A class to zip a string.

Zipfile.php

<?php

class zipfile {

    var $datasec = array();
    var $ctrl_dir = array();
    var $eof_ctrl_dir = "\x50\x4b\x05\x06\x00\x00\x00\x00";
    var $old_offset = 0;

    function add_string($data, $name) {
        $unc_len = strlen($data);
        $crc = crc32($data);
        $zdata = gzcompress($data);
        $zdata = substr($zdata, 2, -4);
        $c_len = strlen($zdata);
        $fr = "\x50\x4b\x03\x04";
        $fr .= "\x14\x00";
        $fr .= "\x00\x00";
        $fr .= "\x08\x00";
        $fr .= "\x00\x00\x00\x00";
        $fr .= pack("V", $crc);
        $fr .= pack("V", $c_len);
        $fr .= pack("V", $unc_len);
        $fr .= pack("v", strlen($name));
        $fr .= pack("v", 0);
        $fr .= $name;
        $fr .= $zdata;
        $fr .= pack("V", $crc);
        $fr .= pack("V", $c_len);
        $fr .= pack("V", $unc_len);

        $this->datasec[] = $fr;
        $new_offset = strlen(implode("", $this->datasec));

        $cdrec = "\x50\x4b\x01\x02";
        $cdrec .="\x00\x00";
        $cdrec .="\x14\x00";
        $cdrec .="\x00\x00";
        $cdrec .="\x08\x00";
        $cdrec .="\x00\x00\x00\x00";
        $cdrec .= pack("V", $crc);
        $cdrec .= pack("V", $c_len);
        $cdrec .= pack("V", $unc_len);
        $cdrec .= pack("v", strlen($name));
        $cdrec .= pack("v", 0);
        $cdrec .= pack("v", 0);
        $cdrec .= pack("v", 0);
        $cdrec .= pack("v", 0);
        $cdrec .= pack("V", 32);
        $cdrec .= pack("V", $this->old_offset);

        $this->old_offset = $new_offset;

        $cdrec .= $name;
        $this->ctrl_dir[] = $cdrec;
    }

    function file() {
        $data = implode("", $this->datasec);
        $ctrldir = implode("", $this->ctrl_dir);

        return
                $data .
                $ctrldir .
                $this->eof_ctrl_dir .
                pack("v", sizeof($this->ctrl_dir)) .
                pack("v", sizeof($this->ctrl_dir)) .
                pack("V", strlen($ctrldir)) .
                pack("V", strlen($data)) .
                "\x00\x00";
    }

}

?>