* filter.[ch]: add f2b_filter_error()

src/filter.c

@@ -154,3 +154,9 @@ f2b_filter_match(f2b_filter_t *filter, const char *line, char *buf, size_t buf_s
 
   return filter->match(filter->cfg, line, buf, buf_size);
 }
+
+const char *
+f2b_filter_error(f2b_filter_t *filter) {
+  assert(filter != NULL);
+  return filter->error(filter->cfg);
+}

src/filter.h

@@ -26,5 +26,6 @@ f2b_filter_t * f2b_filter_create (f2b_config_section_t *config, const char *id);
 void           f2b_filter_destroy(f2b_filter_t *b);
 
 bool f2b_filter_match(f2b_filter_t *b, const char *line, char *buf, size_t buf_size);
+const char * f2b_filter_error(f2b_filter_t *b);
 
 #endif /* FILTER_H_ */