promise wrapped ( with progress ) get random bytes from /dev/random

random.js

var
    Q = require('q'),
    fs = require('fs');


function get ( o ) {

    var requiredLength, SOURCE;

    if ( typeof o === 'object' ) {
        requiredLength = o.length;
        SOURCE = o.source || '/dev/random';
    } else {
        requiredLength = o;
        SOURCE = '/dev/random';
    }


    var D = Q.defer();

    var fd = fs.open(SOURCE, 'r', function (error, fd){

        if ( error ) D.reject(error);
    
        var stream          = fs.createReadStream(SOURCE, {fd : fd}),
            isDone          = false,
            result          = new Buffer(0),
            oldPercents     = 0,
            currentPercents = 0;

        stream.on('readable', function () {
            if ( isDone ) return;
    
            var chunk = stream.read();
        
            if ( chunk === null ) {
                isDone = true;
                D.reject('unexpected end of ' + SOURCE + ' stream');
            }
        
            result = Buffer.concat([result, chunk]);

            currentPercents = Math.floor(result.length/requiredLength*100);

            if ( currentPercents >= 100 ) {
                currentPercents = 100;
                isDone = true;
                result = result.slice(0, requiredLength);

                return closeFd(fd)
                .then(D.resolve.bind(D, result))
                .fail(D.reject.bind(D));
            }
    
            if ( oldPercents !== currentPercents ) {
                oldPercents = currentPercents;
                D.notify(currentPercents);
            }
        });
        
        stream.on('end', function () {
            isDone = true;
            D.reject('unexpected end of ' + SOURCE + ' stream');
        });
        
        stream.on('error', function (error) {
            isDone = true;
            D.reject(error);
        });
    });

    return D.promise;
}

function closeFd ( fd ) {
    var D = Q.defer();

    fs.close(fd, function(error){
        error
            ? D.reject(error)
            : D.resolve();
    });

    return D.promise;
}

module.exports.get = get;


// ---------------------------------------------------------------------- usage:
var
    StringDecoder = require('string_decoder').StringDecoder,
    decoder       = new StringDecoder('base64');

get(1024)
.then(function(buffer){
    var string = decoder.write(buffer);
    console.log('[DONE] : %s bytes', string.length);
    //console.log('\n\n', string);
})
.fail(function(error){
    console.log('[ERROR] : ', error);
})
.progress(function(progress){
    console.log('[PROGRESS] : %s%', progress);
});