PHP中实现GZIP解压缩函数

nainai1

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;
}