feat(external-endpoint): Implement heartbeat (#1173)

Fixes #741

storage/store/memory/memory.go

@@ -211,6 +211,23 @@ func (s *Store) DeleteAllTriggeredAlertsNotInChecksumsByEndpoint(ep *endpoint.En
 	return 0
 }
 
+// HasEndpointStatusNewerThan checks whether an endpoint has a status newer than the provided timestamp
+func (s *Store) HasEndpointStatusNewerThan(key string, timestamp time.Time) (bool, error) {
+	s.RLock()
+	defer s.RUnlock()
+	endpointStatus := s.cache.GetValue(key)
+	if endpointStatus == nil {
+		// If no endpoint exists, there's no newer status, so return false instead of an error
+		return false, nil
+	}
+	for _, result := range endpointStatus.(*endpoint.Status).Results {
+		if result.Timestamp.After(timestamp) {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
 // Clear deletes everything from the store
 func (s *Store) Clear() {
 	s.cache.Clear()

storage/store/memory/memory_test.go

@@ -84,6 +84,7 @@ var (
 // This test is simply an extra sanity check
 func TestStore_SanityCheck(t *testing.T) {
 	store, _ := NewStore(storage.DefaultMaximumNumberOfResults, storage.DefaultMaximumNumberOfEvents)
+	defer store.Clear()
 	defer store.Close()
 	store.Insert(&testEndpoint, &testSuccessfulResult)
 	endpointStatuses, _ := store.GetAllEndpointStatuses(paging.NewEndpointStatusParams())
@@ -134,3 +135,30 @@ func TestStore_Save(t *testing.T) {
 	store.Clear()
 	store.Close()
 }
+
+func TestStore_HasEndpointStatusNewerThan(t *testing.T) {
+	store, _ := NewStore(storage.DefaultMaximumNumberOfResults, storage.DefaultMaximumNumberOfEvents)
+	defer store.Clear()
+	defer store.Close()
+	// Insert a result
+	err := store.Insert(&testEndpoint, &testSuccessfulResult)
+	if err != nil {
+		t.Fatalf("expected no error while inserting result, got %v", err)
+	}
+	// Check with a timestamp in the past
+	hasNewerStatus, err := store.HasEndpointStatusNewerThan(testEndpoint.Key(), time.Now().Add(-time.Hour))
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if !hasNewerStatus {
+		t.Fatal("expected to have a newer status, but didn't")
+	}
+	// Check with a timestamp in the future
+	hasNewerStatus, err = store.HasEndpointStatusNewerThan(testEndpoint.Key(), time.Now().Add(time.Hour))
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if hasNewerStatus {
+		t.Fatal("expected not to have a newer status, but did")
+	}
+}