Add Sprint 3 task: off-the-shelf middleware version

Author: ebrahimbeiati

middleware-off-the-shelf/.gitignore

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+node_modules

middleware-off-the-shelf/app.js

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+import express from "express";
+import usernameMiddleware from "./middleware/usernameMiddleware.js";
+
+const app = express();
+app.use(express.json());
+
+function jsonArrayValidator(req, res, next) {
+  const body = req.body;
+
+  if (!Array.isArray(body)) {
+    return res.status(400).send("Bad Request: Expected a JSON array.");
+  }
+
+  const allStrings = body.every((item) => typeof item === "string");
+  if (!allStrings) {
+    return res
+      .status(400)
+      .send("Bad Request: All items in the array must be strings.");
+  }
+  req.subjects = body;
+  next();
+}
+
+app.post("/", usernameMiddleware, jsonArrayValidator, (req, res) => {
+  const username = req.username;
+  const subjects = req.subjects;
+
+  const authMessage = username
+    ? `You are authenticated as ${username}!`
+    : "You are not authenticated.";
+
+  const count = subjects.length;
+  const list = subjects.join(", ");
+
+  let subjectMessage;
+  if (count === 0) {
+    subjectMessage = "You have no subjects.";
+  } else if (count === 1) {
+    subjectMessage = `You have 1 subject: ${list}.`;
+  } else {
+    subjectMessage = `You have ${count} subjects: ${list}.`;
+  }
+  res.send(`${authMessage} ${subjectMessage}`);
+});
+
+app.listen(3000, () => {
+  console.log("Off-the-shelf server is running on port 3000");
+});

middleware-off-the-shelf/middleware/usernameMiddleware.js

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+export default function usernameMiddleware(req, res, next) {
+  const username = req.header("X-Username");
+  req.username = username ?? null;
+  next();
+}