chnaging to to express.json() and updating curl request format

Author: SaraTahir28

builtinmiddleware/index.js

@@ -0,0 +1,47 @@
+/*
+Removed custom middleware that manually parsed raw text bodies
+Enabled Express’s built‑in JSON parser
+Updated validation middleware to work with parsed JSON
+Fixed curl command by switching Content-Type 
+to application/json (using: curl -X POST http://localhost:3000/subjects 
+-H "Content-Type: application/json"
+-H "X-Username: Ahmed"
+--data '["Bees"]')
+*/
+import express from "express";
+const app = express();
+app.use(express.json()); // express builtin JSON parser
+
+
+// Middleware - Extracting username 
+
+function usernameMiddleware(req, res, next){ //middleware always has three parameters. req from client, res you send back and a next function that passes controls to next middleware
+    const userName = req.header("X-Username"); //getting a custom HTTP Header from the request 
+    req.userName = userName || null; //if username is not presnet store null
+    next(); // this passes control to the next middleware.
+}
+
+
+app.post("/subjects",usernameMiddleware, (req, res) => { 
+    const userName = req.userName; 
+    const subjects = req.body; 
+    const count = subjects.length;
+    const authMessage = userName ? `You are authenticated as ${userName}.` : `You are not authenticated.`;
+// Subject message
+  let subjectMessage;
+  if (count === 0) {
+    subjectMessage = "You have requested information about 0 subjects.";
+  } else if (count === 1) {
+    subjectMessage = `You have requested information about 1 subject: ${subjects[0]}.`;
+  } else {
+    subjectMessage = `You have requested information about ${count} subjects: ${subjects.join(", ")}.`;
+  }
+
+  // Send final response
+  res.send(`${authMessage}\n\n${subjectMessage}`);
+});
+
+const PORT = 3000
+app.listen(PORT, () => {
+    console.log(`Server running on http://localhost:${PORT}`)
+});