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;
}

THANK YOU. This is so much better than the older examples found on the libcurl website that calculate timeout and issue their own select. curl_multi_wait FTW.

Thank you.

Thanks.

Excellent example, thank you.

How to take information such as download size, transfer time from multi interface?

Excellent example, test success!

This example works, but if you set the CURLMOPT_MAX_HOST_CONNECTIONS this code will never exit from first loop ( while(still_running) ).
The fix is to call curl_multi_info_read also inside first loop.

Hey, how to set timeout time for every individual request. Do you have any idea?

Hello, thanks for your example, but thiere is a bug on ending of main. You use curl_global_init(CURL_GLOBAL_ALL) but no curl_global_cleanup().