CURLOPT_RESOLVER_START_FUNCTION(3)                    curl_easy_setopt options

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
       _RESOLVER_START_DATA&section=3">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, "https://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)

libcurl 7.77.0                 November 4, 2020
                                            CURLOPT_RESOLVER_START_FUNCTION(3)