NestJS Google Pubsub Connector

This package includes two pieces, a NestJS microservice strategy as well as a client proxy. Together this enable easy integration with Google PubSub in a NestJS-y way.

Features

• Seamlessly integrate your subscription listeners as controllers in the robust NestJS framework!
• Creates subscriptions on demand, with self-service naming strategies!
• A "just-works" approach means that zero configuration is needed out of the box, just insert the strategy and let the framework do the rest.
• Oh-so Extensible:
  • Subscription naming strategies let you dynamically name subscriptions how you want to!
  • Ack/nack strategies let you decouple your business logic from how you respond to messages!
• Decorators! Decorators!! Decorators!!!

Microservice Strategy

The server/transport strategy component is inserted as a strategy when creating a microservice, taking a few configuration parameters, as well as an optional PubSub instance, like so:

async function bootstrap() {
    const app: INestMicroservice = await NestFactory.createMicroservice<MicroserviceOptions>(
        ExampleModule,
        {
            strategy: new GooglePubSubTransport({
                createSubscriptions: true,
                // The microservice will configure its own PubSub instance, but you're free to
                // supply your own
                // client: new PubSub()
            }),
        },
    );

    // It's also possible to connect as a hybrid app:
    // const app = await NestFactory.create(HttpAppModule);
    // const microservice = app.connectMicroservice({
    //      strategy: new GooglePubSubTransport({
    //          createSubscriptions: true,
    //          // The microservice will configure its own PubSub instance, but you're free to
    //          // supply your own
    //          // client: new PubSub
    //      }),
    // });

    return app.listen(() => {
        console.log('example app started!');
    });
}
bootstrap();

With just the configuration above you can have working controllers responding to messages in minutes.

Decorators

Parameter decorators are one of the best ease-of-use features in NestJS, and this library offers a few that will make parsing PubSub Messages easy, simple and fun:

Name	Desscription
@GooglePubSubMessageHandler	Takes a subscription name and optionally a topic name. A subscription will be created if it does not already exits if: a topic name is supplied and createSubscriptions was set to true when the microservice was created
@GooglePubSubMessageBody	This will retrieve and JSON.parse() the body of the incoming message. You may optionally include a key and the corresponding value will be returned.
@GooglePubSubMessageAttributes	This will retrieve attributes of the incoming message. You may optionally include a key, and the corresponding value will be returned.
@Ack	This will return a function that will ack the incoming message. N.B. this will disable any auto-acking.
@Nack	Same as above, but for nacking.

Subscription creation

If createSubscriptions is set as true on transporter setup, then the service will attempt to create a new subscription if the requested subscription for a handler is not already present.The microservice takes a subscriptionNamingStrategy as an argument, which expects a class conforming to the SubscriptionNamingStrategy interface. A basic strategy is included by default:

import {
  SubscriptionNamingStrategy
} from '@flosports/nestjs-google-pubsub-microservice';
import { NamingDependencyTag, SubscriptionNameDependencies } from './interfaces';

export class BasicSubscriptionNamingStrategy
        implements SubscriptionNamingStrategy {
  public generateSubscriptionName(
          deps: SubscriptionNameDependencies
  ): string {
    switch (deps._tag) {
      case NamingDependencyTag.TOPIC_AND_SUBSCRIPTION_NAMES:
      case NamingDependencyTag.SUBSCRIPTION_NAME_ONLY:
        return deps.subscriptionName;
      case NamingDependencyTag.TOPIC_NAME_ONLY:
        return `${deps.topicName}-sub`;
    }
  }
}

The string returned from this strategy will be used as the name for the created subscription.

Acking and Nacking

In the interest of giving you, the user, the power over your own destiny this library takes both a hands-off and "just works" approach to acking and nacking messages. This is accomplished through "strategies" confirming to the AckStrategy, NackStrategy interfaces which are supplied at transport creation.

Ack Strategies

Ack strategies are guaranteed to run after a handler completes successfully, and expose functions for acking and nacking the message, as well as the messages GooglePubSubContext. The default is shown in the example below:

import { GooglePubSubContext } from '../ctx-host';
import { AckFunction, AckStrategy, NackFunction } from '../interfaces';

export class BasicAckStrategy implements AckStrategy {
    public ack(ack: AckFunction, nack: NackFunction, ctx: GooglePubSubContext): Promise<void> {
        if (ctx.getAutoAck()) {
            ack();
        }
        return Promise.resolve();
    }
}

The flow here is simple, if autoAck is set to true then this message will be acked and the function will return.

Nack Strategies

Nack strategies are guaranteed to run if any error is thrown from the handler.
N.B. This will occur after exception filters.
The signature is the same as an ack strategies with the exception of the thrown Error (pun intended) being included as the first argument. The default is shown below:

import { GooglePubSubContext } from '../ctx-host';
import { AckFunction, NackFunction, NackStrategy } from '../interfaces';

export class BasicNackStrategy implements NackStrategy {
    public nack(
        error: Error,
        ack: AckFunction,
        nack: NackFunction,
        ctx: GooglePubSubContext,
    ): Promise<void> {
        if (ctx.getAutoNack()) {
            nack();
        }
        return Promise.resolve();
    }
}

No strategy/hybrid acking and nacking

In addition to using these strategies, the library also makes available ack and nack functions through decorators to the controller as well as from the GooglePubSubContext. When ack or nack functions are retrieved from the context (either directly or through the decorator) the autoAck/autoNack methods will return false, disabling the basic strategies and optionally any strategies you should choose to create.

Usage

// src/main.ts
import { NestFactory } from '@nestjs/core';
import {
    GooglePubSubTransport
} from '@flosports/nestjs-google-pubsub-microservice';
import { TestModule } from './test.module';

async function bootstrap() {
    const app = await NestFactory.createMicroservice(TestModule, {
        strategy: new GooglePubSubTransport({
            createSubscriptions: true,
            // The microservice will configure its own PubSub instance, but you're free to
            // supply your own
            // client: new PubSub
        }),
    });
    return app.listen(() => {
        console.log('app started!');
    });
}
bootstrap();

// src/test.module.ts
import { Module } from "@nestjs/common";
import { TestController } from "./test.controller";

@Module({
    controllers: [TestController],
})
export class TestModule {
}

// src/test.controller.ts
import { Controller } from '@nestjs/common';
import {
    GooglePubSubMessageBody,
    GooglePubSubMessageHandler
} from '@flosports/nestjs-google-pubsub-microservice';
@Controller()
export class TestController {
    constructor(
        private readonly diService: DiService;
    ) { }
    @GooglePubSubMessageHandler({
        subscriptionName: 'my-existing-subscription',
    })
    public handler1(@GooglePubSubMessageBody() data: { foo: boolean }): void {
        return this.diService.handleFoo(data);
    }

    @GooglePubSubMessageHandler({
        subscriptionName: 'my-subscription-that-or-may-not-exist',
        topicName: 'my-existing-topic'
    })
    public handler2(@GooglePubSubMessageBody('bar') bar:  boolean ): void {
        return this.diService.handleBar(data);
    }
}

Client Proxy

This library also provides a basic client proxy that wraps a PubSub instance.

This proxy supports:

• Publishing
• Topic/Subscription creation
• Topic/Subscription deletion

You can find a number of working examples in the examples directory.

Usage

import {
    ClientGooglePubSub
} from '@flosports/nestjs-google-pubsub-microservice';

const msg = 'beam me up scotty';

new ClientGooglePubSub()
    .publishToTopic(
        'my-test-topic',
        Buffer.from(msg),
    );

Authentication

In keeping with the hand-off "just works" approach in this library, authentication is handled entirely by the underlying PubSub client. This means that the credentials pointed to by the GOOGLE_APPLICATION_CREDENTIALS will be used, as well as emulator support if PUBSUB_EMULATOR_HOST is set. If you need a more advanced configuration, then both the transport strategy and the client proxy will take a PubSub client instance as a constructor parameter - you can simply build the client you need and then hand it off.

Examples

A working example server can be found in the examples directory.

Prerequisites for running the example server

In order to run the example server you must either:

• Have GOOGLE_APPLICATION_CREDENTIALS set in your environment, and pointed to a valid credentials, or
• Have a running PubSub emulator and have PUBSUB_EMULATOR_HOST set in your environment

In both cases you will need to create any topics present in the example server (or change them to topics) that already exist.

Running the example server

To run the server, simply invoke the provided npm script:

npm run example:server

Assuming all prerequisites are met you should see something like the following:

> @flosportsinc/nestjs-google-pubsub-connector@0.0.0-development example:server /Users/haroldwaters/repos/nestjs-google-pubsub-transport
> node --inspect -r ts-node/register examples/server/main.ts

Debugger listening on ws://127.0.0.1:9229/d23772bb-0e6d-40f8-b47d-d0fc94c7c8c2
For help, see: https://nodejs.org/en/docs/inspector
[Nest] 90792   - 04/17/2021, 7:04:02 PM   [NestFactory] Starting Nest application...
[Nest] 90792   - 04/17/2021, 7:04:02 PM   [InstanceLoader] ExampleService dependencies initialized +28ms
[Nest] 90792   - 04/17/2021, 7:04:02 PM   [InstanceLoader] ExampleModule dependencies initialized +0ms
[Nest] 90792   - 04/17/2021, 7:04:02 PM   [NestMicroservice] Nest microservice successfully started +5ms
[Nest] 90792   - 04/17/2021, 7:04:02 PM   [GooglePubSubTransport] Mapped {projects/flosports-174016/subscriptions/lee-christmas-notifications} handler
example app started!