Your IP : 192.168.165.1
<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle 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 3 of the License, or
// (at your option) any later version.
//
// Moodle 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 Moodle. If not, see <http://www.gnu.org/licenses/>.
/**
* Baking badges library.
*
* @package core
* @subpackage badges
* @copyright 2012 onwards Totara Learning Solutions Ltd {@link http://www.totaralms.com/}
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
* @author Yuliya Bozhko <yuliya.bozhko@totaralms.com>
*/
defined('MOODLE_INTERNAL') || die();
/**
* Information on PNG file chunks can be found at http://www.w3.org/TR/PNG/#11Chunks
* Some other info on PNG that I used http://garethrees.org/2007/11/14/pngcrush/
*
* Example of use:
* $png = new PNG_MetaDataHandler('file.png');
*
* if ($png->check_chunks("tEXt", "openbadge")) {
* $newcontents = $png->add_chunks("tEXt", "openbadge", 'http://some.public.url/to.your.assertion.file');
* }
*
* file_put_contents('file.png', $newcontents);
*/
class PNG_MetaDataHandler
{
/** @var string File content as a string */
private $_contents;
/** @var int Length of the image file */
private $_size;
/** @var array Variable for storing parsed chunks */
private $_chunks;
/**
* Prepares file for handling metadata.
* Verifies that this file is a valid PNG file.
* Unpacks file chunks and reads them into an array.
*
* @param string $contents File content as a string
*/
public function __construct($contents) {
$this->_contents = $contents;
$png_signature = pack("C8", 137, 80, 78, 71, 13, 10, 26, 10);
// Read 8 bytes of PNG header and verify.
$header = substr($this->_contents, 0, 8);
if ($header != $png_signature) {
debugging('This is not a valid PNG image');
}
$this->_size = strlen($this->_contents);
$this->_chunks = array();
// Skip 8 bytes of IHDR image header.
$position = 8;
do {
$chunk = @unpack('Nsize/a4type', substr($this->_contents, $position, 8));
$this->_chunks[$chunk['type']][] = substr($this->_contents, $position + 8, $chunk['size']);
// Skip 12 bytes chunk overhead.
$position += $chunk['size'] + 12;
} while ($position < $this->_size);
}
/**
* Checks if a key already exists in the chunk of said type.
* We need to avoid writing same keyword into file chunks.
*
* @param string $type Chunk type, like iTXt, tEXt, etc.
* @param string $check Keyword that needs to be checked.
*
* @return boolean (true|false) True if file is safe to write this keyword, false otherwise.
*/
public function check_chunks($type, $check) {
if (array_key_exists($type, $this->_chunks)) {
foreach (array_keys($this->_chunks[$type]) as $typekey) {
list($key, $data) = explode("\0", $this->_chunks[$type][$typekey]);
if (strcmp($key, $check) == 0) {
debugging('Key "' . $check . '" already exists in "' . $type . '" chunk.');
return false;
}
}
}
return true;
}
/**
* Adds a chunk with keyword and data to the file content.
* Chunk is added to the end of the file, before IEND image trailer.
*
* @param string $type Chunk type, like iTXt, tEXt, etc.
* @param string $key Keyword that needs to be added.
* @param string $value Currently an assertion URL that is added to an image metadata.
*
* @return string $result File content with a new chunk as a string. Can be used in file_put_contents() to write to a file.
* @throws \moodle_exception when unsupported chunk type is defined.
*/
public function add_chunks($type, $key, $value) {
if (strlen($key) > 79) {
debugging('Key is too big');
}
$dataparts = [];
if ($type === 'iTXt') {
// International textual data (iTXt).
// Keyword: 1-79 bytes (character string).
$dataparts[] = $key;
// Null separator: 1 byte.
$dataparts[] = "\x00";
// Compression flag: 1 byte
// A value of 0 means no compression.
$dataparts[] = "\x00";
// Compression method: 1 byte
// If compression is disabled, the method should also be 0.
$dataparts[] = "\x00";
// Language tag: 0 or more bytes (character string)
// When there is no language specified leave empty.
// Null separator: 1 byte.
$dataparts[] = "\x00";
// Translated keyword: 0 or more bytes
// When there is no translation specified, leave empty.
// Null separator: 1 byte.
$dataparts[] = "\x00";
// Text: 0 or more bytes.
$dataparts[] = $value;
} else if ($type === 'tEXt') {
// Textual data (tEXt).
// Keyword: 1-79 bytes (character string).
$dataparts[] = $key;
// Null separator: 1 byte.
$dataparts[] = "\0";
// Text: n bytes (character string).
$dataparts[] = $value;
} else {
throw new \moodle_exception('Unsupported chunk type: ' . $type);
}
$data = implode($dataparts);
$crc = pack("N", crc32($type . $data));
$len = pack("N", strlen($data));
// Chunk format: length + type + data + CRC.
// CRC is a CRC-32 computed over the chunk type and chunk data.
$newchunk = $len . $type . $data . $crc;
$this->_chunks[$type] = $data;
$result = substr($this->_contents, 0, $this->_size - 12)
. $newchunk
. substr($this->_contents, $this->_size - 12, 12);
return $result;
}
}