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                     23: .TH CURLOPT_RESOLVER_START_FUNCTION 3 "February 14, 2018" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_RESOLVER_START_FUNCTION \- set callback to be called before a new resolve request is started
                     27: .SH SYNOPSIS
                     28: .nf
                     29: #include <curl/curl.h>
                     30: 
                     31: int resolver_start_cb(void *resolver_state, void *reserved, void *userdata);
                     32: 
                     33: CURLcode curl_easy_setopt(CURL *handle,
                     34:                           CURLOPT_RESOLVER_START_FUNCTION,
                     35:                           resolver_start_cb);
                     36: .SH DESCRIPTION
                     37: Pass a pointer to your callback function, which should match the prototype
                     38: shown above.
                     39: 
                     40: This callback function gets called by libcurl every time before a new resolve
                     41: request is started.
                     42: 
                     43: \fIresolver_state\fP points to a backend-specific resolver state. Currently
                     44: only the ares resolver backend has a resolver state. It can be used to set up
                     45: any desired option on the ares channel before it's used, for example setting up
                     46: socket callback options.
                     47: 
                     48: \fIreserved\fP is reserved.
                     49: 
                     50: \fIuserdata\fP is the user pointer set with the
                     51: \fICURLOPT_RESOLVER_START_DATA(3)\fP option.
                     52: 
                     53: The callback must return 0 on success. Returning a non-zero value will cause
                     54: the resolve to fail.
                     55: .SH DEFAULT
                     56: NULL (No callback)
                     57: .SH PROTOCOLS
                     58: All
                     59: .SH EXAMPLE
                     60: .nf
                     61: static int resolver_start_cb(void *resolver_state, void *reserved,
                     62:                              void *userdata)
                     63: {
                     64:   (void)reserved;
                     65:   printf("Received resolver_state=%p userdata=%p\\n",
                     66:          resolver_state, userdata);
                     67:   return 0;
                     68: }
                     69: 
                     70: CURL *curl = curl_easy_init();
                     71: if(curl) {
                     72:   curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, resolver_start_cb);
                     73:   curl_easy_setopt(curl, CURLOPT_RESOLVER_START_DATA, curl);
                     74:   curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
                     75:   curl_easy_perform(curl);
                     76:   curl_easy_cleanup(curl);
                     77: }
                     78: .fi
                     79: .SH AVAILABILITY
                     80: Added in 7.59.0
                     81: .SH RETURN VALUE
                     82: Returns CURLE_OK
                     83: .SH "SEE ALSO"
                     84: .BR CURLOPT_RESOLVER_START_DATA "(3) "