c++ How to continuously loop using Curl Multi Interface - c++

Question

im trying to loop continuously using curl multi interface. I have a timer function that needs to continuously loop through 4 urls at once, and go to the next 4, and so on etc.. I have successfully got the curl to poll my handles for its status, but when the handle hits 0, I try to reset the curl handle to loop again using new urls, but its not working. My timer function keeps working as it should, but curl multi stops, and gives me the same curl response using the same 4 urls, even though I try to reset the handles each time. Any help on this please, and thanks.. Below is a snippet of my code..
// Timer function that fires every 30 seconds with 4 different URL's each time
void timerFunction (QString url1,QString url2,QString url3,QString url4)
{
CURLMsg *msg = NULL;
std::string url1_ = url1.toStdString();
std::string url2_ = url2.toStdString();
std::string url3_ = url3.toStdString();
std::string url4_ = url4.toStdString();
CURLM *curlm;
int handle_count;
curlm = curl_multi_init();
CURL *curl1 = NULL;
curl1 = curl_easy_init();
CURL *curl2 = NULL;
curl2 = curl_easy_init();
CURL *curl3 = NULL;
curl3 = curl_easy_init();
CURL *curl4 = NULL;
curl4 = curl_easy_init();
if(curl1 && curl2 && curl3 && curl4)
{
curl_easy_setopt(curl1, CURLOPT_URL, url1_.c_str());
curl_easy_setopt(curl1, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl1);
curl_easy_setopt(curl2, CURLOPT_URL, url2_.c_str());
curl_easy_setopt(curl2, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl2);
curl_easy_setopt(curl3, CURLOPT_URL, url3_.c_str());
curl_easy_setopt(curl3, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl3);
curl_easy_setopt(curl4, CURLOPT_URL, url4_.c_str());
curl_easy_setopt(curl4, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl4);
CURLMcode code;
while(1)
{
code = curl_multi_perform(curlm, &handle_count);
if(handle_count == 0)
{
qDebug() << "Handle is 0, CURL Processing is done -- Repeat Process ";
break;
}
while ((msg = curl_multi_info_read(curlm, &handle_count)))
{
if (msg->msg == CURLMSG_DONE)
{
qDebug() << msg->msg;
curl_easy_reset(curl1);
curl_easy_reset(curl2);
curl_easy_reset(curl3);
curl_easy_reset(curl4);
handle_count = 4;
code = curl_multi_perform(curlm, &handle_count);
}
}
}
}

Answer 1

curl_easy_reset states clearly:
Re-initializes all options previously set on a specified CURL handle
to the default values. This puts back the handle to the same state as
it was in when it was just created with curl_easy_init.
It does not change the following information kept in the handle: live
connections, the Session ID cache, the DNS cache, the cookies and
shares.
What you need to do is use curl_multi_remove_handle and then curl_easy_cleanup for each handle in the loop once you are done with the response.
However you also need to use curl_multi_cleanup after the loop to remove all handles.
Your code would look like this:
// Timer function that fires every 30 seconds with 4 different URL's each time
void timerFunction (QString url1,QString url2,QString url3,QString url4)
{
CURLMsg *msg = NULL;
std::string url1_ = url1.toStdString();
std::string url2_ = url2.toStdString();
std::string url3_ = url3.toStdString();
std::string url4_ = url4.toStdString();
CURLM *curlm;
CURL* eh = NULL;
int still_running = 0, i = 0, msgs_left = 0;
curlm = curl_multi_init();
CURL *curl1 = NULL;
curl1 = curl_easy_init();
CURL *curl2 = NULL;
curl2 = curl_easy_init();
CURL *curl3 = NULL;
curl3 = curl_easy_init();
CURL *curl4 = NULL;
curl4 = curl_easy_init();
if(curl1 && curl2 && curl3 && curl4)
{
curl_easy_setopt(curl1, CURLOPT_URL, url1_.c_str());
curl_easy_setopt(curl1, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl1);
curl_easy_setopt(curl2, CURLOPT_URL, url2_.c_str());
curl_easy_setopt(curl2, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl2);
curl_easy_setopt(curl3, CURLOPT_URL, url3_.c_str());
curl_easy_setopt(curl3, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl3);
curl_easy_setopt(curl4, CURLOPT_URL, url4_.c_str());
curl_easy_setopt(curl4, CURLOPT_WRITEFUNCTION, writeCallback);
curl_multi_add_handle(curlm, curl4);
while(1)
{
curl_multi_perform(curlm, &still_running);
do {
int numfds = 0;
CURLMcode res = curl_multi_wait(curlm, NULL, 0, MAX_WAIT_MSECS, &numfds);
if (res != CURLM_OK) {
// handle error your way
}
curl_multi_perform(curlm, &still_running);
} while (still_running);
while ((msg = curl_multi_info_read(curlm, &msgs_left)))
{
if (msg->msg == CURLMSG_DONE)
{
eh = msg->easy_handle;
qDebug() << msg->msg;
curl_multi_remove_handle(curlm, eh);
curl_easy_cleanup(eh);
}
}
curl_multi_cleanup(cm);
}
}
Have not tested your code, but I modified it so you get an idea of how you should do it.