Use Interceptor inside another Interceptor In nestjs - node.js

Question

I am creating a interceptor Inside that I want to use FileInterceptor but I am getting error Declaration Expected after FileInterceptor
import { CallHandler, ExecutionContext, Injectable, NestInterceptor, UseInterceptors } from '#nestjs/common';
import { Observable } from 'rxjs';
import { FileInterceptor } from '#nestjs/platform-express';
import { diskStorage } from 'multer';
import { extname } from 'path';
#Injectable()
export class UploaderInterceptor implements NestInterceptor {
intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
#UseInterceptors(FileInterceptor('file', {
storage: diskStorage({
destination: './uploads'
, filename: (req, file, cb) => {
// Generating a 32 random chars long string
const randomName = Array(32).fill(null).map(() => (Math.round(Math.random() * 16)).toString(16)).join('')
//Calling the callback passing the random name generated with the original extension name
cb(null, `${randomName}${extname(file.originalname)}`)
}
})
}));
return next.handle();
}
}

Answer 1

FileInterceptor is a mixin meaning it is a function that returns a class. This function takes in a configuration for the interceptor to actually use. What you can do instead of trying to make a class that makes use of the interceptor under the hood or extends it, is essentially make an alias for the configuration like so:
export const UploadInterceptor = FileInterceptor('file', {
storage: diskStorage({
destination: './uploads',
filename: (req, file, cb) => {
// Generating a 32 random characters long string
const randomName = Array(32).fill(null).map(() => (Math.round(Math.random() * 16)).toString(16)).join('')
//Calling the callback passing the random name generated with the original extension name
cb(null, `${randomName}${extname(file.originalname)}`)
}
})
})
Now with this exported constant (that is actually a class), you can then make use of the interceptor as such:
#Controller('upload')
export class UploadController {
#UseInterceptors(UploadInterceptor)
#Post()
uploadFile() {
// do logic;
}
}
And everything should work out for you.