<?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.

 */

if (!defined('RANDOM_COMPAT_READ_BUFFER')) {

    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'

        );

    }

}