Update middleware exercise

Author: shreefAhmedM

middlewareExercise/.gitignore

@@ -0,0 +1 @@
+node_modules/

middlewareExercise/exisMiddleware.js

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+
+import express from "express";
+
+const app = express();
+
+const usernameMiddleware = (req, res, next) => {
+    req.username = req.get("X-Username") || null;
+    next();
+};
+
+const validateBodyMiddleware = (req, res, next) => {
+    if (!Array.isArray(req.body)) {
+        return res.status(400).send("Body must be a JSON array");
+    }
+
+    for (const subject of req.body) {
+        if (typeof subject !== "string") {
+            return res
+                .status(400)
+                .send("All array items must be strings");
+        }
+    }
+
+    next();
+};
+
+app.use(express.json());
+app.use(usernameMiddleware);
+app.use(validateBodyMiddleware);
+
+app.post("/", (req, res) => {
+    let authMessage;
+
+    if (req.username) {
+        authMessage =
+            `You are authenticated as ${req.username}.`;
+    } else {
+        authMessage =
+            "You are not authenticated.";
+    }
+
+    const requestedSubjects = req.body;
+    const subjectCount = requestedSubjects.length;
+
+    let responseMessage =
+        `You have requested information about ${subjectCount} subject`;
+
+    if (subjectCount !== 1) {
+        responseMessage += "s";
+    }
+
+    if (subjectCount > 0) {
+        responseMessage += `: ${requestedSubjects.join(", ")}`;
+    }
+
+    responseMessage += ".";
+
+    res.send(
+        `${authMessage}\n\n${responseMessage}\n`
+    );
+});
+
+app.listen(3000, () => {
+    console.log("Server running on port 3000");
+});