xref: /aosp_15_r20/external/curl/docs/libcurl/opts/CURLOPT_RESOLVE.md (revision 6236dae45794135f37c4eb022389c904c8b0090d)

---
c: Copyright (C) Daniel Stenberg, <[email protected]>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_RESOLVE
Section: 3
Source: libcurl
See-also:
  - CURLOPT_CONNECT_TO (3)
  - CURLOPT_DNS_CACHE_TIMEOUT (3)
  - CURLOPT_IPRESOLVE (3)
Protocol:
  - All
Added-in: 7.21.3
---

# NAME

CURLOPT_RESOLVE - provide custom hostname to IP address resolves

# SYNOPSIS

~~~c
#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.

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 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.

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%

# EXAMPLE

~~~c
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%

# RETURN VALUE

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