backoff/lib/backoff.js

/*
 * Copyright (c) 2012 Mathieu Turcotte
 * Licensed under the MIT license.
 */

var events = require('events');
var util = require('util');

/**
 * Backoff driver.
 * @param backoffStrategy Backoff delay generator/strategy.
 * @constructor
 */
function Backoff(backoffStrategy) {
    events.EventEmitter.call(this);

    this.backoffStrategy_ = backoffStrategy;
    this.maxNumberOfRetry_ = -1;
    this.backoffNumber_ = 0;
    this.backoffDelay_ = 0;
    this.timeoutID_ = -1;

    this.handlers = {
        backoff: this.onBackoff_.bind(this)
    };
}
util.inherits(Backoff, events.EventEmitter);

/**
 * Sets a limit, greater than 0, on the maximum number of backoffs. A 'fail'
 * event will be emitted when the limit is reached.
 * @param maxNumberOfRetry The maximum number of backoffs.
 */
Backoff.prototype.failAfter = function(maxNumberOfRetry) {
    if (maxNumberOfRetry < 1) {
        throw new Error('Maximum number of retry must be greater than 0. ' +
                        'Actual: ' + maxNumberOfRetry);
    }

    this.maxNumberOfRetry_ = maxNumberOfRetry;
};

/**
 * Starts a backoff operation.
 * @param err Optional paramater to let the listeners know why the backoff
 *     operation was started.
 */
Backoff.prototype.backoff = function(err) {
    if (this.timeoutID_ !== -1) {
        throw new Error('Backoff in progress.');
    }

    if (this.backoffNumber_ === this.maxNumberOfRetry_) {
        this.emit('fail', err);
        this.reset();
    } else {
        this.backoffDelay_ = this.backoffStrategy_.next();
        this.timeoutID_ = setTimeout(this.handlers.backoff, this.backoffDelay_);
        this.emit('backoff', this.backoffNumber_, this.backoffDelay_, err);
    }
};

/**
 * Handles the backoff timeout completion.
 * @private
 */
Backoff.prototype.onBackoff_ = function() {
    this.timeoutID_ = -1;
    this.emit('ready', this.backoffNumber_, this.backoffDelay_);
    this.backoffNumber_++;
};

/**
 * Stops any backoff operation and resets the backoff delay to its inital
 * value.
 */
Backoff.prototype.reset = function() {
    this.backoffNumber_ = 0;
    this.backoffStrategy_.reset();
    clearTimeout(this.timeoutID_);
    this.timeoutID_ = -1;
};

module.exports = Backoff;