pub fn with_context(context: Arc<ServiceContext>, client_addr: ServerAddr) -> Self {
        Self {
            context,
            mode: Mode::TcpAndUdp,
            client_addr,
            database_path: "shadowsocks-fakedns.sled".into(),
            ipv4_network: Ipv4Net::new(Ipv4Addr::new(172, 16, 0, 0), 12).unwrap(),
            ipv6_network: Ipv6Net::new(Ipv6Addr::new(0xfc00, 0, 0, 0, 0, 0, 0, 0), 7).unwrap(),
            expire_duration: Duration::from_secs(10),
        }
    }
Create a new Fake DNS server with context
crates/shadowsocks-service/src/local/fake_dns/server.rs