curl / libcurl / API / curl_easy_setopt / CURLOPT_RESOLVE



CURLOPT_RESOLVE - provide custom hostname to IP address resolves


#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_RESOLVE,
                          struct curl_slist *hosts);


Pass a pointer to a linked list of strings with hostname resolve information to use for requests with this handle. The linked list should be a fully valid list of struct curl_slist structs properly filled in. Use curl_slist_append to create the list and curl_slist_free_all to clean up an entire list.

Each resolve rule to add should be written using the format


HOST is the name libcurl wants to resolve, PORT is the port number of the service where libcurl wants to connect to the HOST and ADDRESS is one or more numerical IP addresses. If you specify multiple IP addresses they need to be separated by comma. If libcurl is built to support IPv6, each of the ADDRESS entries can of course be either IPv4 or IPv6 style addressing.

This option effectively populates the DNS cache with entries for the host+port pair so redirects and everything that operations against the HOST+PORT instead use your provided ADDRESS.

The optional leading "+" specifies that the new entry should time-out. Entries added without the leading plus character never times out whereas entries added with "+HOST:..." times out just like ordinary DNS cache entries.

If the DNS cache already has an entry for the given host+port pair, the new entry overrides the former one.

An ADDRESS provided by this option is only used if not restricted by the setting of CURLOPT_IPRESOLVE to a different IP version.

To remove names from the DNS cache again, to stop providing these fake resolves, include a string in the linked list that uses the format


The entry to remove must be prefixed with a dash, and the hostname and port number must exactly match what was added previously.






int main(void)
  CURL *curl;
  struct curl_slist *host = NULL;
  host = curl_slist_append(NULL, "");
  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_RESOLVE, host);
    curl_easy_setopt(curl, CURLOPT_URL, "");
    /* always cleanup */


Added in 7.21.3. Removal support added in 7.42.0.

Support for providing the ADDRESS within [brackets] was added in 7.57.0.

Support for providing multiple IP addresses per entry was added in 7.59.0.

Support for adding non-permanent entries by using the "+" prefix was added in 7.75.0.

Return value

Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.

See also


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