[wp-trac] [WordPress Trac] #65251: Response from media library API query includes an empty array rather than an empty object

[WordPress Trac]

#65251: Response from media library API query includes an empty array rather than
an empty object
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 Reporter:  frankieandshadow  |      Owner:  (none)
     Type:  defect (bug)      |     Status:  new
 Priority:  normal            |  Milestone:  Awaiting Review
Component:  REST API          |    Version:  6.9.4
 Severity:  normal            |   Keywords:
  Focuses:                    |
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 In the response to a media library query over the REST API, I am seeing
 that $wpimage->media_details->sizes is an empty array when there are no
 sizes, rather than an empty object (as a non-empty instance is an object).
 This discrepancy is inconsistent and breaks my recipient code. It's
 characteristic of json_encode being used on a keyed PHP array, when it
 can't tell the difference between keys and numeric indexes when empty.

 I asked claude.ai to locate the bug to make it easy for you to fix. It
 agreed with my diagnosis and said:

 File: wp-includes/rest-api/endpoints/class-wp-rest-attachments-
 controller.php

 Method: prepare_item_for_response()

 The bug: when wp_get_attachment_metadata() returns metadata with an empty
 sizes array (image too small for sub-sizes), the method populates
 `$data['media_details']` from that metadata but never explicitly sets
 `$data['media_details']['sizes']` to new stdClass. The `else {
 $data['media_details']['sizes'] = new stdClass; }` branch is only reached
 when $metadata itself is empty/falsy. The result is that sizes is either
 absent or an empty PHP array `[]` in the JSON output, rather than `{}`.

 Prior art: reference Trac #51393, which addressed a related inconsistency
 but didn't fix this code path.

 Your fix suggestion: initialise `$data['media_details']['sizes']` to `new
 stdClass` (or cast with (object)) before the loop that populates it, so
 the empty case is covered unconditionally.

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Ticket URL: <https://core.trac.wordpress.org/ticket/65251>
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