refactor: change Routes.RandomNeighbours return for consistency

PeerNameSet -> []PeerName, which is what the other functions
return. This is also easier to deal with at the call site.

mesh/gossip_channel.go

@@ -167,20 +167,18 @@ func (c *GossipChannel) sendBroadcast(srcName PeerName, update GossipData) {
 func (c *GossipChannel) Send(srcName PeerName, data GossipData) {
 	// do this outside the lock below so we avoid lock nesting
 	c.routes.EnsureRecalculated()
-	selectedConnections := make(ConnectionSet)
-	for name := range c.routes.RandomNeighbours(srcName) {
-		if conn, found := c.ourself.ConnectionTo(name); found {
-			selectedConnections[conn] = void
-		}
+	destinations := c.routes.RandomNeighbours(srcName)
+	if len(destinations) == 0 {
+		return
 	}
-	c.sendDown(selectedConnections, data)
+	c.sendDown(c.ourself.ConnectionsTo(destinations), data)
 }
 
 func (c *GossipChannel) SendDown(conn Connection, data GossipData) {
-	c.sendDown(ConnectionSet{conn: void}, data)
+	c.sendDown([]Connection{conn}, data)
 }
 
-func (c *GossipChannel) sendDown(selectedConnections ConnectionSet, data GossipData) {
+func (c *GossipChannel) sendDown(selectedConnections []Connection, data GossipData) {
 	if len(selectedConnections) == 0 {
 		return
 	}
@@ -207,7 +205,7 @@ func (c *GossipChannel) sendDown(selectedConnections ConnectionSet, data GossipD
 		}
 	}
 	// start senders, if necessary, and send.
-	for conn := range selectedConnections {
+	for _, conn := range selectedConnections {
 		sender, found := c.senders[conn]
 		if !found {
 			sender = c.makeSender(conn)

mesh/routes.go

@@ -92,20 +92,24 @@ func (routes *Routes) BroadcastAll(name PeerName) []PeerName {
 // returns a higher proportion of neighbours than elsewhere. In
 // extremis, on peers with fewer than log2(n_peers) neighbours, all
 // neighbours are returned.
-func (routes *Routes) RandomNeighbours(except PeerName) PeerNameSet {
-	res := make(PeerNameSet)
+func (routes *Routes) RandomNeighbours(except PeerName) []PeerName {
+	destinations := make(PeerNameSet)
 	routes.RLock()
 	defer routes.RUnlock()
 	count := int(math.Log2(float64(len(routes.unicastAll))))
 	// depends on go's random map iteration
 	for _, dst := range routes.unicastAll {
 		if dst != UnknownPeerName && dst != except {
-			res[dst] = void
-			if len(res) >= count {
+			destinations[dst] = void
+			if len(destinations) >= count {
 				break
 			}
 		}
 	}
+	res := make([]PeerName, 0, len(destinations))
+	for dst := range destinations {
+		res = append(res, dst)
+	}
 	return res
 }