
#include <curl/curl.h>
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_TO,
struct curl_slist *connect_to);
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 requests'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.
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, "");
curl_easy_perform(curl);
/* always cleanup */
curl_easy_cleanup(curl);
}
curl_slist_free_all(connect_to);