Adding middleware for extracting username and Validating JSON array body-

Author: SaraTahir28

.gitignore

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+node_modules
+package-lock.json

middleware/script.js

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+import express from "express";
+const app = express();
+app.use(express.text());
+
+//1st 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.
+}
+
+//2nd Middleware - Validating JSON array body
+function jsonArrayMiddleware(req, res, next){
+    let data;
+    try {
+    data = JSON.parse(req.body);
+} 
+catch(err){
+    return res.status(400).send("Body must be valid JSON");
+}
+if(!Array.isArray(data)){
+    return res.status(400).send("Body must be JSON array");
+
+}
+if (!data.every(item => typeof item === "string")) { //every item in the array is a string = NOT TRUE
+  return res.status(400).send("Array must contain only strings");
+}
+req.body = data; //store validated array
+next() //allows req to continue to next middleware
+}
+
+// POST route using both middlewares
+app.post("/subjects",usernameMiddleware, jsonArrayMiddleware, (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}`)
+});

package.json

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+{
+  "dependencies": {
+    "express": "^5.2.1"
+  }
+}