NestJS share dynamic module instance - nestjs

Question

I'm struggling a bit with Nest's dynamic modules.
I have a utility service which needs a password to be injected on startup.
#Injectable()
export class CryptoService {
constructor(
#Inject("password") private password: string
) {}
...
}
This service is part of a "shared" CryptoModule...
#Module({
providers: [CryptoService]
,exports: [CryptoService]
})
export class CryptoModule {
public static forRoot(password: string): DynamicModule {
const providers = [{
provide: "password"
,useValue: password
}];
return {
module: CryptoModule
,providers: providers
};
}
}
With "shared" I mean that it's not specific to the current app, so it can be reused in other Nest apps as well.
I import the CryptoModule in my AppModule like so...
#Module({
imports: [
...
,CryptoModule.forRoot("super-secure-password")
,EmailModule
]
,controllers: [...]
,providers: [...]
,exports: [CryptoModule]
})
export class AppModule {
...
}
This works and I can inject the CryptoService in my AppModule classes/services/controllers.
Now I have a 3rd Module (EmailModule) which should be independent from my app, so I can reuse it in other Nest apps as well.
Question now is, how do I import the CryptoModule in the EmailModule without having to set the password in the EmailModule? It should use the password that was passed to the CryptoModule in AppModule.
I tried importing CryptoModule like so...
#Module({
imports: [
...
,CryptoModule
]
,providers: [EmailService]
,exports: [EmailService]
})
export class EmailModule {
...
}
This code however triggers an exception on startup saying:
Nest can't resolve dependencies of the CryptoService...
If password is a provider, is it part of the current CryptoModule?
Is there a best practice of how to achieve this? I could make EmailModule dynamic as well and pass in the password, so it can forward it to the CryptoModule, but somehow that doesn't feel right.
Thanks!

Answer 1

I ended up doing the following (probably there are better ways of doing this)...
Added a static forChildren() function to the CryptoModule, which is used to initialize the module when being imported by the EmailModule (or any other module). The forRoot() method stores the password in an Observable, which is used by forChildren() to asynchronously retrieve the password. Doing this async is required to defeat the race condition between forChildren() and forRoot().
import { firstValueFrom, ReplaySubject } from 'rxjs';
...
#Module({
providers: [CryptoService]
,exports: [CryptoService]
})
export class CryptoModule {
private static readonly credentialsResolved = new ReplaySubject<string>(1);
public static forRoot(password: string): DynamicModule {
CryptoModule.credentialsResolved.next(password);
const providers = [{
provide: "password"
,useValue: password
}];
return {
module: CryptoModule
,providers: providers
};
}
public static forChildren(): DynamicModule {
const providers = [{
provide: "password"
,useFactory: async () => await firstValueFrom(CryptoModule.credentialsResolved)
}];
return {
module: CryptoModule
,providers: providers
};
}
}
Usage in EmailModule:
#Module({
imports: [
...
,CryptoModule.forChildren()
]
,providers: [EmailService]
,exports: [EmailService]
})
export class EmailModule {
...
}