CURL finish executing and timeout - c++

Question

I'm performing a server request with curl in C++ which return responses in pieces and those pieces's size may also vary.
At the time of arrival of each piece, the callback function is being called. The problem is I can't detect when the connection finished in order to perform an another callback to my parent class.
And by the way, I want to know if we can set and detect timeout for a curl?
Here is my code in short:
CURL *curl = curl_easy_init();
curl_global_init(CURL_GLOBAL_ALL);
curl_easy_setopt(curl, CURLOPT_URL, "My URL");
curl_easy_setopt(curl, CURLOPT_POST, 1);
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "My Postfields");
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeCallback);
curl_easy_perform(curl);
curl_easy_cleanup(curl);
curl_global_cleanup();
The default callback:
size_t writeCallback(char* buf, size_t size, size_t nmemb, void* up)
{
//do something
//But how can I detect the last callback when connection finished
//in order to call an another one?
return size*nmemb;
}

Answer 1

The data you want can be saved off during the callback, then used once curl_easy_perform returns. Example:
CURL *curl = curl_easy_init();
curl_global_init(CURL_GLOBAL_ALL);
// NOTE: added to accumulate data.
std::string result;
curl_easy_setopt(curl, CURLOPT_URL, "My URL");
curl_easy_setopt(curl, CURLOPT_POST, 1);
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "My Postfields");
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeCallback);
curl_easy_setopt(curl, CURLOPT_WRITEDATA, &result); // NOTE: added
curl_easy_perform(curl);
// TODO: do something with your data stored in result
curl_easy_cleanup(curl);
curl_global_cleanup();
And in your write callback:
size_t writeCallback(char* buf, size_t size, size_t nmemb, void* up)
{
std::string* pstr = static_cast<std::string*>(up);
std::copy(buf, buf+size*nmemb, std::back_inserter(*pstr));
return size*nmemb;
}
or something along those lines. I leave all the error checking to you (and sorry for any typos; I don't have a compiler to validate this on immediately available to me).
Regarding timeout length, there are a multitude of timeout options available to a easy-mode curl request. Too many to mention here, in fact. See the documentation for curl_easy_setopt, in particular the connection options approximately 2/3rd of the way down the page.
Best of luck.