Make Optimal strategy default. Collapse routing tables based on strategy

router/default.go

@@ -682,9 +682,11 @@ func (r *router) flushRouteEvents(evType EventType) ([]*Event, error) {
 		return nil, fmt.Errorf("failed listing routes: %s", err)
 	}
 
-	// TODO: flush the routes based on strategy here
-	// - collapse the routes per service-metric-locality (prefer your routes)
+	r.RLock()
+	advertStrategy := r.options.Advertise
+	r.RUnlock()
 
+	if advertStrategy == All {
 		// build a list of events to advertise
 		events := make([]*Event, len(routes))
 		for i, route := range routes {
@@ -695,6 +697,45 @@ func (r *router) flushRouteEvents(evType EventType) ([]*Event, error) {
 			}
 			events[i] = event
 		}
+		return events, nil
+	}
+
+	// routeMap stores optimal routes per service
+	optimalRoutes := make(map[string]Route)
+
+	// go through all routes found in the routing table and collapse them to optimal routes
+	for _, route := range routes {
+		optimal, ok := optimalRoutes[route.Service]
+		if !ok {
+			optimalRoutes[route.Service] = route
+			continue
+		}
+		// if the current optimal route metric is higher than routing table route, replace it
+		if optimal.Metric > route.Metric {
+			optimalRoutes[route.Service] = route
+			continue
+		}
+		// if the metrics are the same, prefer advertising your own route
+		if optimal.Metric == route.Metric {
+			if route.Router == r.options.Id {
+				optimalRoutes[route.Service] = route
+				continue
+			}
+		}
+	}
+
+	// build a list of events to advertise
+	events := make([]*Event, len(optimalRoutes))
+	i := 0
+	for _, route := range optimalRoutes {
+		event := &Event{
+			Type:      evType,
+			Timestamp: time.Now(),
+			Route:     route,
+		}
+		events[i] = event
+		i++
+	}
 
 	return events, nil
 }

router/options.go

@@ -80,5 +80,6 @@ func DefaultOptions() Options {
 		Address:   DefaultAddress,
 		Network:   DefaultNetwork,
 		Registry:  registry.DefaultRegistry,
+		Advertise: Optimal,
 	}
 }

router/router.go

@@ -149,6 +149,18 @@ const (
 	Optimal
 )
 
+// String returns human readable Strategy
+func (s Strategy) String() string {
+	switch s {
+	case All:
+		return "all"
+	case Optimal:
+		return "optimal"
+	default:
+		return "unknown"
+	}
+}
+
 // NewRouter creates new Router and returns it
 func NewRouter(opts ...Option) Router {
 	return newRouter(opts...)