1---
2c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_RESOLVE
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_CONNECT_TO (3)
9  - CURLOPT_DNS_CACHE_TIMEOUT (3)
10  - CURLOPT_IPRESOLVE (3)
11---
12
13# NAME
14
15CURLOPT_RESOLVE - provide custom hostname to IP address resolves
16
17# SYNOPSIS
18
19~~~c
20#include <curl/curl.h>
21
22CURLcode curl_easy_setopt(CURL *handle, CURLOPT_RESOLVE,
23                          struct curl_slist *hosts);
24~~~
25
26# DESCRIPTION
27
28Pass a pointer to a linked list of strings with hostname resolve information
29to use for requests with this handle. The linked list should be a fully valid
30list of **struct curl_slist** structs properly filled in. Use
31curl_slist_append(3) to create the list and curl_slist_free_all(3) to clean up
32an entire list.
33
34Each resolve rule to add should be written using the format
35
36~~~c
37 [+]HOST:PORT:ADDRESS[,ADDRESS]
38~~~
39
40HOST is the name libcurl wants to resolve, PORT is the port number of the
41service where libcurl wants to connect to the HOST and ADDRESS is one or more
42numerical IP addresses. If you specify multiple IP addresses they need to be
43separated by comma. If libcurl is built to support IPv6, each of the ADDRESS
44entries can of course be either IPv4 or IPv6 style addressing.
45
46This option effectively populates the DNS cache with entries for the host+port
47pair so redirects and everything that operations against the HOST+PORT instead
48use your provided ADDRESS.
49
50The optional leading "+" specifies that the new entry should time-out. Entries
51added without the leading plus character never times out whereas entries added
52with "+HOST:..." times out just like ordinary DNS cache entries.
53
54If the DNS cache already has an entry for the given host+port pair, the new
55entry overrides the former one.
56
57An ADDRESS provided by this option is only used if not restricted by the
58setting of CURLOPT_IPRESOLVE(3) to a different IP version.
59
60To remove names from the DNS cache again, to stop providing these fake
61resolves, include a string in the linked list that uses the format
62
63~~~c
64  -HOST:PORT
65~~~
66
67The entry to remove must be prefixed with a dash, and the hostname and port
68number must exactly match what was added previously.
69
70# DEFAULT
71
72NULL
73
74# PROTOCOLS
75
76All
77
78# EXAMPLE
79
80~~~c
81int main(void)
82{
83  CURL *curl;
84  struct curl_slist *host = NULL;
85  host = curl_slist_append(NULL, "example.com:443:127.0.0.1");
86
87  curl = curl_easy_init();
88  if(curl) {
89    curl_easy_setopt(curl, CURLOPT_RESOLVE, host);
90    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
91
92    curl_easy_perform(curl);
93
94    /* always cleanup */
95    curl_easy_cleanup(curl);
96  }
97
98  curl_slist_free_all(host);
99}
100~~~
101
102# AVAILABILITY
103
104Added in 7.21.3. Removal support added in 7.42.0.
105
106Support for providing the ADDRESS within [brackets] was added in 7.57.0.
107
108Support for providing multiple IP addresses per entry was added in 7.59.0.
109
110Support for adding non-permanent entries by using the "+" prefix was added in
1117.75.0.
112
113# RETURN VALUE
114
115Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
116