从（服务器发送的）EventSource 创建一个 RxJS Observable

Question

我想从 EventSource（服务器发送的事件）创建一个 RxJs Observable。

我尝试了以下方法：

import {Component, OnInit} from 'angular2/core';
import {Subject, Observable}  from 'rxjs/Rx';

@Component({
    selector: 'my-app',
    template: `<h1>My second Angular 2 App</h1>
    <ul>
        <li *ngFor="#s of someStrings">
           a string: {{ s }}
        </li>
    </ul>
    `
})
export class AppComponent implements OnInit {

    someStrings:string[] = [];

    ngOnInit() {
        let eventSource = new EventSource('/interval-sse-observable');
        let observable = Observable.create(eventSource);
        observable.subscribe({
            next: aString => this.someStrings.push(aString.data),
            error: err => console.error('something wrong occurred: ' + err)
        });
    }
}

但我得到以下异常：

EXCEPTION: Error: Uncaught (in promise): EXCEPTION: TypeError: this._subscribe is not a function in [null]
ORIGINAL EXCEPTION: TypeError: this._subscribe is not a function
ORIGINAL STACKTRACE:
TypeError: this._subscribe is not a function
    at Observable.subscribe (https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/Rx.js:11210:29)
    at AppComponent.ngOnInit (http://localhost:8080/scripts/app.component.ts!transpiled:30:28)
    at AbstractChangeDetector.ChangeDetector_HostAppComponent_0.detectChangesInRecordsInternal (viewFactory_HostAppComponent:21:99)
    at AbstractChangeDetector.detectChangesInRecords (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:9689:14)
    at AbstractChangeDetector.runDetectChanges (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:9672:12)
    at AbstractChangeDetector.detectChanges (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:9661:12)
    at ChangeDetectorRef_.detectChanges (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:5280:16)
    at https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:13048:27
    at Array.forEach (native)
    at ApplicationRef_.tick (https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js:13047:34)

为了完整起见，这里是我的 index.html:

的内容

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>sse demo</title>
    <!-- 1. Load libraries -->
    <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/angular2-polyfills.js"></script>
    <script src="https://code.angularjs.org/tools/system.js"></script>
    <script src="https://code.angularjs.org/tools/typescript.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/Rx.js"></script>
    <script src="https://code.angularjs.org/2.0.0-beta.15/angular2.dev.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/2.0.0-beta.15/http.dev.js"></script>

    <!-- 2. Configure SystemJS -->
    <script>
        System.config({
            transpiler: 'typescript',
            typescriptOptions: { emitDecoratorMetadata: true }
        });
        System.import('./scripts/app.ts')
                .then(null, console.error.bind(console));
    </script>
</head>
<body>

<my-app>Loading...</my-app>

</body>
</html>

有人可以帮忙吗？

edit 1: 按照Yurzui的建议，我修改了我的代码如下：

ngOnInit() {
    let observable = Observable.create(observer => {
        const eventSource = new EventSource('/interval-sse-observable');
        eventSource.onmessage = x => observer.next(console.log(x));
        eventSource.onerror = x => observer.error(console.log('EventSource failed'));

        return () => {
            eventSource.close();
        };
    });
    observable.subscribe({
        next: aString => this.someStrings.push(aString.data),
        error: err => console.error('something wrong occurred: ' + err)
    });
}

它确实在控制台中记录了第一条消息，如下所示：

MessageEvent {isTrusted: true, data: "c374a15b-b37d-498e-8ab0-49643b79c1bb", origin: "http://localhost:8080", lastEventId: "", source: null…}bubbles: falsecancelBubble: falsecancelable: falsecurrentTarget: EventSourcedata: "c374a15b-b37d-498e-8ab0-49643b79c1bb"defaultPrevented: falseeventPhase: 0isTrusted: trueisTrusted: truelastEventId: ""origin: "http://localhost:8080"path: Array[0]ports: nullreturnValue: truesource: nullsrcElement: EventSourcetarget: EventSourcetimeStamp: 6257.125type: "message"__proto__: MessageEvent
Rx.js:10982 Uncaught TypeError: Cannot read property 'data' of undefinedSystem.register.exports_1.execute.AppComponent.ngOnInit.observable.subscribe.next @ app.component.ts:29SafeSubscriber.__tryOrUnsub @ Rx.js:10979SafeSubscriber.next @ Rx.js:10934Subscriber._next @ Rx.js:10894Subscriber.next @ Rx.js:10871System.register.exports_1.execute.AppComponent.ngOnInit.Rx_1.Observable.create.eventSource.onmessage @ app.component.ts:21

现在，如果不是在控制台中记录 x 变量，我只是将它传递给下一个方法，如下所示：

eventSource.onmessage = x => observer.next(x);

服务器发送的事件由客户端检索（我在 chrome 开发工具中看到它们）但模板中没有显示任何内容，表明字符串数组未填充...

顺便说一下，我不得不删除 JSON.parse(x.data)，因为它导致了错误。

Answer 1

您可以使用以下代码为 EventSource 流手动创建 Observable：

export class AppComponent implements OnInit {
  someStrings:string[] = [];

  constructor(private zone: NgZone) {}

  ngOnInit(){
    const observable = Observable.create(observer => {
      const eventSource = new EventSource('/interval-sse-observable');
      eventSource.onmessage = x => observer.next(x.data);
      eventSource.onerror = x => observer.error(x);

      return () => {
        eventSource.close();
      };
    });

    this.subscription = observable.subscribe({
      next: guid => {
        this.zone.run(() => this.someStrings.push(guid));
      },
      error: err => console.error('something wrong occurred: ' + err)
    });
  }
}

// somewhere
// this.subscription.unsubscribe()

不要忘记导入 NgZone class:

import {Component, OnInit, NgZone} from '@angular/core';

另见 Angular2 View Not Changing After Data Is Updated

Answer 2

我应该完成Yurzui的回答：

就我而言，在使用 Angular 6 时，我在将函数分配给 onmessage 时出现了一些奇怪的行为。因此，我添加了一个事件侦听器，它非常有效：

const observable = Observable.create(observer => {
  const eventSource = new EventSource('/interval-sse-observable');
  eventSource.addEventListener("message", (event: MessageEvent) => observer.next(event.data));
  eventSource.addEventListener("error", (event: MessageEvent) => observer.error(event));

  return () => {
    eventSource.close();
  };
});

从（服务器发送的）EventSource 创建一个 RxJS Observable

Creating an RxJS Observable from a (server sent) EventSource

typescript

angular

rxjs5

eventsource