Add periodic cleanup job for DecayMap (#8) (#158)

* Add periodic cleanup job for DecayMap

see https://github.com/TecharoHQ/anubis/issues/8

* Refactor: Improve DecayMap cleanup tests and add Len method

- Refactored DecayMap cleanup tests to use the new Len method
  for more precise assertions.
- Added a Len method to DecayMap to retrieve the number of
  entries.
- Simplified conditional checks in Get method.

* chore(changelog): add entry

* fix(tests): Use Impl.expire for decaymap cleanup

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

---------

Signed-off-by: Jason Cameron <git@jasoncameron.dev>

cmd/anubis/main.go

@@ -135,6 +135,20 @@ func makeReverseProxy(target string) (http.Handler, error) {
 	return rp, nil
 }
 
+func startDecayMapCleanup(ctx context.Context, s *libanubis.Server) {
+	ticker := time.NewTicker(1 * time.Hour)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			s.CleanupDecayMap()
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
 func main() {
 	flagenv.Parse()
 	flag.Parse()
@@ -210,6 +224,8 @@ func main() {
 		go metricsServer(ctx, wg.Done)
 	}
 
+	go startDecayMapCleanup(ctx, s)
+
 	var h http.Handler
 	h = s
 	h = internal.RemoteXRealIP(*useRemoteAddress, *bindNetwork, h)