Add support for uploading arrayed $_FILES

[kontur]

When you have form code that references [several file uploads](​http://php.net/manual/en/features.file-upload.multiple.php) as array, the media_handle_upload() function fails to handle this.
For example this:

<input type="file" name="documents[]">
<input type="file" name="documents[]">

Will result in a $_FILES array that's creates subarrays shaped like so:

$_FILES['userfile']['name'][0]
$_FILES['userfile']['name'][1]
$_FILES['userfile']['tmp_name'][0]
$_FILES['userfile']['tmp_name'][1]
$_FILES['userfile']['size'][0]
$_FILES['userfile']['size'][1]
$_FILES['userfile']['type'][0] 
$_FILES['userfile']['type'][1]

This will fail when passed to media_handle_upload, since the implementation does not handle this array structure nor is this documented.

[kontur]

The obvious but unelegant workaround is to name each upload file input with an index or the like, and manually pick them apart before passing them separately to the media_upload_handle()

[joemcgill]

Hi @kontur,

Thanks for the ticket.

The media_handle_upload function is meant to handle a single file at a time, from which it will generate and return a single attachment. If you're writing custom code, I would suggest handling the $_FILES object yourself, as you are suggesting.

See examples: ​https://wordpress.stackexchange.com/questions/173197/upload-multiple-files-with-media-handle-upload

If we want to support this in WordPress core, we should add handling for multiple file outside media_handle_upload, in places like wp_ajax_upload_attachment and WP_REST_Attachments_Controller->upload_from_file().