Editor: PHP backports for Client Side Media #10868

adamsilverstein · 2026-02-04T22:44:59Z

This PR contains the PHP backports for the client-side media processing feature, enabling the editor to perform client-side image resizing, thumbnail generation, and format conversion using WebAssembly.

Preloaded Settings

The following site settings are now preloaded in both the post editor and site editor:

image_sizes - Available image size configurations
image_size_threshold - Big image size threshold (default 2560px)
image_output_formats - Output format mappings for image conversion
jpeg_interlaced - Whether to use progressive/interlaced JPEG encoding
png_interlaced - Whether to use interlaced PNG encoding
gif_interlaced - Whether to use interlaced GIF encoding

REST API: Index Endpoint

Added media processing settings to the REST API index (/wp-json/wp/v2/):

image_sizes - All registered image sizes with dimensions and crop settings
image_size_threshold - Big image size threshold
image_output_formats - Format conversion mappings

REST API: Attachments Endpoint

New Fields

filename - Original attachment file name
filesize - File size in bytes
exif_orientation - EXIF orientation value (1-8) for client-side rotation handling

New Parameters

generate_sub_sizes - When false, disables server-side sub-size generation and EXIF rotation
convert_format - When false, disables automatic image format conversion

New Sideload Endpoint

Added /wp/v2/media/{id}/sideload endpoint for uploading sub-sized images to an existing attachment. Used by client-side media processing to upload generated image sizes without creating new attachments. Supports both images and PDFs.

PDF Improvements

Improved missing_image_sizes field handling for PDFs, which use the fallback_intermediate_image_sizes filter instead of wp_get_missing_image_subsizes().

Cross-Origin Isolation

Added COOP (Cross-Origin-Opener-Policy) and COEP (Cross-Origin-Embedder-Policy) headers in the block editor to enable SharedArrayBuffer for WebAssembly-based processing. Includes:

Output buffer to automatically add crossorigin="anonymous" attributes to external resources
Media templates updated with crossorigin attributes for audio, img, and video tags

WASM Support

Added AddType directive for WebAssembly files to .htaccess rules, enabling serving .wasm files for client-side media processing libraries like wasm-vips.

Tests

Updated REST API tests for the new attachment fields and sideload endpoint.

Gutenberg PRs:

Gutenberg tracking issue: WordPress/gutenberg#75062

Trac ticket: https://core.trac.wordpress.org/ticket/62243

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

github-actions · 2026-02-04T22:50:41Z

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Add filename and filesize REST fields to the attachments endpoint for client-side media processing. The filename returns the original attachment file name, and filesize returns the file size in bytes.

Add exif_orientation field to the attachments REST endpoint for client-side EXIF rotation handling. Values 1-8 follow the EXIF specification, where 1 means no rotation is needed.

Add generate_sub_sizes and convert_format parameters to the attachments POST endpoint for client-side media processing control. When generate_sub_sizes is false, server-side sub-size generation and EXIF rotation are disabled. When convert_format is false, automatic image format conversion is disabled.

Add sideload endpoint at /wp/v2/media/{id}/sideload for uploading sub-sized images to an existing attachment. Used by client-side media processing to upload generated image sizes without creating new attachments. Supports both images and PDFs.

Add PDF-specific handling for the missing_image_sizes field in the attachments endpoint. PDFs use fallback_intermediate_image_sizes filter to determine which thumbnail sizes should be generated, unlike regular images which use wp_get_missing_image_subsizes().

Add COOP and COEP headers in the block editor to enable SharedArrayBuffer for WebAssembly-based client-side media processing. Includes output buffer to automatically add crossorigin="anonymous" attributes to external resources.

Add AddType directive for WebAssembly files to the mod_rewrite_rules filter. This enables serving .wasm files for client-side media processing using libraries like wasm-vips.

Override wp_print_media_templates to add crossorigin="anonymous" attributes to audio, img, and video tags. Required for cross-origin isolation compliance in the media library modal.

Update test_get_item_schema to expect 32 properties instead of 29, adding assertions for the new filename, filesize, and exif_orientation fields. Add the sideload endpoint to expected routes in schema test. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

westonruter

Sorry for what may be an unsolicited early review, as the PR is still a draft.

src/wp-includes/rest-api/class-wp-rest-server.php

westonruter · 2026-02-08T01:11:59Z

src/wp-includes/media.php

+	$user_id = get_current_user_id();
+	if ( ! $user_id ) {
+		return;
+	}
+
+	// Cross-origin isolation is not needed if users can't upload files anyway.
+	if ( ! user_can( $user_id, 'upload_files' ) ) {


Suggested change

$user_id = get_current_user_id();

if ( ! $user_id ) {

return;

}

// Cross-origin isolation is not needed if users can't upload files anyway.

if ( ! user_can( $user_id, 'upload_files' ) ) {

// Cross-origin isolation is not needed if users can't upload files anyway.

if ( ! current_user_can( 'upload_files' ) ) {

westonruter · 2026-02-08T01:13:50Z

src/wp-includes/media.php

+	$tag_names = array_keys( $tags );
+


Suggested change

$tag_names = array_keys( $tags );

westonruter · 2026-02-08T01:14:26Z

src/wp-includes/media.php

+	while ( $processor->next_tag() ) {
+		$tag = $processor->get_tag();
+
+		if ( ! in_array( $tag, $tag_names, true ) ) {


Suggested change

if ( ! in_array( $tag, $tag_names, true ) ) {

if ( ! isset( $tags[ $tag ] ) ) {

westonruter · 2026-02-08T01:15:30Z

src/wp-includes/media.php

+}
+
+/**
+ * Filters the list of rewrite rules formatted for output to an .htaccess file.


What about for Nginx?

westonruter · 2026-02-08T01:16:13Z

src/wp-includes/media.php

+			foreach ( $tags as $tag ) {
+				$html = (string) str_replace( "<$tag", "<$tag crossorigin=\"anonymous\"", $html );
+			}


This should use the HTML Tag Processor too as it has been leveraged above.

westonruter · 2026-02-08T01:17:40Z

src/wp-includes/rest-api/class-wp-rest-server.php

+			$sizes = wp_get_registered_image_subsizes();
+			foreach ( $sizes as $name => &$size ) {
+				$size['height'] = (int) $size['height'];
+				$size['width']  = (int) $size['width'];
+				$size['name']   = $name;
+			}
+			unset( $size );
+			$available['image_sizes'] = $sizes;


Suggested change

$sizes = wp_get_registered_image_subsizes();

foreach ( $sizes as $name => &$size ) {

$size['height'] = (int) $size['height'];

$size['width'] = (int) $size['width'];

$size['name'] = $name;

}

unset( $size );

$available['image_sizes'] = $sizes;

$available['image_sizes'] = array();

foreach ( wp_get_registered_image_subsizes() as $name => $size ) {

$available['image_sizes'][] = array(

'height' => (int) $size['height'],

'width' => (int) $size['width'],

'name' => $name,

);

}

add preload patchs for client side media

3ddfba4

REST API: Add media processing settings to index endpoint

86938a4

adamsilverstein mentioned this pull request Feb 4, 2026

Create sub-sized images WordPress/gutenberg#74566

Open

36 tasks

adamsilverstein added 8 commits February 4, 2026 15:28

REST API: Add filename and filesize fields to attachments

21c0229

Add filename and filesize REST fields to the attachments endpoint for client-side media processing. The filename returns the original attachment file name, and filesize returns the file size in bytes.

REST API: Add exif_orientation field to attachments

b912c2f

Add exif_orientation field to the attachments REST endpoint for client-side EXIF rotation handling. Values 1-8 follow the EXIF specification, where 1 means no rotation is needed.

Media: Add cross-origin isolation support

5356039

Add COOP and COEP headers in the block editor to enable SharedArrayBuffer for WebAssembly-based client-side media processing. Includes output buffer to automatically add crossorigin="anonymous" attributes to external resources.

Media: Add WASM MIME type to .htaccess rules

357c406

Add AddType directive for WebAssembly files to the mod_rewrite_rules filter. This enables serving .wasm files for client-side media processing using libraries like wasm-vips.

Media: Add crossorigin attributes to media templates

78abc16

Override wp_print_media_templates to add crossorigin="anonymous" attributes to audio, img, and video tags. Required for cross-origin isolation compliance in the media library modal.

adamsilverstein changed the title ~~Editor: Add REST API preloaded paths for client-side media processing~~ Editor: PHP back posrts for client-side media Feb 5, 2026

adamsilverstein changed the title ~~Editor: PHP back posrts for client-side media~~ Editor: PHP backports for client-side media Feb 5, 2026

adamsilverstein changed the title ~~Editor: PHP backports for client-side media~~ Editor: PHP backports for Client Side Media Feb 5, 2026

adamsilverstein added sync-gutenberg and removed sync-gutenberg labels Feb 5, 2026

adamsilverstein self-assigned this Feb 5, 2026

adamsilverstein and others added 2 commits February 4, 2026 22:10

Docs: Update @SInCE tags from 6.9.0 to 7.0.0

e847d8c

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

westonruter reviewed Feb 8, 2026

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Editor: PHP backports for Client Side Media #10868

Editor: PHP backports for Client Side Media #10868

adamsilverstein commented Feb 4, 2026 •

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	if ( ! in_array( $tag, $tag_names, true ) ) {
	if ( ! isset( $tags[ $tag ] ) ) {

Editor: PHP backports for Client Side Media #10868

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Editor: PHP backports for Client Side Media #10868

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Preloaded Settings

REST API: Index Endpoint

REST API: Attachments Endpoint

New Fields

New Parameters

New Sideload Endpoint

PDF Improvements

Cross-Origin Isolation

WASM Support

Tests

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github-actions bot commented Feb 4, 2026

Test using WordPress Playground

Some things to be aware of

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adamsilverstein commented Feb 4, 2026 •

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