Get the main Gtk struct
Asynchronously determines a proxy URI to use for @msg and calls @callback.
Synchronously determines a proxy URI to use for @uri. If @uri should be sent via proxy, *@proxy_uri will be set to the URI of the proxy, else it will be set to %NULL.
Deprecated: #SoupSession now has a #SoupSession:proxy-resolver property that takes a #GProxyResolver (which is semantically identical to #SoupProxyURIResolver).
Even in older releases of libsoup, you are not likely to have to implement this interface on your own; instead, you should usually just be able to use #SoupProxyResolverDefault.
#SoupProxyURIResolver is an interface for finding appropriate HTTP proxies to use.