Initializing SSL and libcurl and getting “out of m

Question

I intend to do https requests with libcurl and openssl with a C++ program.

I initialized libcurl with curl_global_init(CURL_GLOBAL_ALL) as described in the documentation. Then I use an curl_easy handle that I initialize, populate with headers and a body, and send everything out to ´https://example.com:443/foo´. It works for non-https connections.

Looking around I find that there may be other libraries that are already getting an SSL context which is what causes libcurl to fail in doing precisely that. I get the following error message:

curl_easy_perform failed: Out of memory

In my case I am using libmicrohttpd which I initialize with

mhdDaemon = MHD_start_daemon(MHD_USE_THREAD_PER_CONNECTION | MHD_USE_SSL,
                               htons(port),
                               NULL,
                               NULL,
                               connectionTreat,                     NULL,
                               MHD_OPTION_HTTPS_MEM_KEY,            httpsKey,
                               MHD_OPTION_HTTPS_MEM_CERT,           httpsCertificate,
                               MHD_OPTION_CONNECTION_MEMORY_LIMIT,  memoryLimit,
                               MHD_OPTION_SOCK_ADDR,                (struct sockaddr*) &sad,
                               MHD_OPTION_NOTIFY_COMPLETED,         requestCompleted, NULL,
                               MHD_OPTION_END);

So I am indeed using openSSL somewhere else. The thing is, if I take out the MHD_USE_SSL part it does not fix the problem.

This is the list of libraries that are linked to the application (I'm using cmake):

-lmicrohttpd
-lmongoclient
-lboost_thread
-lboost_filesystem
-lboost_system
-lpthread

Is there any of the others that could be loading SSL? Is microhttpd loading it anyways even if I comment out the MHD_USE_SSL flag (plus all other related flags)? Could there be any other reason for this error?

Answer 1

As the descibed in this answer, you might need to disable SSLv3 if you are on Ubuntu 16.04 like so

curl_easy_setopt(curl_, CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1_2));

It was disabled on Ubuntu 16.04 for security reasons, see more here.

Answer 2

I'm not aware of any problem in libcurl that would cause this error code to get returned if indeed a memory allocation function doesn't fail. Using OpenSSL in multiple modules does not cause such a failure. (I am the lead developer of libcurl.)

So, run your app with VERBOSE set to libcurl, or even strace to see which syscall that fails and it should give you more clues.