docs/libcurl/opts/CURLOPT_RESOLVER_START_FUNCTION.3

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  23 .TH CURLOPT_RESOLVER_START_FUNCTION 3 "February 14, 2018" "libcurl 7.59.0" "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) "