NAME

       CURLOPT_RESOLVER_START_FUNCTION  -  set callback to be called before a new resolve request
       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'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.

DEFAULT

       NULL (No callback)

PROTOCOLS

       All

EXAMPLE

       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, "http://example.com");
         curl_easy_perform(curl);
         curl_easy_cleanup(curl);
       }

AVAILABILITY

       Added in 7.59.0

RETURN VALUE

       Returns CURLE_OK

SEE ALSO

       CURLOPT_RESOLVER_START_DATA(3)