streaming: apply filter to a single item

Instead of the whole map. This should save a lot of time performing reflecting on a large map.
The filter does not change, so there is no reason to re-apply it to older entries.

agent/cache-types/streaming_health_services.go

@@ -3,6 +3,7 @@ package cachetype
 import (
 	"context"
 	"fmt"
+	"reflect"
 	"time"
 
 	"github.com/hashicorp/go-bexpr"
@@ -138,15 +139,14 @@ func (s *streamingHealthState) Fetch(opts cache.FetchOptions) (cache.FetchResult
 }
 
 func newHealthView(filterExpr string) (*healthView, error) {
-	s := &healthView{state: make(map[string]structs.CheckServiceNode)}
-
-	// We apply filtering to the raw CheckServiceNodes before we are done mutating
-	// state in Update to save from storing stuff in memory we'll only filter
-	// later. Because the state is just a map of those types, we can simply run
-	// that map through filter and it will remove any entries that don't match.
-	var err error
-	s.filter, err = bexpr.CreateFilter(filterExpr, nil, s.state)
-	return s, err
+	fe, err := newFilterEvaluator(filterExpr)
+	if err != nil {
+		return nil, err
+	}
+	return &healthView{
+		state:  make(map[string]structs.CheckServiceNode),
+		filter: fe,
+	}, nil
 }
 
 // healthView implements submatview.View for storing the view state
@@ -156,7 +156,7 @@ func newHealthView(filterExpr string) (*healthView, error) {
 // involves re-sorting each time etc. though.
 type healthView struct {
 	state  map[string]structs.CheckServiceNode
-	filter *bexpr.Filter
+	filter filterEvaluator
 }
 
 // Update implements View
@@ -171,24 +171,41 @@ func (s *healthView) Update(events []*pbsubscribe.Event) error {
 		id := serviceHealth.CheckServiceNode.UniqueID()
 		switch serviceHealth.Op {
 		case pbsubscribe.CatalogOp_Register:
-			csn := pbservice.CheckServiceNodeToStructs(serviceHealth.CheckServiceNode)
-			s.state[id] = *csn
+			csn := *pbservice.CheckServiceNodeToStructs(serviceHealth.CheckServiceNode)
+			passed, err := s.filter.Evaluate(csn)
+			switch {
+			case err != nil:
+				return err
+			case passed:
+				s.state[id] = csn
+			}
+
 		case pbsubscribe.CatalogOp_Deregister:
 			delete(s.state, id)
 		}
 	}
-	// TODO(streaming): should this filter be applied to only the new CheckServiceNode
-	// instead of the full map, which should already be filtered.
-	if s.filter != nil {
-		filtered, err := s.filter.Execute(s.state)
-		if err != nil {
-			return err
-		}
-		s.state = filtered.(map[string]structs.CheckServiceNode)
-	}
 	return nil
 }
 
+type filterEvaluator interface {
+	Evaluate(datum interface{}) (bool, error)
+}
+
+func newFilterEvaluator(expr string) (filterEvaluator, error) {
+	if expr == "" {
+		return noopFilterEvaluator{}, nil
+	}
+	return bexpr.CreateEvaluatorForType(expr, nil, reflect.TypeOf(structs.CheckServiceNode{}))
+}
+
+// noopFilterEvaluator may be used in place of a bexpr.Evaluator. The Evaluate
+// method always return true, so no items will be filtered out.
+type noopFilterEvaluator struct{}
+
+func (noopFilterEvaluator) Evaluate(_ interface{}) (bool, error) {
+	return true, nil
+}
+
 // Result returns the structs.IndexedCheckServiceNodes stored by this view.
 func (s *healthView) Result(index uint64) (interface{}, error) {
 	result := structs.IndexedCheckServiceNodes{