code: def fetch(self, command):
          
          logging.debug('SENT: %s: %s' % (self.host, command))
          self.write('%s\n' % command)
          while 1:
              buffer = self.read_until('\n').strip()
              if len(buffer):
                  break
          status, length = map(int, buffer.split())
          content = ''
          assert status == 200, 'Bad response code: {status} {text} ({command})'.format(status=status, text=self.read_until('\n').strip(), command=command)
          while len(content) < length:
              content += self.read_until('\n')
          logging.debug('RECV: %s: %dB %s' % (status,length,content[:30]))
          self.read_eager()
          return (status, length), content
docs: Run a command on the Varnish backend and return the result
          return value is a tuple of ((status, length), content)