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curl/docs/libcurl/opts/CURLOPT_HTTPPROXYTUNNEL.3

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+.\" **************************************************************************
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+.\" *                             / __| | | | |_) | |
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+.\" * Copyright (C) 1998 - 2020, Daniel Stenberg, <[email protected]>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
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+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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+.\" **************************************************************************
+.\"
+.TH CURLOPT_HTTPPROXYTUNNEL 3 "November 04, 2020" "libcurl 7.75.0" "curl_easy_setopt options"
+
+.SH NAME
+CURLOPT_HTTPPROXYTUNNEL \- tunnel through HTTP proxy
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPPROXYTUNNEL, long tunnel);
+.SH DESCRIPTION
+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 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
+\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 an 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
+.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
+Returns CURLE_OK
+.SH "SEE ALSO"
+.BR CURLOPT_PROXY "(3), " CURLOPT_PROXYTYPE "(3), " CURLOPT_PROXYPORT "(3), "