docs/libcurl/opts/CURLOPT_RESOLVER_START_FUNCTION.3

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.TH CURLOPT_RESOLVER_START_FUNCTION 3 "November 04, 2020" "libcurl 7.78.0" "curl_easy_setopt options"

.SH NAME
CURLOPT_RESOLVER_START_FUNCTION \- set callback to be called before a new resolve request 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);
.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's 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 will cause
the resolve to fail.
.SH DEFAULT
NULL (No callback)
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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);
}
.fi
.SH AVAILABILITY
Added in 7.59.0
.SH RETURN VALUE
Returns CURLE_OK
.SH "SEE ALSO"
.BR CURLOPT_RESOLVER_START_DATA "(3) "