# Server-sent events

Server-sent events let you push data to the client. It's a simple way to send data from the server to the client. The data is sent as a stream of messages, with an optional event name and id. It's a simple way to send data from the server to the client.

# Installation

Before using the Server-sent events, we need to install the @tsed/sse module.

Then add the following configuration in your Server:

import {Configuration} from "@tsed/common";
import "@tsed/sse"; // import sse Ts.ED module

@Configuration({
  acceptMimes: ["application/json", "text/event-stream"]
})
export class Server {}

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WARNING

There is a known issue with the compression middleware. The compression middleware should be disabled to work correctly with Server-sent events.

# Features

Support decorator usage to enable event-stream on an endpoint,
Support Node.js stream like EventEmmiter to emit events from your controller to your consumer,
Support Observable from rxjs to emit events from your controller to your consumer.
Support @tsed/json-mapper to serialize your model before sending it to the client.
Gives an API compatible with Express.js and Koa.js.

# Enable event-stream

To enable the event-stream on an endpoint, you need to use the @EventStream() decorator on a method of a controller.

import {Controller} from "@tsed/di";
import {Get} from "@tsed/schema";
import {EventStream, EventStreamCtx} from "@tsed/sse";

@Controller("/sse")
export class MyCtrl {
  @Get("/events")
  @EventStream()
  events(@EventStreamCtx() eventStream: EventStreamCtx) {
    let intervalId: ReturnType<typeof setInterval>;

    eventStream.on("close", () => {
      clearInterval(intervalId);
    });

    eventStream.on("end", () => {
      clearInterval(intervalId);
    });

    intervalId = setInterval(() => {
      // Ts.ED support Model serialization using json-mapper here
      eventStream.emit("event", new Date());
    }, 1000);
  }
}

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# Stream events

You can use Node.js stream like EventEmmiter to emit events from your controller to your consumer:

import {EventStream} from "@tsed/sse";
import {Controller} from "@tsed/di";
import {Get} from "@tsed/schema";

@Controller("/sse")
export class MyCtrl {
  private eventEmitter = new EventEmitter();

  $onInit() {
    setInterval(() => {
      this.eventEmitter.emit("message", new Date());
    }, 1000);
  }

  @Get("/events")
  @EventStream()
  events() {
    return this.eventEmitter;
  }
}

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# Observable

You can also use Observable from rxjs to emit events from your controller to your consumer:

import {Controller} from "@tsed/di";
import {Get} from "@tsed/schema";
import {EventStream} from "@tsed/sse";
import {Observable} from "rxjs";

@Controller("/sse")
export class MyCtrl {
  @Get("/events")
  @EventStream()
  events() {
    const observable = new Observable((observer) => {
      setInterval(() => {
        observer.next(new Date());
      }, 1000);
    });

    return observable;
  }
}

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# Author

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