cometd-nodejs-server

The CometD Project

CometD NodeJS Server

Server side ES6 APIs and implementation of the Bayeux Protocol for NodeJS 18.x or greater. WebSocket not (yet) supported.

NPM Installation

npm install cometd-nodejs-server

Running the tests

npm install mocha
npm install cometd
npm install cometd-nodejs-client
npm test

Minimal Application

import * as http from "node:http";
import * as cometd from "cometd-nodejs-server";

// Create the CometD server instance.
const cometdServer = cometd.createCometDServer();

// Create an HTTP server, and bind request/response handling to the CometD server.
const httpServer = http.createServer((request, response) => cometdServer.handle(request, response));
httpServer.listen(0, "localhost", () => {
    // Your application code here, see examples below.
});

Customizing the CometDServer Configuration

import * as cometd from "cometd-nodejs-server";

const cometdServer = cometd.createCometDServer({
    logLevel: "debug", // Emits logging on the console
    timeout: 10000, // Heartbeat timeout in milliseconds
    maxInterval: 15000, // Server-side session expiration in milliseconds
    ...
});

Server timeout and CometD timeout

CometD clients send periodic heartbeat messages on the /meta/connect channel. The CometD server holds these heartbeat messages for at most the timeout value (see above), by default 20 seconds.

The NodeJS server also has a timeout property that controls the maximum time to handle a request/response cycle, by default 120 seconds.

You want to be sure that NodeJS' Server.timeout is greater than CometD"s CometDServer.options.timeout, especially if you plan to increase the CometD timeout.

Creating Channels and Receiving Messages

const channel = cometdServer.createServerChannel("/service/chat");

// Add a listener to be notified when a message arrives on the channel.
channel.addListener("message", function(session, channel, message, callback) {
    // Your message handling here.

    // Invoke the callback to signal that handling is complete.
    callback();
});

Publishing a Broadcast Message on a Channel

const channel = cometdServer.createServerChannel("/chat");

// Publishes the data string "hello" to all subscribers of the given channel.
channel.publish(null, "hello");

Installing a Security Policy

cometdServer.policy = {
    canHandshake: (session, message, callback) => {
        // Your handshake policy here.
        const allowed = ...;
        
        // Invoke the callback to signal the policy result. 
        callback(null, allowed);
    }
};

Sending a Direct Message to a Session

const session = cometdServer.getServerSession(sessionId);

// Deliver the message only to the given session.
session.deliver(null, "/service/chat", {
    text: "lorem ipsum"
});

Reacting to Session Timeout/Disconnection

session.addListener("removed", (session, timeout) => {
    if (timeout) {
        // Session was expired by the server.
    } else {
        // Session was explicitly disconnected.
    }
});

Accessing Contextual Information

In certain cases it is necessary to access contextual information such as the HTTP request that carries incoming CometD messages, or the HTTP response that carries outgoing CometD messages.

const channel = cometdServer.createServerChannel("/chat");

channel.addListener("message", (session, channel, message, callback) => {
    // Access contextual information.
    const request = cometdServer.context.request;
    if (request) {
        // You can read headers from the NodeJS HTTP request.
        const myHeader = request.headers["X-My-Header"];
        ...
    }

    var response = cometdServer.context.response;
    if (response) {
        // You can add headers to the NodeJS HTTP response.
        response.setHeader("X-My-Header", "foo_bar");
        ...
    }

    // Invoke the callback to signal that handling is complete.
    callback();
});

NOTE: always check if the request and response objects are defined; they may not be defined if the transport used is not HTTP but, for example in the future, WebSocket.