SFN-SSE

Sugar Featured Node.js Server-Sent Events implementation based on HTML5 API.

Install

npm install sfn-sse

Example

import * as http from "http";
import SSE from "sfn-sse";

const server = http.createServer((req, res) => {
    if (!SSE.isEventSource(req)) {
        res.end();
        return;
    }

    var sse = new SSE(req, res);

    if (sse.isClosed) { // check if the the connection has been marked closed.
        return;
    } else {
        let i = 0,
        timer = setInterval(() => {
            i += 1;
            sse.send(`This is msg ${i}.`); // Send message every seconds.
            if (i === 10) {
                sse.close(); // Close the connection.
                clearInterval(timer);
            }
        }, 1000);
    }
});

server.listen(80);

Client Side:

const source = new EventSource("http://localhost");

source.onmessage = (event) => {
    console.log(event.data);

    if (event.data.match(/10/)) {
        // Must close connection here, otherwise the client will reconnect.
        source.close();
    }
};

API

• new SSE(req, res, retry?: number)
  • retry The re-connection time to use when attempting to send the event.
• sse.id: string The unique ID of the SSE connection, also used as lastEventId of the client EventSource, when the client reconnect, this ID will be reused.
• sse.isNew: boolean Whether the connection is new.
• sse.isClosed: boolean Whether the connection is closed. This property is used to check whether a re-connection has been marked closed, once closed, the server must not do anything continuing.
• writeHead(code: number, headers?: { [x: string]: string | string[] }): this Sends a response header to the client.
• send(data: any): boolean Sends data to the client.
• emit(event: string, data?: any): boolean Emits an event to the client, the message will be dispatched on the browser to the listener for the specified event name; the website source code should use addEventListener() to listen for named events.
• close(cb?: () => void): void Closes the connection.

About Closing

According to the Server-Sent Events protocol, the server cannot entirely close the connection without re-connection firing on the client, unless the server send a 204 status code telling the client not to, so SFN-SSE provided an approach to handle this procedure internally. Once close() method is called, the server will close the current HTTP connection, and mark the id closed, so that when the client try to reconnect, the server can identify it as a closed connection and send 204 automatically and immediately to prevent the client re-connecting. That said, the server should check the property isClosed at the very beginning of the request life cycle, to see if a connection has been marked closed, once closed, the server must not do anything continuing.

Warning

IE and Edge does not support EventSource, you must use a polyfill for them.