论坛 › PHP › PHP中实现GZIP解压缩函数

luinstein 发表于 2012-10-20 00:10:19

PHP中实现GZIP解压缩函数

function gzdecode($data) {
$len = strlen($data);
if ($len < 18 || strcmp(substr($data,0,2),\"x1fx8b\")) {
   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;
$xfl= substr($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 = $extralen;
   if ($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 = $headercrc;
   if ($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;
$isize = unpack(\"V\",substr($data,-4));
$isize = $isize;

// 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;
}




from:http://nakupanda.iteye.com/blog/441234

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