out_queue.js

/*
 * JavaScript tracker for Snowplow: out_queue.js
 * 
 * Significant portions copyright 2010 Anthon Pang. Remainder copyright 
 * 2012-2014 Snowplow Analytics Ltd. All rights reserved. 
 * 
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions are 
 * met: 
 *
 * * Redistributions of source code must retain the above copyright 
 *   notice, this list of conditions and the following disclaimer. 
 *
 * * Redistributions in binary form must reproduce the above copyright 
 *   notice, this list of conditions and the following disclaimer in the 
 *   documentation and/or other materials provided with the distribution. 
 *
 * * Neither the name of Anthon Pang nor Snowplow Analytics Ltd nor the
 *   names of their contributors may be used to endorse or promote products
 *   derived from this software without specific prior written permission. 
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

;(function() {

	var
		json2 = require('JSON'),
		lodash = require('./lib_managed/lodash'),
		localStorageAccessible = require('./lib/detectors').localStorageAccessible(),
		object = typeof exports !== 'undefined' ? exports : this; // For eventual node.js environment support

	/**
	 * Object handling sending events to a collector.
	 * Instantiated once per tracker instance.
	 *
	 * @param string functionName The Snowplow function name (used to generate the localStorage key)
	 * @param string namespace The tracker instance's namespace (used to generate the localStorage key)
	 * @param object mutSnowplowState Gives the pageUnloadGuard a reference to the outbound queue
	 *                                so it can unload the page when all queues are empty
	 * @param useLocalStorage Whether to use localStorage at all
	 * @return object OutQueueManager instance
	 */
	object.OutQueueManager = function (functionName, namespace, mutSnowplowState, useLocalStorage) {
		var	queueName = ['snowplowOutQueue', functionName, namespace].join('_'),
			executingQueue = false,
			configCollectorUrl,
			outQueue;

		if (localStorageAccessible && useLocalStorage) {
			// Catch any JSON parse errors that might be thrown
			try {
				outQueue = json2.parse(localStorage.getItem(queueName));
			}
			catch(e) {}
		}

		// Initialize to and empty array if we didn't get anything out of localStorage
		if (!lodash.isArray(outQueue)) {
			outQueue = [];
		}

		// Used by pageUnloadGuard
		mutSnowplowState.outQueues.push(outQueue);

		/*
		 * Queue an image beacon for submission to the collector.
		 * If we're not processing the queue, we'll start.
		 */
		function enqueueRequest (request, url) {
			outQueue.push(request);
			configCollectorUrl = url;
			if (localStorageAccessible && useLocalStorage) {
				localStorage.setItem(queueName, json2.stringify(outQueue));
			}

			if (!executingQueue) {
				executeQueue();
			}
		}

		/*
		 * Run through the queue of image beacons, sending them one at a time.
		 * Stops processing when we run out of queued requests, or we get an error.
		 */
		function executeQueue () {

			// Failsafe in case there is some way for a bad value like "null" to end up in the outQueue
			while (outQueue.length && typeof outQueue[0] !== 'string') {
				outQueue.shift();
			}

			if (outQueue.length < 1) {
				executingQueue = false;
				return;
			}

			// Let's check that we have a Url to ping
			if (!lodash.isString(configCollectorUrl)) {
				throw "No Snowplow collector configured, cannot track";
			}

			executingQueue = true;

			var nextRequest = outQueue[0];
			var image = new Image(1, 1);

			image.onload = function () {
				outQueue.shift();
				if (localStorageAccessible && useLocalStorage) {
					localStorage.setItem(queueName, json2.stringify(outQueue));
				}
				executeQueue();
			};

			image.onerror = function () {
				executingQueue = false;
			};

			image.src = configCollectorUrl + nextRequest;
		}

		return {
			enqueueRequest: enqueueRequest
		};
	};

}());