CURLOPT_HTTPPROXYTUNNEL: clarify, add example

.\" *                            | (__| |_| |  _ <| |___

.\" *                             \___|\___/|_| \_\_____|

.\" *

.\" * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.

.\" * Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.

.\" *

.\" * This software is licensed as described in the file COPYING, which

.\" * you should have received as part of this distribution. The terms

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPPROXYTUNNEL, long tunnel);

.SH DESCRIPTION

Set the parameter to 1 to make libcurl tunnel all operations through the HTTP

proxy. There is a big difference between using a proxy and to tunnel through

it. If you don't know what this means, you probably don't want this tunneling

option.

Set the \fBtunnel\fP parameter to 1L to make libcurl tunnel all operations

through the HTTP proxy (set with \fICURLOPT_PROXY(3)\fP). There is a big

difference between using a proxy and to tunnel through it.

Tunneling essentially means that a CONNECT is sent to the proxy, asking it to

connect to a remote host on a specific port number and then the traffic is

just passed through the proxy. Proxies tend to whitelist specific port numbers

Tunneling means that a HTTP CONNECT request is sent to the proxy, asking it

to connect to a remote host on a specific port number and then the traffic is

just passed through the proxy. Proxies tend to white-list specific port numbers

it allows CONNECT requests to and often only port 80 and 443 are allowed.

When using this, it only makes sense to use \fICURLOPT_PROXYTYPE(3)\fP set to

a HTTP proxy.

To suppress proxy CONNECT response headers from user callbacks use

\fICURLOPT_SUPPRESS_CONNECT_HEADERS(3)\fP.

HTTP proxies can generally only speak HTTP (for obvious reasons), which makes

libcurl convert non-HTTP requests to HTTP when using an HTTP proxy without

this tunnel option set. For example, asking for an FTP URL and specifying an

HTTP proxy will make libcurl send an FTP URL in a HTTP GET request to the

proxy. By instead tunneling through the proxy, you avoid that conversion (that

rarely works through the proxy anyway).

.SH DEFAULT

0

.SH PROTOCOLS

All network protocols

.SH EXAMPLE

TODO

.nf

CURL *curl = curl_easy_init();

if(curl) {

  curl_easy_setopt(curl, CURLOPT_URL, "ftp://example.com/file.txt");

  curl_easy_setopt(curl, CURLOPT_PROXY, "http://127.0.0.1:80");

  curl_easy_setopt(curl, CURLOPT_HTTPPROXYTUNNEL, 1L);

  curl_easy_perform(curl);

}

.fi

.SH AVAILABILITY

Always

.SH RETURN VALUE