Add Express middleware exercise using built-in middleware

Author: AliQassab

sprint3_exercises/middleware-existing.js

@@ -0,0 +1,50 @@
+import express from "express";
+
+const app = express();
+const PORT = 3000;
+
+// Middleware 1: Extract username from X-Username header
+function extractUsername(req, res, next) {
+  const username = req.headers["x-username"];
+  req.username = username || null;
+  next();
+}
+
+// Use built-in Express JSON middleware instead of custom one
+app.use(extractUsername);
+app.use(express.json());
+
+app.post("/", (req, res) => {
+  // Validate that body is an array
+  if (!Array.isArray(req.body)) {
+    return res.status(400).send("Request body must be a JSON array");
+  }
+
+  // Check if all elements are strings
+  const allStrings = req.body.every((item) => typeof item === "string");
+  if (!allStrings) {
+    return res.status(400).send("All array elements must be strings");
+  }
+
+  const authMessage = req.username
+    ? `You are authenticated as ${req.username}.`
+    : "You are not authenticated.";
+
+  const count = req.body.length;
+  let subjectsMessage;
+  if (count === 0) {
+    subjectsMessage = "You have requested information about 0 subjects.";
+  } else if (count === 1) {
+    subjectsMessage = `You have requested information about 1 subject: ${req.body[0]}.`;
+  } else {
+    subjectsMessage = `You have requested information about ${count} subjects: ${req.body.join(
+      ", "
+    )}.`;
+  }
+
+  res.send(`${authMessage}\n\n${subjectsMessage}\n`);
+});
+
+app.listen(PORT, () => {
+  console.log(`Server running on http://localhost:${PORT}`);
+});