yEnc is an informal standard for efficiently encoding binary files for transmission on Usenet, in email, and in other similar mediums. It is more efficient than other widely-used encoding methods, resulting in smaller files (which in turn results in smaller downloads, which makes people happy).

This class implements a working yEnc encoder and decoder according to the yEncode working draft specification as of version 1.3, which can be found at http://www.yenc.org/yenc-draft.1.3.txt. The only part of the yEnc spec that this class does not implement is encoding and decoding of multipart yEncoded binaries. Support for this may be added at a later date, but don't get your hopes up.

PHP is not an ideal language for implementing something like this. The main issue is speed. The first thing you'll notice when you use the class is that it is incredibly slow. Despite the fact that the calculations involved are very simple, and as optimized as they can possibly be, the problem is that there are just a lot of them, and PHP is not a speedy language. If you want a fast yEnc implementation, you should use C.

So why, then, did I write this class? I don't know really. I was bored. It's entirely possible that it could come in handy for dealing with very small binary files in a PHP-only environment. Mostly, I just like toying with new concepts.

Enjoy, and please /msg me with feedback. By the way, you can parse this code with Doxygen to produce helpful documentation if you so desire (or you can just interpret the comments yourself).


<?
/*
* yenc.class.php - yEnc PHP Class.
* Copyright (c) 2002 Ryan Grove <ryan@wonko.com>. 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 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.
*/

/**
* yEnc PHP Class.
*
* This class provides functions to encode and decode yEnc files
* and strings. It meets the specifications of version 1.3 of the
* yEnc working draft (http://www.yenc.org/yenc-draft.1.3.txt)
* and also incorporates several unofficial (but recommended) features such
* as escaping of tab, space and period (.) characters.
*
* @author Ryan Grove (ryan\@wonko.com)
* @date November 26, 2002
* @version 1.0.0
*/

class yenc
{
    /** Text of the most recent error message (if any). */
    var $error;

    /**
     * yEncodes a string and returns it.
     *
     * @param string String to encode.
     * @param filename Name to use as the filename in the yEnc header (this
     *   does not have to be an actual file).
     * @param linelen Line length to use (can be up to 254 characters).
     * @param crc32 Set to <i>true</i> to include a CRC checksum in the
     *   trailer to allow decoders to verify data integrity.
     * @return yEncoded string or <i>false</i> on error.
     * @see decode()
     */
    function encode($string, $filename, $linelen = 128, $crc32 = true)
    {
        // yEnc 1.3 draft doesn't allow line lengths of more than 254 bytes.
        if ($linelen > 254)
            $linelen = 254;
            
        if ($linelen < 1)
        {
            $this->error = "$linelen is not a valid line length.";
            return false;
        }            

        // Encode each character of the string one at a time.
        for( $i = 0; $i < strlen($string); $i++)
        {
            $value = (ord($string{$i}) + 42) % 256;
            
            // Escape NULL, TAB, LF, CR, space, . and = characters.
            if ($value == 0 || $value == 9 || $value == 10 || $value == 13 || $value == 32 || $value == 46 || $value == 61)
                $encoded .= "=".chr(($value + 64) % 256);
            else
                $encoded .= chr($value);
        }
        
        // Wrap the lines to $linelen characters
        // TODO: Make sure we don't split escaped characters in half, as per the yEnc spec.
        $encoded = trim(chunk_split($encoded, $linelen));
        
        // Tack a yEnc header onto the encoded string.
        $encoded = "=ybegin line=$linelen size=".strlen($string)." name=".trim($filename)."\r\n".$encoded;
        $encoded .= "\r\n=yend size=".strlen($string);
        
        // Add a CRC32 checksum if desired.
        if ($crc32 === true)
            $encoded .= " crc32=".strtolower(sprintf("%04X", crc32($string)));

        return $encoded."\r\n";
    }
    
    /**
     * yDecodes an encoded string and either writes the result to a file
     * or returns it as a string.
     *
     * @param string yEncoded string to decode.
     * @param destination Destination directory where the decoded file will
     *   be written. This must be a valid directory <b>with no trailing
     *   slash</b> to which PHP has write access. If <i>destination</i> is
     *   not specified, the decoded file will be returned rather than
     *   written to the disk.
     * @return If <i>destination</i> is not set, the decoded file will be
     *   returned as a string. Otherwise, <i>true</i> will be returned on
     *   success. In either case, <i>false</i> will be returned on error.
     * @see encode()
     */
    function decode($string, $destination = "")
    {
        $encoded = array();
        $header  = array();
        $trailer = array();
        
        // Extract the yEnc string itself.
        preg_match("/^(=ybegin.*=yend[^$]*)$/ims", $string, $encoded);
        $encoded = $encoded[1];
        
        // Extract the file size from the header.
        preg_match("/^=ybegin.*size=([^ $]+)/im", $encoded, $header);
        $headersize = $header[1];
        
        // Extract the file name from the header.
        preg_match("/^=ybegin.*name=([^\\r\\n]+)/im", $encoded, $header);
        $filename = trim($header[1]);
        
        // Extract the file size from the trailer.
        preg_match("/^=yend.*size=([^ $\\r\\n]+)/im", $encoded, $trailer);
        $trailersize = $trailer[1];
        
        // Extract the CRC32 checksum from the trailer (if any).
        preg_match("/^=yend.*crc32=([^ $\\r\\n]+)/im", $encoded, $trailer);
        $crc = @trim(@$trailer[1]);
        
        // Remove the header and trailer from the string before parsing it.
        $encoded = preg_replace("/(^=ybegin.*\\r\\n)/im", "", $encoded, 1);
        $encoded = preg_replace("/(^=yend.*)/im", "", $encoded, 1);        

        // Remove linebreaks from the string.
        $encoded = trim(str_replace("\r\n", "", $encoded));
        
        // Make sure the header and trailer filesizes match up.
        if ($headersize != $trailersize)
        {
            $this->error = "Header and trailer file sizes do not match. This is a violation of the yEnc specification.";
            return false;
        }
        
        // Decode
        for( $i = 0; $i < strlen($encoded); $i++)
        {
            if ($encoded{$i} == "=")
            {
                $i++;
                $decoded .= chr((ord($encoded{$i}) - 64) - 42);
            }
            else
            {
                $decoded .= chr(ord($encoded{$i}) - 42);
            }
        }
        
        // Make sure the decoded filesize is the same as the size specified in the header.
        if (strlen($decoded) != $headersize)
        {
            $this->error = "Header file size and actual file size do not match. The file is probably corrupt.";
            return false;
        }
        
        // Check the CRC value
        if ($crc != "" && strtolower($crc) != strtolower(sprintf("%04X", crc32($decoded))))
        {
            $this->error = "CRC32 checksums do not match. The file is probably corrupt.";
            return false;
        }
        
        // Should we write to a file or spit back a string?
        if ($destination == "")
        {
            // Spit back a string.
            return $decoded;
        }
        else
        {
            // Make sure the destination directory exists.
            if (!is_dir($destination))
            {
                $this->error = "Destination directory ($destination) does not exist.";
                return false;
            }

            // Write the file.
            // TODO: Replace invalid characters in $filename with underscores.
            if ($fp = @fopen("$destination/$filename", "wb"))
            {
                fwrite($fp, $decoded);
                fclose($fp);
                return true;
            }
            else
            {
                $this->error = "Could not open $destination/$filename for write access.";
                return false;
            }
        }
    }
    
    /**
     * yEncodes a file and returns it as a string.
     *
     * @param filename Full path and filename of the file to be encoded.
     *   This can also be a URL (http:// or ftp://).
     * @param linelen Line length to use (can be up to 254 characters).
     * @param crc32 Set to <i>true</i> to include a CRC checksum in the
     *   trailer to allow decoders to verify data integrity.
     * @return yEncoded file, or <i>false</i> on error.
     * @see decodeFile()
     */
    function encodeFile($filename, $linelen = 128, $crc32 = true)
    {
        // Read the file into memory.
        if ($fp = @fopen($filename, "rb"))
        {
            while (!feof($fp))
                $file .= fread($fp, 8192);
            
            fclose($fp);
        
            // Encode the file.
            return $this->encode($file, $filename, $linelen, $crc32);
        }
        else
        {
            $this->error = "Could not open $filename for read access.";
            return false;
        }
    }
    
    /**
     * yDecodes an encoded file and writes the decoded file to the
     * specified directory, or returns it as a string if no directory is
     * specified.
     *
     * @param filename Full path and filename of the file to be decoded.
     * @param destination Destination directory where the decoded file will
     *   be written. This must be a valid directory <b>with no trailing
     *   slash</b> to which PHP has write access. If <i>destination</i> is
     *   not specified, the decoded file will be returned rather than
     *   written to the disk.
     * @return If <i>destination</i> is not set, the decoded file will be
     *   returned as a string. Otherwise, <i>true</i> will be returned on
     *   success. In either case, <i>false</i> will be returned on error.
     * @see encodeFile()
     */
    function decodeFile($filename, $destination = "")
    {
        // Read the encoded file into memory.
        if ($fp = @fopen($filename, "rb"))
        {
            while (!feof($fp))
                $infile .= fread($fp, 8192);
                
            fclose($fp);
            
            // Send the file to the decoder.
            if ($out = $this->decode($infile, $destination))
            {
                return $out;
            }
            else
            {
                // Decoding error.
                return false;
            }
        }
        else
        {
            $this->error = "Could not open $filename for read access.";
            return false;
        }
    }
}

/*========================================================================*
* Documentation (there's no actual code below here)                      *
*========================================================================*/

/**
* @mainpage yEnc PHP Class
*
* @section intro Introduction
*
* yEnc is an informal standard for efficiently encoding binary files for
* transmission on Usenet, in email, and in other similar mediums. It is
* more efficient than other widely-used encoding methods, resulting in
* smaller files (which in turn results in smaller downloads, which makes
* people happy).
*
* This class implements a working yEnc encoder and decoder according
* to the yEncode working draft specification as of version 1.3, which can
* be found at http://www.yenc.org/yenc-draft.1.3.txt
*
* The only part of the yEnc spec that this class does not implement is
* encoding and decoding of multipart yEncoded binaries. Support for this
* may be added at a later date, but don't get your hopes up.
*
* @section limitations Limitations of PHP
*
* PHP is not an ideal language for implementing something like this. The
* main issue is speed. The first thing you'll notice when you use the
* class is that it is @em incredibly slow. Despite the fact that the
* calculations involved are very simple, and as optimized as they can
* possibly be, the problem is that there are just a @em lot of them, and
* PHP is not a speedy language.
*
* If you want a fast yEnc implementation, you should use C.
*
* So why, then, did I write this class? I don't know really. I was bored.
* It's entirely possible that it could come in handy for dealing with
* very small binary files in a PHP-only environment. Mostly, I just like
* toying with new concepts.
*
* @section support Support & Contact Info
*
* If you find a bug, or if you have a suggestion or comment, I'd love to
* hear from you. If you need someone to hold your hand, please don't waste
* my time. I went to a lot more trouble than I probably should have making

* this class extremely easy to use, and I've also done my best to provide
* thorough documentation, so stupid questions will very likely be met with
* anger and profanity.
*
* That said, you can contact me via email at ryan\@wonko.com and you'll
* always be able to find the latest version of this class and its
* documentation at http://wonko.com/yenc/
*
* @section license License & Copyright
*
* Copyright (c) 2002 Ryan Grove. 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 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.
*/
?> 

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