implemented backend validation for valid email and domain

backend/package.json

@@ -38,6 +38,7 @@
     "db-migrate": "^0.11.11",
     "db-migrate-pg": "^1.2.2",
     "dotenv": "^16.0.3",
+    "email-validator": "^2.0.4",
     "express": "^4.17.1",
     "express-rate-limit": "^7.2.0",
     "express-validator": "^7.0.1",

backend/src/middleware/emailValidator.test.ts

@@ -0,0 +1,45 @@
+import { isValidEmail } from './emailValidator'; 
+import dns from 'dns';
+
+jest.mock('dns');
+
+const mockedDns = dns as jest.Mocked<typeof dns>;
+
+describe('isValidEmail Function', () => {
+
+    afterEach(() => {
+        jest.resetAllMocks();
+    });
+
+    test('should return false for an invalid email format', async () => {
+        const result = await isValidEmail('invalid-email');
+        expect(result).toBe(false);
+    });
+
+    test('should return true for a valid email with MX records', async () => {
+        mockedDns.resolveMx.mockImplementation((domain, callback) => {
+            callback(null, [{ exchange: 'mail.google.com', priority: 10 }]);
+        });
+
+        const result = await isValidEmail('[email protected]');
+        expect(result).toBe(true);
+    });
+
+    test('should return false for a valid email but no MX records', async () => {
+        mockedDns.resolveMx.mockImplementation((domain, callback) => {
+            callback(null, []);
+        });
+
+        const result = await isValidEmail('[email protected]');
+        expect(result).toBe(false);
+    });
+
+    test('should return false for a domain with an error during MX lookup', async () => {
+        mockedDns.resolveMx.mockImplementation((domain, callback) => {
+            callback(new Error('Domain not found'), []);
+        });
+
+        const result = await isValidEmail('[email protected]');
+        expect(result).toBe(false);
+    });
+});

backend/src/middleware/emailValidator.ts

@@ -0,0 +1,33 @@
+import dns from 'dns';
+import * as EmailValidator from 'email-validator';
+
+export const isValidEmail = async (email: string): Promise<boolean> => {
+    if (!EmailValidator.validate(email)) {
+        console.log("Invalid email format");
+        return false;
+    }
+
+    try {
+        const isValidDomain = await validateDomainMX(email);
+        return isValidDomain;
+    } catch (error) {
+        console.error("Error during MX record validation:", error);
+        return false;
+    }
+};
+
+const validateDomainMX = (email: string): Promise<boolean> => {
+    const domain = email.split('@')[1];
+    return new Promise((resolve) => {
+        dns.resolveMx(domain, (err, addresses) => {
+            if (err || addresses.length === 0) {
+                console.log(`Invalid domain or no MX records for: ${domain}`);
+                resolve(false);
+            } else {
+                console.log(`Valid MX records found for ${domain}:`, addresses);
+                resolve(true);
+            }
+        });
+    });
+};
+