[wp-trac] [WordPress Trac] #64906: Media: Remove client-side media processing from 7.0

[WordPress Trac]

#64906: Media: Remove client-side media processing from 7.0
-----------------------------+--------------------
 Reporter:  adamsilverstein  |      Owner:  (none)
     Type:  defect (bug)     |     Status:  new
 Priority:  normal           |  Milestone:  7.0
Component:  Media            |    Version:  trunk
 Severity:  normal           |   Keywords:
  Focuses:                   |
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 == Description

 The client-side media processing feature (wasm-vips) should be removed
 from WordPress 7.0 and punted to 7.1. The feature adds approximately 16MB
 of inlined WASM to the build output (the `vips/worker.min.js` file alone
 accounts for ~36% of the `script-modules/` directory), which is too much
 build size overhead relative to the value the feature currently provides.

 This ticket tracks the complete removal of all backported client-side
 media processing code from core.

 === Background

 Client-side media processing was backported from Gutenberg to allow
 browsers to handle image resizing, format conversion, and thumbnail
 generation using a WebAssembly build of the libvips image processing
 library. The feature requires cross-origin isolation (via Document-
 Isolation-Policy on Chromium 137+) and SharedArrayBuffer, limiting it to
 secure contexts on modern Chromium browsers.

 While the feature shows promise, the build size cost is significant and
 the browser support is limited. The decision is to remove it from 7.0 and
 revisit for 7.1 once the build size and browser compatibility concerns are
 addressed.

 == What Is Being Removed

 === PHP functions (`wp-includes/media.php`)
 - `wp_is_client_side_media_processing_enabled()` — feature gate
 - `wp_set_client_side_media_processing_flag()` — sets JS flags and VIPS
 module dependency
 - `wp_get_chromium_major_version()` — browser detection for DIP support
 - `wp_set_up_cross_origin_isolation()` — enables isolation in block editor
 - `wp_start_cross_origin_isolation_output_buffer()` — sends DIP header
 - `wp_add_crossorigin_attributes()` — adds `crossorigin="anonymous"` to
 HTML tags

 === Hook registrations (`wp-includes/default-filters.php`)
 - `admin_init` → `wp_set_client_side_media_processing_flag`
 - `load-post.php` / `load-post-new.php` / `load-site-editor.php` / `load-
 widgets.php` → `wp_set_up_cross_origin_isolation`

 === REST API (`wp-includes/rest-api/`)
 - `POST /wp/v2/media/{id}/sideload` endpoint — uploads client-processed
 image sub-sizes
 - `POST /wp/v2/media/{id}/finalize` endpoint — triggers
 `wp_generate_attachment_metadata` filter after client processing
 - `generate_sub_sizes` and `convert_format` request parameters on `POST
 /wp/v2/media`
 - `get_endpoint_args_for_item_schema()` override in attachments controller
 - `remove_client_side_media_processing_filters()`, `sideload_item()`,
 `filter_wp_unique_filename()`, `finalize_item()`,
 `sideload_item_permissions_check()` methods
 - REST index additions: `image_sizes`, `image_size_threshold`,
 `image_output_formats`, `jpeg_interlaced`, `png_interlaced`,
 `gif_interlaced`

 === Media templates (`wp-includes/media-template.php`)
 - Cross-origin isolation output buffer in `wp_print_media_templates()`
 - `crossorigin="anonymous"` attribute injection for media template tags

 === Script modules (`wp-includes/script-modules.php`)
 - VIPS minified filename forcing logic

 === Build assets
 - VIPS module entries in `script-modules-packages.min.php`
 - `@wordpress/vips/worker` dependency in `script-loader-packages.min.php`
 - VIPS exclusion rules in `Gruntfile.js` and `tools/gutenberg/copy.js`

 === Test files
 - `tests/phpunit/tests/media/wpCrossOriginIsolation.php` (deleted)
 - Sideload/finalize/generate_sub_sizes tests in `rest-attachments-
 controller.php`
 - Client-side media processing setup in `rest-schema-setup.php`
 - Sideload/finalize route fixtures in `wp-api-generated.js`

 == What Is Preserved

 The following independent features are **not** removed:

 - `wp_prevent_unsupported_mime_type_uploads` filter (Trac ticket 64836,
 added in 6.8.0)
 - `X-WP-Upload-Attachment-ID` response header (useful for error recovery)
 - Pre-existing `post-process` endpoint (since 5.3.0) and `edit` endpoint
 (since 5.5.0)
 - `exif_orientation`, `filename`, `filesize`, `missing_image_sizes` schema
 properties
 - The `client-side-media-experiments/` plugin directory (not part of core)

 == Proposed Fix

 PR: https://github.com/WordPress/wordpress-develop/pull/11309

 12 files changed, 1,507 lines deleted. All changes are deletions with no
 new code added.

 == Testing

 1. Run `phpunit tests/phpunit/tests/media/` — no failures.
 2. Run `phpunit tests/phpunit/tests/rest-api/rest-attachments-
 controller.php` — no failures.
 3. Run `phpunit tests/phpunit/tests/rest-api/rest-schema-setup.php` —
 route list correct.
 4. Upload images via the block editor and media library — standard server-
 side sub-size generation works.
 5. Run `npx grunt build --dev` — build succeeds without VIPS.
 6. Confirm `build/wp-includes/js/dist/script-modules/vips/` no longer
 exists.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/64906>
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