Initialize Express app, add PORT env fallback, harden JSON parsing, add route and start server

- Create Express app instance and use PORT from process.env with 3000 fallback.
- Add try/catch around JSON.parse in array middleware and return 400 on invalid JSON.
- Add POST "/" route that composes response using usernameMiddleware and arrayMiddleware.
- Start server with app.listen.

Author: Iswanna

middleware-exercise/app.js

@@ -1,5 +1,9 @@
 import express from "express";
 
+const app = express();
+
+const PORT = process.env.PORT ? parseInt(process.env.PORT, 10) : 3000;
+
 const usernameMiddleware = (req, res, next) => {
   const headerValue = req.get("X-username");
 
@@ -24,7 +28,13 @@ const arrayMiddleware = (req, res, next) => {
   req.on("end", () => {
     const bodyString = String.fromCharCode(...bodyBytes);
 
-    const bodyObject = JSON.parse(bodyString);
+    let bodyObject;
+    try {
+      bodyObject = JSON.parse(bodyString);
+    } catch (error) {
+      res.status(400).send("Invalid JSON");
+      return;
+    }
 
     if (
       Array.isArray(bodyObject) &&
@@ -41,3 +51,32 @@ const arrayMiddleware = (req, res, next) => {
     }
   });
 };
+
+// Hey Express, whenever a POST request arrives at '/', please call this person first (usernameMiddleware), then this person (arrayMiddleware), then finally do the route logic.
+app.post("/", usernameMiddleware, arrayMiddleware, (req, res) => {
+  let authPart;
+  if (req.username) {
+    authPart = `You are authenticated as ${req.username}`;
+  } else {
+    authPart = "You are not authenticated";
+  }
+  const MessageCount = req.body.length;
+
+  const messageJoined = req.body.join(",");
+
+  const word = MessageCount <= 1 ? "subject" : "subjects";
+
+  if (MessageCount > 0) {
+    res.send(
+      `${authPart}\n\nYou have requested information about ${MessageCount} ${word}: ${messageJoined}.`,
+    );
+  } else {
+    res.send(
+      `${authPart}\n\nYou have requested information about ${MessageCount} ${word}.`,
+    );
+  }
+});
+
+app.listen(PORT, () => {
+  console.log("Type your message here");
+});