code: func (srv *Server) PeerCount() int {
  	var count int
  	select {
  	case srv.peerOp <- func(ps map[enode.ID]*Peer) { count = len(ps) }:
  		<-srv.peerOpDone
  	case <-srv.quit:
  	}
  	return count
  }
docs: // PeerCount returns the number of connected peers.