handleRequest (ctx, fnMiddleware) {
    const res = ctx.res
    res.statusCode = 404
    const onerror = (err) => ctx.onerror(err)
    const handleResponse = () => respond(ctx)
    onFinished(res, onerror)
    return fnMiddleware(ctx).then(handleResponse).catch(onerror)
  }
Handle request in callback.

@api private