@steelbreeze/broker/lib/server.js

Lightweight publish and subscribe using Server-Sent Events for node and express

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var express_1 = require("express");
// find or create a topic given its name
function getTopic(topics, topic) {
    return topics[topic] || (topics[topic] = { lastEventId: -1, data: undefined, subscribers: [] });
}
// write a single message to a client
function sendEvent(client, eventId, data) {
    setImmediate(function (client, eventId, data) {
        client.write("id:" + eventId + "\ndata:" + data + "\n\n");
    }, client, eventId, data);
}
/**
 * Creates an instance of a message broker server.
 * Many message broker servers may be created, each bound to a different base url.
 * @param cacheLastMessage When true, subscribers will receive the last message upon subscrition.
 * @returns Returns an express Router for use within an express application.
 */
function server(cacheLastMessage) {
    if (cacheLastMessage === void 0) { cacheLastMessage = false; }
    var router = express_1.Router();
    var topics = {};
    // GET method is used to subscribe by EventSource clients
    router.get('*', function (req, res) {
        var topic = getTopic(topics, req.url);
        // remove the subscription when the connection closes
        req.on('close', function () {
            topic.subscribers.splice(topic.subscribers.indexOf(res), 1);
        });
        // create the subscription
        topic.subscribers.push(res);
        // set the response headers to specify this is an event stream
        res.set({ 'Content-Type': 'text/event-stream', 'Cache-Control': 'no-cache', 'Connection': 'keep-alive' });
        // update the client with the last message if required
        if (cacheLastMessage && topic.data) {
            sendEvent(res, topic.lastEventId, topic.data);
        }
    });
    router.post('*', function (req, res) {
        var topic = getTopic(topics, req.url);
        var body = [];
        // read the post body
        req.on('data', function (chunk) {
            body.push(chunk);
        });
        req.on('end', function () {
            // update the topic with the new event details
            topic.data = Buffer.concat(body).toString();
            topic.lastEventId = (topic.lastEventId === Number.MAX_VALUE ? -1 : topic.lastEventId) + 1;
            // queue dispatch of event to all current subscribers
            topic.subscribers.forEach(function (subscriber) {
                sendEvent(subscriber, topic.lastEventId, topic.data); // NOTE: as we have just set topic.data we know it's not undefined
            });
        });
        // send response to publisher
        res.sendStatus(200);
    });
    return router;
}
exports.server = server;