mwe.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include "curl/curl.h"

#define OUTPUTFILE "download"
#define URL "https://http2-server-push-demo.keksi.io"

static bool setup(CURL* hnd)
{
    FILE* out = fopen(OUTPUTFILE, "wb");
    if(!out)
        return false;

    // write to this file
    curl_easy_setopt(hnd, CURLOPT_WRITEDATA, out);
    // set URL
    curl_easy_setopt(hnd, CURLOPT_URL, URL);
    // be verbose
    curl_easy_setopt(hnd, CURLOPT_VERBOSE, 1);
    // enable HTTP/2
    curl_easy_setopt(hnd, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2_0);
    // wait for pipe connection to confirm
    curl_easy_setopt(hnd, CURLOPT_PIPEWAIT, 1);

    return true;
}

#define UNUSED __attribute__ ((unused))

// called when there's an incoming server push
static int server_push_callback(UNUSED CURL* parent,
                                UNUSED CURL* easy,
                                UNUSED size_t num_headers,
                                UNUSED struct curl_pushheaders* headers,
                                UNUSED void* userp)
{
    puts("Got incoming HTTP/2 server push");
    return CURL_PUSH_DENY;
}

#define TIMEOUT 1000

int main(void)
{
    CURLM* multi_handle = curl_multi_init();
    CURL* easy = curl_easy_init();
    if(!setup(easy))
    {
        fprintf(stderr, "failed\n");
        return EXIT_FAILURE;
    }

    curl_multi_add_handle(multi_handle, easy);

    curl_multi_setopt(multi_handle, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
    curl_multi_setopt(multi_handle, CURLMOPT_PUSHFUNCTION, server_push_callback);
    int transfers = 1; // we start with one

    do
    {
        int still_running; // keep number of running handles
        CURLMcode mc = curl_multi_perform(multi_handle, &still_running);

        int numfds;
        if(still_running)
            // wait for activity, timeout or "nothing"
            mc = curl_multi_wait(multi_handle, NULL, 0, TIMEOUT, &numfds);

        if(mc)
            break;

        struct CURLMsg* m;
        do
        {
            int msgq = 0;
            m = curl_multi_info_read(multi_handle, &msgq);
            if(m && (m->msg == CURLMSG_DONE))
            {
                CURL* e = m->easy_handle;
                transfers--;
                curl_multi_remove_handle(multi_handle, e);
                curl_easy_cleanup(e);
            }
        } while(m);
    } while(transfers);

    curl_multi_cleanup(multi_handle);

    return EXIT_SUCCESS;
}