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ILshat Khamitov
ILshat Khamitov

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Getting server time via WebSockets and displaying It in Angular application

#angular #websockets #nestjsmod #fullstack

In this post I will describe how to create a web socket stream in the backend on NestJS and subscribe to it from the frontend application on Angular.

1. Install additional libraries

Install NestJS modules to work with websockets.

Commands

npm install --save @nestjs/websockets @nestjs/platform-socket.io @nestjs/platform-ws
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Console output 
$ npm install --save @nestjs/websockets @nestjs/platform-socket.io @nestjs/platform-ws

added 4 packages, removed 2 packages, and audited 2938 packages in 1m

360 packages are looking for funding
  run `npm fund` for details

42 vulnerabilities (21 low, 3 moderate, 18 high)

To address issues that do not require attention, run:
  npm audit fix

To address all issues possible (including breaking changes), run:
  npm audit fix --force

Some issues need review, and may require choosing
a different dependency.

Run `npm audit` for details.
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2. Create a controller that returns server time

The controller has a method for issuing the current time and a web socket that returns the current backend time every second.

Create a file apps/server/src/app/time.controller.ts

import { Controller, Get } from '@nestjs/common';

import { AllowEmptyUser } from '@nestjs-mod/authorizer';
import { ApiOkResponse } from '@nestjs/swagger';
import { OnGatewayConnection, SubscribeMessage, WebSocketGateway, WsResponse } from '@nestjs/websockets';
import { interval, map, Observable } from 'rxjs';

export const ChangeTimeStream = 'ChangeTimeStream';

@AllowEmptyUser()
@WebSocketGateway({
  cors: {
    origin: '*',
  },
  path: '/ws/time',
  transports: ['websocket'],
})
@Controller()
export class TimeController implements OnGatewayConnection {
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  handleConnection(client: any, ...args: any[]) {
    client.headers = args[0].headers;
  }

  @Get('/time')
  @ApiOkResponse({ type: Date })
  time() {
    return new Date();
  }

  @SubscribeMessage(ChangeTimeStream)
  onChangeTimeStream(): Observable<WsResponse<Date>> {
    return interval(1000).pipe(
      map(() => ({
        data: new Date(),
        event: ChangeTimeStream,
      }))
    );
  }
}
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3. Adding a controller to AppModule

Since the controller also includes the gateway logic, we provide the controller in the controllers and providers sections.

Updating the file apps/server/src/app/app.module.ts

import { createNestModule, NestModuleCategory } from '@nestjs-mod/common';

import { WebhookModule } from '@nestjs-mod-fullstack/webhook';
import { PrismaModule } from '@nestjs-mod/prisma';
import { ServeStaticModule } from '@nestjs/serve-static';
import { join } from 'path';
import { AppController } from './app.controller';
import { AppService } from './app.service';
import { TimeController } from './time.controller';

export const { AppModule } = createNestModule({
  moduleName: 'AppModule',
  moduleCategory: NestModuleCategory.feature,
  imports: [
    WebhookModule.forFeature({
      featureModuleName: 'app',
    }),
    PrismaModule.forFeature({
      contextName: 'app',
      featureModuleName: 'app',
    }),
    ...(process.env.DISABLE_SERVE_STATIC
      ? []
      : [
          ServeStaticModule.forRoot({
            rootPath: join(__dirname, '..', 'client', 'browser'),
          }),
        ]),
  ],
  controllers: [AppController, TimeController],
  providers: [AppService, TimeController],
});
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4. Rebuilding SDK for frontend and tests

Commands

npm run generate
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5. Adding a utility for convenient work with web sockets from an Angular application

Create a file libs/common-angular/src/lib/utils/web-socket.ts

import { Observable, finalize } from 'rxjs';

export function webSocket<T>({
  address,
  eventName,
  options,
}: {
  address: string;
  eventName: string;
  // eslint-disable-next-line @typescript-eslint/no-explicit-any
  options?: any;
}) {
  const wss = new WebSocket(address.replace('/api', '').replace('http', 'ws'), options);
  return new Observable<{ data: T; event: string }>((observer) => {
    wss.addEventListener('open', () => {
      wss.addEventListener('message', ({ data }) => {
        observer.next(JSON.parse(data.toString()));
      });
      wss.addEventListener('error', (err) => {
        observer.error(err);
        if (wss?.readyState == WebSocket.OPEN) {
          wss.close();
        }
      });
      wss.send(
        JSON.stringify({
          event: eventName,
          data: true,
        })
      );
    });
  }).pipe(
    finalize(() => {
      if (wss?.readyState == WebSocket.OPEN) {
        wss.close();
      }
    })
  );
}
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6. Adding retrieval and display of the current server time in the page footer

Updating the file apps/client/src/app/app.component.ts

import { AsyncPipe } from '@angular/common';
import { ChangeDetectionStrategy, Component, OnInit } from '@angular/core';
import { Router, RouterModule } from '@angular/router';
import { User } from '@authorizerdev/authorizer-js';
import { AppRestService, TimeRestService } from '@nestjs-mod-fullstack/app-angular-rest-sdk';
import { AuthService } from '@nestjs-mod-fullstack/auth-angular';
import { webSocket } from '@nestjs-mod-fullstack/common-angular';
import { UntilDestroy, untilDestroyed } from '@ngneat/until-destroy';
import { NzLayoutModule } from 'ng-zorro-antd/layout';

import { NzMenuModule } from 'ng-zorro-antd/menu';
import { NzTypographyModule } from 'ng-zorro-antd/typography';
import { BehaviorSubject, map, merge, Observable, tap } from 'rxjs';

@UntilDestroy()
@Component({
  standalone: true,
  imports: [RouterModule, NzMenuModule, NzLayoutModule, NzTypographyModule, AsyncPipe],
  selector: 'app-root',
  templateUrl: './app.component.html',
  changeDetection: ChangeDetectionStrategy.OnPush,
})
export class AppComponent implements OnInit {
  title = 'client';
  serverMessage$ = new BehaviorSubject('');
  serverTime$ = new BehaviorSubject('');
  authUser$: Observable<User | undefined>;

  constructor(private readonly timeRestService: TimeRestService, private readonly appRestService: AppRestService, private readonly authService: AuthService, private readonly router: Router) {
    this.authUser$ = this.authService.profile$.asObservable();
  }

  ngOnInit() {
    this.appRestService
      .appControllerGetData()
      .pipe(
        tap((result) => this.serverMessage$.next(result.message)),
        untilDestroyed(this)
      )
      .subscribe();

    merge(
      this.timeRestService.timeControllerTime(),
      webSocket<string>({
        address: this.timeRestService.configuration.basePath + '/ws/time',
        eventName: 'ChangeTimeStream',
      }).pipe(map((result) => result.data))
    )
      .pipe(
        tap((result) => this.serverTime$.next(result as string)),
        untilDestroyed(this)
      )
      .subscribe();
  }

  signOut() {
    this.authService
      .signOut()
      .pipe(
        tap(() => this.router.navigate(['/home'])),
        untilDestroyed(this)
      )
      .subscribe();
  }
}
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Updating the file apps/client/src/app/app.component.html

<nz-layout class="layout">
  <nz-header>
    <div class="logo flex items-center justify-center">{{ title }}</div>
    <ul nz-menu nzTheme="dark" nzMode="horizontal">
      <li nz-menu-item routerLink="/home">Home</li>
      <li nz-menu-item routerLink="/demo">Demo</li>
      @if (authUser$|async; as authUser) {
      <li nz-menu-item routerLink="/webhook">Webhook</li>
      <li nz-submenu [nzTitle]="'You are logged in as ' + authUser.email" [style]="{ float: 'right' }">
        <ul>
          <li nz-menu-item routerLink="/profile">Profile</li>
          <li nz-menu-item (click)="signOut()">Sign-out</li>
        </ul>
      </li>
      } @else {
      <li nz-menu-item routerLink="/sign-up" [style]="{ float: 'right' }">Sign-up</li>
      <li nz-menu-item routerLink="/sign-in" [style]="{ float: 'right' }">Sign-in</li>
      }
    </ul>
  </nz-header>
  <nz-content>
    <router-outlet></router-outlet>
  </nz-content>
  <nz-footer class="flex justify-between">
    <div id="serverMessage">{{ serverMessage$ | async }}</div>
    <div id="serverTime">{{ serverTime$ | async }}</div>
  </nz-footer>
</nz-layout>
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7. Create an E2E test to check the operation of time-related logics

Create a file apps/server-e2e/src/server/time.spec.ts

import { RestClientHelper } from '@nestjs-mod-fullstack/testing';
import { isDateString } from 'class-validator';
import { lastValueFrom, take, toArray } from 'rxjs';

describe('Get server time from rest api and ws', () => {
  jest.setTimeout(60000);

  const correctStringDateLength = '2024-11-20T11:58:03.338Z'.length;
  const restClientHelper = new RestClientHelper();
  const timeApi = restClientHelper.getTimeApi();

  it('should return time from rest api', async () => {
    const time = await timeApi.timeControllerTime();

    expect(time.status).toBe(200);
    expect(time.data).toHaveLength(correctStringDateLength);
    expect(isDateString(time.data)).toBeTruthy();
  });

  it('should return time from ws', async () => {
    const last3ChangeTimeEvents = await lastValueFrom(
      restClientHelper
        .webSocket<string>({
          path: '/ws/time',
          eventName: 'ChangeTimeStream',
        })
        .pipe(take(3), toArray())
    );

    expect(last3ChangeTimeEvents).toHaveLength(3);
    expect(last3ChangeTimeEvents[0].data).toHaveLength(correctStringDateLength);
    expect(last3ChangeTimeEvents[1].data).toHaveLength(correctStringDateLength);
    expect(last3ChangeTimeEvents[2].data).toHaveLength(correctStringDateLength);
    expect(isDateString(last3ChangeTimeEvents[0].data)).toBeTruthy();
    expect(isDateString(last3ChangeTimeEvents[1].data)).toBeTruthy();
    expect(isDateString(last3ChangeTimeEvents[2].data)).toBeTruthy();
  });
});
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8. We launch the infrastructure with applications in development mode and check the operation through E2E tests

Commands

npm run pm2-full:dev:start
npm run pm2-full:dev:test:e2e
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Conclusion

In the current post and project, when sending time via a web socket, there is no user authorization check and the web socket stream is available to any user, in a real application there are usually many web socket streams that check the authorization token.

Perhaps in the next posts there will be an example with authorizations, but the preparatory code is also in the current version (search for: handleConnection).

Plans

In the next post I will add handling of server validation errors on the frontend...

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