curl / libcurl / API / curl_easy_setopt / CURLOPT_RESOLVER_START_FUNCTION

CURLOPT_RESOLVER_START_FUNCTION explained

Name

CURLOPT_RESOLVER_START_FUNCTION - callback called before a new name resolve is started

Synopsis

#include <curl/curl.h>
 
int resolver_start_cb(void *resolver_state, void *reserved, void *userdata);
 
CURLcode curl_easy_setopt(CURL *handle,
                          CURLOPT_RESOLVER_START_FUNCTION,
                          resolver_start_cb);

Description

Pass a pointer to your callback function, which should match the prototype shown above.

This callback function gets called by libcurl every time before a new resolve request is started.

resolver_state points to a backend-specific resolver state. Currently only the ares resolver backend has a resolver state. It can be used to set up any desired option on the ares channel before it is used, for example setting up socket callback options.

reserved is reserved.

userdata is the user pointer set with the CURLOPT_RESOLVER_START_DATA option.

The callback must return 0 on success. Returning a non-zero value causes the resolve to fail.

Default

NULL (No callback)

Protocols

This functionality affects all supported protocols

Example

static int start_cb(void *resolver_state, void *reserved,
                    void *userdata)
{
  (void)reserved;
  printf("Received resolver_state=%p userdata=%p\n",
         resolver_state, userdata);
  return 0;
}
 
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, start_cb);
    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_DATA, curl);
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
    curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

Availability

Added in curl 7.59.0

Return value

Returns CURLE_OK