Curl - checking connection - c++

Question

I used Curl 7.2.9 and checked connection this way:
Here's example:
curl = curl_easy_init();
bool result = false;
if(curl)
{
curl_easy_setopt(curl, CURLOPT_URL, m_checkConnectionUrl);
CURLcode res = curl_easy_perform(curl);
}
if(res != CURLE_OK)
{
}
else
{
// connection is available
}
Now I switched to curl-7.33.0 and got *CURLE_WRITE_ERROR* error,
and to make it work I must code it like
std::string output;
char* encodedUrl = curl_easy_escape(curl, m_checkConnectionUrl, 0);
curl_easy_setopt(curl, CURLOPT_POST, 0);
curl_easy_setopt(curl, CURLOPT_URL, encodedUrl);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, writeMemoryCurlCallbackStub);
CURLcode res = curl_easy_perform(curl);
But I don't need to write anything. Any ideas?

Answer 1

Manily the Curl option *CURLOPT_WRITEFUNCTION* is used to have a certain amount of data periodically(at the callback functoin) to handle a large file download. I don't see any reason to use this with your curl purpose, regardless the version.
Remove the *CURLOPT_POST*(by default its 0) and *CURLOPT_WRITEFUNCTION* from the code and it should work. If it doesn't, then you are doing something wrong at other places in your code!
Also, if you are checking whether the URL is ok or not, then using CURL is ok. But to only check for connection, you can only check whether the port 80 of the domain is on or not.

Answer 2

You need to write a writecallback as well
size_t CurlWriteCallback(char* buf, size_t size, size_t nmemb, void* up)
{
TRACE("CURL - Response received:\n%s", buf);
TRACE("CURL - Response handled %d bytes:\n%s", size*nmemb);
// tell curl how many bytes we handled
return size*nmemb;
}
if(curl)
{
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, &CurlWriteCallback);
curl_easy_setopt(curl, CURLOPT_URL, m_checkConnectionUrl);
CURLcode res = curl_easy_perform(curl);
}

Answer 3

Old question, but I have just encountered a similar problem. After some more googling this is the solution:
curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 1L);
curl_easy_perform(curl);
// OK, now we are connected (if nothing bad happened),
// but it would be nice to communicate with the server:
curl_easy_setopt(curl, CURLOPT_CONNECT_ONLY, 0L);
//now we can do the actual communication
I used this to separate authentication from the actual emails sending.