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+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_RESOLVER_START_FUNCTION
+Section: 3
+Source: libcurl
+See-also:
+ - CURLOPT_PREREQFUNCTION (3)
+ - CURLOPT_RESOLVER_START_DATA (3)
+---
+
+# NAME
+
+CURLOPT_RESOLVER_START_FUNCTION - callback called before a new name resolve is started
+
+# SYNOPSIS
+
+~~~c
+#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);
+~~~
+
+# 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.
+
+*resolver_state* 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 is used, for example setting up
+socket callback options.
+
+*reserved* is reserved.
+
+*userdata* is the user pointer set with the
+CURLOPT_RESOLVER_START_DATA(3) option.
+
+The callback must return 0 on success. Returning a non-zero value causes the
+resolve to fail.
+
+# DEFAULT
+
+NULL (No callback)
+
+# PROTOCOLS
+
+All
+
+# EXAMPLE
+
+~~~c
+static int start_cb(void *resolver_state, void *reserved,
+ void *userdata)
+{
+ (void)reserved;
+ printf("Received resolver_state=%p userdata=%p\n",
+ resolver_state, userdata);
+ return 0;
+}
+
+int main(void)
+{
+ CURL *curl = curl_easy_init();
+ if(curl) {
+ curl_easy_setopt(curl, CURLOPT_RESOLVER_START_FUNCTION, 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);
+ }
+}
+~~~
+
+# AVAILABILITY
+
+Added in 7.59.0
+
+# RETURN VALUE
+
+Returns CURLE_OK