[openssl-dev] Adding async support

[Devchandra L Meetei]

Hello Mark
I have been working recently on evt <https://github.com/deleisha/evt>,
which is still in WIP, exposing a callback based async API's on top of
libssl.

The idea was to abstract libssl with well defined APIs that can be
integrated with libraries like libevent and libuv.

Thought It might be of interest to libevent.

On Wed, Oct 7, 2015 at 7:35 PM, Mark Ellzey <ellzey at strcpy.net> wrote:

> As a maintainer of libevent, and spending heaps of time in the ssl
> abstractions, anything to remove all the insane things you must do now for
> async io would be a reprieve of the horrors we've dealt with over the
> years.
>
> I do worry that these patches may take too much of the work away to the
> point of no decent control mechanism. When I see poll() everywhere, it
> throws up red flags.
>
> I will spend some time with the proposed patches here, and see if I can
> make libevent happy, and hopefully very less complex.
>
> Fingers crossed. Cheers!
>
> On Wed, Oct 7, 2015 at 6:43 AM Matt Caswell <matt at openssl.org> wrote:
>
>>
>>
>> On 07/10/15 14:29, Viktor Dukhovni wrote:
>> > On Wed, Oct 07, 2015 at 10:46:26AM +0100, Matt Caswell wrote:
>> >
>> >> I have also added async support to s_server and s_client through the
>> new
>> >> "-async" flag. The will set the SSL_MODE_ASYNC mode. In order to have
>> an
>> >> effect you will obviously also need an async engine (such as dasync)
>> >> loaded through the "-engine" flag. Note that dasync will only be loaded
>> >> dynamically and thus OpenSSL must be built "shared" for this to work.
>> >>
>> >> Documentation including some example code is available on all of this
>> here:
>> >>
>> https://github.com/mattcaswell/openssl/blob/main-async/doc/crypto/ASYNC_start_job.pod
>> >>
>> https://github.com/mattcaswell/openssl/blob/main-async/doc/ssl/SSL_get_error.pod
>> >>
>> https://github.com/mattcaswell/openssl/blob/main-async/doc/ssl/SSL_get_async_wait_fd.pod
>> >>
>> https://github.com/mattcaswell/openssl/blob/main-async/doc/ssl/SSL_CTX_set_mode.pod
>> >>
>> >> I'd be interested to hear your thoughts.
>> >
>> > Will existing applications doing non-blocking I/O with OpenSSL need
>> > to be modified to handle SSL_ERROR_WANT_ASYNC?  Or does that happen
>> > only if they explicitly request "async mode"?
>>
>> No, they should not need to be modified. You will only get
>> SSL_ERROR_WANT_ASYNC if you have enabled SSL_MODE_ASYNC.
>>
>> >
>> > Should applications generally enable async mode because that might
>> > be beneficial down the road?  Or is this just for exotic hardware
>> > not likely to be seen in most environments?
>>
>> It will only be helpful if you have an engine capable of supporting
>> async. I can't really answer the question because I don't know how
>> common this will be. My hope is that this will become relatively common.
>> I have been toying with the idea of creating a multi-threaded async
>> engine where the engine manages a pool of threads to offload async work
>> to which would then offer true async support even if you don't have
>> specialist hardware.
>>
>> > For example, should Postfix enable "async" support?  It does timed
>> > non-blocking TLS I/O and currently handles SSL_ERROR_WANT_{READ,WRITE}.
>>
>> If applications already handle SSL_ERROR_WANT_READ/WRITE then IMO it is
>> not much extra effort to additionally handle SSL_ERROR_WANT_ASYNC so I
>> would encourage making the changes. You may want to consider making it a
>> configurable option. There is a small overhead with creating ASYNC_JOBs
>> and context switching into them when they start and finish.
>>
>> Matt
>>
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-- 
Warm Regards
--Dev
OpenPegasus Developer

"I'm one of those people that think Thomas Edison and the light bulb
changed the world more than Karl Marx ever did,” Steve Jobs
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