<form method="POST">
    <h3>Editing: CartItems.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php
namespace Automattic\WooCommerce\StoreApi\Routes\V1;

use Automattic\WooCommerce\StoreApi\Exceptions\RouteException;

/**
 * CartItems class.
 */
class CartItems extends AbstractCartRoute {
	/**
	 * The route identifier.
	 *
	 * @var string
	 */
	const IDENTIFIER = 'cart-items';

	/**
	 * The routes schema.
	 *
	 * @var string
	 */
	const SCHEMA_TYPE = 'cart-item';

	/**
	 * Get the path of this REST route.
	 *
	 * @return string
	 */
	public function get_path() {
		return self::get_path_regex();
	}

	/**
	 * Get the path of this rest route.
	 *
	 * @return string
	 */
	public static function get_path_regex() {
		return '/cart/items';
	}

	/**
	 * Get method arguments for this REST route.
	 *
	 * @return array An array of endpoints.
	 */
	public function get_args() {
		return [
			[
				'methods'             =&gt; \WP_REST_Server::READABLE,
				'callback'            =&gt; [ $this, 'get_response' ],
				'permission_callback' =&gt; '__return_true',
				'args'                =&gt; [
					'context' =&gt; $this-&gt;get_context_param( [ 'default' =&gt; 'view' ] ),
				],
			],
			[
				'methods'             =&gt; \WP_REST_Server::CREATABLE,
				'callback'            =&gt; array( $this, 'get_response' ),
				'permission_callback' =&gt; '__return_true',
				'args'                =&gt; $this-&gt;schema-&gt;get_endpoint_args_for_item_schema( \WP_REST_Server::CREATABLE ),
			],
			[
				'methods'             =&gt; \WP_REST_Server::DELETABLE,
				'callback'            =&gt; [ $this, 'get_response' ],
				'permission_callback' =&gt; '__return_true',
			],
			'schema'      =&gt; [ $this-&gt;schema, 'get_public_item_schema' ],
			'allow_batch' =&gt; [ 'v1' =&gt; true ],
		];
	}

	/**
	 * Get a collection of cart items.
	 *
	 * @throws RouteException On error.
	 * @param \WP_REST_Request $request Request object.
	 * @return \WP_REST_Response
	 */
	protected function get_route_response( \WP_REST_Request $request ) {
		$cart_items = $this-&gt;cart_controller-&gt;get_cart_items();
		$items      = [];

		foreach ( $cart_items as $cart_item ) {
			$data    = $this-&gt;prepare_item_for_response( $cart_item, $request );
			$items[] = $this-&gt;prepare_response_for_collection( $data );
		}

		$response = rest_ensure_response( $items );

		return $response;
	}

	/**
	 * Creates one item from the collection.
	 *
	 * @throws RouteException On error.
	 * @param \WP_REST_Request $request Request object.
	 * @return \WP_REST_Response
	 */
	protected function get_route_post_response( \WP_REST_Request $request ) {
		// Do not allow key to be specified during creation.
		if ( ! empty( $request['key'] ) ) {
			throw new RouteException( 'woocommerce_rest_cart_item_exists', __( 'Cannot create an existing cart item.', 'woocommerce' ), 400 );
		}

		$result = $this-&gt;cart_controller-&gt;add_to_cart(
			[
				'id'        =&gt; $request['id'],
				'quantity'  =&gt; $request['quantity'],
				'variation' =&gt; $request['variation'],
			]
		);

		$response = rest_ensure_response( $this-&gt;prepare_item_for_response( $this-&gt;cart_controller-&gt;get_cart_item( $result ), $request ) );
		$response-&gt;set_status( 201 );
		return $response;
	}

	/**
	 * Deletes all items in the cart.
	 *
	 * @throws RouteException On error.
	 * @param \WP_REST_Request $request Request object.
	 * @return \WP_REST_Response
	 */
	protected function get_route_delete_response( \WP_REST_Request $request ) {
		$this-&gt;cart_controller-&gt;empty_cart();
		return new \WP_REST_Response( [], 200 );
	}

	/**
	 * Prepare links for the request.
	 *
	 * @param array            $cart_item Object to prepare.
	 * @param \WP_REST_Request $request Request object.
	 * @return array
	 */
	protected function prepare_links( $cart_item, $request ) {
		$base  = $this-&gt;get_namespace() . $this-&gt;get_path();
		$links = array(
			'self'       =&gt; array(
				'href' =&gt; rest_url( trailingslashit( $base ) . $cart_item['key'] ),
			),
			'collection' =&gt; array(
				'href' =&gt; rest_url( $base ),
			),
		);
		return $links;
	}
}
</textarea><br>
    <input type="submit" value="Save">
</form>