I'm currently struggling with service injection in a guard.

Well, the thing is I made a JwtAuthGuard, that needs both my FirebaseService and my UserService.

So I thought it'd be useful to create a AuthGuardModule so i only need to import my AuthGuardModules in the modules that have a Controller, to use my Guard.

The thing is that unfortunately, i need this guard for my UserModule too. So that's natural that i get a Circular Dependency Error When i import my AuthGuardModule in my UserModule.

Then, i tried all the things more or less related to Circular Dependency Error in Nest.js, but no can do.

Can someone tell me if:

• I am totally wrong thinking about making a module only for my guards ?
• If I'm not, how can I fix my Circular Dependency Error ?
• If I misunderstood that part, why isn't it right and what's the best way to do so ?

JwtAuthGuard

@Injectable()
export class JwtAuthGuard implements CanActivate {
  private readonly logger = new Logger(JwtAuthGuard.name)

  constructor(
    private readonly firebaseService: FirebaseService,
    private readonly userService: UserService
  ) { }

  async canActivate(context: ExecutionContext): Promise<boolean> {
    const request = context.switchToHttp().getRequest();
    const token = request.headers['authorization'];

    if (!token) {
      throw new UnauthorizedException
    }

    try {
      const firebaseUser = await this.firebaseService.getUserByToken(token)
      request.user = await this.userService.getByEmail(firebaseUser.email)
      return true
    } catch (error) {
      this.logger.error(this.canActivate.name, error)
      throw new UnauthorizedException
    }
  }
}

AuthGuardModule

@Module({
    imports: [UserModule],
    providers: [FirebaseService, JwtAuthGuard],
    exports: [JwtAuthGuard]
})

export class AuthGuardModule {}

EDIT

Well, jmcdo29 of the NestJS discord explained me that:

Your AuthGuardModule should export the UserModule and the FirebaseService. Guards, when used in the @UseGuards() decorator, are used in the context of the current controller's module, instead of being looked at as an Injectable provider

So I did that way and it did solve my initial issue, but i have another circular dependency issue.

First, let's resume resume the architecture i have:

AuthModule

• It handles the routes for register, and the routes that send some emails like the password reset or the email verifying.
• It needs the UserModule to create a user into my db when i call the register route

@Module({
  imports: [
    AuthGuardModule
  ],
  controllers: [AuthController],
  providers: [AuthService, EmailService, FirebaseService],
})

export class AuthModule {}

FileModule

• It handles the file upload and deletion.

@Module({
    imports: [
        forwardRef(() => AuthGuardModule),
        BlobModule,
        MongooseModule.forFeature([{ name: File.name, schema: FileSchema }])
    ],
    controllers: [FileController],
    providers: [FileService],
    exports: [FileService],
})

export class FileModule {}

UserModule

• It handles all the users routes.
• It needs the FileModule, to check if the avatar exists when it's modified (i have only one route that updates all my users personal data)
• It also needs the AuthGuardModule to use my JwtAuthGuard

@Module({
    imports: [
      forwardRef(() => AuthGuardModule),
      forwardRef(() => FileModule),
      MongooseModule.forFeature([{ name: User.name, schema: UserSchema }])
    ],
    controllers: [UserController],
    providers: [UserService, FirebaseService],
    exports: [UserService, FileModule]
  })

  export class UserModule {}

AuthGuardsModule

• It contains my JWT check guard, and then i check if a user in my db is linked to the connected user
• It needs the UserModule to get the user in my db

@Module({
    imports: [forwardRef(() => UserModule), FirebaseModule],
    providers: [JwtAuthGuard, RegisterAuthGuard],
    exports: [JwtAuthGuard, RegisterAuthGuard, FirebaseModule, UserModule]
})

export class AuthGuardModule {}

I could use firebase to store my users avatars and do it front side, but i have to store it in Azure Blob Storage (it's imposed to my), so the FileModule handle all that thing

So, now, that i solved my AuthGuardsModule -> UserModule circular dependecy thanks to you guys, i have a new circular dependency issue: AuthGuardsModule -> UserModule -> FileModule

I set a forwardRef of the AuthGuardsModule inside the FileModule but nest naturally said me that make sure that each side of a bidirectional relationships are decorated with "forwardRef()"

So i put a forwardRef to my FileModule import inside my UserModule, but same thing.

Any idea ?