libcurl multi interface example

curl_multi_test.c

/* curl_multi_test.c

   Clemens Gruber, 2013
   <clemens.gruber@pqgruber.com>

   Code description:
    Requests 4 Web pages via the CURL multi interface
    and checks if the HTTP status code is 200.

   Update: Fixed! The check for !numfds was the problem.
*/

#include <stdio.h>
#include <stdlib.h>
#ifndef WIN32
#include <unistd.h>
#endif
#include <curl/multi.h>

#define MAX_WAIT_MSECS 30*1000 /* Wait max. 30 seconds */

static const char *urls[] = {
  "http://www.microsoft.com",
  "http://www.yahoo.com",
  "http://www.wikipedia.org",
  "http://slashdot.org"
};
#define CNT 4

static size_t cb(char *d, size_t n, size_t l, void *p)
{
  /* take care of the data here, ignored in this example */
  (void)d;
  (void)p;
  return n*l;
}

static void init(CURLM *cm, int i)
{
  CURL *eh = curl_easy_init();
  curl_easy_setopt(eh, CURLOPT_WRITEFUNCTION, cb);
  curl_easy_setopt(eh, CURLOPT_HEADER, 0L);
  curl_easy_setopt(eh, CURLOPT_URL, urls[i]);
  curl_easy_setopt(eh, CURLOPT_PRIVATE, urls[i]);
  curl_easy_setopt(eh, CURLOPT_VERBOSE, 0L);
  curl_multi_add_handle(cm, eh);
}

int main(void)
{
    CURLM *cm=NULL;
    CURL *eh=NULL;
    CURLMsg *msg=NULL;
    CURLcode return_code=0;
    int still_running=0, i=0, msgs_left=0;
    int http_status_code;
    const char *szUrl;

    curl_global_init(CURL_GLOBAL_ALL);

    cm = curl_multi_init();

    for (i = 0; i < CNT; ++i) {
        init(cm, i);
    }

    curl_multi_perform(cm, &still_running);

    do {
        int numfds=0;
        int res = curl_multi_wait(cm, NULL, 0, MAX_WAIT_MSECS, &numfds);
        if(res != CURLM_OK) {
            fprintf(stderr, "error: curl_multi_wait() returned %d\n", res);
            return EXIT_FAILURE;
        }
        /*
         if(!numfds) {
            fprintf(stderr, "error: curl_multi_wait() numfds=%d\n", numfds);
            return EXIT_FAILURE;
         }
        */
        curl_multi_perform(cm, &still_running);

    } while(still_running);

    while ((msg = curl_multi_info_read(cm, &msgs_left))) {
        if (msg->msg == CURLMSG_DONE) {
            eh = msg->easy_handle;

            return_code = msg->data.result;
            if(return_code!=CURLE_OK) {
                fprintf(stderr, "CURL error code: %d\n", msg->data.result);
                continue;
            }

            // Get HTTP status code
            http_status_code=0;
            szUrl = NULL;

            curl_easy_getinfo(eh, CURLINFO_RESPONSE_CODE, &http_status_code);
            curl_easy_getinfo(eh, CURLINFO_PRIVATE, &szUrl);

            if(http_status_code==200) {
                printf("200 OK for %s\n", szUrl);
            } else {
                fprintf(stderr, "GET of %s returned http status code %d\n", szUrl, http_status_code);
            }

            curl_multi_remove_handle(cm, eh);
            curl_easy_cleanup(eh);
        }
        else {
            fprintf(stderr, "error: after curl_multi_info_read(), CURLMsg=%d\n", msg->msg);
        }
    }

    curl_multi_cleanup(cm);

    return EXIT_SUCCESS;
}