CURLOPT_RESOLVE(3) Library Functions Manual CURLOPT_RESOLVE(3)
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 infor-
mation 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.
libcurl does not copy the list, it needs to be kept around until after
the transfer has completed.
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 asterisk (*) to match all names. This wild-
card is resolved last so any resolve with a specific host and port num-
ber 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 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(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.
Provide IPv6 addresses within [brackets].
Using this option multiple times makes the last set list override the
previous ones. Set it to NULL to disable its use again.
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");
host = curl_slist_append(host, "example.com:443:[2001:db8::252f:efd6]");
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.
Support for specifying the host component as an IPv6 address was added
in 8.13.0.
AVAILABILITY
Added in curl 7.21.3
RETURN VALUE
curl_easy_setopt(3) returns a CURLcode indicating success or error.
CURLE_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLOPT_CONNECT_TO(3), CURLOPT_DNS_CACHE_TIMEOUT(3), CURLOPT_IPRE-
SOLVE(3)
libcurl 2026-07-12 CURLOPT_RESOLVE(3)
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