refactor(server): separate server from app

我們需要 NCM API 的伺服器部分，但 app.js
目前的做法讓我們不太好單獨啟動伺服器。

我將 app.js 的伺服器部分抽成各個函數，並將原有
會 blocking 的函數更改為非同步函式。
這樣不僅能最大化善用 Node.js 的 Event Loop，
亦能提升未來維護的程式碼易讀性。

app.js

@@ -1,146 +1,4 @@
 #!/usr/bin/env node
-const fs = require('fs')
+require('./server')({
-const path = require('path')
+  checkVersion: true,
-const express = require('express')
-const bodyParser = require('body-parser')
-const request = require('./util/request')
-const packageJSON = require('./package.json')
-const exec = require('child_process').exec
-const cache = require('./util/apicache').middleware
-const { cookieToJson } = require('./util/index')
-const fileUpload = require('express-fileupload')
-const decode = require('safe-decode-uri-component')
-
-// version check
-exec('npm info NeteaseCloudMusicApi version', (err, stdout, stderr) => {
-  if (!err) {
-    let version = stdout.trim()
-    if (packageJSON.version < version) {
-      console.log(
-        `最新版本: ${version}, 当前版本: ${packageJSON.version}, 请及时更新`,
-      )
-    }
-  }
 })
-
-const app = express()
-app.set('trust proxy', true)
-
-// CORS & Preflight request
-app.use((req, res, next) => {
-  if (req.path !== '/' && !req.path.includes('.')) {
-    res.set({
-      'Access-Control-Allow-Credentials': true,
-      'Access-Control-Allow-Origin': req.headers.origin || '*',
-      'Access-Control-Allow-Headers': 'X-Requested-With,Content-Type',
-      'Access-Control-Allow-Methods': 'PUT,POST,GET,DELETE,OPTIONS',
-      'Content-Type': 'application/json; charset=utf-8',
-    })
-  }
-  req.method === 'OPTIONS' ? res.status(204).end() : next()
-})
-
-// cookie parser
-app.use((req, res, next) => {
-  req.cookies = {}
-  //;(req.headers.cookie || '').split(/\s*;\s*/).forEach((pair) => { //  Polynomial regular expression //
-  ;(req.headers.cookie || '').split(/;\s+|(?<!\s)\s+$/g).forEach((pair) => {
-    let crack = pair.indexOf('=')
-    if (crack < 1 || crack == pair.length - 1) return
-    req.cookies[decode(pair.slice(0, crack)).trim()] = decode(
-      pair.slice(crack + 1),
-    ).trim()
-  })
-  next()
-})
-
-// body parser
-app.use(bodyParser.json())
-app.use(bodyParser.urlencoded({ extended: false }))
-
-app.use(fileUpload())
-
-// static
-app.use(express.static(path.join(__dirname, 'public')))
-
-// cache
-app.use(cache('2 minutes', (req, res) => res.statusCode === 200))
-// router
-const special = {
-  'daily_signin.js': '/daily_signin',
-  'fm_trash.js': '/fm_trash',
-  'personal_fm.js': '/personal_fm',
-}
-
-fs.readdirSync(path.join(__dirname, 'module'))
-  .reverse()
-  .forEach((file) => {
-    if (!file.endsWith('.js')) return
-    let route =
-      file in special
-        ? special[file]
-        : '/' + file.replace(/\.js$/i, '').replace(/_/g, '/')
-    let question = require(path.join(__dirname, 'module', file))
-
-    app.use(route, (req, res) => {
-      ;[req.query, req.body].forEach((item) => {
-        if (typeof item.cookie === 'string') {
-          item.cookie = cookieToJson(decode(item.cookie))
-        }
-      })
-      let query = Object.assign(
-        {},
-        { cookie: req.cookies },
-        req.query,
-        req.body,
-        req.files,
-      )
-
-      question(query, request)
-        .then((answer) => {
-          console.log('[OK]', decode(req.originalUrl))
-
-          const cookies = answer.cookie
-          if (Array.isArray(cookies) && cookies.length > 0) {
-            if (req.protocol === 'https') {
-              // Try to fix CORS SameSite Problem
-              res.append(
-                'Set-Cookie',
-                cookies.map((cookie) => {
-                  return cookie + '; SameSite=None; Secure'
-                }),
-              )
-            } else {
-              res.append('Set-Cookie', cookies)
-            }
-          }
-          res.status(answer.status).send(answer.body)
-        })
-        .catch((answer) => {
-          console.log('[ERR]', decode(req.originalUrl), {
-            status: answer.status,
-            body: answer.body,
-          })
-          if (!answer.body) {
-            res.status(404).send({
-              code: 404,
-              data: null,
-              msg: 'Not Found',
-            })
-            return
-          }
-          if (answer.body.code == '301') answer.body.msg = '需要登录'
-          res.append('Set-Cookie', answer.cookie)
-          res.status(answer.status).send(answer.body)
-        })
-    })
-  })
-
-const port = process.env.PORT || 3000
-const host = process.env.HOST || ''
-
-app.server = app.listen(port, host, () => {
-  console.log(`server running @ http://${host ? host : 'localhost'}:${port}`)
-})
-
-module.exports = app

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "NeteaseCloudMusicApi",
-  "version": "4.2.0",
+  "version": "4.3.0",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "NeteaseCloudMusicApi",
-      "version": "4.2.0",
+      "version": "4.3.0",
       "license": "MIT",
       "dependencies": {
         "axios": "^0.24.0",
@@ -1502,6 +1502,8 @@
       "resolved": "https://registry.npm.taobao.org/enquirer/download/enquirer-2.3.6.tgz?cache=0&sync_timestamp=1593693291943&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Fenquirer%2Fdownload%2Fenquirer-2.3.6.tgz",
       "integrity": "sha1-Kn/l3WNKHkElqXXsmU/1RW3Dc00=",
       "dev": true,
+      "optional": true,
+      "peer": true,
       "dependencies": {
         "ansi-colors": "^4.1.1"
       },
@@ -6743,6 +6745,8 @@
       "resolved": "https://registry.npm.taobao.org/enquirer/download/enquirer-2.3.6.tgz?cache=0&sync_timestamp=1593693291943&other_urls=https%3A%2F%2Fregistry.npm.taobao.org%2Fenquirer%2Fdownload%2Fenquirer-2.3.6.tgz",
       "integrity": "sha1-Kn/l3WNKHkElqXXsmU/1RW3Dc00=",
       "dev": true,
+      "optional": true,
+      "peer": true,
       "requires": {
         "ansi-colors": "^4.1.1"
       }

server.js

@@ -0,0 +1,263 @@
+#!/usr/bin/env node
+const fs = require('fs')
+const path = require('path')
+const express = require('express')
+const bodyParser = require('body-parser')
+const request = require('./util/request')
+const packageJSON = require('./package.json')
+const exec = require('child_process').exec
+const cache = require('./util/apicache').middleware
+const { cookieToJson } = require('./util/index')
+const fileUpload = require('express-fileupload')
+const decode = require('safe-decode-uri-component')
+
+/**
+ * The version check result.
+ * @readonly
+ * @enum {number}
+ */
+const VERSION_CHECK_RESULT = {
+  FAILED: -1,
+  NOT_LATEST: 0,
+  LATEST: 1,
+}
+
+/**
+ * @typedef {{
+ *   port?: number,
+ *   host?: string,
+ *   checkVersion?: boolean,
+ * }} NcmApiOptions
+ */
+
+/**
+ * @typedef {{
+ *   status: VERSION_CHECK_RESULT,
+ *   ourVersion?: string,
+ *   npmVersion?: string,
+ * }} VersionCheckResult
+ */
+
+/**
+ * @typedef {{
+ *  server?: import('http').Server,
+ * }} ExpressExtension
+ */
+
+/**
+ * Check if the version of this API is latest.
+ *
+ * @returns {Promise<VersionCheckResult>} If true, this API is up-to-date;
+ * otherwise, this API should be upgraded and you would
+ * need to notify users to upgrade it manually.
+ */
+async function checkVersion() {
+  return new Promise((resolve, reject) => {
+    exec('npm info NeteaseCloudMusicApi version', (err, stdout, stderr) => {
+      if (!err) {
+        let version = stdout.trim()
+
+        /**
+         * @param {VERSION_CHECK_RESULT} status
+         */
+        const resolveStatus = (status) =>
+          resolve({
+            status,
+            ourVersion: packageJSON.version,
+            npmVersion: version,
+          })
+
+        resolveStatus(
+          packageJSON.version < version
+            ? VERSION_CHECK_RESULT.NOT_LATEST
+            : VERSION_CHECK_RESULT.LATEST,
+        )
+      }
+    })
+
+    resolve({
+      status: VERSION_CHECK_RESULT.FAILED,
+    })
+  })
+}
+
+/**
+ * Construct the server of NCM API.
+ *
+ * @returns {Promise<import("express").Express>} The server instance.
+ */
+async function consturctServer() {
+  const app = express()
+  app.set('trust proxy', true)
+
+  /**
+   * CORS & Preflight request
+   */
+  app.use((req, res, next) => {
+    if (req.path !== '/' && !req.path.includes('.')) {
+      res.set({
+        'Access-Control-Allow-Credentials': true,
+        'Access-Control-Allow-Origin': req.headers.origin || '*',
+        'Access-Control-Allow-Headers': 'X-Requested-With,Content-Type',
+        'Access-Control-Allow-Methods': 'PUT,POST,GET,DELETE,OPTIONS',
+        'Content-Type': 'application/json; charset=utf-8',
+      })
+    }
+    req.method === 'OPTIONS' ? res.status(204).end() : next()
+  })
+
+  /**
+   * Cookie Parser
+   */
+  app.use((req, res, next) => {
+    req.cookies = {}
+    //;(req.headers.cookie || '').split(/\s*;\s*/).forEach((pair) => { //  Polynomial regular expression //
+    ;(req.headers.cookie || '').split(/;\s+|(?<!\s)\s+$/g).forEach((pair) => {
+      let crack = pair.indexOf('=')
+      if (crack < 1 || crack == pair.length - 1) return
+      req.cookies[decode(pair.slice(0, crack)).trim()] = decode(
+        pair.slice(crack + 1),
+      ).trim()
+    })
+    next()
+  })
+
+  /**
+   * Body Parser and File Upload
+   */
+  app.use(bodyParser.json())
+  app.use(bodyParser.urlencoded({ extended: false }))
+
+  app.use(fileUpload())
+
+  /**
+   * Serving static files
+   */
+  app.use(express.static(path.join(__dirname, 'public')))
+
+  /**
+   * Cache
+   */
+  app.use(cache('2 minutes', (_, res) => res.statusCode === 200))
+
+  /**
+   * Special Routers
+   */
+  const special = {
+    'daily_signin.js': '/daily_signin',
+    'fm_trash.js': '/fm_trash',
+    'personal_fm.js': '/personal_fm',
+  }
+
+  /**
+   * Load every modules in this directory
+   */
+  const modules = (
+    await fs.promises.readdir(path.join(__dirname, 'module'))
+  ).reverse()
+  for (const file of modules) {
+    // Check if the file is written in JS.
+    if (!file.endsWith('.js')) continue
+
+    // Get the route path.
+    const route =
+      file in special
+        ? special[file]
+        : '/' + file.replace(/\.js$/i, '').replace(/_/g, '/')
+
+    // Get the module itself.
+    const module = require(path.join(__dirname, 'module', file))
+
+    // Register the route.
+    app.use(route, async (req, res) => {
+      ;[req.query, req.body].forEach((item) => {
+        if (typeof item.cookie === 'string') {
+          item.cookie = cookieToJson(decode(item.cookie))
+        }
+      })
+
+      let query = Object.assign(
+        {},
+        { cookie: req.cookies },
+        req.query,
+        req.body,
+      )
+
+      try {
+        const moduleResponse = await module(query, request)
+        console.log('[OK]', decode(req.originalUrl))
+
+        const cookies = moduleResponse.cookie
+        if (Array.isArray(cookies) && cookies.length > 0) {
+          if (req.protocol === 'https') {
+            // Try to fix CORS SameSite Problem
+            res.append(
+              'Set-Cookie',
+              cookies.map((cookie) => {
+                return cookie + '; SameSite=None; Secure'
+              }),
+            )
+          } else {
+            res.append('Set-Cookie', cookies)
+          }
+        }
+        res.status(moduleResponse.status).send(moduleResponse.body)
+      } catch (/** @type {*} */ moduleResponse) {
+        console.log('[ERR]', decode(req.originalUrl), {
+          status: moduleResponse.status,
+          body: moduleResponse.body,
+        })
+        if (!moduleResponse.body) {
+          res.status(404).send({
+            code: 404,
+            data: null,
+            msg: 'Not Found',
+          })
+          return
+        }
+        if (moduleResponse.body.code == '301')
+          moduleResponse.body.msg = '需要登录'
+        res.append('Set-Cookie', moduleResponse.cookie)
+        res.status(moduleResponse.status).send(moduleResponse.body)
+      }
+    })
+  }
+
+  return app
+}
+
+/**
+ * Serve the NCM API.
+ * @param {NcmApiOptions} options
+ * @returns {Promise<import('express').Express & ExpressExtension>}
+ */
+async function serveNcmApi(options) {
+  const port = Number(options.port || process.env.PORT || '3000')
+  const host = options.host || process.env.HOST || ''
+
+  const checkVersionSubmission =
+    options.checkVersion &&
+    checkVersion().then(({ npmVersion, ourVersion, status }) => {
+      if (status == VERSION_CHECK_RESULT.NOT_LATEST) {
+        console.log(
+          `最新版本: ${npmVersion}, 当前版本: ${ourVersion}, 请及时更新`,
+        )
+      }
+    })
+  const constructServerSubmission = consturctServer()
+
+  const [_, app] = await Promise.all([
+    checkVersionSubmission,
+    constructServerSubmission,
+  ])
+
+  /** @type {import('express').Express & ExpressExtension} */
+  const appExt = app
+  appExt.server = app.listen(port, host, () => {
+    console.log(`server running @ http://${host ? host : 'localhost'}:${port}`)
+  })
+
+  return appExt
+}
+
+module.exports = serveNcmApi