routes.go
func (r *routes) calculateBroadcast(name PeerName, establishedAndSymmetric bool) []PeerName {
	hops := []PeerName{}
	peer, found := r.peers.byName[name]
	if !found {
		return hops
	}
	if found, reached := peer.routes(r.ourself.Peer, establishedAndSymmetric); found {
		r.ourself.forEachConnectedPeer(establishedAndSymmetric, reached,
			func(remotePeer *Peer) { hops = append(hops, remotePeer.Name) })
	}
	return hops
}
func (r *routes) calculateBroadcast(name PeerName, establishedAndSymmetric bool) []PeerName {
	hops := []PeerName{}
	peer, found := r.peers.byName[name]
	if !found {
		return hops
	}
	if found, reached := peer.routes(r.ourself.Peer, establishedAndSymmetric); found {
		r.ourself.forEachConnectedPeer(establishedAndSymmetric, reached,
			func(remotePeer *Peer) { hops = append(hops, remotePeer.Name) })
	}
	return hops
}
// Calculate the route to answer the question: if we receive a
// broadcast originally from Peer X, which peers should we pass the
// frames on to?
//
// When the topology is stable, and thus all peers perform route
// calculations based on the same data, the algorithm ensures that
// broadcasts reach every peer exactly once.
//
// This is largely due to properties of the Peer.Routes algorithm. In
// particular:
//
// ForAll X,Y,Z in Peers.
//     X.Routes(Y) <= X.Routes(Z) \/
//     X.Routes(Z) <= X.Routes(Y)
// ForAll X,Y,Z in Peers.
//     Y =/= Z /\ X.Routes(Y) <= X.Routes(Z) =>
//     X.Routes(Y) u [P | Y.HasSymmetricConnectionTo(P)] <= X.Routes(Z)
// where <= is the subset relationship on keys of the returned map.