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permissions.class.php

This class uses integer bitmasks to represent permissions. This allows for easy and acurate storage of complex permissions. To aid in ease of use the class will convert bitmasks to an associative array of boolean permissions and then convert the array back to a bitmask for easy storage.

Info

Source Code ( 130 lines )

<?php
/****************************************************************
*****************************************************************
Copyright (C) 2003  Keith Ganger

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 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.

You can find more information about GPL licence at:
http://www.gnu.org/licenses/gpl.html

****************************************************************
****************************************************************/
/**
*This class uses a bit mask to represent user permissions.  
*This will allow you to store a singe integer representing a users permission set. 
*You can then covert this integer back into an associative array with boolean 
*values showing the users permission set.
*@author      Keith Ganger <ganger2@adelphia.net>
* @version     1.0
* @since       March 3 2004
*/

class permissions
{
	/**
	 * This array is used to represent the users permission in usable format.  
	 *You can change remove or add valuesto suit your needs.  
	 *Just ensure that each element defaults to false. Once you have started storing
	 *users permsisions a change to the order of this array will cause the 
	 *permissions to be incorectly interpreted.  
	 * @type Associtive array
	 */
	var $permissions=array("read"=>false,"write"=>false,"delete"=>false,"change_permissions"=>false,"admin"=>false);
	
	/**
	*This function will use an integer bitmask(as created by toBitmask())
	*to populate the class vaiable
	*$this->permissions with the users permissions as boolean values. 
	*@param int $bitmask an integer representation of the users permisions. 
	*This integer is created by toBitmask();
	*@return an associatve array with the users permissions. 
	*/
	function getPermissions($bitMask=0){
		
		/*
		*The following explains how this code works. 
		*
		*This table shows how bitmasks will represent a particular permission.
		*element bin number -- 2^i -- decimal equiv
		*read	 00000001   -- 2^0 -- 1
		*write   00000010   -- 2^1 -- 2
		*delete  00000100   -- 2^2 -- 4
		*
		*
		*
		*The following code block loops through the permissions it uses a bitwise AND(&)
		*along with the terinary operator to assign the permissions.
		*You may want to visit the documentation at www.php.net on the pow function, 
		*the terinary operator, and the bitwise AND(&). 
		*When using the bitwise AND(&) all bits that are set in both $bitMask and the 
		*return value of pow(2($i) are set to 1.
		*
		*For this example refer to the above table  
		*A user with read and delete permissions would be represented as 00000101 
		*which would be an integer bitmask of 5
		*when this code is executed the following would happen. 
		*The bitmask of 5 would be passed into the function 
		*so $bitmask is set to 5 or in binary(00000101). 
		*The first time through the loop the function pow(2,0) returns 1 (00000001)
		*the bitwise AND(&) then compares
		*(00000001) to (00000101) and returns 00000001 this is not equal to 0 
		*so the first element in the array "read" is set to true. 
		*
		*The second time through the loop the function pow(2,1) returns 2 (00000010) 
		*the bitwise AND(&) then compares
		*(00000010) to (00000101) and returns 00000000 this is equal to 0 
		*so the second element in the array "write" is set to false.
		*
		**The second time through the loop the function pow(2,2) returns 4 (00000100)
		*the bitwise AND(&) then compares
		*(00000100) to (00000101) and returns 00000100 this is 4 and is not equal to 0
		*so the third element in the array "delete" is set to false.
		*
		*The code will loop through the remaining elements setting all of them to false.
		*/
		$i=0;
		foreach($this->permissions as $key=>$value){
			$this->permissions[$key]= (($bitMask & pow(2,$i)) !=0) ? true: false;
			//uncomment the next line if you would like to see what is happening. 
			//echo $key . " i= ".strval($i)." power=" . strval(pow(2,$i)). "bitwise & = " . strval($bitMask & pow(2,$i))."<br>";
			$i++; 				
		}
		return $this->permissions;
	}
	
	
	/**This function will create and return and integer bitmask based on the permission values set in
	*the class variable $permissions. To use you would want to set the fields in $permissions to true for the permissions you want to grant. 
	*Then call toBitmask() and store the integer value.  Later you can pass that integer into getPermissions() to convert it back to an assoicative 
	*array. 
	*@return int an integer bitmask represeting the users permission set. 
	*/
	function toBitmask(){
		$bitmask=0;
		$i=0;
		foreach($this->permissions as $key=>$value){
			
			if($value){
				$bitmask+=pow(2,$i);
			}
			$i++;	
		}
		return $bitmask;
	}
			
	
}
?>