Merge pull request #8 from AnoldGH/haotian/main

Separated token utilities and unified spotify router

backend/routes/spotifyRouter.js

@@ -1,7 +1,25 @@
 const express = require("express");
 const router = express.Router();
 const axios = require("axios");
-const { getAccessToken } = require("./spotifyAuth");
+const { getAccessToken } = require("../utility/tokenManager");
+
+// Get spotify access token with client credentials flow
+//  see https://developer.spotify.com/documentation/web-api/tutorials/client-credentials-flow
+router.get('/token', async (req, res) => {
+  try {
+      const accessToken = await getAccessToken()
+      res.json({
+          success: true,
+          access_token: accessToken
+      })
+  } catch (error) {
+      res.status(500).json({
+          success: false,
+          message: "Failed to retrieve access token",
+          details: error.message
+      })
+  }
+})
 
 // Get track from track ID
 router.get("/track/:id", async (req, res) => {

backend/server.js

@@ -5,7 +5,6 @@ const validator = require('validator');
 const http = require('http');
 const socketIo = require('socket.io');
 const cron = require('node-cron');
-const spotifyAuth = require('./routes/spotifyAuth.js').router
 const spotifyRouter = require('./routes/spotifyRouter.js')
 
 const app = express();
@@ -19,7 +18,7 @@ const db = require('./db.js');
 
 // Routes
 // --- Spotify access token
-app.use('/api', spotifyAuth)
+app.use('/api/spotify', spotifyRouter)
 // spotify song routes
 app.use('/songModel', spotifyRouter)
 

backend/utility/tokenManager.js

@@ -0,0 +1,114 @@
+const express = require('express')
+const query = require('querystring')
+const axios = require('axios')
+
+// Client ID and Secret
+require("dotenv").config()
+const CLIENT_ID = process.env.REACT_APP_SPOTIFY_CLIENT_ID
+const CLIENT_SECRET = process.env.REACT_APP_SPOTIFY_CLIENT_SECRET
+
+// Spotify Access Token
+let accessToken = ""
+let tokenExpires = 0        // when the token expires, milliseconds UTC
+let refreshTimeout = null   // timeout for the next refresh
+
+// Max Retries to get Token
+const PRELOAD_INT = 300000      // refresh PRELOAD_INT milliseconds before actual token expiration
+const MAX_RETRIES = 10          // max retries when asking spotify server for an access token
+
+// Fetch the access token
+//  returns (access_token, expires_in) or throws an error
+const fetchToken = async() => {
+    console.log("Started to fetch token")
+
+    const authOptions = {
+        method: 'post',
+        url: 'https://accounts.spotify.com/api/token',
+        headers: {
+            'Authorization': 'Basic ' + (new Buffer.from(CLIENT_ID + ':' + CLIENT_SECRET).toString('base64')),
+            'Content-Type': 'application/x-www-form-urlencoded'
+        },
+        data: query.stringify({
+            grant_type: 'client_credentials'
+        }),
+        json: true
+    }
+
+    console.log("Formed authOptions")
+
+    try {
+        const response = await axios(authOptions)
+
+        console.log("Fetched token: ", response.data)
+        return [response.data.access_token, response.data.expires_in]
+    } catch(error) {
+        console.log("Failed to retrieve token")
+        if (error.response) {
+            console.log(error.response.data)
+            console.log(error.response.status)
+            console.log(error.response.headers)
+        } else if (error.request) {
+            console.log(error.request)
+        } else {
+            console.log("Error", error.message)
+        }
+        console.log(error.config)
+        throw error
+    }
+}
+
+// Fetch and stores the token, along with its expiration
+const fetchAndStoreToken = async() => {
+    try {
+        let expiresIn
+        [accessToken, expiresIn] = await fetchToken()
+        tokenExpires = Date.now() + expiresIn * 1000    // converts seconds to milliseconds UTC
+        scheduleTokenRefresh(expiresIn)                 // schedule a refresh
+        return accessToken
+    } catch(error) {
+        console.log("Error fetching and storing token")
+        throw error
+    }
+}
+
+// Schedule a token refresh to occur after expires_in seconds
+const scheduleTokenRefresh = (expiresIn) => {
+    console.log(`Scheduling token-refresh in ${expiresIn * 1000 - PRELOAD_INT} milliseconds`)
+
+    // Clear existing timeout event
+    if (refreshTimeout) {
+        clearTimeout(refreshTimeout)
+    }
+
+    // Schedule a new timeout event
+    refreshTimeout = setTimeout(fetchAndStoreToken, expiresIn * 1000 - PRELOAD_INT)
+}
+
+// Get access token
+//  automaticlaly get a new one if token already timeout
+const getAccessToken = async() => {
+    console.log("Getting request for Spotify access token")
+
+    // Get new token if don't have one / token expired
+    if (!accessToken || Date.now() >= tokenExpires) {
+        console.log("Retrieving new access token")
+
+        let count = 0
+        while (true) {
+            try {
+                console.log(`Retry: ${count} times...`)
+                await fetchAndStoreToken()
+                break
+            } catch(error) {
+                // TODO: handling error
+                if (++count == MAX_RETRIES) throw error
+            }
+        }
+    }
+    console.log(`Returning access token ${accessToken}`)
+    return accessToken
+}
+
+module.exports = {
+    getAccessToken
+}

frontend/src/App.js

@@ -47,7 +47,7 @@ function App() {
             value={selectedGenre}
             onChange={(e) => setSelectedGenre(e.target.value)}
           >
-            <option value="" 
+            <option value=""
               disabled>Choose Genre
             </option>
             <option value="pop">Pop</option>