Ubuntu Manpage: CURLOPT_RESOLVE - provide custom hostname to IP address resolves

Provided by: libcurl4-doc_8.9.1-2ubuntu2.2_all

NAME

       CURLOPT_RESOLVE - provide custom hostname 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 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(3) to create the list and curl_slist_free_all(3) to clean up an entire list.

Each resolve rule to add should be written using the format

[+]HOST:PORT:ADDRESS[,ADDRESS]

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.

Specify the host as a single ampersand (*) to match all names. This wildcard is resolved last so any
resolve with a specific host and port number is given priority.

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 plus (+) specifies that the new entry should timeout. 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(3)
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

-HOST:PORT

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

DEFAULT

       NULL

PROTOCOLS

       This functionality affects all supported protocols

EXAMPLE

       int main(void)
       {
         CURL *curl;
         struct curl_slist *host = NULL;
         host = curl_slist_append(NULL, "example.com:443:127.0.0.1");

         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);
       }

HISTORY

       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.

AVAILABILITY

       Added in curl 7.21.3

RETURN VALUE

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