refactoring with existing middleware.

Author: eyuell21

Off-the-shelf middleware/script.js

@@ -0,0 +1,40 @@
+import express from 'express';
+const app = express();
+
+// Built-in middleware to parse JSON bodies
+app.use(express.json());
+
+// Middleware 1: Extract username from header or set to null
+function usernameMiddleware(req, res, next) {
+  const username = req.header('X-Username');
+  req.username = username || null;
+  next();
+}
+
+app.post('/info', usernameMiddleware, function(req, res) {
+  // req.body is now automatically parsed by express.json()
+  if (
+    !Array.isArray(req.body) ||
+    !req.body.every(function(item) { return typeof item === 'string'; })
+  ) {
+    return res.status(400).send('Invalid body: must be JSON array of strings');
+  }
+
+  const authMessage = req.username
+    ? 'You are authenticated as ' + req.username + '.'
+    : 'You are not authenticated.';
+
+  const count = req.body.length;
+  const subjects = req.body.join(', ');
+  const subjectWord = count === 1 ? 'subject' : 'subjects';
+  const subjectMessage = count
+    ? 'You have requested information about ' + count + ' ' + subjectWord + ': ' + subjects + '.'
+    : 'You have requested information about 0 subjects.';
+
+  res.send(authMessage + '\n\n' + subjectMessage);
+});
+
+const PORT = 3000;
+app.listen(PORT, function() {
+  console.log('Server running on http://localhost:' + PORT);
+});