Implementations of GProxyResolver based on libproxy and GNOME settings can be found in glib-networking. GIO comes with an implementation for use inside Flatpak portals.
Get the main Gtk struct
Checks if resolver can be used on this system. (This is used internally; g_proxy_resolver_get_default() will only return a proxy resolver that returns TRUE for this method.)
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.
Asynchronous lookup of proxy. See g_proxy_resolver_lookup() for more details.
Call this function to obtain the array of proxy URIs when g_proxy_resolver_lookup_async() is complete. See g_proxy_resolver_lookup() for more details.