NestJS - Use service inside Interceptor (not global interceptor) - nestjs

Question

I have a controller that uses custom interceptor:
Controller:
#UseInterceptors(SignInterceptor)
#Get('users')
async findOne(#Query() getUserDto: GetUser) {
return await this.userService.findByUsername(getUserDto.username)
}
I have also I SignService, which is wrapper around NestJwt:
SignService module:
#Module({
imports: [
JwtModule.registerAsync({
imports: [ConfigModule],
useFactory: async (configService: ConfigService) => ({
privateKey: configService.get('PRIVATE_KEY'),
publicKey: configService.get('PUBLIC_KEY'),
signOptions: {
expiresIn: configService.get('JWT_EXP_TIME_IN_SECONDS'),
algorithm: 'RS256',
},
}),
inject: [ConfigService],
}),
],
providers: [SignService],
exports: [SignService],
})
export class SignModule {}
And Finally SignInterceptor:
#Injectable()
export class SignInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
return next.handle().pipe(map(data => this.sign(data)))
}
sign(data) {
const signed = {
...data,
_signed: 'signedContent',
}
return signed
}
}
SignService works properly and I use it. I would like to use this as an interceptor
How can I inject SignService in to SignInterceptor, so I can use the functions it provides?

Answer 1

I assume that SignInterceptor is part of the ApiModule:
#Module({
imports: [SignModule], // Import the SignModule into the ApiModule.
controllers: [UsersController],
providers: [SignInterceptor],
})
export class ApiModule {}
Then inject the SignService into the SignInterceptor:
#Injectable()
export class SignInterceptor implements NestInterceptor {
constructor(private signService: SignService) {}
//...
}
Because you use #UseInterceptors(SignInterceptor) to use the interceptor in your controller Nestjs will instantiate the SignInterceptor for you and handle the injection of dependencies.