Add post thumbnail (featured image) url to WP-API response

thumbnail-featured-url-wp-api.php

<?php
/**
 * Add featured image url to api response
 * This will (hopefully) be unnecessary if the API team adds it to core
 *
 */

add_action( 'rest_api_init', 'sb_register_featured_urls' );
function sb_register_featured_urls() {
    register_api_field( 'post',
        'featured_image_urls',
        array(
            'get_callback'    => 'sb_api_featured_images'
        )
    );
}


function sb_api_featured_images( $data, $post ) {

	$featured_id = get_post_thumbnail_id( $post->ID );

	$sizes = wp_get_attachment_metadata( $featured_id );
	
	$size_data = new stdClass();
			
	if ( ! empty( $sizes['sizes'] ) ) {

		foreach ( $sizes['sizes'] as $key => $size ) {
			// Use the same method image_downsize() does
			$image_src = wp_get_attachment_image_src( $featured_id, $key );

			if ( ! $image_src ) {
				continue;
			}
			
			$size_data->$key = $image_src[0];
			
		}

	}

	return $size_data;
}