stream, contentType, entryToUpdate.Title.Text) as DocumentEntry;
    } finally {
      stream.Close();
    }

    return entry;
  }
}