Test number of file descriptors

fdtest.c

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

size_t do_nothing(void *contents, size_t sz, size_t nmemb, void *ctx){
  return sz * nmemb;
}

CURL *make_handle(char *url){
  CURL *handle = curl_easy_init();
  curl_easy_setopt(handle, CURLOPT_URL, url);
  curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, do_nothing);
  curl_easy_setopt(handle, CURLOPT_FOLLOWLOCATION, 1L);
  curl_easy_setopt(handle, CURLOPT_HTTP_VERSION, 2L);

  return handle;
}

void print_fd_count(CURLM *multi, int still_running){
  fd_set read_fd_set, write_fd_set, exc_fd_set;
  int read_fd = 0, write_fd = 0, exc_fd = 0, max_fd = 0;
  FD_ZERO(&read_fd_set);
  FD_ZERO(&write_fd_set);
  FD_ZERO(&exc_fd_set);
  curl_multi_fdset(multi, &read_fd_set, &write_fd_set, &exc_fd_set, &max_fd);
  for (int i = 0; i <= max_fd; i++){
    if (FD_ISSET(i, &read_fd_set)) read_fd++;
    if (FD_ISSET(i, &write_fd_set)) write_fd++;
    if (FD_ISSET(i, &exc_fd_set)) exc_fd++;
  }
  printf("Pending: %d. FD count: (read) %d, (write) %d, (exc) %d\n", still_running, read_fd, write_fd, exc_fd);
}

int main(void) {
  const curl_version_info_data *data = curl_version_info(CURLVERSION_NOW);
  printf("Using curl %s\n", data->version);
  curl_global_init(CURL_GLOBAL_DEFAULT);
  CURLM *multi_handle = curl_multi_init();
  curl_multi_setopt(multi_handle, CURLMOPT_MAX_HOST_CONNECTIONS, 5L);
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/4"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/3"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/2"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/1"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/0"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/1"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/2"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/3"));
  curl_multi_add_handle(multi_handle, make_handle("https://hb.opencpu.org/delay/4"));

  int msgs_left;
  int pending = 0;
  int complete = 0;
  int still_running = 1;
  while(still_running) {
    int numfds;
    curl_multi_perform(multi_handle, &still_running);
    curl_multi_wait(multi_handle, NULL, 0, 1000, &numfds);


    /* See how the transfers went */
    CURLMsg *m = NULL;
    while((m = curl_multi_info_read(multi_handle, &msgs_left))) {
      if(m->msg == CURLMSG_DONE) {
        CURL *handle = m->easy_handle;
        curl_multi_remove_handle(multi_handle, handle);
        curl_easy_cleanup(handle);
      }
      print_fd_count(multi_handle, still_running);
    }
  }
  curl_multi_cleanup(multi_handle);
  curl_global_cleanup();
  return 0;
}