DLL gets locked when linked against OpenSSL 1.1.1j

[hbeni]

Hi there,
I really could use some help with the following issue.

I have a plugin for mumble in the works, which faciliates an updater. Mumble can load and unload the plugins. They are just DLLs exporting a bunch of functions. Mumble also has an updater, that calls a plugin function to get the latest download URL. It then fetches the new plugin, unloads the current one if loaded, and then ⚠️ deletes the old plugin dll to overwrite it with the downloaded version.

This is the point where I get problems:
As soon as I compile against OpenSSL (1.1.1j is in effect here) the DLL gets locked and thus cannot be deleted by mumble.

• We already tracked this down to be specifically related to cpp-httplib and/or OpenSSL
• We ruled out it'ts a mumble or generic plugin issue
• I think the Problem is something in OpenSSL or maybe the way cpp-httplib instanciates/uses it
• Just linking OpenSSL does not trigger the issue, it is only there if #define CPPHTTPLIB_OPENSSL_SUPPORT 1

I hoped you could see if there is a problem in the cpp-httplib regarding usage of OpenSSL.

---

Details:

• Code is specifically here: https://github.com/hbeni/fgcom-mumble/blob/master/client/mumble-plugin/lib/updater.cpp
• We track it here, for further information: Bug: Windows updater cannot replace old version due to locked DLL hbeni/fgcom-mumble#131

[yhirose]

@hbeni, thanks for the feedback, but I probably cannot give you any meaningful help since I don't fully understand your environment. The only thing I can tell at this point is that you may want to look into the constructor and destructor of SSLServer and SSLClient where all the OpenSSL activities start. Hope it help!

[hbeni]

Thank you, will do!
But maybe you could skim trough my updater code if you see something I do wrong wit the httplib?

https://github.com/hbeni/fgcom-mumble/blob/5d2125f1c296bc7cd64537a14eab2f828d766486/client/mumble-plugin/lib/updater.cpp#L143-L260

[hbeni]

Just as an idea: wolfSSL is not supported, I guess?

[yhirose]

No, also I am not planning to support it. You may want to check the following as well.

cpp-httplib/httplib.h

Line 6738 in 80be649

static SSLInit sslinit_;

[hbeni]

Looking at it again; I have a question.

In my code, inside a function, I do:

void fgcom_getLatestReleaseFromGithub_Web() {
  ...
  httplib::SSLClient cli(host.c_str());
  ...
}

I assumed that after the function is complete, everything is cleaned up automatically.
Is that maybe not the case, and I have to unload/destroy/free something regarding cli manually?

[yhirose]

Yes or no. Everything in httplib::SSLClient is cleaned up, but the global variable static SSLInit sslinit_; stays. You probably have to change the global variable to be unloadable manually.

[hbeni]

OK, I found out something by accident.
I wondered if it might have to do with the OpenSSL version, and indeed it has.

Versions 1.1.1a and 1.1.1b are working fine, but any 1.1.1 after that has the issue.
So it is surely something in OpenSSL's codebase.