<?php
function gzdecode($data, $verify = false)
{
	$len = strlen($data); 
	if ($len < 18 || strcmp(substr($data,0,2),"\x1f\x8b")) { 
		return null;  // Not GZIP format (See RFC 1952) 
	}
	$method = ord(substr($data,2,1));  // Compression method 
	$flags  = ord(substr($data,3,1));  // Flags 
	if ($flags & 31 != $flags) { 
		// Reserved bits are set -- NOT ALLOWED by RFC 1952 
		return null; 
	} 
	// NOTE: $mtime may be negative (PHP integer limitations) 
	$mtime = unpack("V", substr($data,4,4)); 
	$mtime = $mtime[1]; 
	$xfl  = substr($data,8,1); 
	$os    = substr($data,8,1); 
	$headerlen = 10; 
	$extralen  = 0; 
	$extra    = ""; 
	if ($flags & 4) { 
		// 2-byte length prefixed EXTRA data in header 
		if ($len - $headerlen - 2 < 8) { 
			return false;    // Invalid format 
		} 
		$extralen = unpack("v",substr($data,8,2)); 
		$extralen = $extralen[1]; 
		if ($len - $headerlen - 2 - $extralen < 8) { 
			return false;    // Invalid format 
		} 
		$extra = substr($data,10,$extralen); 
		$headerlen += 2 + $extralen; 
	} 

	$filenamelen = 0; 
	$filename = ""; 
	if ($flags & 8) { 
		// C-style string file NAME data in header 
		if ($len - $headerlen - 1 < 8) { 
		return false;    // Invalid format 
		} 
		$filenamelen = strpos(substr($data,8+$extralen),chr(0)); 
		if ($filenamelen === false || $len - $headerlen - $filenamelen - 1 < 8) { 
			return false;    // Invalid format 
		} 
		$filename = substr($data,$headerlen,$filenamelen); 
		$headerlen += $filenamelen + 1; 
	} 

	$commentlen = 0; 
	$comment = ""; 
	if ($flags & 16) { 
		// C-style string COMMENT data in header 
		if ($len - $headerlen - 1 < 8) { 
			return false;    // Invalid format 
		} 
		$commentlen = strpos(substr($data,8+$extralen+$filenamelen),chr(0)); 
		if ($commentlen === false || $len - $headerlen - $commentlen - 1 < 8) { 
			return false;    // Invalid header format 
		} 
		$comment = substr($data,$headerlen,$commentlen); 
		$headerlen += $commentlen + 1; 
	} 

	$headercrc = ""; 
	if ($flags & 1) { 
		// 2-bytes (lowest order) of CRC32 on header present 
		if ($len - $headerlen - 2 < 8) { 
			return false;    // Invalid format 
		} 
		$calccrc = crc32(substr($data,0,$headerlen)) & 0xffff; 
		$headercrc = unpack("v", substr($data,$headerlen,2)); 
		$headercrc = $headercrc[1]; 
		if ($headercrc != $calccrc) { 
			return false;    // Bad header CRC 
		} 
		$headerlen += 2; 
	} 

	// GZIP FOOTER - These be negative due to PHP's limitations 
	$datacrc = unpack("V",substr($data,-8,4)); 
	$datacrc = $datacrc[1]; 
	$isize = unpack("V",substr($data,-4)); 
	$isize = $isize[1]; 

	// Perform the decompression: 
	$bodylen = $len-$headerlen-8; 
	if ($bodylen < 1) { 
		// This should never happen - IMPLEMENTATION BUG! 
		return null; 
	} 
	$body = substr($data,$headerlen,$bodylen); 
	$data = ""; 
	if ($bodylen > 0) { 
		switch ($method) { 
			case 8: 
			// Currently the only supported compression method: 
				$data = gzinflate($body); 
				break; 
			default: 
			// Unknown compression method 
				return false; 
		} 
	} else { 
		// I'm not sure if zero-byte body content is allowed.
		// Allow it for now...  Do nothing...
	}
	if (true === $verify) {
		// Verifiy decompressed size and CRC32: 
		// NOTE: This may fail with large data sizes depending on how
		//      PHP's integer limitations affect strlen() since $isize
		//      may be negative for large sizes.
		if ($isize != strlen($data) || crc32($data) != $datacrc) { 
			// Bad format!  Length or CRC doesn't match! 
			return false;
		}
	}
	return $data; 
}
?>