服务器发送事件； `EventSource.onmessage`没有触发

Posted 2023-03-07

【中文标题】服务器发送事件； `EventSource.onmessage`没有触发

【英文标题】：Server Sent Event; `EventSource.onmessage` not firing

【发布时间】：2022-01-22 16:59:55

【问题描述】：

我正在尝试使用服务器发送事件的following example。似乎服务器正在发送数据，但事件没有触发，并且事件流中没有记录任何数据（通过开发人员工具）。

Angular 代码（服务）：

getAlertsEvent(fieldIds: Guid[]): Observable<responseModel.LoanAlert> 
    return new Observable(obs => 
      fieldIds.forEach(fieldId => 
        const source = new EventSource(`http://localhost:3000/loan/alerts/$fieldId`);
        alert('Succesfully creates the EventSource, I see reuslt 200 in Networking tab but with 0 events');
        source.onmessage = (ev): void => 
          this.zone.run(() => 
              alert('This alert will not happen');
              obs.next(ev.data);
            );
          ;
        source.onerror = (err): void => this.zone.run(() => obs.error(err));
        // Also tried this way with no luck:
        // source.addEventListener('message', (event) => 
        //   obs.next(event.data);
        // );
      );
    );
  

组件：

      this.loansService.getAlertsEvent(this.fields.map(field => field.fieldId)).subscribe(alert => 
        console.log(alert);
      );

Node.js 代码：

const express = require('express');
const parser = require('body-parser');
const app = express();
const EventEmitter = require('events');

const Stream = new EventEmitter();

app.unsubscribe(parser.json());
app.use(
    parser.urlencoded(
        extended: true,
    )
);

app.get('/loan/alerts/:fieldId', function(req, res) 
    res.writeHead(200, 
        'Content-Type': 'text/event-stream',
        'Cache-Control': 'no-cache',
        'Access-Control-Allow-Origin': "*",
        Conection: 'keep-alive'
    );

    Stream.on(req.params.fieldId, function(event, data) 
        res.write(JSON.stringify(data));
    );
);

setInterval(function() 
    const item = 
        formId: 51415,
        alertId: 'asdfasdfasdf',
        messageStatus: 'NEW',
        messageType: 'ACTION_MESSAGE_FROM_SERVER',
        actionType: 'NAVIGATION',
        message: 'New Message!',
        archiverId: '12345',
        documentCode: 3,
        from: 'Internal Server Message',
        messageTimestamp: new Date().toJSON(),
        markedAsRead: false,
      ;
    Stream.emit('aed29580-09fd-e411-b8e1-e61f13cf5d4b', 'message', item);
, 5000);

app.listen(3000);

console.log('Express E2e Mock server is running');

当手动访问 http://localhost:3000/loan/alerts/aed29580-09fd-e411-b8e1-e61f13cf5d4b 时，我看到消息打印到屏幕上，所以我猜这是 Angular 或缺少安全标头。 谢谢！

【参考方案1】：

我刚刚意识到，感谢this 的回答，事件必须以特定方式格式化。我相应地更改了res.write 的值：

Stream.on(req.params.fieldId, function(event, data) 
    res.write('event: ' + String(event) + '\n' + 'data: ' + JSON.stringify(data) + '\n\n');
);