1---
2c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
3SPDX-License-Identifier: curl
4Title: CURLOPT_CONNECT_TO
5Section: 3
6Source: libcurl
7See-also:
8  - CURLOPT_FOLLOWLOCATION (3)
9  - CURLOPT_HTTPPROXYTUNNEL (3)
10  - CURLOPT_RESOLVE (3)
11  - CURLOPT_URL (3)
12Protocol:
13  - All
14---
15
16# NAME
17
18CURLOPT_CONNECT_TO - connect to another host and port instead
19
20# SYNOPSIS
21
22~~~c
23#include <curl/curl.h>
24
25CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_TO,
26                          struct curl_slist *connect_to);
27~~~
28
29# DESCRIPTION
30
31Pass a pointer to a linked list of strings with "connect to" information to
32use for establishing network connections with this handle. The linked list
33should be a fully valid list of **struct curl_slist** structs properly filled
34in. Use curl_slist_append(3) to create the list and curl_slist_free_all(3) to
35clean up an entire list.
36
37Each single string should be written using the format
38HOST:PORT:CONNECT-TO-HOST:CONNECT-TO-PORT where HOST is the host of the
39request, PORT is the port of the request, CONNECT-TO-HOST is the hostname to
40connect to, and CONNECT-TO-PORT is the port to connect to.
41
42The first string that matches the request's host and port is used.
43
44Dotted numerical IP addresses are supported for HOST and CONNECT-TO-HOST.
45A numerical IPv6 address must be written within [brackets].
46
47Any of the four values may be empty. When the HOST or PORT is empty, the host
48or port always match (the request's host or port is ignored). When
49CONNECT-TO-HOST or CONNECT-TO-PORT is empty, the "connect to" feature is
50disabled for the host or port, and the request's host or port are used to
51establish the network connection.
52
53This option is suitable to direct the request at a specific server, e.g. at a
54specific cluster node in a cluster of servers.
55
56The "connect to" host and port are only used to establish the network
57connection. They do NOT affect the host and port that are used for TLS/SSL
58(e.g. SNI, certificate verification) or for the application protocols.
59
60In contrast to CURLOPT_RESOLVE(3), the option CURLOPT_CONNECT_TO(3) does not
61pre-populate the DNS cache and therefore it does not affect future transfers
62of other easy handles that have been added to the same multi handle.
63
64The "connect to" host and port are ignored if they are equal to the host and
65the port in the request URL, because connecting to the host and the port in
66the request URL is the default behavior.
67
68If an HTTP proxy is used for a request having a special "connect to" host or
69port, and the "connect to" host or port differs from the request's host and
70port, the HTTP proxy is automatically switched to tunnel mode for this
71specific request. This is necessary because it is not possible to connect to a
72specific host or port in normal (non-tunnel) mode.
73
74When this option is passed to curl_easy_setopt(3), libcurl does not copy the
75list so you **must** keep it around until you no longer use this *handle* for
76a transfer before you call curl_slist_free_all(3) on the list.
77
78# DEFAULT
79
80NULL
81
82# EXAMPLE
83
84~~~c
85int main(void)
86{
87  CURL *curl;
88  struct curl_slist *connect_to = NULL;
89  connect_to = curl_slist_append(NULL, "example.com::server1.example.com:");
90
91  curl = curl_easy_init();
92  if(curl) {
93    curl_easy_setopt(curl, CURLOPT_CONNECT_TO, connect_to);
94    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");
95
96    curl_easy_perform(curl);
97
98    /* always cleanup */
99    curl_easy_cleanup(curl);
100  }
101
102  curl_slist_free_all(connect_to);
103}
104~~~
105
106# AVAILABILITY
107
108Added in 7.49.0
109
110# RETURN VALUE
111
112Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
113