Request object for validate_callback

I’m trying to define a new REST Api endpoint based on WP REST API (version 2) and have question relating to what arguments are available to the validate_callback and sanitize_callback. Is the Request object made available for these callbacks?

For example:

add_action( 'rest_api_init', function () {
    register_rest_route( 'myplugin/v1', '/author/(?P<id>\d+)', array(
        'methods' => 'GET',
        'callback' => 'my_awesome_func',
        'args' => array(
            'id' => array(
                'validate_callback' => 'my_validation'
            ),
        ),
    ) );
} );

function my_validation (WP_REST_Request $request) {
   return is_numeric( $request['id'] );   // Is this acceptable???
}

A quick search through the WP-API source revealed where validate_callback is being used:

wp-api/lib/infrastructure/class-wp-rest-request.php

$valid_check = call_user_func( $arg['validate_callback'], $param, $this, $key );

In this case, $this is an instance of WP_Rest_Request – so there’s one. Now, for sanitize_callback:

$this->params[ $type ][ $key ] = call_user_func( $attributes['args'][ $key ]['sanitize_callback'], $value, $this, $key );

Same file, there’s the $this you’re looking for. So yes, both should get an instance of WP_Rest_Request as their second argument.