Ubuntu Manpage: CURLOPT_CONNECT_TO - connect to a specific host and port instead of the URL's host and

NAME

       CURLOPT_CONNECT_TO  -  connect  to  a specific host and port instead of the URL's host and
       port

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_TO,
                                 struct curl_slist *connect_to);

DESCRIPTION

Pass a pointer to a linked list of strings with "connect to" information to use for
establishing network connections 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.

Each single string should be written using the format HOST:PORT:CONNECT-TO-HOST:CONNECT-
TO-PORT where HOST is the host of the request, PORT is the port of the request, CONNECT-
TO-HOST is the host name to connect to, and CONNECT-TO-PORT is the port to connect to.

The first string that matches the request's host and port is used.

Dotted numerical IP addresses are supported for HOST and CONNECT-TO-HOST. A numerical
IPv6 address must be written within [brackets].

Any of the four values may be empty. When the HOST or PORT is empty, the host or port will
always match (the request's host or port is ignored). When CONNECT-TO-HOST or CONNECT-TO-
PORT is empty, the "connect to" feature will be disabled for the host or port, and the
request's host or port will be used to establish the network connection.

This option is suitable to direct the request at a specific server, e.g. at a specific
cluster node in a cluster of servers.

The "connect to" host and port are only used to establish the network connection. They do
NOT affect the host and port that are used for TLS/SSL (e.g. SNI, certificate
verification) or for the application protocols.

In contrast to CURLOPT_RESOLVE(3), the option CURLOPT_CONNECT_TO(3) does not pre-populate
the DNS cache and therefore it does not affect future transfers of other easy handles that
have been added to the same multi handle.

The "connect to" host and port are ignored if they are equal to the host and the port in
the request URL, because connecting to the host and the port in the request URL is the
default behavior.

If an HTTP proxy is used for a request having a special "connect to" host or port, and the
"connect to" host or port differs from the request's host and port, the HTTP proxy is
automatically switched to tunnel mode for this specific request. This is necessary because
it is not possible to connect to a specific host or port in normal (non-tunnel) mode.

When this option is passed to curl_easy_setopt(3), libcurl will not copy the entire list
so you must keep it around until you no longer use this handle for a transfer before you
call curl_slist_free_all(3) on the list.

DEFAULT

       NULL

PROTOCOLS

All

EXAMPLE

       CURL *curl;
       struct curl_slist *connect_to = NULL;
       connect_to = curl_slist_append(NULL, "example.com::server1.example.com:");

       curl = curl_easy_init();
       if(curl) {
         curl_easy_setopt(curl, CURLOPT_CONNECT_TO, connect_to);
         curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

         curl_easy_perform(curl);

         /* always cleanup */
         curl_easy_cleanup(curl);
       }

       curl_slist_free_all(connect_to);

AVAILABILITY

       Added in 7.49.0

RETURN VALUE

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