How to use asyncore with SSL?

[Marko Rauhamaa]

Grant Edwards <grant.b.edwards at gmail.com>:

> On 2018-01-20, Marko Rauhamaa <marko at pacujo.net> wrote:
>> Also, a subsidiary thread is not necessary. Everything can be done
>> within an async framework (in C anyway).
>
> Of course it can. But (ISTM) either the async framework has to be
> SSL-aware, or the sockets have to be wrapped and "proxied" using
> another socket or pipe -- I don't see how else you can provide
> something that has the same select/poll and send/recv semantacs that
> an unwrapped, non-blocking socket provides.

If you mean that user-space software can't create new file descriptor
types, you would be painfully correct. The read(2) and write(2) (as well
as recv(2) and send(2)) system calls necessarily cross into the
kernel-space. User-space file descriptors can be emulated but generally
that requires the use of auxiliary processes or threads.

If you relax your requirement a bit and let the async framework define
its own I/O methods, the magic becomes possible: you can make TLS an
asynchronous drop-in replacement for TCP. (I suppose every async
framework defines its own I/O methods.)

If all you need is a file-descriptor-based notification scheme, Linux
can manage that through epollfd, eventfd and timerfd. My async framework
does not offer such a notification interface but instead uses callback
functions.


Marko