parse ()

Decode the GZIP stream

Access

public

Source

Method defined in utilities/gzipdecode.class.php | Toggle source view (169 lines) | View on GitHub

public function parse()
{
    if ($this->compressed_size >= $this->min_compressed_size)
    {
        // Check ID1, ID2, and CM
        if (substr($this->compressed_data, 0, 3) !== "\x1F\x8B\x08")
        {
            return false;
        }

        // Get the FLG (FLaGs)
        $this->flags = ord($this->compressed_data[3]);

        // FLG bits above (1 << 4) are reserved
        if ($this->flags > 0x1F)
        {
            return false;
        }

        // Advance the pointer after the above
        $this->position += 4;

        // MTIME
        $mtime = substr($this->compressed_data, $this->position, 4);
        // Reverse the string if we're on a big-endian arch because l is the only signed long and is machine endianness
        if (current(unpack('S', "\x00\x01")) === 1)
        {
            $mtime = strrev($mtime);
        }
        $this->MTIME = current(unpack('l', $mtime));
        $this->position += 4;

        // Get the XFL (eXtra FLags)
        $this->XFL = ord($this->compressed_data[$this->position++]);

        // Get the OS (Operating System)
        $this->OS = ord($this->compressed_data[$this->position++]);

        // Parse the FEXTRA
        if ($this->flags & 4)
        {
            // Read subfield IDs
            $this->SI1 = $this->compressed_data[$this->position++];
            $this->SI2 = $this->compressed_data[$this->position++];

            // SI2 set to zero is reserved for future use
            if ($this->SI2 === "\x00")
            {
                return false;
            }

            // Get the length of the extra field
            $len = current(unpack('v', substr($this->compressed_data, $this->position, 2)));
            $position += 2;

            // Check the length of the string is still valid
            $this->min_compressed_size += $len + 4;
            if ($this->compressed_size >= $this->min_compressed_size)
            {
                // Set the extra field to the given data
                $this->extra_field = substr($this->compressed_data, $this->position, $len);
                $this->position += $len;
            }
            else
            {
                return false;
            }
        }

        // Parse the FNAME
        if ($this->flags & 8)
        {
            // Get the length of the filename
            $len = strcspn($this->compressed_data, "\x00", $this->position);

            // Check the length of the string is still valid
            $this->min_compressed_size += $len + 1;
            if ($this->compressed_size >= $this->min_compressed_size)
            {
                // Set the original filename to the given string
                $this->filename = substr($this->compressed_data, $this->position, $len);
                $this->position += $len + 1;
            }
            else
            {
                return false;
            }
        }

        // Parse the FCOMMENT
        if ($this->flags & 16)
        {
            // Get the length of the comment
            $len = strcspn($this->compressed_data, "\x00", $this->position);

            // Check the length of the string is still valid
            $this->min_compressed_size += $len + 1;
            if ($this->compressed_size >= $this->min_compressed_size)
            {
                // Set the original comment to the given string
                $this->comment = substr($this->compressed_data, $this->position, $len);
                $this->position += $len + 1;
            }
            else
            {
                return false;
            }
        }

        // Parse the FHCRC
        if ($this->flags & 2)
        {
            // Check the length of the string is still valid
            $this->min_compressed_size += $len + 2;
            if ($this->compressed_size >= $this->min_compressed_size)
            {
                // Read the CRC
                $crc = current(unpack('v', substr($this->compressed_data, $this->position, 2)));

                // Check the CRC matches
                if ((crc32(substr($this->compressed_data, 0, $this->position)) & 0xFFFF) === $crc)
                {
                    $this->position += 2;
                }
                else
                {
                    return false;
                }
            }
            else
            {
                return false;
            }
        }

        // Decompress the actual data
        if (($this->data = gzinflate(substr($this->compressed_data, $this->position, -8))) === false)
        {
            return false;
        }
        else
        {
            $this->position = $this->compressed_size - 8;
        }

        // Check CRC of data
        $crc = current(unpack('V', substr($this->compressed_data, $this->position, 4)));
        $this->position += 4;
        /*if (extension_loaded('hash') && sprintf('%u', current(unpack('V', hash('crc32b', $this->data)))) !== sprintf('%u', $crc))
        {
            return false;
        }*/

        // Check ISIZE of data
        $isize = current(unpack('V', substr($this->compressed_data, $this->position, 4)));
        $this->position += 4;
        if (sprintf('%u', strlen($this->data) & 0xFFFFFFFF) !== sprintf('%u', $isize))
        {
            return false;
        }

        // Wow, against all odds, we've actually got a valid gzip string
        return true;
    }
    else
    {
        return false;
    }
}

Copyright © 2010–2013 Amazon Web Services, LLC


Feedback