get_rest_url

/**
 * Retrieves the URL prefix for any API resource.
 *
 * @since 4.4.0
 *
 * @return string Prefix.
 */
function rest_get_url_prefix() {
	/**
	 * Filters the REST URL prefix.
	 *
	 * @since 4.4.0
	 *
	 * @param string $prefix URL prefix. Default 'wp-json'.
	 */
	return apply_filters( 'rest_url_prefix', 'wp-json' );
}

/**
 * Retrieves the URL to a REST endpoint on a site.
 *
 * Note: The returned URL is NOT escaped.
 *
 * @since 4.4.0
 *
 * @todo Check if this is even necessary
 * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
 *
 * @param int    $blog_id Optional. Blog ID. Default of null returns URL for current blog.
 * @param string $path    Optional. REST route. Default '/'.
 * @param string $scheme  Optional. Sanitization scheme. Default 'rest'.
 * @return string Full URL to the endpoint.
 */
function get_rest_url( $blog_id = null, $path = '/', $scheme = 'rest' ) {
	if ( empty( $path ) ) {
		$path = '/';
	}

	$path = '/' . ltrim( $path, '/' );

	if ( is_multisite() && get_blog_option( $blog_id, 'permalink_structure' ) || get_option( 'permalink_structure' ) ) {
		global $wp_rewrite;

		if ( $wp_rewrite->using_index_permalinks() ) {
			$url = get_home_url( $blog_id, $wp_rewrite->index . '/' . rest_get_url_prefix(), $scheme );
		} else {
			$url = get_home_url( $blog_id, rest_get_url_prefix(), $scheme );
		}

		$url .= $path;
	} else {
		$url = trailingslashit( get_home_url( $blog_id, '', $scheme ) );
		// nginx only allows HTTP/1.0 methods when redirecting from / to /index.php.
		// To work around this, we manually add index.php to the URL, avoiding the redirect.
		if ( 'index.php' !== substr( $url, 9 ) ) {
			$url .= 'index.php';
		}