Source

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

public function prepare_item_for_response( $post, $request ) {
		$response = parent::prepare_item_for_response( $post, $request );
		$fields   = $this->get_fields_for_response( $request );
		$data     = $response->get_data();

		if ( in_array( 'description', $fields, true ) ) {
			$data['description'] = array(
				'raw'      => $post->post_content,
				/** This filter is documented in wp-includes/post-template.php */
				'rendered' => apply_filters( 'the_content', $post->post_content ),
			);
		}

		if ( in_array( 'caption', $fields, true ) ) {
			/** This filter is documented in wp-includes/post-template.php */
			$caption = apply_filters( 'get_the_excerpt', $post->post_excerpt, $post );

			/** This filter is documented in wp-includes/post-template.php */
			$caption = apply_filters( 'the_excerpt', $caption );

			$data['caption'] = array(
				'raw'      => $post->post_excerpt,
				'rendered' => $caption,
			);
		}

		if ( in_array( 'alt_text', $fields, true ) ) {
			$data['alt_text'] = get_post_meta( $post->ID, '_wp_attachment_image_alt', true );
		}

		if ( in_array( 'media_type', $fields, true ) ) {
			$data['media_type'] = wp_attachment_is_image( $post->ID ) ? 'image' : 'file';
		}

		if ( in_array( 'mime_type', $fields, true ) ) {
			$data['mime_type'] = $post->post_mime_type;
		}

		if ( in_array( 'media_details', $fields, true ) ) {
			$data['media_details'] = wp_get_attachment_metadata( $post->ID );

			// Ensure empty details is an empty object.
			if ( empty( $data['media_details'] ) ) {
				$data['media_details'] = new stdClass;
			} elseif ( ! empty( $data['media_details']['sizes'] ) ) {

				foreach ( $data['media_details']['sizes'] as $size => &$size_data ) {

					if ( isset( $size_data['mime-type'] ) ) {
						$size_data['mime_type'] = $size_data['mime-type'];
						unset( $size_data['mime-type'] );
					}

					// Use the same method image_downsize() does.
					$image_src = wp_get_attachment_image_src( $post->ID, $size );
					if ( ! $image_src ) {
						continue;
					}

					$size_data['source_url'] = $image_src[0];
				}

				$full_src = wp_get_attachment_image_src( $post->ID, 'full' );

				if ( ! empty( $full_src ) ) {
					$data['media_details']['sizes']['full'] = array(
						'file'       => wp_basename( $full_src[0] ),
						'width'      => $full_src[1],
						'height'     => $full_src[2],
						'mime_type'  => $post->post_mime_type,
						'source_url' => $full_src[0],
					);
				}
			} else {
				$data['media_details']['sizes'] = new stdClass;
			}
		}

		if ( in_array( 'post', $fields, true ) ) {
			$data['post'] = ! empty( $post->post_parent ) ? (int) $post->post_parent : null;
		}

		if ( in_array( 'source_url', $fields, true ) ) {
			$data['source_url'] = wp_get_attachment_url( $post->ID );
		}

		if ( in_array( 'missing_image_sizes', $fields, true ) ) {
			require_once ABSPATH . 'wp-admin/includes/image.php';
			$data['missing_image_sizes'] = array_keys( wp_get_missing_image_subsizes( $post->ID ) );
		}

		$context = ! empty( $request['context'] ) ? $request['context'] : 'view';

		$data = $this->filter_response_by_context( $data, $context );

		$links = $response->get_links();

		// Wrap the data in a response object.
		$response = rest_ensure_response( $data );

		foreach ( $links as $rel => $rel_links ) {
			foreach ( $rel_links as $link ) {
				$response->add_link( $rel, $link['href'], $link['attributes'] );
			}
		}

		/**
		 * Filters an attachment returned from the REST API.
		 *
		 * Allows modification of the attachment right before it is returned.
		 *
		 * @since 4.7.0
		 *
		 * @param WP_REST_Response $response The response object.
		 * @param WP_Post          $post     The original attachment post.
		 * @param WP_REST_Request  $request  Request used to generate the response.
		 */
		return apply_filters( 'rest_prepare_attachment', $response, $post, $request );
	}