NestJS-Spelunker

Description

This module does a bit of a dive through the provided module and reads through the dependency tree from the point of entry given. It will find what a module imports, provides, has controllers for, and exports and will recursively search through the dependency tree until all modules have been scanned. For providers if there is a custom provider, the Spelunker will do its best to determine if Nest is to use a value, a class/standard, or a factory, and if a factory, what value is to be injected.

Installation

Pretty straightforward installation:

npm i nestjs-spelunker
yarn add nestjs-spelunker
pnpm i nestjs-spelunker

Exploration Mode

Exploration Usage

Much like the SwaggerModule, the SpelunkerModule is not a module that you register within Nest's DI system, but rather use after the DI system has done all of the heavy lifting. Simple usage of the Spelunker could be like:

// ...
import { SpelunkerModule } from 'nestjs-spelunker'; 

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  // const app = await NestFactory.createApplicationContext(AppModule);
  console.log(SpelunkerModule.explore(app));
  // ...
}
// ...

The SpelunkerModule will not get in the way of application bootstrapping, and will still allow for the server to listen.

Exploration Sample Output

Given the following source code

// main.ts
import * as util from 'util'
import { NestFactory } from '@nestjs/core'
import { SpelunkerModule } from 'nestjs-spelunker'
import { AppModule } from './app.module'

async function bootstrap() {
  const app = await NestFactory.createApplicationContext(AppModule, { logger: false })
  console.log(
    util.inspect( SpelunkerModule.explore(app), { depth: Infinity, colors: true } )
  )
}
bootstrap();

// src/app.module.ts
import { Module, Injectable, Controller } from '@nestjs/common'

@Controller('hamsters')
export class HamstersController {}
@Injectable()
export class HamstersService {}

@Module({
  controllers: [HamstersController],
  providers: [HamstersService],
})
export class HamstersModule {}


@Controller('dogs')
export class DogsController {}
export class DogsService {}

@Module({
  controllers: [DogsController],
  providers: [
    {
      provide: DogsService,
      inject: ['someString'],
      useFactory: (str: string) => new DogsService(),
    },
    {
      provide: 'someString',
      useValue: 'my string',
    },
  ],
  exports: [DogsService],
})
export class DogsModule {}


@Controller('cats')
export class CatsController {}
@Injectable()
export class CatsService {}

@Module({
  controllers: [CatsController],
  providers: [CatsService],
})
export class CatsModule {}


export class AnimalsService {}
@Controller('animals')
export class AnimalsController {}

@Module({
  imports: [CatsModule, DogsModule, HamstersModule],
  controllers: [AnimalsController],
  providers: [
    {
      provide: AnimalsService,
      useValue: new AnimalsService(),
    }
  ],
  exports: [DogsModule],
})
export class AnimalsModule {}


@Module({
  imports: [AnimalsModule],
})
export class AppModule {}

it outputs this:

[
  {
    name: 'AppModule',
    imports: [ 'AnimalsModule' ],
    providers: {},
    controllers: [],
    exports: []
  },
  {
    name: 'AnimalsModule',
    imports: [ 'CatsModule', 'DogsModule', 'HamstersModule' ],
    providers: { AnimalsService: { method: 'value' } },
    controllers: [ 'AnimalsController' ],
    exports: [ 'DogsModule' ]
  },
  {
    name: 'CatsModule',
    imports: [],
    providers: { CatsService: { method: 'standard' } },
    controllers: [ 'CatsController' ],
    exports: []
  },
  {
    name: 'DogsModule',
    imports: [],
    providers: {
      DogsService: { method: 'factory', injections: [ 'someString' ] },
      someString: { method: 'value' }
    },
    controllers: [ 'DogsController' ],
    exports: [ 'DogsService' ]
  },
  {
    name: 'HamstersModule',
    imports: [],
    providers: { HamstersService: { method: 'standard' } },
    controllers: [ 'HamstersController' ],
    exports: []
  }
]

In this example, AppModule imports AnimalsModule, and AnimalsModule imports CatsModule, DogsModule, and HamstersModule and each of those has its own set of providers and controllers.

Graph Mode

Sometimes you want to visualize the module inter-dependencies so you can better reason about them. The SpelunkerModule has a graph method that builds on the output of the explore method by generating a doubly-linked graph where each node represents a module and each edge a link to that module's dependencies or dependents. The getEdges method can traverse this graph from from the root (or any given) node, recursively following dependencies and returning a flat array of edges. These edges can be easily mapped to inputs for graphing tools, such as Mermaid.

Graphing Usage

Assume you have the sample output of the above explore section in a variable called tree. The following code will generate the list of edges suitable for pasting into a Mermaid graph.

const tree = SpelunkerModule.explore(app);
const root = SpelunkerModule.graph(tree);
const edges = SpelunkerModule.findGraphEdges(root);
console.log('graph LR');
const mermaidEdges = edges.map(
  ({ from, to }) => `  ${from.module.name}-->${to.module.name}`,
);
console.log(mermaidEdges.join('\n'));

graph LR
  AppModule-->AnimalsModule
  AnimalsModule-->CatsModule
  AnimalsModule-->DogsModule
  AnimalsModule-->HamstersModule

The edges can certainly be transformed into formats more suitable for other visualization tools. And the graph can be traversed with other strategies.

Debug Mode

Every now again again you may find yourself running into problems where Nest can't resolve a provider's dependencies. The SpelunkerModule has a debug method that's meant to help out with this kind of situation.

Debug Usage

Assume you have a DogsModule with the following information:

@Module({
  controller: [DogsController],
  exports: [DogsService],
  providers: [
    {
      provide: 'someString',
      useValue: 'something',
    },
    {
      provide: DogsService,
      inject: ['someString'],
      useFactory: (someStringInjection: string) => {
        return new DogsService(someStringInjection),
      },
    }
  ]
})
export class DogsModule {}

Now the SpelunkerModule.debug() method can be used anywhere with the DogsModule to get the dependency tree of the DogsModule including what the controller depends on, what imports are made, and what providers exist and their token dependencies.

async function bootstrap() {
  const dogsDeps = await SpelunkerModule.debug(DogsModule);
  const app = await NestFactory.create(AppModule);
  await app.listen(3000);
}

Because this method does not require the INestApplicationContext it can be used before the NestFactory allowing you to have insight into what is being seen as the injection values and what's needed for the module to run.

Debug Sample Output

The output of the debug() method is an array of metadata, imports, controllers, exports, and providers. The DogsModule from above would look like this:

[
  {
    name: 'DogsModule',
    imports: [],
    providers: [
      {
        name: 'someString',
        dependencies: [],
        type: 'value',
      },
      {
        name: 'DogsService',
        dependencies: ['someString'],
        type: 'factory',
      },
    ],
    controllers: [
      {
        name: 'DogsController',
        dependencies: ['DogsService'],
      },
    ],
    exports: [
      {
        name: 'DogsService',
        type: 'provider',
      },
    ],
  },
];

Debug Messages

If you are using the debug method and happen to have an invalid circular, the SpelunkerModule will write message to the log about the possibility of an unmarked circular dependency, meaning a missing forwardRef and the output will have ***** in place of the imports where there's a problem reading the imported module.

Caution

This package is in early development, and any bugs found or improvements that can be thought of would be amazingly helpful. You can log a bug here, and you can reach out to me on Discord at PerfectOrphan#6003.