kast

An UDP multicast framework.

Usage example

Let's say we want to start two kast servers, each of which provides a command to check if the respective host is alive.

Host A

var kast = require('kast');
 
var server = kast();
 
server.command('/alive', function (req, res) {
    res.send('Hey! Host A is alive!');
});
 
server.listen(5000);

Host B

var kast = require('kast');
 
var server = kast();
 
server.command('/alive', function (req, res) {
    res.send('This is Host B speaking! How can I help you?');
});
 
server.listen(5000);

Client

A client can now send a broadcast request to all the hosts without knowing each individual ip address / host name.

var kast = require('kast');
 
kast.broadcast({
    port: 5000,
    command: '/alive',
}, function onResults (err, results) {
    console.log(results);
});

The results of the hosts which have responded in a timely manner will be collected in the results argument, like:

{
    '10.0.0.1': 'Hey! Host A is alive!',
    '10.0.0.23': 'This is Host B speaking! How can I help you?'
}

API

Install

$ npm install --save kast

Basic usage

 
var kast = require('kast');
 
var server = kast();

Creating a server instance

server.listen(port, [host], [callback])

Binds and listens for new connections on the given host and post. Please note that the host parameter is optional. kast uses 224.1.1.1 as a default multicast group.

The callback function will be executed as callback(err) after the binding process has been finished.

This method will return an instance of Socket which exposes the following API:

socket.close(callback)

Possibility for shutting the whole kast server down.

Registering commands

server.command(name, handlerFn)

The handlerFn will receive two ordinary parameters: A request and a response parameter. Pretty much like Express - You're welcome :).

Request

An object with the following information:

• req.id: An unique request id (will be generated by kast).
• req.connection.remoteAddress: The ip address of the host which has sent the request.
• req.connection.remotePort: The remote port of the host which has sent the request.
• req.command: The name of the command.
• req.body: A possible request body with additional data (comparable with a HTTP request body).

Response

While the req object provides pure information without any kind of functionality, the res object exposes a method with which you can answer a command and send the result back to the client.

res.send(body)

Sends a response with the given body as string.

Send a broadcast to the servers

kast.broadcast(options, callback)

The broadcast method will usually be called by a client which wants to execute several commands on the respective hosts (within the multicast group).

Possible options are:

• port: The port on which the other hosts are listening.
• command: The name of the command which should be executed.
• body: (optional) Additional data that should be passed to the command.
• `timeout: (optional; default=2000ms) The timeout after which the broadcast should stop waiting for responses.
• host: (optional; default='224.1.1.1') The ip address of the multicast group.

The callback function will be executed as callback(err, results). results will be an object with the ip addresses of the hosts as keys and the respective responses as values.

Development

Tests

In order to run the test suite, install the dependencies first, then run npm test:

$ npm install
$ npm test

License

MIT © 2014, André König (andre.koenig@posteo.de)