speed limited stream

limited.js

var Stream = require('stream')
  , util   = require('util')


util.inherits(Limited, Stream.Transform)

function Limited( options ) {

    if(!(this instanceof Limited)) {
        return new Limited( options )
    }

    this.options = options || {}
    Stream.Transform.call(this, this.options)

    this._limit = this.options.limit || 0
    this._stopwatch = new TimeWindowBuffer(10)
    this._speed  = 0
}

Limited.prototype._transform = function(chunk, enc, cb) {
    var len = chunk.length;

    if(this._limit > 0 && this._speed > this._limit) {
        var delay = (this._speed / this._limit) * 1000
        setTimeout(
            function() {
                cb(null, chunk)
                this._stopwatch.push(len)
            }.bind(this),
            Math.min(delay, 10000)
        )
    }
    else {
        cb(null, chunk)
        this._stopwatch.push(len)
    }

    this._speed  = this._stopwatch.calc()
    if(isNaN(this._speed)) {
        this._speed = 0;
    }
    //console.log(this._speed/1000, 'KB/s');
}


function TimeWindowBuffer(seconds) {
    this._maxAge = seconds * 1000
    this._buffer = []
}

TimeWindowBuffer.prototype.push = function(value) {
    this._buffer.push({
        time: Date.now(),
        value: value
    })
}

TimeWindowBuffer.prototype._trim = function() {
    var maxAge = Date.now() - this._maxAge
    this._buffer = this._buffer.filter(function(x) {
        return x.time > maxAge
    })
}

TimeWindowBuffer.prototype.calc = function(cb) {
    this._trim()
    if(this._buffer.length === 0) {
        return 0
    }
    var secondCnt = 0
    var secondSum = 0
    var startTime = this._buffer[0].time
    var tmp = 0
    for(var x=0;x<this._buffer.length;x++) {
        if(this._buffer[x].time > startTime + 1000) {
            secondSum += tmp
            secondCnt ++
            startTime = this._buffer[x].time
            tmp = 0;
        }
        tmp += this._buffer[x].value
    }
    secondCnt++
    secondSum += tmp
    //console.log(seconds, seconds.length, this._buffer.length)
    return secondSum / secondCnt
}


module.exports = Limited

Seems perfectly legit to me. What exactly are you using it for?