A class to quickly read Ragnarok Online's GRF Format and extract files from it. Supports version 0x200 and unencrypted files only.

FastGrf.php

<?php

class FastGrf
{

    private $files;
    private $path;
    private $handle;

    public function __construct($path)
    {

        $this->files = [];
        $this->path = $path;
        $this->handle = fopen($path, 'rb');

        //Jump to important info directly
        fseek($this->handle, 30);
        list($ftOffset, $seed, $fCount) = array_values(unpack('VftOffset/Vseed/VfCount', fread($this->handle, 12)));

        //Jump to FT offset
        fseek($this->handle, $ftOffset + 46);

        //Unpack FT
        $cSize = unpack('V', fread($this->handle, 4))[1];

        fseek($this->handle, 4, SEEK_CUR);
        //Read the compressed file table
        $cft = fread($this->handle, $cSize);

        //Decompress table (Not using the second parameter, it leads to insufficient memory errors :()
        $ft = @zlib_decode($cft);
        $cft = null;

        $fCount = $fCount - $seed - 7;
        for ($i = 0, $o = 0; $i < $fCount; $i++) {

            //read filename until 0x00
            $path = '';
            $null = chr(0x00);
            while (($char = substr($ft, $o, 1)) !== $null) {

                $path .= $char;
                $o++;
            }
            $o++;

            $path = mb_convert_encoding($path, 'UTF-8', 'EUC-KR');

            list($cSize, $aSize, $size, $flags, $offset) = array_values(unpack(
                'VcSize/VaSize/Vsize/Cflags/Voffset',
                substr($ft, $o, 17)
            ));
            $o += 17;

            $file = [
                'cSize' => $cSize,
                'aSize' => $aSize,
                'size' => $size,
                'flags' => $flags,
                'offset' => $offset
            ];

            $file['crc32'] = sprintf('%u', crc32(implode(':', [$path, $file['size']])));

            $this->files[$path] = $file;
        }
        $ft = null;
    }

    public function close()
    {

        if (is_resource($this->handle))
            fclose($this->handle);
    }

    public function getFiles()
    {

        return $this->files;
    }

    /**
     * @param $path
     * @return bool
     */
    public function hasFile($path)
    {

        return isset($this->files[$path]);
    }

    /**
     * @param $path
     * @return array
     */
    public function getFileInfo($path)
    {

        return $this->files[$path];
    }

    public function getFileHandle($path)
    {

        $fInfo = $this->files[$path];

        if ($fInfo['flags'] !== 1)
            throw new \RuntimeException(
                "Encrypted GRF file $path. Unencrypt prior to using it."
            );

        $fp = fopen('php://memory', 'rb+');

        fseek($this->handle, $fInfo['offset'] + 46);
        $cContent = fread($this->handle, $fInfo['aSize']);
        $content = zlib_decode($cContent);
        $cContent = null;
        fwrite($fp, $content);
        fseek($fp, 0, SEEK_SET);
        $content = null;

        return $fp;
    }

    public function getFileTextContent($path)
    {

        $content = stream_get_contents($this->getFileHandle($path));
        return mb_convert_encoding($content, 'UTF-8', 'EUC-KR');
    }
}