WP Custom HTML Pages plugin API support

//API fields

add_action( 'rest_api_init', 'WPCHTML_create_api_fields' ); //or whatever name you give to the function below

function WPCHTML_create_api_fields() {

    //register_rest_field ( 'name-of-post-type', 'name-of-field-to-return', array-of-callbacks-and-schema() )
    //for custom permalink
    register_rest_field( 'wpchtmlp_page', 'html_permalink', array(
           'get_callback'    => 'WPCHTMLP_get_api_post_meta_permalink', //or whatever you name the callback function below
           'update_callback' => 'WPCHTMLP_update_api_post_meta_permalink', //name of update callback function at bottom
           'schema'          => null,
        )
    );
    //for HTML content
    register_rest_field( 'wpchtmlp_page', 'html_code', array(
           'get_callback'    => 'WPCHTMLP_get_api_post_meta_code', //or whatever you name the callback function below
           'update_callback' => 'WPCHTMLP_update_api_post_meta_code', //name of update callback function at bottom
           'schema'          => null,
        )
    );
}

function WPCHTMLP_get_api_post_meta_permalink( $object, $field_name, $request ) {
    $meta = get_post_meta( $object['id'], 'WPCHTMLP_page_meta_box', true );
    //return the post meta
    return $meta['html_permalink'];
}

function WPCHTMLP_get_api_post_meta_code( $object, $field_name, $request ) {
    $meta = get_post_meta( $object['id'], 'WPCHTMLP_page_meta_box', true );
    //return the post meta
    return $meta['html_code'];
}

function WPCHTMLP_update_api_post_meta_permalink($value, $object, $field_name){
  return update_post_meta($object['id'], 'WPCHTMLP_page_meta_box', array('html_permalink', $value));
}

function WPCHTMLP_update_api_post_meta_code($value, $object, $field_name){
 return update_post_meta($object['id'], 'WPCHTMLP_page_meta_box', array('html_code', $value));
}