docs/libcurl/opts/CURLOPT_CONNECT_TO.3

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.TH CURLOPT_CONNECT_TO 3 "November 04, 2020" "libcurl 7.78.0" "curl_easy_setopt options"

.SH NAME
CURLOPT_CONNECT_TO \- Connect to a specific host and port instead of the URL's host and port
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_CONNECT_TO,
                          struct curl_slist *connect_to);
.fi
.SH 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 \fBstruct curl_slist\fP structs properly
filled in. Use \fIcurl_slist_append(3)\fP to create the list and
\fIcurl_slist_free_all(3)\fP 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 \fICURLOPT_RESOLVE(3)\fP, the option
\fICURLOPT_CONNECT_TO(3)\fP 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 \fIcurl_easy_setopt(3)\fP, libcurl will not copy
the entire list so you \fBmust\fP keep it around until you no longer use this
\fIhandle\fP for a transfer before you call \fIcurl_slist_free_all(3)\fP on
the list.

.SH DEFAULT
NULL
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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);
.fi
.SH AVAILABILITY
Added in 7.49.0
.SH RETURN VALUE
Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_URL "(3), " CURLOPT_RESOLVE "(3), " CURLOPT_FOLLOWLOCATION "(3), " CURLOPT_HTTPPROXYTUNNEL  "(3), "