[Feature] Loopback proxy for re-running rules with a new IN-NAME / sub-rules

[Medium1992]

Verification Steps

• I have read the documentation and confirmed that this feature is not implemented
• I have searched for the feature request I want to propose in the Issue Tracker and did not find it
• I am a non-Chinese user.

Description

[Feature] Loopback proxy for re-running rules with a new IN-NAME / sub-rules

Problem

In mihomo, a proxy-group is currently effectively the point where the final outbound is selected. If a rules entry selects a group, and the user then selects a specific proxy inside that group, there is no way to run rules again after that selection.

This makes the following use case difficult:

• incoming traffic goes into one common proxy-group, for example GLOBAL;
• inside GLOBAL, the user selects a special outbound with one button;
• this outbound should not perform a real network dial, but should send the connection back to the rule matcher;
• after that, rules should decide again where to route the traffic, for example YouTube to one group, AI/ChatGPT to another group, and everything else to DIRECT.

Proposal

Add a new proxy type:

proxies:
  - name: LB
    type: loopback
    target-in-name: LB_TEST
    target-sub-rules: loopback-test
    max-hops: 2

loopback is not a real network outbound. Instead, it triggers another rule matching pass.

Fields

target-in-name

Sets a new metadata.InName value before the second rule matching pass. After that, normal rules can match it:

rules:
  - AND,((IN-NAME,LB_TEST),(RULE-SET,geosite_youtube)),LINK_YOUTUBE
  - AND,((IN-NAME,LB_TEST),(RULE-SET,geosite_ai)),LINK_AI
  - IN-NAME,mixed-in,GLOBAL
  - MATCH,DIRECT

target-sub-rules

Optionally selects a sub-rules set for the second rule matching pass. If the target set does not exist, mihomo could log a warning and fall back to the default rules.

Example:

sub-rules:
  loopback-test:
    - RULE-SET,geosite_youtube,LINK_YOUTUBE
    - RULE-SET,geosite_ai,LINK_AI
    - MATCH,DIRECT

max-hops

Limits the number of loopback jumps for one connection. This is a guard against invalid configs and routing loops.

Example scenario

proxy-groups:
  - name: GLOBAL
    type: select
    proxies:
      - LB
      - DIRECT
      - SomeProxy

proxies:
  - name: LB
    type: loopback
    target-in-name: LB_TEST
    max-hops: 2

rules:
  - AND,((IN-NAME,LB_TEST),(RULE-SET,geosite_youtube)),LINK_YOUTUBE
  - AND,((IN-NAME,LB_TEST),(RULE-SET,geosite_ai)),LINK_AI
  - IN-NAME,mixed-in,GLOBAL
  - MATCH,DIRECT

Flow:

1. A client connects through mixed-in.
2. The rule IN-NAME,mixed-in,GLOBAL sends traffic to GLOBAL.
3. The user selects LB inside GLOBAL.
4. LB triggers another rule matching pass and sets IN-NAME=LB_TEST.
5. The second rule matching pass routes YouTube, AI/ChatGPT, and everything else using normal rules.

Loop protection

There should be protection against accidental infinite loopback routing.

Suggested behavior:

• if the same loopback transition is detected again, drop the connection;
• if max-hops is exceeded, drop the connection;
• both cases should be logged as warnings;
• a missing target-sub-rules should not drop the connection, a warning plus fallback to default rules should be enough.

url-test / health-check behavior

Because loopback can be selected inside a proxy-group, it would be useful if url-test did not fail immediately on the loopback proxy itself. Instead, it should run the same second rule matching pass and test the final selected outbound.

For example, if the health-check URL https://www.gstatic.com/generate_204 is routed to DIRECT after the second rule matching pass, the test should go through DIRECT.

Connections display

For debugging, it would be useful if chains showed that the connection passed through loopback, for example:

LINK_YOUTUBE -> LB -> GLOBAL -> FinalProxy

Otherwise, the web panel only shows the final rule and final group, but not the intermediate loopback step.

Prototype

I made an experimental prototype based on v1.19.24:

https://github.com/Medium1992/mihomo-loopback/commit/d8b73e2283657eead03589e15eddd3c09facf5b2

I tested the prototype locally in an Alpine container on RouterOS:

• re-running rules works;
• IN-NAME after loopback works;
• RULE-SET after loopback works;
• fallback for missing target-sub-rules works;
• url-test behavior for loopback is included in the prototype;
• go test ./... passes.

The prototype was made with the help of Codex: I described the desired behavior and tested the result, because I am not very strong in Go programming myself.

I do not insist on this exact implementation. I would be very happy if the idea of such a loopback proxy could be considered and integrated into mihomo in a form that fits the project. In my opinion, this proxy could add a lot of flexibility: the user can select one item in a proxy-group, and then normal rules can handle the rest of the routing, instead of creating many separate groups for different resources.

[Medium1992]

#2862