服务端代答主机指标与公网 IP 检测

mihomo 的管理接口只报自己的内存，CPU、主机内存、网关、内网地址只有
跑在同一台机器上的 Patchbay 服务端答得出，所以加 /api/host 由它代答。
/api/host/exit 把本机某个入站端口设成代理去访问 ip.sb——浏览器发不出
「经由某个端口」的请求，这条只能走服务端。

shared/host-info.test.ts

@@ -0,0 +1,53 @@
+import { describe, expect, test } from 'bun:test'
+import {
+  cpuUsageBetween,
+  parseGateway,
+  parseMemAvailable,
+  parseNameservers,
+} from './host-info.ts'
+
+describe('parseMemAvailable', () => {
+  test('取 MemAvailable 并换算成字节', () => {
+    const meminfo = 'MemTotal:  2048000 kB\nMemFree:   100000 kB\nMemAvailable:  512000 kB\n'
+    expect(parseMemAvailable(meminfo)).toBe(512000 * 1024)
+  })
+
+  test('没有这一行（老内核）返回 null', () => {
+    expect(parseMemAvailable('MemTotal: 1 kB\nMemFree: 1 kB\n')).toBeNull()
+  })
+})
+
+describe('parseGateway', () => {
+  test('默认路由的网关按小端序倒回来', () => {
+    // 0102A8C0 → c0.a8.02.01 → 192.168.2.1
+    const table = [
+      'Iface\tDestination\tGateway\tFlags\tRefCnt\tUse\tMetric\tMask\t\tMTU\tWindow\tIRTT',
+      'eth0\t00000000\t0102A8C0\t0003\t0\t0\t0\t00000000\t0\t0\t0',
+      'eth0\t0002A8C0\t00000000\t0001\t0\t0\t0\t00FFFFFF\t0\t0\t0',
+    ].join('\n')
+    expect(parseGateway(table)).toBe('192.168.2.1')
+  })
+
+  test('没有默认路由返回 null', () => {
+    const table = 'Iface\tDestination\tGateway\neth0\t0002A8C0\t00000000'
+    expect(parseGateway(table)).toBeNull()
+  })
+})
+
+describe('parseNameservers', () => {
+  test('按出现顺序取 nameserver', () => {
+    const conf = '# comment\nnameserver 223.5.5.5\nsearch lan\nnameserver 114.114.114.114\n'
+    expect(parseNameservers(conf)).toEqual(['223.5.5.5', '114.114.114.114'])
+  })
+})
+
+describe('cpuUsageBetween', () => {
+  test('按两次快照的差值算百分比', () => {
+    const usage = cpuUsageBetween({ busy: 100, total: 1000 }, { busy: 350, total: 2000 })
+    expect(usage).toBe(25)
+  })
+
+  test('时间没有前进时返回 null', () => {
+    expect(cpuUsageBetween({ busy: 1, total: 10 }, { busy: 1, total: 10 })).toBeNull()
+  })
+})