London | 25-SDC-Nov | Emiliano Uruena | Sprint 3 | Decomposition Middleware

.gitignore

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+/node_modules
+package-lock.json

middlewares/middleware.js

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+const express = require('express');
+const app = express();
+
+// middleware for  x-user header
+const usernameMiddleware = (req,res,next) => {
+    const usernameHeader = req.get('X-Username');
+    // if exists, set if, otherwise set to null
+    req.username = usernameHeader || null;
+    next();
+};
+
+// middleware for body parsing and validation
+
+app.use(express.text({ type: 'application/json'}));
+
+const validateArrayMiddleware = (req, res, next) => {
+
+    try {
+        // attempt to parse the raw text body
+        const data = JSON.parse(req.body);
+
+        //check if it is an array AND every element is a string
+        const isStringArray = Array.isArray(data) && data.every(item => typeof item === 'string');
+         if (!isStringArray){
+            return res.status(400).send("invalid input: body must be JSON array of strings");
+         }
+
+         // attach the parsed array to req.body for next handler
+         req.body = data;
+         next();       
+    } catch (error){
+        return res.status(400).send("invalid JSON format");
+    }
+};
+ // Applying the middlewares to the POST endpoint
+
+ app.post('/subjects', usernameMiddleware, validateArrayMiddleware, (req,res) => {
+    const userText = req.username
+    ? `You are authenticated as ${req.username}.`
+    : "Your are not authenticated.";
+
+    const subjectCount = req.body.length;
+    const subjectList = req.body.join(', ');
+    const subjectSuffix = subjectCount === 1 ? 'subject' : 'subjects';
+
+    const subjectsText = `You have requested information about ${subjectCount} ${subjectSuffix} ${subjectCount > 0 ? ': ' + subjectList : ''}.`;
+
+    res.send(`${userText}\n\n${subjectsText}`);
+ }
+);
+
+app.listen(3000, () => console.log('server running on http://localhost:3000'));

off-the-shelf-middleware/built-in-middleware.js

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+const express = require('express');
+const app = express();
+
+app.use(express.json());
+
+// middleware for  x-user header
+const usernameMiddleware = (req,res,next) => {
+    const usernameHeader = req.get('X-Username');
+    // if exists, set if, otherwise set to null
+    req.username = usernameHeader || null;
+    next();
+};
+
+// middleware for body parsing and validation
+
+app.use(express.text({ type: 'application/json'}));
+
+const validateArrayMiddleware = (req, res, next) => {
+    // express.json() did the parsing, so..
+    const data = req.body;
+
+    //check if it is an array AND every element is a string
+    const isStringArray = Array.isArray(data) && data.every(item => typeof item === 'string');
+        if (!isStringArray){
+        return res.status(400).send("invalid input: body must be JSON array of strings");
+        }
+        next();       
+};
+ // Applying the middlewares to the POST endpoint
+
+ app.post('/subjects', usernameMiddleware, validateArrayMiddleware, (req,res) => {
+    const userText = req.username
+    ? `You are authenticated as ${req.username}.`
+    : "Your are not authenticated.";
+
+    const subjectCount = req.body.length;
+    const subjectList = req.body.join(', ');
+    const subjectSuffix = subjectCount === 1 ? 'subject' : 'subjects';
+
+    const subjectsText = `You have requested information about ${subjectCount} ${subjectSuffix} ${subjectCount > 0 ? ': ' + subjectList : ''}.`;
+
+    res.send(`${userText}\n\n${subjectsText}`);
+ }
+);
+
+app.listen(3000, () => console.log('server running on http://localhost:3000'));

package.json

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+{
+  "dependencies": {
+    "express": "^5.2.1"
+  }
+}