How can I return 304 for php static files? Prompt page not updated

How can I return 304 for php static files? Prompt page not updated

Private function _ addEtag ($ file ){ $ Last_modified_time = filemtime ($ file ); $ Etag = md5_file ($ file ); // Always send headers Header ("Last-Modified:". gmdate ("D, d m y h: I: s", $ last_modified_time). "GMT "); Header ("Etag: $ etag "); // Exit if not modified If (@ strtotime ($ _ SERVER ['http _ IF_MODIFIED_SINCE ']) = $ last_modified_time | @ Trim ($ _ SERVER ['http _ IF_NONE_MATCH ']) = $ etag ){ Header ("HTTP/1.1 304 Not Modified "); Exit; } } Note: This function can be called before static files (slices) are output.