`Event::fflags()` accessor missing for `EVFILT_READ`/`EVFILT_WRITE` kqueue events

[larseggert]

The event::kqueue::Event struct does not expose the fflags field of the underlying kevent for EVFILT_READ and EVFILT_WRITE events. That field is currently only accessible indirectly through the filter() method for EVFILT_VNODE, EVFILT_PROC and EVFILT_USER.

Per the kqueue(2) man page on macOS/FreeBSD:

If the read direction of the socket has shutdown, then the filter also sets EV_EOF in flags, and returns the socket error (if any) in fflags.

So it is kinda important to have access to that. There are workarounds of course, but an accessor would be cleaner:

  impl Event {
      /// Get the filter-specific flags for this event.
      ///
      /// For `EVFILT_READ`/`EVFILT_WRITE` on sockets, this contains the socket
      /// error (e.g. `ECONNRESET`) when `EV_EOF` is set in `flags()`.
      pub fn fflags(&self) -> u32 {
          self.inner.fflags
      }
  }