Dynamic registeration of plugins #144

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1. radhay-1199 commented on May 28, 2023

   

   radhay-1199

   on May 28, 2023

   Last edited by radhay-1199

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   POC:

   • Define an annotation decorator for your plugins:

   // plugin.decorator.ts
   import { SetMetadata } from '@nestjs/common';
   
   export const PLUGIN_TOKEN = 'PLUGIN_TOKEN';
   
   export const Plugin = (token: string): ClassDecorator => {
     return SetMetadata(PLUGIN_TOKEN, token);
   };

   • Use the Plugin decorator to mark your plugin classes with the corresponding token:

   // pdf-plugin.ts
   import { Plugin } from './plugin.decorator';
   
   @Plugin('pdf-plugin')
   export class PdfPlugin {
     generateDoc(): string {
       // Logic to generate a PDF document
       return 'Generated PDF document';
     }
   }

   • Create a factory class that will instantiate the plugins based on their tokens:

   // plugin.factory.ts
   import { Injectable } from '@nestjs/common';
   import { PLUGIN_TOKEN } from './plugin.decorator';
   
   @Injectable()
   export class PluginFactory {
     private plugins: Map<string, any> = new Map();
   
     registerPlugin(token: string, plugin: any) {
       this.plugins.set(token, plugin);
     }
   
     createPlugin(token: string): any {
       const plugin = this.plugins.get(token);
       if (!plugin) {
         throw new Error(`Plugin not found for token: ${token}`);
       }
       return new plugin();
     }
   }

   • Scan for classes with the Plugin decorator in your app module and register them dynamically:

   // app.module.ts
   import { Module, ModuleRef, OnModuleInit, Reflector } from '@nestjs/common';
   import { AppController } from './app.controller';
   import { PluginFactory } from './plugin.factory';
   import { PLUGIN_TOKEN } from './plugin.decorator';
   
   @Module({
     controllers: [AppController],
     providers: [PluginFactory],
   })
   export class AppModule implements OnModuleInit {
     constructor(
       private readonly moduleRef: ModuleRef,
       private readonly reflector: Reflector,
       private readonly pluginFactory: PluginFactory,
     ) {}
   
     onModuleInit() {
       const providers = this.moduleRef.getProviders();
       providers.forEach((provider) => {
         const pluginToken = this.reflector.get<string>(PLUGIN_TOKEN, provider.metatype);
         if (pluginToken) {
           const pluginInstance = this.moduleRef.get(provider.metatype);
           this.pluginFactory.registerPlugin(pluginToken, pluginInstance);
         }
       });
     }
   }

   • Create a controller that injects the PluginFactory and uses the plugins:

   // doc.controller.ts
   import { Controller, Get, Param, Inject } from '@nestjs/common';
   import { PluginFactory } from './plugin.factory';
   
   @Controller('documents')
   export class DocController {
     constructor(
       @Inject(PluginFactory) private readonly pluginFactory: PluginFactory,
     ) {}
   
     @Get(':plugin/')
     generateDocument(@Param('plugin') pluginToken: string): string {
       const plugin = this.pluginFactory.createPlugin(pluginToken);
       const generatedDoc = plugin.generateDoc();
       return generatedDoc;
     }
   }

   With this approach, we can create new plugin classes with the Plugin decorator and their respective tokens. They will be automatically discovered and registered in the PluginFactory during the runtime of your NestJS application.
2. radhay-1199 commented on May 28, 2023

   

   radhay-1199

   on May 28, 2023

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   Long term goals: Implement awilix DI for plugins with scoped lifetime management for each plugins
   References- https://github.com/jeffijoe/awilix
3. yuvrajsab commented on May 28, 2023

   

   yuvrajsab

   on May 28, 2023

   Last edited by yuvrajsab

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   @radhay-1199 but here

     createPlugin(token: string): any {
       const plugin = this.plugins.get(token);
       if (!plugin) {
         throw new Error(`Plugin not found for token: ${token}`);
       }
       return new plugin();
     }

   we are newing up the plugin instance whenever a request comes. These plugin classes should be singleton.
4. AnshulMalik commented on May 29, 2023

   

   AnshulMalik

   on May 29, 2023

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   Looks good, agree with @yuvrajsab , let's make don't make these objects if already have one.

   Now this is out of they way, we need to work on the signature of the input and output plugin methods.
5. radhay-1199 commented on May 29, 2023

   

   radhay-1199

   on May 29, 2023

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   @yuvrajsab No actually, this map will already have beans associated with the name in them. NestJs assures that threads are singleton only.
6. yuvrajsab commented on May 29, 2023

   

   yuvrajsab

   on May 29, 2023

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   okay and @radhay-1199 one more question ki if a plugin class needs DI for let's say ConfigService or any other service then how are we gonna inject that or does this approach already handle that.
7. Samagra-Development

   locked and limited conversation to collaborators on Jun 4, 2023
8. AnshulMalik

   converted this issue into a discussion #154 on Jun 4, 2023