adding dns service

src/app.module.ts

@@ -1,9 +1,11 @@
 import { Module } from '@nestjs/common';
 import { AppController } from './app.controller';
 import { UrlShortenerModule } from './url-shortener/url-shortener.module';
+import { DnsService } from './dns/dns.service';
 
 @Module({
   imports: [UrlShortenerModule],
   controllers: [AppController],
+  providers: [DnsService],
 })
 export class AppModule {}

src/dns/dns.service.spec.ts

@@ -0,0 +1,18 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { DnsService } from './dns.service';
+
+describe('DnsService', () => {
+  let service: DnsService;
+
+  beforeEach(async () => {
+    const module: TestingModule = await Test.createTestingModule({
+      providers: [DnsService],
+    }).compile();
+
+    service = module.get<DnsService>(DnsService);
+  });
+
+  it('should be defined', () => {
+    expect(service).toBeDefined();
+  });
+});

src/dns/dns.service.ts

@@ -0,0 +1,20 @@
+import { Injectable } from '@nestjs/common';
+import * as dns from 'dns';
+import * as util from 'util';
+
+@Injectable()
+export class DnsService {
+  private lookup = util.promisify(dns.lookup);
+
+  async isValidUrl(url: string): Promise<boolean> {
+    console.log('HERE!!!')
+    try {
+      const hostname = new URL(url).hostname;
+      await this.lookup(hostname);
+      console.log('HERE!')
+      return true;
+    } catch {
+      return false;
+    }
+  }
+}

src/url-shortener/url-shortener.controller.ts

@@ -6,12 +6,12 @@ export class UrlShortenerController {
   constructor(private readonly urlShortenerService: UrlShortenerService) {}
 
   @Post('shorten')
-  shortenUrl(@Body('url') url: string): { shortUrl: string } {
+  async shortenUrl(@Body('url') url: string): Promise<{ shortUrl: string }> {
     // example route http://localhost:3000/url-shortener/shorten POST body { url: 'https://www.google.com' }
     if (!url) {
       throw new HttpException('URL is required', HttpStatus.BAD_REQUEST);
     }
-    const shortUrl = this.urlShortenerService.generateShortUrl(url);
+    const shortUrl = await this.urlShortenerService.generateShortUrl(url);
     return { shortUrl };
   }
 

src/url-shortener/url-shortener.module.ts

@@ -1,9 +1,10 @@
 import { Module } from '@nestjs/common';
 import { UrlShortenerService } from './url-shortener.service';
 import { UrlShortenerController } from './url-shortener.controller';
+import { DnsService } from '../dns/dns.service';
 
 @Module({
-  providers: [UrlShortenerService],
+  providers: [UrlShortenerService, DnsService],
-  controllers: [UrlShortenerController]
+  controllers: [UrlShortenerController],
 })
 export class UrlShortenerModule {}

src/url-shortener/url-shortener.service.ts

@@ -1,14 +1,23 @@
 import { Injectable } from '@nestjs/common';
 import * as shortid from 'shortid';
+import { DnsService } from '../dns/dns.service';
+
 
 @Injectable()
 export class UrlShortenerService {
+
   private urlMap = new Map<string, string>();
   
-  generateShortUrl(originalUrl: string): string {
+  constructor(private readonly dnsService: DnsService) {}
+
+  async generateShortUrl(originalUrl: string): Promise<string> {
     if(!originalUrl) {
       throw new Error('URL is required');
     }
+    let isValid = await this.dnsService.isValidUrl(originalUrl);
+    if(!isValid) {
+      throw new Error('URL is invalid');
+    }
     let shortUrl = shortid.generate();
     this.urlMap.set(shortUrl, originalUrl);
     return shortUrl