Tribblix: manual page: CURLOPT

CURLOPT_HTTPPROXYTUNNEL(3) Introduction to Library Functions

NAME

CURLOPT_HTTPPROXYTUNNEL - tunnel through HTTP proxy

SYNOPSIS

#include <curl/curl.h>

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

DESCRIPTION

Set the tunnel parameter to 1L to make libcurl tunnel all operations
through the HTTP proxy (set with CURLOPT_PROXY(3)). There is a big
difference between using a proxy and to tunnel through it.

Tunneling means that an 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.

To suppress proxy CONNECT response headers from user callbacks use
CURLOPT_SUPPRESS_CONNECT_HEADERS(3).

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 makes libcurl send an FTP URL in
an HTTP GET request to the proxy. By instead tunneling through the
proxy, you avoid that conversion (that rarely works through the proxy
anyway).

DEFAULT

PROTOCOLS

This functionality affects all supported protocols

EXAMPLE

int main(void)
{
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);
}
}

AVAILABILITY

Added in curl 7.3

RETURN VALUE

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error
occurred, see libcurl-errors(3).