node.js EventEmitter wrapper for the wmii event loop.

wmii_events.js

// wmii event handler module
// Adam R. Nelson
// August 2013

var events = require('events');
var util   = require('util');
var wmiir  = require('./wmiir.js');

function WmiiEvents() {

    events.EventEmitter.call(this);

    var me = this;
    me.readProc = wmiir.read('/event', function(err, line) {
        var tokens;
        if (err) {
            // In the event of an error, emit a 'FatalError' event.
            tokens = ['FatalError', err.message || err];
        } else {
            // Split the line (minus the trailing newline) into tokens.
            tokens = line.split(" ");
        }
        // Emit a Node event based on the wmii event.
        // (The emit method is renamed below so that it can be overridden).
        me.emit_.apply(me, tokens);
    });

    // Turn off the max-listeners limit, since there will be a LOT of listeners
    // attached to this object.
    me.setMaxListeners(0);

    // The wmiir process will keep running forever until it is killed. Make
    // sure it is always killed before Node exits.
    function cleanup() {
        me.readProc.kill();
    }
    process.on('exit', cleanup);
    me.on('FatalError', function(/* varargs */) {
        // The message will be split up into string-separated tokens, which
        // need to be rejoined. Array.prototype.slice is needed to convert
        // 'arguments' to a real array, because Javascript.
        var message = Array.prototype.slice.apply(arguments).join(' ');
        console.log("Fatal error occurred! - " + message);
        cleanup();
    });
}

// Extend EventEmitter.
util.inherits(WmiiEvents, events.EventEmitter);

// Rename the original emit method...
WmiiEvents.prototype.emit_ = WmiiEvents.prototype.emit;

// ... and add a new one that broadcasts events globally.
WmiiEvents.prototype.emit = function(/* No arg names; this is varargs. */) {
    // Convert 'arguments' to an array, because it's not by default.
    // (*sigh* Javascript...)
    var eventParts = Array.prototype.slice.call(arguments);
    var me = this;

    // Remove any problematic newline-containing elements and non-string
    // elements from the array.
    eventParts = eventParts.filter(function(e) {
        return (typeof e == 'string' || e instanceof String) && e.indexOf('\n') == -1;
    });

    // Write a space-separated event string to the /event file.
    wmiir.write('/event', eventParts.join(' '), function(err) {
        if (err) {
            // If an error occurs, broadcast an event.
            me.emit_('Error', err);
        }
    });
    
    // Always return true... the original emit() returns true if there was a
    // listener for the event, but there may always be another process
    // listening in this case.
    return true;
};

// Call this function to terminate the event listener without terminating Node.
WmiiEvents.stopListening = function() {
    this.readProc.kill('SIGHUP');
};

// Export a single copy of the event handler object.
module.exports = new WmiiEvents();