Rxjs in nestjs - Observable subscription error

I am newbie trying out rxjs and nestjs. The use case that I am currently trying to accomplish is for educational purpose. So I wanted to read a json file (throw an observable error in case of the file being empty or cannot be read) using the "fs" module. Now I create an observable by reading the file asynchronously, set the observer in the subject and then subscribe to the subject in the controller. Here is my code in the service

@Injectable()
export class NewProviderService {
    private serviceSubject: BehaviorSubject<HttpResponseModel[]>;
    // this is the variable that should be exposed. make the subject as private
    // this allows the service to be the sole propertier to modify the stream and
    // not the controller or components
    serviceSubject$:  Observable<HttpResponseModel[]>;

    private serviceErrorSubject: BehaviorSubject<any>;
    serviceErrorSubject$: Observable<any>;
    filePath: string;
    httpResponseObjectArray: HttpResponseModel[];
    constructor() {
        this.serviceSubject = new BehaviorSubject<HttpResponseModel[]>([]);
        this.serviceSubject$ = this.serviceSubject.asObservable();

        this.serviceErrorSubject = new BehaviorSubject<any>(null);
        this.serviceErrorSubject$ = this.serviceErrorSubject.asObservable();

        this.filePath = path.resolve(__dirname, './../../shared/assets/httpTest.json');
    }
     readFileFromJson() {
          return new Promise((resolve, reject) => {
            fs.exists(this.filePath.toString(), exists => {
                if (exists) {
                    fs.readFile(this.filePath.toString(), 'utf-8' , (err, data) => {
                        if (err) {
                            logger.info('error in reading file', err);
                            return reject('Error in reading the file' + err.message);
                        }

                        logger.info('file read without parsing fg', data.length);
                        if ((data.length !== 0) && !isNullOrUndefined(data) && data !== null) {
                            // this.httpResponseObjectArray = JSON.parse(data).HttpTestResponse;
                            // logger.info('array obj is:', this.httpResponseObjectArray);
                            logger.info('file read after parsing new', JSON.parse(data));
                            return resolve(JSON.parse(data).HttpTestResponse);
                        } else {
                            return reject(new FileExceptionHandler('no data in file'));
                        }
                    });
                } else {
                    return reject(new FileExceptionHandler('file cannot be read at the moment'));
                }
            });
          });
    }


        getData() {
                 from(this.readFileFromJson()).pipe(map(data => {
                        logger.info('data in obs', data);
                        this.httpResponseObjectArray = data as HttpResponseModel[];
                        return this.httpResponseObjectArray;
                 }), catchError(error => {
                     return Observable.throw(error);
                 }))
                 .subscribe(actualData => {
                    this.serviceSubject.next(actualData);
                }, err => {
                    logger.info('err in sub', typeof err, err);
                    this.serviceErrorSubject.next(err);
                });
            }

Now this is the controller class

@Get('/getJsonData')
public async getJsonData(@Req() requestAnimationFrame,@Req() req, @Res() res) {

  await this.newService.getData();
  this.newService.serviceSubject$.subscribe(data => {
    logger.info('data subscribed', data, _.isEmpty(data));
    if (!isNullOrUndefined(data) && !_.isEmpty(data)) {
      logger.info('coming in');
      res.status(HttpStatus.OK).send(data);
      res.end();
    }
  });
}

The problem I face is that I can get the file details for the first time and the subscription is getting called once > its working fine. On the subsequent requests

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
    at ServerResponse.setHeader (_http_outgoing.js:470:11)
    at ServerResponse.header (C:\personal\Node\test-nest.js\prj-sample\node_modules\express\lib\response.js:767:10)
    at Ser

and the endpoint /getJsonData results in an error. Could someone help me out. i believe the subscription is not getting properly after the first call, but not sure how to end that and how to resolve that