file_event_handlers add before_open function

include/spdlog/details/file_helper-inl.h

@@ -37,6 +37,10 @@ SPDLOG_INLINE void file_helper::open(const filename_t &fname, bool truncate)
     auto *mode = SPDLOG_FILENAME_T("ab");
     auto *trunc_mode = SPDLOG_FILENAME_T("wb");
 
+    if (event_handlers_.before_open)
+    {
+        event_handlers_.before_open(filename_);
+    }
     for (int tries = 0; tries < open_tries_; ++tries)
     {
         // create containing folder if not exists already.

include/spdlog/details/file_helper.h

@@ -51,7 +51,7 @@ private:
     const unsigned int open_interval_ = 10;
     std::FILE *fd_{nullptr};
     filename_t filename_;
-    file_event_handlers_t event_handlers_{nullptr, nullptr, nullptr};
+    file_event_handlers_t event_handlers_;
 };
 } // namespace details
 } // namespace spdlog