CURLOPT_RESOLVE

Section: curl_easy_setopt options (3)
Updated: February 25, 2021
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NAME

CURLOPT_RESOLVE - provide custom host name to IP address resolves

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_RESOLVE,
                          struct curl_slist *hosts);

DESCRIPTION

Pass a pointer to a linked list of strings with host name 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(3) to create the list and curl_slist_free_all(3) to clean up an entire list.

Each single name resolve string should be written using the format [+]HOST:PORT:ADDRESS[,ADDRESS]... where HOST is the name libcurl will try 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 pre-populates the DNS cache with entries for the host+port pair so redirects and everything that operations against the HOST+PORT will instead use your provided ADDRESS.

The optional leading "+" signifies whether the new entry should time-out or not. Entries added with "HOST:..." will never time-out whereas entries added with "+HOST:..." will time-out just like ordinary DNS cache entries.

If the DNS cache already has an entry for the given host+port pair, then this entry will be removed and a new entry will be created. This is because the old entry may have have different addresses or a different time-out setting.

The provided ADDRESS set by this option will be used even if CURLOPT_IPRESOLVE(3) is set to make libcurl use another IP version.

Remove names from the DNS cache again, to stop providing these fake resolves, by including a string in the linked list that uses the format "-HOST:PORT". The host name must be prefixed with a dash, and the host name and port number must exactly match what was already added previously.

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.

DEFAULT

NULL

PROTOCOLS

All

EXAMPLE

CURL *curl;
struct curl_slist *host = NULL;
host = curl_slist_append(NULL, "example.com:80:127.0.0.1");

curl = curl_easy_init();
if(curl) {
  curl_easy_setopt(curl, CURLOPT_RESOLVE, host);
  curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

  curl_easy_perform(curl);

  /* always cleanup */
  curl_easy_cleanup(curl);
}

curl_slist_free_all(host);

AVAILABILITY

Added in 7.21.3. Removal support added in 7.42.0.

RETURN VALUE

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