Function wrapSubAppMiddleware

packages/hono/src/shared/patchRoute.ts:118–137

(routes: HonoRoute[])

 *    See: https://github.com/honojs/hono/blob/18fe604c8cefc2628240651b1af219692e1918c1/src/hono-base.ts#L156-L168
 */
export function wrapSubAppMiddleware(routes: HonoRoute[]): void {
  const lastIndexByKey = new Map<string, number>();
  for (const [i, route] of routes.entries()) {
    // \0 (null byte) is a collision-free delimiter: it cannot appear in a valid HTTP method name or URL path
    lastIndexByKey.set(`${route.method}\0${route.path}`, i);
  }

  for (const [i, route] of routes.entries()) {
    if (typeof route.handler !== 'function') {
      continue;
    }

    const isLastForGroup = lastIndexByKey.get(`${route.method}\0${route.path}`) === i;

    const isMW = !isLastForGroup || (route.method === 'ALL' && isMiddleware(route.handler));
    if (isMW) {
      route.handler = wrapMiddlewareWithSpan(route.handler);
    }
  }
}