Thanks Matt, this was very helpful. I'll dig into libcurl to understand better. I appreciated your help. Kind regards, Valerio -- Valerio Di Gregorio ENGINEER.SOFTWARE ENGINEERING vadigreg@xxxxxxxxx | +41 21 694 3840 .:|:.:|:. Cisco Systems International Sàrl EPFL, Quartier de l'Innovation Batiment E, 2nd Floor, Desk A4-7 1015 Ecublens, Vaud Switzerland -----Original Message----- From: Matt Caswell <matt@xxxxxxxxxxx> Sent: Tuesday, February 11, 2020 4:14 PM To: Valerio Di Gregorio (vadigreg) <vadigreg@xxxxxxxxx>; openssl-users@xxxxxxxxxxx Subject: Re: Issues with ASYNC_pause_job() wake up On 11/02/2020 14:49, Valerio Di Gregorio (vadigreg) wrote: > My understanding is that libcurl's multi interface is async. I know nothing about curl, but a quick search of the codebase does turn up some evidence that it seems to be ASYNC aware. At least it is prepared to accept SSL_ERROR_WANT_ASYNC as a return value from SSL_get_error(): https://github.com/curl/curl/blob/355a5a310019659d9bf6818d2fd66fbb214dfed7/lib/vtls/openssl.c#L2940-L2955 > That's > the interface I'm using. I configured SSL_CTX_set_mode(ssl_ctx, > SSL_MODE_ASYNC) as you pointed out. I did in the same libcurl callback > I used for SSL_CTX_set_cert_verify_callback(). I can see > ASYNC_pause_job() actually pausing and returning with no error, so I > must assume I'm into an async job. > > Should I call ASYNC_start_job() right after the write() to wake-up and > read()? When your application knows that the callback is ready to continue it must ensure that whatever OpenSSL I/O operation was in progress prior to the pause is then invoked again. So if SSL_connect() was being called at the time of the pause, then SSL_connect() needs to be called again. I don't know what that means you need to do in libcurl terms. Matt > > Val > > -----Original Message----- From: Matt Caswell <matt@xxxxxxxxxxx> > Sent: Tuesday, February 11, 2020 3:36 PM To: Valerio Di Gregorio > (vadigreg) <vadigreg@xxxxxxxxx>; openssl-users@xxxxxxxxxxx Subject: > Re: Issues with ASYNC_pause_job() wake up > > > > On 11/02/2020 14:26, Valerio Di Gregorio (vadigreg) wrote: >> Hi Matt, Thanks for your reply. HTTPS request is initiated using >> libcurl. I've installed a callback in libcurl as >> CURLOP_T_SSL_CTX_FUNCTION which in turn installs a callback using >> SSL_CTX_set_cert_verify_callback(). So my application never calls >> ASYNC_start_job(). >> >> I expected my application to write() on the write file descriptor of >> the pipe and that was enough to un-pause, without any need of calling >> ASYNC_start_job() explicitily. >> >> What's the right usage of this async APIs in my case? > > Hmm. Well, unfortunately if libcurl is managing the interaction with > libssl then this won't work unless libcurl is async aware (I don't > know if it is or not). > > ASYNC_pause_job() does nothing at all if you are not running within an > async job. An async job is *not* started automatically by libssl. > In order for that to happen you have to put the SSL object into ASYNC > mode using a call to SSL_set_mode() or SSL_CTX_set_mode(), and passing > the `SSL_MODE_ASYNC` value. See: > > https://www.openssl.org/docs/man1.1.1/man3/SSL_set_mode.html > > Once set into async mode libssl will call ASYNC_start_job() > automatically for all IO functions (e.g. SSL_read()/SSL_write() etc) > > Further, when the application calls SSL_get_error(), it must be > prepared to handle SSL_ERROR_WANT_ASYNC as a return value. > > So, probably, you need to investigate whether libcurl can do this. > > Matt > >> >> Many thanks for helping! >> >> Val >> >> >> -----Original Message----- From: openssl-users >> <openssl-users-bounces@xxxxxxxxxxx> On Behalf Of Matt Caswell >> Sent: Tuesday, February 11, 2020 2:52 PM To: >> openssl-users@xxxxxxxxxxx Subject: Re: Issues with >> ASYNC_pause_job() wake up >> >> >> >> On 11/02/2020 13:05, Valerio Di Gregorio (vadigreg) via openssl-users >> wrote: >>> 1. ASYNC_pause_job() can wake up before write(). It will then block >>> on the read(), which is too bad in my single-threaded code. >>> 2. I fixed case 1 by making read() non-blocking, I then run >>> ASYNC_pause_job() again and again until write() is actually >>> performed. So now I hit another issue. Time between >>> printf("pause") and write() is ~100/200 milliseconds. However time >>> between write() and printf("resume") is usually ~4.5 seconds and >>> this way too much. >> >> >> It's not clear from your description how your application starts the >> ASYNC job in the first place. Are you using libssl to do this, or >> does your application call ASYNC_start_job() directly? >> >> When your certificate validation code calls ASYNC_pause_job() control >> will return to your application. Control will not return until >> ASYNC_start_job() is called again. Depending on how you started the >> job in the first place this will either be due to your application >> explicitly calling ASYNC_start_job() directly, or (if it used libssl >> to start the job), then by recalling the I/O function that hit the >> pause originally. >> >> Once ASYNC_start_job() is invoked then context swap should happen >> immediately (so ~4.5 seconds would be totally unexpected). >> >> So please explain a little more about how your application starts the >> job, and how it monitors its progress in order to know when to >> resume. >> >> Matt >> >> >>> >>> >>> >>> Is there a reliable way (only when data is really ready) and a >>> prompt way (in order of micro/milli-seconds) to wake up from >>> ASYNC_pause_job()? >>> >>> >>> >>> Many thanks, any help would be much appreciated. >>> >>> >>> >>> Kind Regards, >>> >>> Valerio Di Gregorio >>> >>
