<?php
/**
 * Random_* Compatibility Library 
 * for using the new PHP 7 random_* API in PHP 5 projects
 * 
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 - 2017 Paragon Initiative Enterprises
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
defined('BASEPATH') OR exit('No direct script access allowed');

defined('RANDOM_COMPAT_READ_BUFFER') OR define('RANDOM_COMPAT_READ_BUFFER', 8);

if (!is_callable('random_bytes'))
{
	/**
	 * Unless open_basedir is enabled, use /dev/urandom for
	 * random numbers in accordance with best practices
	 *
	 * Why we use /dev/urandom and not /dev/random
	 * @ref http://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers
	 *
	 * @param int $bytes
	 *
	 * @throws Exception
	 *
	 * @return string
	 */
	function random_bytes($bytes)
	{
		static $fp = null;
		/**
		 * This block should only be run once
		 */
		if (empty($fp))
		{
			/**
			 * We use /dev/urandom if it is a char device.
			 * We never fall back to /dev/random
			 */
			$fp = fopen('/dev/urandom', 'rb');
			if (!empty($fp))
			{
				$st = fstat($fp);
				if (($st['mode'] & 0170000) !== 020000)
				{
					fclose($fp);
					$fp = false;
				}
			}
			
			if (!empty($fp))
			{
				/**
				 * stream_set_read_buffer() does not exist in HHVM
				 *
				 * If we don't set the stream's read buffer to 0, PHP will
				 * internally buffer 8192 bytes, which can waste entropy
				 *
				 * stream_set_read_buffer returns 0 on success
				 */
				if (is_callable('stream_set_read_buffer'))
				{
					stream_set_read_buffer($fp, RANDOM_COMPAT_READ_BUFFER);
				}
				if (is_callable('stream_set_chunk_size'))
				{
					stream_set_chunk_size($fp, RANDOM_COMPAT_READ_BUFFER);
				}
			}
		}
		
		try
		{
			$bytes = RandomCompat_intval($bytes);
		}
		catch (TypeError $ex)
		{
			throw new TypeError('random_bytes(): $bytes must be an integer');
		}
		
		if ($bytes < 1)
		{
			throw new Error('Length must be greater than 0');
		}
		
		/**
		 * This if() block only runs if we managed to open a file handle
		 *
		 * It does not belong in an else {} block, because the above
		 * if (empty($fp)) line is logic that should only be run once per
		 * page load.
		 */
		if (!empty($fp))
		{
			/**
			 * @var int
			 */
			$remaining = $bytes;
			
			/**
			 * @var string|bool
			 */
			$buf = '';
			
			/**
			 * We use fread() in a loop to protect against partial reads
			 */
			do
			{
				/**
				 * @var string|bool
				 */
				$read = fread($fp, $remaining);
				if (!is_string($read))
				{
					if ($read === false)
					{
						/**
						 * We cannot safely read from the file. Exit the
						 * do-while loop and trigger the exception condition
						 *
						 * @var string|bool
						 */
						$buf = false;
						break;
					}
				}
				/**
				 * Decrease the number of bytes returned from remaining
				 */
				$remaining -= RandomCompat_strlen($read);
				/**
				 * @var string|bool
				 */
				$buf = $buf . $read;
			} while ($remaining > 0);
			
			/**
			 * Is our result valid?
			 */
			if (is_string($buf))
			{
				if (RandomCompat_strlen($buf) === $bytes)
				{
					/**
					 * Return our random entropy buffer here:
					 */
					return $buf;
				}
			}
		}
		
		/**
		 * If we reach here, PHP has failed us.
		 */
		throw new Exception('Error reading from source device');
	}
}
