gzcompat.php

<?php

if(!function_exists('gzdecode')) {
	function gzdecode( $data ) {
		$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...
		}

		// 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;
	}
}