docs/libcurl/opts/CURLOPT_RESOLVE.3

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.TH CURLOPT_RESOLVE 3 "April 24, 2021" "libcurl 7.78.0" "curl_easy_setopt options"

.SH NAME
CURLOPT_RESOLVE \- provide custom host name to IP address resolves
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_RESOLVE,
                          struct curl_slist *hosts);
.SH 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 \fBstruct curl_slist\fP structs properly filled in. Use
\fIcurl_slist_append(3)\fP to create the list and \fIcurl_slist_free_all(3)\fP
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.

An ADDRESS provided by this option will only be use if not restricted by
the setting of \fICURLOPT_IPRESOLVE(3)\fP to a different 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.
.SH DEFAULT
NULL
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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);
.fi
.SH AVAILABILITY
Added in 7.21.3. Removal support added in 7.42.0.
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_IPRESOLVE "(3), " CURLOPT_DNS_CACHE_TIMEOUT "(3), " CURLOPT_CONNECT_TO "(3), "