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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) "