Angular5 HttpInterceptor 取决于 Observable 的结果答案

【问题标题】：Angular5 HttpInterceptor depending on the result of an ObservableAngular5 HttpInterceptor 取决于 Observable 的结果
【发布时间】：2018-08-21 16:26:34
【问题描述】：

我正在尝试使用 Angular5 实现 HttpInterceptor 在所有 HTTP 请求中注入 Authorization 标头。

我依靠第三方库（ADAL，这里称为 AuthService）公开了一个 acquireToken() 方法来获取用于承载授权的令牌。

问题是 aquireToken() 返回一个 observable，我必须订阅才能获得我需要的真实字符串。

因此，我的代码从不注入标头，我想是因为next.handle() 在acquireToken() 返回任何值之前执行。

如何确保仅在检索到令牌后才调用下一个处理程序？

import { Injectable, Injector } from '@angular/core';
import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

import {AuthService} from 'mylibrary';

@Injectable()
export class MyInterceptor implements HttpInterceptor {

    constructor(private auth: AuthService) { }

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

        let headers = req.headers || new HttpHeaders();

        this.auth.acquireToken(req.url)
            .subscribe((token: string) => {
                headers = headers.append('Authorization', 'Bearer ' + token);
            });

        return next.handle(req.clone({ headers: headers }));
    }
}

【问题讨论】：

标签： angular5 angular-http-interceptors adal.js angular-observable

【解决方案1】：

这段代码可以完成这项工作，诀窍是使用mergeMap

import { Injectable, Injector } from '@angular/core';
import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs/Observable';
import { AdalService } from './adal.service';
import 'rxjs/add/operator/mergeMap';

@Injectable()
export class AdalInterceptor implements HttpInterceptor {

    constructor(private adal: AdalService) { }

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

        // if the endpoint is not registered then pass
        // the request as it is to the next handler
        const resource = this.adal.GetResourceForEndpoint(req.url);
        if (!resource) {
            return next.handle(req.clone());
        }

        // if the endpoint is registered then acquire and inject token
        let headers = req.headers || new HttpHeaders();
        return this.adal.acquireToken(resource)
            .mergeMap((token: string) => {
                // if the user is not authenticated then drop the request
                if (!this.adal.userInfo.authenticated) {
                    throw new Error('Cannot send request to registered endpoint if the user is not authenticated.');
                }

                // inject the header
                headers = headers.append('Authorization', 'Bearer ' + token);
                return next.handle(req.clone({ headers: headers }));
            }
        );
    }
}

【讨论】：

您好朋友，我很难理解mergeMap 运算符的使用，以至于我到这个问题到处寻找信息。我知道它用于混合两个或多个 observables 并且只获得一个。但我见过他们将其与单个可观察对象一起使用的代码，这让我感到困惑。
仅供参考，如果是可观察的，请添加return this.adal.acquireToken(resource).pipe(mergeMap(...))。

【解决方案2】：

可能的问题在这里

 constructor(private auth: AuthService) { }

提供者在拦截器中不可用

解决方案

使用Injector 注入您的服务

// 1. import the injector
import { Injectable, Injector } from '@angular/core';
// 2. create a constant of your service
private auth: AuthService;
// 3. add injector into contsructor; remove authService from constructor
constructor(private injector: Injector) { }
// 4. now create instance of your service inside intercept()
intercept() {
const auth = this.injector.get(AuthService);
// 5. now call method on this auth object

【讨论】：