Change the default behavior of IPOnDemand domain strategy

[ghost]

Hi everyone,

I noticed that the previous domain strategy will nullify domain rules when ip_on_demand is used.

Therefore here is my proposal on this section that:

1. For IP, nothing is changed;
2. For domains, "as_is" checks only domain list, "ip_on_demand" checks ip list before domain list, and "ip_if_non_match" checks domain list before ip list.

I am looking forward to your ideas and feedback.

Regards,
Chinese White Dolphin

[Loyalsoldier]

This changes the default behavior of IPOnDemand, but I think it's more appropriate than it used to be.

[Loyalsoldier]

For users don't know what's going on:

The concept of domain strategy(AsIs, IPOnDemand and IPIfNonMatch) is originated from V2Ray. The routing system of V2Ray supports priority(from top to bottom) when setting geoip and geosite rules, which makes IPOnDemand and IPIfNonMatch diverse and easy to understand. (Docs)

In Trojan-Go(<= v0.10.0) instead, no priority between geoip rules and geosite rules. In other words, all geoip rules or all geosite rules are treated as a whole, therefore the major difference between IPOnDemand and IPIfNonMatch then will be whether to resolve the destination address(domain) to IP immediately.

After this PR, the new default behavior will be:

• When the destination address is an IP: just match geoip rules.
• When the destination address is a domain:
  • AsIs: just match geosite rules; do NOT resolve domain to IP;
  • IPOnDemand: resolve domain to IP, match geoip rules first; if no match, then match geosite rules;
  • IPIfNonMatch: match geosite rules first; if no match, resolve domain to IP, then match geoip rules.

The resolved IP will just be used to pick a route policy(block, bypass or proxy), the destination address(domain) will not be changed.