Optimization: Prevent redundant process search for non-local inbound traffic in Route Rules

1. Description

Currently, when a process_name or process_path rule exists in route.rules, sing-box appears to trigger a system process search (PID lookup) for every incoming packet, even if the packet originates from an external LAN device (e.g., via TUN inbound) that cannot possibly have a local PID.

This results in:

1.Log Spam: Constant INFO router: failed to search process: process not found messages.

2.Performance Overhead: Unnecessary syscalls/kernel lookups for every forwarded packet from LAN clients.

2. Actual Behavior (Log)

INFO [tun-in]: inbound packet connection from 192.168.102.188:57805
router: failed to search process: process not found

Even when using logical and with source_ip filtering, the process search seems to be pre-fetched or executed regardless of the previous match results.

3. Expected Behavior / Suggestion

Implement Short-circuit Evaluation for metadata fetching in the routing engine.

If a rule is structured like this:
JSON

{
  "type": "logical", "mode": "and",
  "rules": [
    { "source_ip": ["127.0.0.1"] },
    { "process_name": ["AdGuardHome"] }
  ]
}

sing-box should only attempt to search for the process AFTER the source_ip condition is met. If the first condition fails, the process lookup should be skipped entirely.

4. Refined Logic Suggestion:
The routing engine should inherently distinguish between locally-initiated requests and forwarded/inbound traffic before executing a process_name lookup. Since connections originating from external clients (e.g., LAN devices via TUN) will never have a corresponding local process name, attempting a lookup is a deterministic failure.

I suggest that process_name matching should only be triggered if the connection's source metadata satisfies the conditions for a local process (e.g., matching loopback interfaces or specific local source IPs). By skipping the process search for all non-local traffic, sing-box can avoid redundant syscalls and keep the logs clean from "process not found" noise in transparent proxy environments.

5. Environment

Version: 1.13.5

Platform: Linux (OpenWrt)

Mode: TUN with auto_route strict_route auto_redirect

Start by tracing route.rules evaluation in the routing engine, focusing on logical and rules that combine source_ip with process_name metadata. Reproduce the TUN inbound case on Linux and inspect when process lookup occurs; done means failed source conditions avoid the lookup and external traffic no longer produces process-not-found log messages.