[adamsilverstein]

Claude Code wrote the fix on top of the tests from #15860, and this description:

On multisite, a sub-size sideloaded by client-side media processing is no longer checked against the site's upload space. That matches the classic path, where only the original upload is checked and the server writes the sub-sizes regardless.

Before this, a site close to its quota accepted the original and then rejected some or all of the sub-sizes with rest_upload_limited_space, leaving the attachment with missing sizes.

This includes the two tests from #15860 by @desrosj (his commit is kept as is), so it supersedes that PR.

What changed

• WP_REST_Attachments_Controller::sideload_item() sets a private flag while the sideloaded file is stored, and check_upload_size() skips its two space checks (space left, and site over quota) when the flag is set. Both upload handlers, multipart and raw body, go through that method.
• The network's maximum upload file size (fileupload_maxk) still applies to a sideloaded file.
• A new upload through POST /wp/v2/media is checked as before. Sideloaded files count toward the space used, so the next upload on a full site is still rejected.
• Tests:
  • test_sideload_sub_size_after_multisite_upload_space_is_used from Media: Demonstrate multisite quota checks on sideloaded sub-sizes #15860 failed before the fix and passes now.
  • test_sideload_sub_size_file_skips_multisite_upload_space_check_once sideloads the sub-size as multipart form data, which is how the browser sends it, then confirms a new upload is still rejected for lack of space.
  • test_sideload_sub_size_exceeds_multisite_max_filesize confirms the per-file limit still rejects a sideload.
  • The tests from Media: Demonstrate multisite quota checks on sideloaded sub-sizes #15860 gained @ticket 66680 and a few type assertions for PHPStan.

Questions for review

• The space check is skipped for every file the sideload endpoint accepts. That includes the source_original (the HEIC or JXL kept next to its JPEG) and the animated_video companions, which are not files the classic path would generate. Should those still count against the quota?
• Nothing limits how far one attachment's sideloads can push a site past its quota, other than the per-file limit and what the client sends. The classic path can overshoot too, but only by the sizes the server decides to generate. Is that acceptable, or does the endpoint need a bound of its own?
• The Gutenberg plugin has its own copy of this endpoint in lib/media/class-gutenberg-rest-attachments-controller.php and needs the same change. Not done yet.

Testing

npm run test:php -- -c tests/phpunit/multisite.xml --filter 'multisite_upload_space|sideload_sub_size_exceeds_multisite_max_filesize'

The full WP_Test_REST_Attachments_Controller class passes on single site and multisite. This was not tested in a browser on a multisite install.

Trac ticket: https://core.trac.wordpress.org/ticket/66680

AI Use

The fix and this description came from 🤖 Claude Code, building on the tests in #15860. I will review and test.

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[adamsilverstein]

Code looks good, running manual tests.

[adamsilverstein]

Manual testing on a multisite install confirms the bug on trunk and the fix in this PR, screencasts below.

Claude ran the before and after on a multisite Playground site:

Setup: WordPress Playground with today's nightly (7.2-beta5-65405) as the "before", and the same build with this PR's class-wp-rest-attachments-controller.php dropped in as the "after". Multisite, site upload space limited to 1.6 MB, max upload file size 10 MB. Each run uploads an 1800x1200, 1.5 MB JPEG to an Image block in the post editor, with client-side media processing active (crossOriginIsolated is true).

Before:

• The original upload (201) and three sub-size sideloads (200) went through, then two sideloads came back 400 rest_upload_limited_space ("Not enough space to upload. 67 KB needed." and "276 KB needed.").
• The attachment ended up with thumbnail, medium and medium_large, but no large or 1536x1536.
• The editor still showed "Upload complete", so nothing tells the user that sizes are missing. That part is separate from this ticket, but probably worth a Gutenberg follow-up.

After:

• All five sideloads returned 200 and the attachment has every sub-size.
• The site ended at about 2.0 MB against the 1.6 MB quota, the kind of overshoot the classic path already allows when the server writes sub-sizes.
• A new upload through POST /wp/v2/media right after was still rejected with rest_upload_limited_space, so the quota still applies to new files.

The dark panel in the top right of each screencast mirrors the media POST responses as they happen, and the table at the end is the attachment's media_details.sizes from GET /wp/v2/media/<id>?context=edit.

Before (trunk):

trac-66680-before.mp4

After (this PR):

trac-66680-after.mp4