libCurl SSL error after fork()

Question

I'm developing a FUSE driver and when I run it as a daemon (without the -f or -d flags) all https request made through libcurl fail. I was able to reproduce the error by making an https request, forking and returning the parent process, and then making a second request from the new process. If I remove the fork call or make an http request there are no errors.

I'm making an official bug report right now, but does anyone know how I can make it work?

Here's my code and the (logfile) output:

Note: if you run my program, pipe to /dev/null because libcurl sends the received buffer to stdout by default.

#include <curl/curl.h>
#include <string>
#include <unistd.h>
#include <iostream>

using namespace std;

void log(string str)
{   //TODO: remove
    static const char logfile[] = "/home/austin/megalog";
    FILE *f = fopen(logfile, "a");
    fwrite(str.data(), str.size(), 1, f);
    fclose(f);
    cout << str;
}

int main(int argc, char *argv[])
{
    string url = "https://www.google.com/";
    char errBuf[1024];
    CURLcode err;

    curl_global_init(CURL_GLOBAL_DEFAULT);
    CURL *handle = curl_easy_init();
    curl_easy_setopt(handle, CURLOPT_URL, url.c_str());
    curl_easy_setopt(handle, CURLOPT_ERRORBUFFER, errBuf);

    if ((err = curl_easy_perform(handle)))
    {
        log("first request failed\n");
        return 1;
    }
    curl_easy_cleanup(handle);

    if(fork())
        return 0;

    handle = curl_easy_init();
    curl_easy_setopt(handle, CURLOPT_URL, url.c_str());
    curl_easy_setopt(handle, CURLOPT_ERRORBUFFER, errBuf);

    if ((err = curl_easy_perform(handle)))
    {
        log(string("curl error while sending: (") + to_string(err) + ") " + curl_easy_strerror(err) + "\n");
        log(errBuf);
    }
    else
        log("no error\n");

    return 0;
}

...and the output:

$ g++ -std=c++11 main.cpp -lcurl
$ rm -f log
$ ./a.out > /dev/null
$ cat log
curl error while sending: (35) SSL connect error
A PKCS #11 module returned CKR_DEVICE_ERROR, indicating that a problem has occurred with the token or slot.

I'm using (the latest) libcurl version 7.29.0, (the latest) openssl version 1.0.1e, and I'm running Fedora 18 with kernel version 3.7.4.

Answer 1

To make this work, you need to call curl_global_cleanup before fork and curl_global_init again after fork. Someone in the libcurl mailing list mentioned that this is a common problem when calling fork after initializing libraries that need to be initialized.