Detailed explanation of steps for php ZIP compression class example

<?php
$zipfiles =array("/root/pooy/test1.txt","/root/pooy/test2.txt");
$z = new PHPZip();
//$randomstr = random(8);
$zipfile = TEMP."/photocome_".$groupid.".zip";
$z->Zip($zipfiles, $zipfile); //添加文件列表

<?php
# 
# PHPZip v1.2 by Sext (sext@neud.net) 2002-11-18
#     (Changed: 2003-03-01)
# 
# Makes zip archive
#
# Based on "Zip file creation class", uses zLib
#
#
class PHPZip
{
    function Zip($dir, $zipfilename)
    {
        if (@function_exists(&#39;gzcompress&#39;))
        {    
            $curdir = getcwd();
            if (is_array($dir)) 
            {
                    $filelist = $dir;
            }
            else
            {
                $filelist = $this -> GetFileList($dir);
            }
            if ((!empty($dir))&&(!is_array($dir))&&(file_exists($dir))) chdir($dir);
            else chdir($curdir);
            if (count($filelist)>0)
            {
                foreach($filelist as $filename)
                {
                    if (is_file($filename))
                    {
                        $fd = fopen ($filename, "r");
                        $content = fread ($fd, filesize ($filename));
                        fclose ($fd);
                        if (is_array($dir)) $filename = basename($filename);
                        $this -> addFile($content, $filename);
                    }
                }
                $out = $this -> file();
                chdir($curdir);
                $fp = fopen($zipfilename, "w");
                fwrite($fp, $out, strlen($out));
                fclose($fp);
            }
            return 1;
        } 
        else return 0;
    }
    function GetFileList($dir)
    {
        if (file_exists($dir))
        {
            $args = func_get_args();
            $pref = $args[1];
            $dh = opendir($dir);
            while($files = readdir($dh))
            {
                if (($files!=".")&&($files!="..")) 
                {
                    if (is_dir($dir.$files)) 
                    {
                        $curdir = getcwd();
                        chdir($dir.$files);
                        $file = array_merge($file, $this -> GetFileList("", "$pref$files/"));
                        chdir($curdir);
                    }
                    else $file[]=$pref.$files;
                }
            }
            closedir($dh);
        }
        return $file;
    }
    var $datasec      = array();
    var $ctrl_dir     = array();
    var $eof_ctrl_dir = "\x50\x4b\x05\x06\x00\x00\x00\x00";
    var $old_offset   = 0;
    /**
     * Converts an Unix timestamp to a four byte DOS date and time format (date
     * in high two bytes, time in low two bytes allowing magnitude comparison).
     *
     * @param  integer  the current Unix timestamp
     *
     * @return integer  the current date in a four byte DOS format
     *
     * @access private
     */
    function unix2DosTime($unixtime = 0) {
        $timearray = ($unixtime == 0) ? getdate() : getdate($unixtime);
        if ($timearray[&#39;year&#39;] < 1980) {
            $timearray[&#39;year&#39;]    = 1980;
            $timearray[&#39;mon&#39;]     = 1;
            $timearray[&#39;mday&#39;]    = 1;
            $timearray[&#39;hours&#39;]   = 0;
            $timearray[&#39;minutes&#39;] = 0;
            $timearray[&#39;seconds&#39;] = 0;
        } // end if
        return (($timearray[&#39;year&#39;] - 1980) << 25) | ($timearray[&#39;mon&#39;] << 21) | ($timearray[&#39;mday&#39;] << 16) |
                ($timearray[&#39;hours&#39;] << 11) | ($timearray[&#39;minutes&#39;] << 5) | ($timearray[&#39;seconds&#39;] >> 1);
    } // end of the &#39;unix2DosTime()&#39; method
    /**
     * Adds "file" to archive
     *
     * @param  string   file contents
     * @param  string   name of the file in the archive (may contains the path)
     * @param  integer  the current timestamp
     *
     * @access public
     */
    function addFile($data, $name, $time = 0)
    {
        $name     = str_replace(&#39;\\&#39;, &#39;/&#39;, $name);
        $dtime    = dechex($this->unix2DosTime($time));
        $hexdtime = &#39;\x&#39; . $dtime[6] . $dtime[7]
                   <a href="http://wutransfer.com/western-union-locations-in-russia-taiynsha/">Western union point</a> .  &#39;\x&#39; . $dtime[4] . $dtime[5]
                  . &#39;\x&#39; . $dtime[2] . $dtime[3]
                  . &#39;\x&#39; . $dtime[0] . $dtime[1];
        eval(&#39;$hexdtime = "&#39; . $hexdtime . &#39;";&#39;);
        $fr   = "\x50\x4b\x03\x04";
        $fr   .= "\x14\x00";            // ver needed to extract
        $fr   .= "\x00\x00";            // gen purpose bit flag
        $fr   .= "\x08\x00";            // compression method
        $fr   .= $hexdtime;             // last mod time and date
        // "local file header" segment
        $unc_len = strlen($data);
        $crc     = crc32($data);
        $zdata   = gzcompress($data);
        $c_len   = strlen($zdata);
        $zdata   = substr(substr($zdata, 0, strlen($zdata) - 4), 2); // fix crc bug
        $fr      .= pack(&#39;V&#39;, $crc);             // crc32
        $fr      .= pack(&#39;V&#39;, $c_len);           // compressed filesize
        $fr      .= pack(&#39;V&#39;, $unc_len);         // uncompressed filesize
        $fr      .= pack(&#39;v&#39;, strlen($name));    // length of filename
        $fr      .= pack(&#39;v&#39;, 0);                // extra field length
        $fr      .= $name;
        // "file data" segment
        $fr .= $zdata;
        // "data descriptor" segment (optional but necessary if archive is not
        // served as file)
        $fr .= pack(&#39;V&#39;, $crc);                 // crc32
        $fr .= pack(&#39;V&#39;, $c_len);               // compressed filesize
        $fr .= pack(&#39;V&#39;, $unc_len);             // uncompressed filesize
        // add this entry to array
        $this -> datasec[] = $fr;
        $new_offset        = strlen(implode(&#39;&#39;, $this->datasec));
        // now add to central directory record
        $cdrec = "\x50\x4b\x01\x02";
        $cdrec .= "\x00\x00";                // version made by
        $cdrec .= "\x14\x00";                // version needed to extract
        $cdrec .= "\x00\x00";                // gen purpose bit flag
        $cdrec .= "\x08\x00";                // compression method
        $cdrec .= $hexdtime;                 // last mod time & date
        $cdrec .= pack(&#39;V&#39;, $crc);           // crc32
        $cdrec .= pack(&#39;V&#39;, $c_len);         // compressed filesize
        $cdrec .= pack(&#39;V&#39;, $unc_len);       // uncompressed filesize
        $cdrec .= pack(&#39;v&#39;, strlen($name) ); // length of filename
        $cdrec .= pack(&#39;v&#39;, 0 );             // extra field length
        $cdrec .= pack(&#39;v&#39;, 0 );             // file comment length
        $cdrec .= pack(&#39;v&#39;, 0 );             // disk number start
        $cdrec .= pack(&#39;v&#39;, 0 );             // internal file attributes
        $cdrec .= pack(&#39;V&#39;, 32 );            // external file attributes - &#39;archive&#39; bit set
        $cdrec .= pack(&#39;V&#39;, $this -> old_offset ); // relative offset of local header
        $this -> old_offset = $new_offset;
        $cdrec .= $name;
        // optional extra field, file comment goes here
        // save to central directory
        $this -> ctrl_dir[] = $cdrec;
    } // end of the &#39;addFile()&#39; method
    /**
     * Dumps out file
     *
     * @return  string  the zipped file
     *
     * @access public
     */
    function file()
    {
        $data    = implode(&#39;&#39;, $this -> datasec);
        $ctrldir = implode(&#39;&#39;, $this -> ctrl_dir);
        return
            $data .
            $ctrldir .
            $this -> eof_ctrl_dir .
            pack(&#39;v&#39;, sizeof($this -> ctrl_dir)) .  // total # of entries "on this disk"
            pack(&#39;v&#39;, sizeof($this -> ctrl_dir)) .  // total # of entries overall
            pack(&#39;V&#39;, strlen($ctrldir)) .           // size of central dir
            pack(&#39;V&#39;, strlen($data)) .              // offset to start of central dir
            "\x00\x00";                             // .zip file comment length
    } // end of the &#39;file()&#39; method
} // end of the &#39;PHPZip&#39; class
?>