CURLOPT_PROXY man page
CURLOPT_PROXY — set proxy to use
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROXY, char *proxy);
Set the proxy to use for the upcoming request. The parameter should be a char * to a zero terminated string holding the host name or dotted numerical IP address. A numerical IPv6 address must be written within [brackets].
To specify port number in this string, append :[port] to the end of the host name. The proxy's port number may optionally be specified with the separate option CURLOPT_PROXYPORT(3). If not specified, libcurl will default to using port 1080 for proxies.
The proxy string may be prefixed with [scheme]:// to specify which kind of proxy is used.
HTTP Proxy. Default when no scheme or proxy type is specified.
HTTPS Proxy. (Added in 7.52.0 for OpenSSL, GnuTLS and NSS)
SOCKS4a Proxy. Proxy resolves URL hostname.
SOCKS5 Proxy. Proxy resolves URL hostname.
Without a scheme prefix, CURLOPT_PROXYTYPE(3) can be used to specify which kind of proxy the string identifies.
When you tell the library to use a HTTP proxy, libcurl will transparently convert operations to HTTP even if you specify an FTP URL etc. This may have an impact on what other features of the library you can use, such as CURLOPT_QUOTE(3) and similar FTP specifics that don't work unless you tunnel through the HTTP proxy. Such tunneling is activated with CURLOPT_HTTPPROXYTUNNEL(3).
libcurl respects the environment variables http_proxy, ftp_proxy, all_proxy etc, if any of those are set. The CURLOPT_PROXY(3) option does however override any possibly set environment variables.
Setting the proxy string to "" (an empty string) will explicitly disable the use of a proxy, even if there is an environment variable set for it.
A proxy host string can also include protocol scheme (http://) and embedded user + password.
The application does not have to keep the string around after setting this option.
Default is NULL, meaning no proxy is used.
When you set a host name to use, do not assume that there's any particular single port number used widely for proxies. Specify it!
All except file://. Note that some protocols don't do very well over proxy.
Since 7.14.1 the proxy environment variable names can include the protocol scheme.
Since 7.21.7 the proxy string supports the socks protocols as "schemes".
Since 7.50.2, unsupported schemes in proxy strings cause libcurl to return error.
Returns CURLE_OK if proxies are supported, CURLE_UNKNOWN_OPTION if not, or CURLE_OUT_OF_MEMORY if there was insufficient heap space.
CURLOPT_PROXYPORT(3), CURLOPT_HTTPPROXYTUNNEL(3), CURLOPT_PROXYTYPE(3)
curl_easy_setopt(3), CURLOPT_HTTPPROXYTUNNEL(3), CURLOPT_NOPROXY(3), CURLOPT_PRE_PROXY(3), CURLOPT_PROXYAUTH(3), CURLOPT_PROXYPORT(3), CURLOPT_PROXY_SERVICE_NAME(3), CURLOPT_PROXY_TRANSFER_MODE(3), CURLOPT_PROXYTYPE(3), CURLOPT_PROXYUSERPWD(3), CURLOPT_SERVICE_NAME(3), CURLOPT_SOCKS5_GSSAPI_NEC(3), CURLOPT_SOCKS5_GSSAPI_SERVICE(3), CURLOPT_SUPPRESS_CONNECT_HEADERS(3), CURLOPT_UNIX_SOCKET_PATH(3), libcurl-tutorial(3).