SWI-Prolog -- try

Availability::- use_module(library(socket)).

[semidet,multifile]try_proxy(+Proxy, +TargetAddress, -Socket, -StreamPair)

Attempt a socket-level connection via the given proxy to TargetAddress. The Proxy argument must match the output argument of proxy_for_url/3. The predicate tcp_connect/3 (and http_open/3 from the library(http/http_open)) collect the results of failed proxies and raise an exception no proxy is capable of realizing the connection.

The default implementation recognises the values for Proxy described below. The library(http/http_proxy) adds proxy(Host,Port) which allows for HTTP proxies using the CONNECT method.

direct: Do not use any proxy
socks(Host, Port): Use a SOCKS5 proxy