.\" generated by cd2nroff 0.1 from CURLOPT_RESOLVER_START_FUNCTION.md
.TH CURLOPT_RESOLVER_START_FUNCTION 3 "2024-11-18" libcurl
.SH NAME
CURLOPT_RESOLVER_START_FUNCTION \- callback called before a new name resolve is started
.SH SYNOPSIS
.nf
#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);
.fi
.SH 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.

\fIresolver_state\fP 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.

\fIreserved\fP is reserved.

\fIuserdata\fP is the user pointer set with the
\fICURLOPT_RESOLVER_START_DATA(3)\fP option.

The callback must return 0 on success. Returning a non\-zero value causes the
resolve to fail.
.SH DEFAULT
NULL (No callback)
.SH PROTOCOLS
This functionality affects all supported protocols
.SH EXAMPLE
.nf
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);
  }
}
.fi
.SH AVAILABILITY
Added in curl 7.59.0
.SH RETURN VALUE
Returns CURLE_OK
.SH SEE ALSO
.BR CURLOPT_PREREQFUNCTION (3),
.BR CURLOPT_RESOLVER_START_DATA (3)