code: def read_content (self):
          
          if self.is_directory():
              self.url_connection.cwd(self.filename)
              self.files = self.get_files()
              # XXX limit number of files?
              data = get_index_html(self.files)
          else:
              # download file in BINARY mode
              ftpcmd = "RETR %s" % self.filename
              buf = StringIO()
              def stor_data (s):
                  """Helper method storing given data"""
                  # limit the download size
                  if (buf.tell() + len(s)) > self.max_size:
                      raise LinkCheckerError(_("FTP file size too large"))
                  buf.write(s)
              self.url_connection.retrbinary(ftpcmd, stor_data)
              data = buf.getvalue()
              buf.close()
          return data
docs: Return URL target content, or in case of directories a dummy HTML
          file with links to the files.