test.c

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

fd_set wfds;
fd_set rfds;
struct timeval tv;
int maxfd = 0;

int socket_callback(CURL *easy,      /* easy handle */
                    curl_socket_t s, /* socket */
                    int what,        /* describes the socket */
                    void *userp,     /* private callback pointer */
                    void *socketp)   /* private socket pointer */
{
    FD_CLR(s, &wfds);
    FD_CLR(s, &rfds);

    if (what == CURL_POLL_IN || what == CURL_POLL_INOUT) {
        FD_SET(s, &rfds);
    }
    if (what == CURL_POLL_OUT || what == CURL_POLL_INOUT) {
        FD_SET(s, &wfds);
    }

    if (s > maxfd) { maxfd = s; }

    return 0;
}

int timer_callback(CURLM *multi,    /* multi handle */
                   long timeout_ms, /* see above */
                   void *userp)     /* private callback pointer */
{
    if (timeout_ms == -1) {
        tv.tv_sec = 10;
        tv.tv_usec = 0;
    } else {
        tv.tv_sec = timeout_ms / 1000;
        tv.tv_usec = (timeout_ms % 1000) * 1000;
    }
    return 0;
}

int main(int argc, char** argv)
{
    int running = 1;
    curl_global_init(CURL_GLOBAL_ALL);

    FD_ZERO(&wfds);
    FD_ZERO(&rfds);

    CURLM *multi = curl_multi_init();
    curl_multi_setopt(multi, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
    curl_multi_setopt(multi, CURLMOPT_SOCKETFUNCTION, socket_callback);
    curl_multi_setopt(multi, CURLMOPT_TIMERFUNCTION, timer_callback);

    int i;
    for (i = 0; i < 2; i++) {
        CURL *easy = curl_easy_init();
        curl_easy_setopt(easy, CURLOPT_URL, "https://google.com");
        curl_easy_setopt(easy, CURLOPT_VERBOSE, 1);
        curl_easy_setopt(easy, CURLOPT_PIPEWAIT, 1);
        curl_easy_setopt(easy, CURLOPT_FOLLOWLOCATION, 1);
        // PROXY: probably not relevant.
        curl_easy_setopt(easy, CURLOPT_NOPROXY, "");
        curl_easy_setopt(easy, CURLOPT_PROXY, "http://my-proxy-server:3128");

        curl_multi_add_handle(multi, easy);
    }

    tv.tv_sec = 0;
    tv.tv_usec = 0;

    running = 1;

    while (running) {
        if (tv.tv_sec == 0 && tv.tv_usec == 0) {
            curl_multi_socket_action(multi, CURL_SOCKET_TIMEOUT, 0, &running);
        }

        fd_set crfds = rfds;
        fd_set cwfds = wfds;

        int count = select(maxfd+1, &crfds, &cwfds, NULL, &tv);
        if (!count) {
            curl_multi_socket_action(multi, CURL_SOCKET_TIMEOUT, 0, &running);
        }

        for (i = 0; i <= maxfd; i++) {
            if (FD_ISSET(i, &crfds)) {
                curl_multi_socket_action(multi, i, CURL_CSELECT_IN, &running);
            }
            if (FD_ISSET(i, &cwfds)) {
                curl_multi_socket_action(multi, i, CURL_CSELECT_OUT, &running);
            }
        }
    }

    return 0;
}