The angular6 interceptor is stuck in an endless loop.

recently, the project has been developing with angular6, encapsulating an interceptor for HttpInterceptor, but has been reporting errors.

< H2 > Code in auth.service.ts < / H2 >

import {Injectable} from "@angular/core";
import {HttpService} from "./services/http.service";


@Injectable()
export class AuthService {
  public timestamp: any = "";

  constructor(private http: HttpService) {

  }

  /*
  * 
  * */
  getTimestamp() {
    this.http.getData("/common/timestamp").subscribe((respData: any) => {
        if (respData.code === "0000") {
          this.timestamp = respData.data;
        }
      }
    );
  }


  //test
  getAuthorizationToken() {
    return "some-auth-token";
  }
}

< hr > < H2 > interceptor.service.ts < / H2 >

import {Injectable} from "@angular/core";
import {HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpResponse} from "@angular/common/http";
import {Observable} from "rxjs";
import {tap} from "rxjs/operators";

import {constant} from "../../providers";
import {AuthService} from "../auth.service";


@Injectable()
export class InterceptorService implements HttpInterceptor {


  constructor(private authService: AuthService) {
  }

  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    // const authToken = this.authService.getTimestamp(); //
    const authToken = this.authService.getAuthorizationToken();
    const clonedRequest = req.clone({
      setHeaders: {
        leo: "test",
        version: constant.VERSIONS,
      },
    });
    console.log(clonedRequest.method);
    return next.handle(clonedRequest).pipe(
      tap(
        event => {
          if (event instanceof HttpResponse) {
            console.log(event);
          }
        },
        error => {
          console.error(error.message);
        }
      )
    );
  }
}

if I release const authToken = this.authService.getTimestamp (); in interceptor.service.ts, I will fall into a loop.

I want to add a timestamp to the header request header of the interceptor for verification. This timestamp must be retrieved from the backend when the post request is made. Now I don"t know how to solve it. Does anyone know? Thank you

export class InterceptorService implements HttpInterceptor { private lastTimestamp; constructor(private authService: AuthService) { } intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> { const authToken; if (req.url !== '/common/timestamp'){ authToken = this.authService.getTimestamp(); this.lastTimestamp = authToken; } else { // authToken = this.lastTimestamp; } const clonedRequest = req.clone({ setHeaders: { leo: 'test', version: constant.VERSIONS, }, }); console.log(clonedRequest.method); return next.handle(clonedRequest).pipe( tap( event => { if (event instanceof HttpResponse) { console.log(event); } }, error => { console.error(error.message); } ) ); } }