peers.go
func (peers *Peers) Fetch(name PeerName) *Peer {
	peers.RLock()
	defer peers.RUnlock()
	return peers.byName[name]
}
func (peers *Peers) Fetch(name PeerName) *Peer {
	peers.RLock()
	defer peers.RUnlock()
	return peers.byName[name]
}
// Fetch returns a peer matching the passed name, without incrementing its
// refcount. If no matching peer is found, Fetch returns nil.