✨ Add express middleware

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## [Unreleased]
 
+### Added
+- Express.js middleware
+
 ## [2.0.0-rc.2] 2024-05-04
 
 ### Added

README.md

@@ -45,4 +45,5 @@ curl http://localhost:46461/healthz --verbose | jq
 
 ### Guides
 
-- [How to use with ExpressJS](./demo/express.ts)
+- [How to use as ExpressJS middleware](./demo/express-mw.ts)
+- [How to use Core with ExpressJS](./demo/express.ts)

demo/express-mw.ts

@@ -0,0 +1,31 @@
+// To run demo: npx ts-node demo/express-mw.ts
+
+import express from 'express'
+import * as healthz from '../dist/index'
+
+const app = express()
+
+app.use((req, res, next) => {
+  healthz.express({
+    // Define checks
+    checks: [
+      {
+        id: 'PostgreSQL',
+        required: true,
+        fn: async () => new Promise((resolve) => setTimeout(resolve, 1000)),
+      },
+      {
+        id: 'Redis',
+        fn: async () => new Promise((resolve) => setTimeout(resolve, 10)),
+      },
+    ],
+    // Make timeout configurable from the outside
+    timeout: parseInt(String(req.query.timeout)) || undefined,
+    // Modify the result if needed
+    transformResult: (x) => (console.log(x), x),
+  })(req, res, next)
+})
+
+const running = app.listen(process.env.PORT ?? 0)
+const port = (running.address() as any).port
+console.log(`Express app running on http://localhost:${port}/healthz`)

demo/express.ts

@@ -36,4 +36,4 @@ app.use('/healthz', async (req, res, next) => {
 
 const running = app.listen(process.env.PORT ?? 0)
 const port = (running.address() as any).port
-console.log(`Express app running on http://localhost:${port}`)
+console.log(`Express app running on http://localhost:${port}/healthz`)

src/express.test.ts

@@ -0,0 +1,26 @@
+import test, { describe } from 'node:test'
+import express from 'express'
+import { middleware } from './express'
+import { equal } from 'node:assert'
+import { Result } from './healthz'
+import { AddressInfo } from 'node:net'
+
+describe('Express integration', () => {
+  test('Middleware', async () => {
+    const app = express()
+    app.use(middleware({
+      checks: [
+        {
+          id: 'a',
+          fn: async () => 1,
+        }
+      ]
+    }))
+    const started = app.listen(0)
+    const response = await fetch(`http://localhost:${(started.address() as AddressInfo).port}/healthz`)
+    equal(response.status, 200)
+    started.close()
+    const body: Result = await response.json()
+    equal(body.status, 'OK')
+  })
+})

src/express.ts

@@ -0,0 +1,50 @@
+import { status } from '.'
+import { check, Option as HOption, Result } from './healthz'
+import { htmlResult, jsonResult } from './http'
+
+export interface Option extends HOption {
+  transformResult?: (result: Result) => Result
+}
+
+type Request = {
+  header: (arg: string) => string | undefined
+  query: Record<string, any>
+  path: string
+}
+
+type Response = {
+  status: (status: number) => Response
+  type: (t: string) => any
+  end: (t: string) => any
+  json: (t: any) => any
+}
+
+export function middleware<Req extends Request, Res extends Response>(
+  option?: Option,
+) {
+  const transformResult: Option['transformResult'] =
+    option?.transformResult ?? ((x) => x)
+  return async function healthzmw(req: Req, res: Res, next: any) {
+    try {
+      if (req.path !== '/healthz') {
+        return next()
+      }
+      const health = transformResult(
+        await check({
+          checks: option?.checks,
+          timeout: option?.timeout,
+        }),
+      )
+
+      res.status(status(health))
+      if (req.header('accept')?.includes('html')) {
+        res.type('html')
+        res.end(htmlResult(health))
+      } else {
+        res.json(jsonResult(health))
+      }
+    } catch (error) {
+      next(error)
+    }
+  }
+}

src/index.ts

@@ -13,3 +13,6 @@ export {
   jsonResult as json,
   resultStatusCode as status,
 } from './http'
+export {
+  middleware as express
+} from './express'