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libcurl multi interface example
/* 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;
}
@jdolan

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@jdolan jdolan commented Dec 23, 2014

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.

@smart--petea

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@smart--petea smart--petea commented Aug 13, 2015

Thank you.

@chideat

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@chideat chideat commented Nov 4, 2015

Thanks.

@iamritpal

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@iamritpal iamritpal commented Jan 23, 2016

Excellent example, thank you.

@mrajiullah

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@mrajiullah mrajiullah commented Feb 16, 2016

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

@wjx0912

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@wjx0912 wjx0912 commented Feb 26, 2017

Excellent example, test success!

@albertino80

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@albertino80 albertino80 commented Mar 7, 2017

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.

@bhardwaj75

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@bhardwaj75 bhardwaj75 commented Sep 28, 2017

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

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