middleware

Author: delmorallopez

existingMiddleware.js

@@ -0,0 +1,60 @@
+const express = require("express");
+const app = express();
+
+// Use built-in JSON middleware 
+app.use(express.json()); // Read the request body, parses it as JSON, automatically sets req.body, rejects invalid JSON with 400
+
+/**
+ * Middleware 1:
+ * Read X-Username header and attach it to req.username
+ */
+const usernameMiddleware = (req, res, next) => {
+  const username = req.header("X-Username");
+  req.username = username ? username : null;
+  next();
+};
+
+/**
+ * Middleware 2 (validation only):
+ * Ensure body is an array of strings
+ */
+
+// We still need to validate the shape of the data
+const validateStringArrayBody = (req, res, next) => {
+  if (!Array.isArray(req.body)) {
+    return res.status(400).send("Request body must be a JSON array");
+  }
+
+  if (!req.body.every(item => typeof item === "string")) {
+    return res.status(400).send("Array must contain only strings");
+  }
+
+  next();
+
+};
+
+/**
+ * POST endpoint
+ */
+
+
+
+app.post(
+  "/",
+  usernameMiddleware,
+  validateStringArrayBody,
+  (req, res) => {
+    const username = req.username ?? "Anonymous";
+    const subjects = req.body;
+
+    res.send(
+`You are authenticated as ${username}.
+
+You have requested information about ${subjects.length} subjects: ${subjects.join(", ")}.`
+    );
+  }
+);
+
+app.listen(3000, () => {
+  console.log("Server running on port 3000");
+});

middleware.js

@@ -0,0 +1,71 @@
+const express = require("express");
+const app = express();
+
+/**
+ * Middleware 1:
+ * Read X-Username header and attach it to req.username
+ */
+const usernameMiddleware = (req, res, next) => {
+  const username = req.header("X-Username");
+  req.username = username ? username : null;
+  next();
+};
+
+
+/**
+ * Middleware 2:
+ * Parse POST body as JSON array of strings
+ */
+const jsonArrayMiddleware = (req, res, next) => {
+  let rawBody = "";
+
+  req.on("data", chunk => {
+    rawBody += chunk;
+  });
+
+  req.on("end", () => {
+    let parsed;
+
+    try {
+      parsed = JSON.parse(rawBody);
+    } catch {
+      return res.status(400).send("Request body must be valid JSON");
+    }
+
+    if (!Array.isArray(parsed)) {
+      return res.status(400).send("Request body must be a JSON array");
+    }
+
+    if (!parsed.every(item => typeof item === "string")) {
+      return res.status(400).send("Array must contain only strings");
+    }
+
+    req.body = parsed;
+    next();
+  });
+};
+
+
+
+/**
+ * POST endpoint
+ */
+app.post(
+  "/",
+  usernameMiddleware,
+  jsonArrayMiddleware,
+  (req, res) => {
+    const username = req.username ?? "Anonymous";
+    const subjects = req.body;
+
+    res.send(
+`You are authenticated as ${username}.
+
+You have requested information about ${subjects.length} subjects: ${subjects.join(", ")}.`
+    );
+  }
+);
+
+app.listen(3000, () => {
+  console.log("Server running on port 3000");
+});