code: def put(self, filepath):
          
          action = self.get_body_argument('action')
  
          if action['action'] == 'update_group':
              newgrp = action['group']
              try:
                  self.fs.update_group(filepath,newgrp)
                  self.write({'msg':'Updated group for {}'.format(filepath)})
              except OSError:
                  raise tornado.web.HTTPError(404)
          elif action['action'] == 'update_permissions':
              newperms = action['permissions']
              try:
                  self.fs.update_permissions(filepath,newperms)
                  self.write({'msg':'Updated permissions for {}'.format(filepath)})
              except OSError:
                  raise tornado.web.HTTPError(404)
          else:
              raise tornado.web.HTTPError(400)
docs: Change the group or permissions of the specified file. Action
          must be specified when calling this method.