Posts Tagged ‘class’

Updated JavaScript UUID Generator v.0.3

Friday, September 5th, 2008

The JavaScript UUID Generator class has been refreshed again and is even more efficient than the 0.2 version due largely in part to heavier reliance on built in JavaScript functions. It’s still not a “REAL” UUID, but it’s good enough for most projects. The changes are as follows:

  • A leaner and more efficient returnBase(val, base) method for conversion to base16 strings. The original version from irt.org has been replaced with built in JavaScript methods. Some testing for your target platforms should be performed to ensure compatibility with your engine.
  • The change from randrange(min, max) in v.0.1 to rand(max) in 0.2 introduced a bug where the maximum value provided would never be matched. This has been fixed to correct for that issue.

Special thanks go out to Robert Kieffer for pointing out these issues and providing the updated code for the base 16 conversion.

Download the latest version.

View Code JAVASCRIPT
/*
uuid.js - Version 0.3
JavaScript Class to create a UUID like identifier
 
Copyright (C) 2006-2008, Erik Giberti (AF-Design), All rights reserved.
 
This program is free software; you can redistribute it and/or modify it under 
the terms of the GNU General Public License as published by the Free Software 
Foundation; either version 2 of the License, or (at your option) any later 
version.
 
This program is distributed in the hope that it will be useful, but WITHOUT ANY 
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 
PARTICULAR PURPOSE. See the GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License along with 
this program; if not, write to the Free Software Foundation, Inc., 59 Temple 
Place, Suite 330, Boston, MA 02111-1307 USA
 
The latest version of this file can be downloaded from
http://www.af-design.com/resources/javascript_uuid.php
 
HISTORY:
6/5/06 	- Initial Release
5/22/08 - Updated code to run faster, removed randrange(min,max) in favor of
          a simpler rand(max) function. Reduced overhead by using getTime() 
          method of date class (suggestion by James Hall).
9/5/08	- Fixed a bug with rand(max) and additional efficiencies pointed out 
	  by Robert Kieffer http://broofa.com/
 
KNOWN ISSUES:
- Still no way to get MAC address in JavaScript
- Research into other versions of UUID show promising possibilities 
  (more research needed)
- Documentation needs improvement
 
*/
 
// On creation of a UUID object, set it's initial value
function UUID(){
	this.id = this.createUUID();
}
 
// When asked what this Object is, lie and return it's value
UUID.prototype.valueOf = function(){ return this.id; }
UUID.prototype.toString = function(){ return this.id; }
 
//
// INSTANCE SPECIFIC METHODS
//
 
UUID.prototype.createUUID = function(){
	//
	// Loose interpretation of the specification DCE 1.1: Remote Procedure Call
	// described at http://www.opengroup.org/onlinepubs/009629399/apdxa.htm#tagtcjh_37
	// since JavaScript doesn't allow access to internal systems, the last 48 bits 
	// of the node section is made up using a series of random numbers (6 octets long).
	//  
	var dg = new Date(1582, 10, 15, 0, 0, 0, 0);
	var dc = new Date();
	var t = dc.getTime() - dg.getTime();
	var h = '-';
	var tl = UUID.getIntegerBits(t,0,31);
	var tm = UUID.getIntegerBits(t,32,47);
	var thv = UUID.getIntegerBits(t,48,59) + '1'; // version 1, security version is 2
	var csar = UUID.getIntegerBits(UUID.rand(4095),0,7);
	var csl = UUID.getIntegerBits(UUID.rand(4095),0,7);
 
	// since detection of anything about the machine/browser is far to buggy, 
	// include some more random numbers here
	// if NIC or an IP can be obtained reliably, that should be put in
	// here instead.
	var n = UUID.getIntegerBits(UUID.rand(8191),0,7) + 
			UUID.getIntegerBits(UUID.rand(8191),8,15) + 
			UUID.getIntegerBits(UUID.rand(8191),0,7) + 
			UUID.getIntegerBits(UUID.rand(8191),8,15) + 
			UUID.getIntegerBits(UUID.rand(8191),0,15); // this last number is two octets long
	return tl + h + tm + h + thv + h + csar + csl + h + n; 
}
 
 
//
// GENERAL METHODS (Not instance specific)
//
 
 
// Pull out only certain bits from a very large integer, used to get the time
// code information for the first part of a UUID. Will return zero's if there 
// aren't enough bits to shift where it needs to.
UUID.getIntegerBits = function(val,start,end){
	var base16 = UUID.returnBase(val,16);
	var quadArray = new Array();
	var quadString = '';
	var i = 0;
	for(i=0;i<base16.length;i++){
		quadArray.push(base16.substring(i,i+1));	
	}
	for(i=Math.floor(start/4);i<=Math.floor(end/4);i++){
		if(!quadArray[i] || quadArray[i] == '') quadString += '0';
		else quadString += quadArray[i];
	}
	return quadString;
}
 
// Replaced from the original function to leverage the built in methods in
// JavaScript. Thanks to Robert Kieffer for pointing this one out
UUID.returnBase = function(number, base){
	return (number).toString(base).toUpperCase();
}
 
// pick a random number within a range of numbers
// int b rand(int a); where 0 <= b <= a
UUID.rand = function(max){
	return Math.floor(Math.random() * (max + 1));
}
 
// end of UUID class file

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Posted in javascript | No Comments »

Memcache Feature-Bug Gotchas

Thursday, July 17th, 2008

Recently I’ve been doing a lot of work with memcached using PHP and have been bitten a few times by different things with how things worked. I’m calling those items out here so anyone getting started with Memcache can learn from my mistakes. Memcached is an amazingly powerful caching layer with lots and lots of online documentation. It’s easy to get running on Linux and hooking PHP into it - I’ll save yet another post about how to do it since there are so many excellent resources already. The hard part is determining where you’ll implement it and in what way. For this post, I’ll leave the implementation strategy aside and walk you through a couple of examples of where I’ve been bit. I’ve created a layer to further abstract the memcache() object in PHP so I can ignore dealing with the add() vs. replace() vs. set() switches and allowing me to have one stop shopping for all of my configuration settings. The source for that basic class is included at the bottom of this post, feel free to use/distribute as you see fit.

One last item before we delve into the examples. Memcached and memcache are not quite the same thing. When I reference Memcached - I’m actually referring to the server instance of Memcache which you are running on the server, which is accessible using a variety of methods, on a variety of platforms including but not limited to PHP. When I use memcache in this post, I’m referring to the API hooks that have been created for PHP to interact with your Memcached server instance. Some (or possibly all) of these items ONLY APPLY TO PHP and shouldn’t be construed as feature-bugs with the Memcached server itself.

Compression and Object Sizes

It took me a while to track down this bug - but I finally read up on memcache a bit more and learned that memcache behaves oddly with small chunks of information if compression is turned on. I’m pretty sure this is memcache not memcached that’s causing the issue because the compression layer happens in PHP. The output for the following code is The value is not the same. However, if $compression is set to false, it will work as expected. Integers and character strings seem to be okay with compression on - as do complex objects. The setCompressThreshold method allows adjustment of this size but I’ve gotten in the habit of not caching simple values like true and false - instead opting to cache objects, classes, arrays and alternately JSON.

View Code PHP
// create the cache
$cache = new Memcache();
$cache->addServer("localhost","11211");
$compression = true;
 
// create the value in the cache
$x = true;
$cache->add("x", $x, $compression, 10);
 
// access the value
$y = $cache->get("x", $compression);
 
// check what happened
if($x == $y){
   print "The value is the same";
} else {
   print "The value is not the same";
}

Caching of Class Objects

When caching complex objects like classes, memcache serializes the entire object and then caches it was as it was instantiated. So be warned if your class definition changes, you’ll need to flush your cache entirely of those objects or you might find it behaves a little differently than your expecting. Let’s say you have a class with a few properties that update multiple properties when certain methods are called and you wish to change one of those properties slightly. Any objects that are in the cache already will continue to work with the old values until they are flushed from the cache. It’s not sufficient to read it out and put it back in - the object really is your OLD class definition.

View Code PHP
class Foo{
   protected $property = array();
   public function __construct($arr){
      if(count($arr) > 0){
         $this->properties = $arr;
      }
   }
   public function __get($key){
      return $this->property[$key];
   }
   public function __set($key, $value){
      $this->property[$key] = $value;
   }
}

So now you can create Foo objects all day and stuff all sorts of information into them and cache them. You can also get them back out willy nilly later (I’ll use my cache class to save time on the code below).

View Code PHP
$foo1 = new Foo(array("apples"=>11,"orange"=>20));
$cache->set("foo1",$foo1, 60);
$foo2 = $cache->get("foo1");
echo $foo2->apples; // should be 11

So we see that all works but, what if we change the way the class works? For example adding a layer of math to calculate a tax or something along those lines.

View Code PHP
class Foo{
   protected $property = array();
   public function __construct($arr){
      if(count($arr) > 0){
         $this->properties = $arr;
      }
   }
   public function __get($key){
      return round($this->property[$key] * .9); // calculate storage/depreciation loss
   }
   public function __set($key, $value){
      $this->property[$key] = $value;
      $this->property['num_items'] = count($this->properties) - 1;
   }
}

Our existing cached object doesn’t behave as expected. One of two things seems to happen, and I haven’t fully flushed it out what happens when. First, the object just comes back as it was initially instantiated or second, it silently dies without returning an error. This might be a good reason to create a version value for your cached objects so you can switch on the version to determine if the cached value is valid.

View Code PHP
// let's access our existing cache object from before again...
$foo2 = $cache->get("foo1");
echo $foo2->apples; // we might hope for 10 but...

Database Results

Caching of resources doesn’t work. The data being cached needs to be able to be serialized by memcache so it can be inserted into memcached. Database handles are much like your memcached connection - they’re a socket you talk to and unfortunately, so are MySQL results. There are good reasons for this so don’t gripe about it. You’ll need to write a simple wrapper that does all of the result parsing for you prior to caching. Then you can easily create a cacheable MySQL object that can be inserted into memcached. It only takes a few minutes to do this and I may even post later describing the wrappers I’m now using to do just this. Until then - know that you can quickly create an array of your data using the following code and cache that result instead.

View Code PHP
// create a cache object (using class from below)
$cache = new Cache();
 
// create an array to populate the data with
$data_array = array();
 
// run the query 
$mysqli_result = $mysqli->query("select * from table where condition=true");
 
// stuff all the data into the array
while($row = $mysqli_result->fetch_assoc()){
   $data_array[] = $row;
}
 
// cache the array
$cache->set("query_data",$data_array,90);

Cache Time to Live

Nothing too big here, but if you provide 0 (zero) or false for a time to live/expiration value, the item never expires, it just gets pushed out if needed later. This all happens on a LRU basis and is well documented.

Protect your Namespaces

This may seem trivial, but I’ve been bit here too. Often it’s sufficient to use one server for multiple tasks. Since Memcached is easy to run in one large pool and share it among multiple resources (much like you would with MySQL) it’s easy to share across multiple applications. There are some nice economies of scale this will afford you. But consider the following bug you could create for yourself in your logic.

Application 1 accessing it’s DB table.

View Code PHP
 
// Application 1 fetching content about a user
$memcache = new Cache();
$query = "select * from users where userid = 12";
$result = $memcache->get(hash(md5,$query));
 
// The data wasn't in cache, so we run the query below and store the data
if(!$result){
     $result = $mysql->query($query);
     $memcache->set(hash(md5,$query), $result, 600);
}

Application 2 accessing it’s DB table.

View Code PHP
// Application 2 fetching content about a user
 
$memcache = new Cache();
$query = "select * from users where userid = 12";
$result = $memcache->get(hash(md5,$query));
 
// the value existed in cache - so it skips the query and uses the cached value
if(!$result){
     $result = $mysql->query($query);
     $memcache->set(hash(md5,$query), $result, 600);
}

Application 2 and Application 1 are using the EXACT same key to reference their data. Unless this is intentional (because they share a common database) it can be a real pain to debug. The easiest way to correct this is to create a namespace for the cache layer and append it to any keys you may use. The example class provided below does just that with minimal fuss. The code above would be changed to reflect the correct namespace for each application and they could co-exist using the memcached server together.

View Code PHP
// in app 1 - use that namespace
$cache = new Cache("app1");
 
// in app 2 - use that namespace
$cache = new Cache("app2");

Memcache Abstraction Class

This is the abstraction class I use to handle all memcache interaction. It’s little more than a thin veneer over the existing PHP object. You can see where it’s easy to expand this basic cache layer within the constructor and you can tune for your data, servers and other bits relevant to your implementation as needed.

View Code PHP
class Cache{
 
   protected $cache = false;
   protected $namespace = "";
 
   public function __construct($namespace = ""){
      $this->cache = new Memcache();
      $this->cache->addServer("localhost","11211");
      $this->cache->setCompressThreshold(127,0.2);
      $this->namespace = $namespace;
   }
 
   public function __destruct(){
      $this->cache->close();
   }
 
   public function set($key, $value, $ttl = 600){
      $this->cache->set($key . $this->namespace, $value, true, $ttl);
   }
 
   public function get($key){
      return $this->cache->get($key . $this->namespace, true);
   }
 
}

Tags: , , , , , ,
Posted in memcached, php, software | No Comments »

JavaScript UUID Generator v. 0.2

Thursday, May 22nd, 2008

Nearly 2 years ago I crafted some JavaScript code to create a properly formatted UUID in JavaScript. Full compliance with specification for version 1 UUID’s still isn’t possible. However, in the interest of keeping the project updated, I’ve made some changes to the code to make it more reliable and more efficient.

  • It now use getTime() from the date object. This reduced the time spent calculating unnecessary values for the timestamp (idea came from James Hall’s canonical name function).
  • The randrange() function was replaced with one that more evenly distributes the random number values while additionally reducing complexity.

Get the download here.

I’d also like to give a shout to some of the folks who have mentioned it in forums, ported it to different libraries, linked to it from Wikipedia, blogs etc and have generally made my efforts worth while. Thank You!

View Code JAVASCRIPT
/*
 
uuid.js - Version 0.2
JavaScript Class to create a UUID like identifier
 
Copyright (C) 2006-2008, Erik Giberti (AF-Design), All rights reserved.
 
This program is free software; you can redistribute it and/or modify it under 
the terms of the GNU General Public License as published by the Free Software 
Foundation; either version 2 of the License, or (at your option) any later 
version.
 
This program is distributed in the hope that it will be useful, but WITHOUT ANY 
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 
PARTICULAR PURPOSE. See the GNU General Public License for more details.
 
You should have received a copy of the GNU General Public License along with 
this program; if not, write to the Free Software Foundation, Inc., 59 Temple 
Place, Suite 330, Boston, MA 02111-1307 USA
 
The latest version of this file can be downloaded from
http://www.af-design.com/resources/javascript_uuid.php
 
HISTORY:
6/5/06 	- Initial Release
5/22/08 - Updated code to run faster, removed randrange(min,max) in favor of
          a simpler rand(max) function. Reduced overhead by using getTime() 
          method of date class (suggestion by James Hall).
 
KNOWN ISSUES:
- Still no way to get MAC address in JavaScript
- Research into other versions of UUID show promising possibilities 
  (more research needed)
- Documentation needs improvement
 
*/
 
// On creation of a UUID object, set it's initial value
function UUID(){
	this.id = this.createUUID();
}
 
// When asked what this Object is, lie and return it's value
UUID.prototype.valueOf = function(){ return this.id; }
UUID.prototype.toString = function(){ return this.id; }
 
//
// INSTANCE SPECIFIC METHODS
//
 
UUID.prototype.createUUID = function(){
	//
	// Loose interpretation of the specification DCE 1.1: Remote Procedure Call
	// described at http://www.opengroup.org/onlinepubs/009629399/apdxa.htm#tagtcjh_37
	// since JavaScript doesn't allow access to internal systems, the last 48 bits 
	// of the node section is made up using a series of random numbers (6 octets long).
	//  
	var dg = new Date(1582, 10, 15, 0, 0, 0, 0);
	var dc = new Date();
	var t = dc.getTime() - dg.getTime();
	var h = '-';
	var tl = UUID.getIntegerBits(t,0,31);
	var tm = UUID.getIntegerBits(t,32,47);
	var thv = UUID.getIntegerBits(t,48,59) + '1'; // version 1, security version is 2
	var csar = UUID.getIntegerBits(UUID.rand(4095),0,7);
	var csl = UUID.getIntegerBits(UUID.rand(4095),0,7);
 
	// since detection of anything about the machine/browser is far to buggy, 
	// include some more random numbers here
	// if NIC or an IP can be obtained reliably, that should be put in
	// here instead.
	var n = UUID.getIntegerBits(UUID.rand(8191),0,7) + 
			UUID.getIntegerBits(UUID.rand(8191),8,15) + 
			UUID.getIntegerBits(UUID.rand(8191),0,7) + 
			UUID.getIntegerBits(UUID.rand(8191),8,15) + 
			UUID.getIntegerBits(UUID.rand(8191),0,15); // this last number is two octets long
	return tl + h + tm + h + thv + h + csar + csl + h + n; 
}
 
 
//
// GENERAL METHODS (Not instance specific)
//
 
 
// Pull out only certain bits from a very large integer, used to get the time
// code information for the first part of a UUID. Will return zero's if there 
// aren't enough bits to shift where it needs to.
UUID.getIntegerBits = function(val,start,end){
	var base16 = UUID.returnBase(val,16);
	var quadArray = new Array();
	var quadString = '';
	var i = 0;
	for(i=0;i<base16.length;i++){
		quadArray.push(base16.substring(i,i+1));	
	}
	for(i=Math.floor(start/4);i<=Math.floor(end/4);i++){
		if(!quadArray[i] || quadArray[i] == '') quadString += '0';
		else quadString += quadArray[i];
	}
	return quadString;
}
 
// Numeric Base Conversion algorithm from irt.org
// In base 16: 0=0, 5=5, 10=A, 15=F
UUID.returnBase = function(number, base){
	//
	// Copyright 1996-2006 irt.org, All Rights Reserved.	
	//
	// Downloaded from: http://www.irt.org/script/146.htm	
	// modified to work in this class by Erik Giberti
	var convert = ['0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'];
    if (number < base) var output = convert[number];
    else {
        var MSD = '' + Math.floor(number / base);
        var LSD = number - MSD*base;
        if (MSD >= base) var output = this.returnBase(MSD,base) + convert[LSD];
        else var output = convert[MSD] + convert[LSD];
    }
    return output;
}
 
// pick a random number within a range of numbers
// int b rand(int a); where 0 <= b <= a
UUID.rand = function(max){
	return Math.floor(Math.random() * max);
}
 
// end of UUID class file

Tags: , ,
Posted in javascript | No Comments »

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