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Re: Do you switch off CURL_GLOBAL_SSL and why?

From: Stefan Eissing <stefan.eissing_at_greenbytes.de>
Date: Fri, 17 Nov 2017 11:07:27 +0100

Not using it - good riddance! ;-)

Longer version: I am even not sure if, in mod_md's case, the curl init happens before or after the mod_ssl init and I really do not want to care.

Cheers,

Stefan

> Am 17.11.2017 um 10:53 schrieb Daniel Stenberg <daniel_at_haxx.se>:
>
> Hi friends!
>
> A long time ago we added the ability to ask libcurl to *not* initialize the TLS library (which iirc only was OpenSSL at the time) if you removed the CURL_GLOBAL_SSL bit from the curl_global_init() call.
>
> The idea was that if you already initialized OpenSSL in your application you might want to avoid that libcurl does it again. I believe there was once a problem in OpenSSL with doing multiple initializations. I don't think it ever made much sense for any other backend, but the option remained and is documented and everything. The default action is of course that libcurl inits the TLS stuff.
>
> Nowadays though. Is anything or anyone using this feature (disabling CURL_GLOBAL_SSL) for a good purpose and if so, can you please elaborate on why and how? (I don't think "I won't use any TLS protocols" is a good reason.)
>
> This feature requires that the application knows very well what TLS backend libcurl uses and that it knows how to init it the same way or at least properly.
>
> When we introduced multissl support in libcurl, the application can ask libcurl in run-time to pick a TLS backend and that makes this case even weirder. So an application disabling the CURL_GLOBAL_SSL bit in a multissl case would also init TLS differently based on the chosen backend libcurl will end up using. Even more unlikely to happen in the real world.
>
> Evgeny Grin recently discovered that libcurl right now crashes when you switch off CURL_GLOBAL_SSL on a multissl build, no matter if you actually use TLS or not. (See his PRs in #2089 and #2083 - two different takes at the same problem.)
>
> Of course we want to fix this, but when working on this case the general question on what disabling CURL_GLOBAL_SSL actually means comes up and if it is actually worth still dealing with.
>
> Thoughts and opinions on this are very welcome!
>
> --
>
> / daniel.haxx.se
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Received on 2017-11-17