template <typename SyncReadStream, typename DynamicBuffer>
auto async_read_until(SyncReadStream &s, DynamicBuffer &&buffers,
                      string delim) {
  struct Awaiter {
    SyncReadStream &s;
    DynamicBuffer &&buffers;
    string delim;

    std::error_code ec;
    size_t sz;

    bool await_ready() { return false; }
    auto await_resume() {
      if (ec)
        throw std::system_error(ec);
      return sz;
    }
    void await_suspend(std::experimental::coroutine_handle<> coro) {
      net::async_read_until(s, std::move(buffers), delim,
                            [this, coro](auto ec, auto sz) {
                              this->ec = ec;
                              this->sz = sz;
                              coro.resume();
                            });
    }
  };
  return Awaiter{ s, std::forward<DynamicBuffer>(buffers), delim };
}