angular - 使用 Angular Universal 时在组件的 ngOnInit 中发出 http 请求是否有问题？

Question

我一直在通过 ng serve for development 运行我的 Angular 应用程序，没有遇到任何错误。然而，当使用 SSR 时，每当我加载一个组件时，我的服务器日志中都会出现错误，该组件发出 http 请求作为其 ngOnInit 方法的一部分。我的策略有问题吗？

我没有通过谷歌搜索我的错误找到任何有用的信息。我应该在页面完全加载之前等待提出请求，还是使用其他方法？如果是这样，我该怎么做？

我正在使用 http-proxy-middleware 包向 Django 服务器发送请求。 https://github.com/chimurai/http-proxy-middleware

这是在 ngOnInit 中发出请求时出现的错误:

ERROR Error
    at XMLHttpRequest.send (C:\{...}\dist\{...}\server\main.js:201490:19)
    at Observable.rxjs__WEBPACK_IMPORTED_MODULE_1__.Observable [as _subscribe] (C:\{...}\dist\{...}\server\main.js:23724:17)
    at Observable._trySubscribe (C:\{...}\dist\{...}\server\main.js:186583:25)
    at Observable.subscribe (C:\{...}\dist\{...}\server\main.js:186569:22)
    at scheduleTask (C:\{...}\dist\{...}\server\main.js:106745:32)
    at Observable.rxjs__WEBPACK_IMPORTED_MODULE_7__.Observable [as _subscribe] (C:\{...}\dist\{...}\server\main.js:106807:13)
    at Observable._trySubscribe (C:\{...}\dist\{...}\server\main.js:186583:25)
    at Observable.subscribe (C:\{...}\dist\{...}\server\main.js:186569:22)
    at subscribeToResult (C:\{...}\dist\{...}\server\main.js:196664:23)
    at MergeMapSubscriber._innerSub (C:\{...}\dist\{...}\server\main.js:191854:116)

这是我的测试组件的相关部分:

export class TestComponent implements OnInit {
  output: String = "The server is not running or is not connected"

  constructor(private httpTestService: HttpTestService) { }

  ngOnInit(): void {
    this.testGetRequest();
  }

  testGetRequest() {
    this.httpTestService.testGetRequest().subscribe(temp => {
      this.output = temp.message; // response is json with a 'message' attribute
    });
  }

}

这是我的 HttpTestService 的相关部分:

import { HttpClient } from '@angular/common/http';

  constructor(private http: HttpClient) { }

  testGetRequest(): Observable<any> {
    return this.http.get('/api/endpoint1');
  }

我相信我的 server.ts 的这一部分可能很重要:

import { createProxyMiddleware } from 'http-proxy-middleware';

export function app() {
  const server = express();
  const distFolder = join(process.cwd(), 'dist/.../browser');
  const indexHtml = existsSync(join(distFolder, 'index.original.html')) ? 'index.original.html' : 'index';

  server.engine('html', ngExpressEngine({
    bootstrap: AppServerModule,
  }));

  server.set('view engine', 'html');
  server.set('views', distFolder);

  // re-route requests to /api/ to the django REST api
  server.use('/api/**', createProxyMiddleware({ target: 'http://localhost:8000', changeOrigin: true }));

即使在使用 SSR 运行时，应用程序也能正常运行，除了我在服务器控制台中遇到的错误。

Answer 1

在进行 HTTP 调用时，您应该使用绝对 URL。 docs

所以问题可能出在这里

testGetRequest(): Observable<any> {
  return this.http.get('/api/endpoint1');
}

要修复它，您可以使用将相对 URL 更改为绝对 URL 的拦截器，并在 AppServerModule 中提供该拦截器。

拦截器是:

import { HttpHandler, HttpInterceptor, HttpRequest } from '@angular/common/http';
import { Inject, Injectable, Optional } from '@angular/core';
import { REQUEST } from '@nguniversal/express-engine/tokens';
import { Request } from 'express';

@Injectable()
export class UniversalInterceptor implements HttpInterceptor {

  constructor(@Optional() @Inject(REQUEST) protected request: Request) {}

  intercept(req: HttpRequest<any>, next: HttpHandler) {
    let serverReq: HttpRequest<any> = req;
    if (this.request && req.url.indexOf('http') !== 0) {
      let newUrl = `${this.request.protocol}://${this.request.get('host')}`;
      if (!req.url.startsWith('/')) {
        newUrl += '/';
      }
      newUrl += req.url;
      serverReq = req.clone({url: newUrl});
    }

    return next.handle(serverReq);
  }
}

AppServerModule 是

@NgModule({
  imports: [
    ...
  ],
  bootstrap: [AppComponent],
  providers: [
    {
      provide: HTTP_INTERCEPTORS,
      useClass: UniversalInterceptor,
      multi: true,
    },
  ],
})
export class AppServerModule {}

希望对你有帮助