CURLOPT_RESOLVER_START_FUNCTION(3)

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NAME

6       CURLOPT_RESOLVER_START_FUNCTION - callback called before a new name re‐
7       solve is started
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SYNOPSIS

10       #include <curl/curl.h>
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12       int resolver_start_cb(void *resolver_state, void *reserved, void *userdata);
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14       CURLcode curl_easy_setopt(CURL *handle,
15                                 CURLOPT_RESOLVER_START_FUNCTION,
16                                 resolver_start_cb);
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DESCRIPTION

19       Pass a pointer to your callback function, which should match the proto‐
20       type shown above.
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22       This  callback  function gets called by libcurl every time before a new
23       resolve request is started.
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25       resolver_state points to a backend-specific resolver  state.  Currently
26       only  the ares resolver backend has a resolver state. It can be used to
27       set up any desired option on the ares channel before it's used, for ex‐
28       ample setting up socket callback options.
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30       reserved is reserved.
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32       userdata    is    the   user   pointer   set   with   the   CURLOPT_RE‐
33       SOLVER_START_DATA(3) option.
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35       The callback must return 0 on success. Returning a non-zero value  will
36       cause the resolve to fail.
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DEFAULT

39       NULL (No callback)
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PROTOCOLS

42       All
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EXAMPLE

45       static int resolver_start_cb(void *resolver_state, void *reserved,
46                                    void *userdata)
47       {
48         (void)reserved;
49         printf("Received resolver_state=%p userdata=%p\n",
50                resolver_state, userdata);
51         return 0;
52       }
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54       CURL *curl = curl_easy_init();
55       if(curl) {
56         curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, resolver_start_cb);
57         curl_easy_setopt(curl, CURLOPT_RESOLVER_START_DATA, curl);
58         curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
59         curl_easy_perform(curl);
60         curl_easy_cleanup(curl);
61       }
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AVAILABILITY

64       Added in 7.59.0
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RETURN VALUE

67       Returns CURLE_OK
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