Feature request: cancel_after, cancel_at

[anarthal]

Possible (untested) implementation:

template <class... Types>
inline capy::io_task<Types...> cancel_at(
   capy::io_task<Types...> task,
   corosio::timer& timer,
   std::chrono::steady_clock::time_point timeout,
   std::error_code cancel_ec = error::canceled)
{
   timer.expires_at(timeout);
   auto [winner_index, result] = co_await capy::when_any(std::move(task), timer.wait());
   if (winner_index == 0u)
      co_return std::move(result);
   else
      co_return {cancel_ec};
}

template <class... Types>
inline capy::io_task<Types...> cancel_after(
   capy::io_task<Types...> task,
   corosio::timer& timer,
   std::chrono::steady_clock::duration timeout,
   std::error_code cancel_ec = error::canceled)
{
   return cancel_at(std::move(task), timer, std::chrono::steady_clock::now() + timeout, cancel_ec);
}

[LegalizeAdulthood]

What are the semantics?

[anarthal]

Same as Asio. It's a shorthand for running an operation with a timeout.

[anarthal]

Note that the above implementation doesn't handle custom awaitables (as returned by resolver::resolve) correctly, though.

[anarthal]

Note that in Asio, you always get operation_aborted if the timer expires first. I'd allow configuring the error code, as shown above.