Looks into the system proxy configuration to determine what proxy, if any, to use to connect to uri. The returned proxy URIs are of the form <protocol>://[user[:password]@]host:port or direct://, where <protocol> could be http, rtsp, socks or other proxying protocol.
If you don't know what network protocol is being used on the socket, you should use none as the URI protocol. In this case, the resolver might still return a generic proxy type (such as SOCKS), but would not return protocol-specific proxy types (such as http).
direct:// is used when no proxy is needed. Direct connection should not be attempted unless it is part of the returned array of proxies.