bug: ping_balancer tests tcp connection in udp_only mode

[fortime]

It prints 'no valid TCP server serving for TCP clients, consider disable TCP with "mode": "udp_only"', even if there is only "udp_only" mode in locals.
I think this line is the cause.

shadowsocks-rust/crates/shadowsocks-service/src/local/mod.rs

Line 186 in fb2192b

let mut mode = Mode::TcpOnly;

It sets "tcp_only" by default. The ping_balancer will always test tcp connection.

[zonyitoo]

shadowsocks-rust/crates/shadowsocks-service/src/local/loadbalancing/ping_balancer.rs

Lines 397 to 419 in fb2192b

	for server in servers.iter() {
	let svr_cfg = server.server_config();
	if self.mode.enable_tcp() && PingBalancerContext::check_server_tcp_enabled(svr_cfg) {
	let checker = PingChecker {
	server: server.clone(),
	server_type: ServerType::Tcp,
	context: self.context.clone(),
	max_server_rtt: self.max_server_rtt,
	};
	vfut_tcp.push(checker.check_update_score());
	}
	if self.mode.enable_udp() && PingBalancerContext::check_server_udp_enabled(svr_cfg) {
	let checker = PingChecker {
	server: server.clone(),
	server_type: ServerType::Udp,
	context: self.context.clone(),
	max_server_rtt: self.max_server_rtt,
	};
	vfut_udp.push(checker.check_update_score());
	}
	}

TCP checker is only enabled if mode has enabled TCP.

[zonyitoo]

Oh, I see. Because mode is TcpOnly by default, so TCP is always enabled no matter what you have configured in mode.