In #49412 a tweak was made to the upload process. When files are uploaded to the WordPress media library, the file’s size is now stored as part of the metadata. This means that when calling the
wp_get_attachment_metadata function, developers will easily be able to receive the file size of a selected image without having to call the php function filesize. This change is especially useful in situations when media is being offloaded to a third party, such as cloud services like Amazon’s S3 and Google cloud storage or a network (versus site, blog) share like NFS; as a call to get the file’s size can result in slow calls to an external server.
Along with saving the file size to the attachment’s metadata, a new function and filter Filters are one of the two types of Hooks https://codex.wordpress.org/Plugin_API/Hooks. They provide a way for functions to modify data of other functions. They are the counterpart to Actions. Unlike Actions, filters are meant to work in an isolated manner, and should never have side effects such as affecting global variables and output. have been added. The new
wp_filesize function is useful when storing attachments on a third party source. It means that value can be filtered, preventing a possibility of a slow call to an external server.
It is recommended that authors and maintainers of plugins designed to offload attachments to external services review this change and check that it does not affect your plugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party.
Props to @milana_cap for review and proofreading.