docs: def send(self, peer_id, message):
          """
          Synchronously sends a message
  
          :param peer_id: UUID of a peer
          :param message: Message to send to the peer
          :raise KeyError: Unknown peer
          :raise ValueError: No link to the peer
          """
          assert isinstance(message, beans.RawMessage)
  
          # Get peer description (raises KeyError)
          peer = self._directory.get_peer(peer_id)
  
          # Get a link to the peer (raises ValueError)
          link = self._get_link(peer)
          assert isinstance(link, beans.AbstractLink)
  
          # Call the link, and return its result
          return link.send(message)