Manpages - CURLOPT_RESOLVER_START_FUNCTION.3

CURLOPT_RESOLVER_START_FUNCTION - callback called before a new name resolve is started

  #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);

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’s used, for example setting up socket callback options.

reserved is reserved.

userdata is the user pointer set with the CURLOPT_RESOLVER_START_DATA(3) option.

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

NULL (No callback)

All

  static int resolver_start_cb(void *resolver_state, void *reserved,
                               void *userdata)
  {
    (void)reserved;
    printf("Received resolver_state=%p userdata=%p\n",
           resolver_state, userdata);
    return 0;
  }

  CURL *curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, resolver_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);
  }

Added in 7.59.0

Returns CURLE_OK

*CURLOPT_RESOLVER_START_DATA*(3)