Add context for valuer interfaces

cmd/jetstream/server.go

@@ -86,6 +86,7 @@ func (s *Server) Emit(ctx context.Context, e *models.Event, asJSON, compBytes []
 		collection = e.Commit.Collection
 	}
 
+	// Wrap the valuer functions for more lightweight event filtering
 	getJSONEvent := func() []byte { return asJSON }
 	getCompressedEvent := func() []byte { return compBytes }
 
@@ -125,6 +126,9 @@ func (s *Server) Emit(ctx context.Context, e *models.Event, asJSON, compBytes []
 	return nil
 }
 
+// emitToSubscriber sends an event to a subscriber if the subscriber wants the event
+// It takes a valuer function to get the event bytes so that the caller can avoid
+// unnecessary allocations and/or reading from the playback DB if the subscriber doesn't want the event
 func emitToSubscriber(ctx context.Context, log *slog.Logger, sub *Subscriber, timeUS int64, did, collection string, playback bool, getEventBytes func() []byte) error {
 	if !sub.WantsCollection(collection) {
 		return nil

pkg/consumer/persist.go

@@ -207,7 +207,8 @@ func (c *Consumer) ReplayEvents(ctx context.Context, compressed bool, cursor int
 			collection = parts[2]
 		}
 
-		// Emit the event
+		// Emit the event with the valuer function so the subscriber can decide if it wants to filter it out
+		// without having to read the entire event from the database
 		err = emit(ctx, timeUS, parts[1], collection, iter.Value)
 		if err != nil {
 			log.Error("failed to emit event", "error", err)