easy:SetOpt_Pre_Proxy(preproxy)
preproxy to use for the upcoming request. The parameter
should be a 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. If not specified, libcurl will default to
using port 1080 for proxies.
A pre proxy is a SOCKS proxy that curl connects to before it connects to the
HTTP(S) proxy specified in the #CURLOPT_PROXY option. The pre proxy can
only be a SOCKS proxy.
The pre proxy string should be prefixed with [scheme]:// to specify which kind
of socks is used. Use socks4://, socks4a://, socks5:// or socks5h:// (the last
one to enable socks5 and asking the proxy to do the resolving, also known as
#CURLPROXY_SOCKS5_HOSTNAME type) to request the specific SOCKS version to
be used. Otherwise SOCKS4 is used as default.
Setting the pre proxy string to "" (an empty string) will explicitly disable the use of a pre proxy.