How to pass reflector to Nest.js global guard?

Question

I am new to nest.js and I have a question. I have a Roles Guard like this

import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
import { Observable } from 'rxjs';
import { Reflector } from '@nestjs/core';

@Injectable()
export class RolesGuard implements CanActivate {
  constructor(private readonly reflector: Reflector) {
  }

  canActivate(context: ExecutionContext): boolean | Promise<boolean> | Observable<boolean> {
    const roles = this.reflector.get<string[]>('roles', context.getHandler());
    if (!roles) {
      return true;
    }
    const request = context.switchToHttp().getRequest();
    const user = request.user;
    return user.role.some(role => !!roles.find(item => item === role));
  }

}

Now I want to use this guard as a global guard like this

app.useGlobalGuards(new RolesGuard())

But it says that I need to pass argument(the reflector) to the guard as I mentioned in the constructor, now will it be okay to initialize the reflector like this?

const reflector:Reflector = new Reflector();
app.useGlobalGuards(new RolesGuard(reflector))

Or is there a better way to do this?

Tuft

Answer 1

On the official Nest JS fundamentals course, in lecture "54 Protect Routes with Guards", the instructor specifies it is not best practice to create instance of reflector yourself.

A better way to resolve dependencies is to create a common module, and register your guard there. That way, reflector instance is resolved by nest runtime and you can also specify imports array for any other dependencies.

import { Module } from '@nestjs/common';
import { APP_GUARD } from '@nestjs/core';
import { AuthTokenGuard } from './guards/auth-token.guard';
import { ConfigModule } from '@nestjs/config';

@Module({
  imports: [ConfigModule],
  providers: [
    {
      provide: APP_GUARD,
      useClass: AuthTokenGuard,
    },
  ],
})
export class CommonModule {}

Demasculinize

Answer 2

  app.useGlobalGuards(new RolesGuard(new Reflector()));

It is working also. Could not find any better solution.

Radiography

SulsDotK's answer is the best practice now which is in the official guide. Another way is app.useGlobalGuards(new AuthGuard(app.get(Reflector))); – Lailalain

Answer 3

Although my answer might not add much value, I just want to re-iterate that is the intended way to get the reflector, this is a quote from NestJS's creator

kamilmysliwiec

When you create instance manually, you can create Reflector by yourself:

new RoleGuard(new Reflector());

Source: https://github.com/nestjs/nest/issues/396#issuecomment-363111707

Spitz

Answer 4

2023, NestJs 9, related problem:

In case you inject request-scoped dependency into the globally registered guard, the reflector will be undefined.

You can solve this issue by resolving such dependencies using ContextIdFactory and moduleRef.resolve() instead of injecting them normally:

const req = context.switchToHttp().getRequest();
const contextId = ContextIdFactory.getByRequest(req);
this.moduleRef.registerRequestByContextId(req, contextId);
this.authorizationService = await this.moduleRef.resolve(
  RequestScopedService,
  contextId
);

References:

• https://docs.nestjs.com/fundamentals/module-ref
• code example
• https://discord.com/channels/520622812742811698/1060904277607985172

Prosthesis

Answer 5

I had two different versions of @nestjs/core installed, npm ls @nestjs/core told me which dependencies caused this issue.

After resolving, everything worked as expected.

Gilles