PHP中实现GZIP解压缩函数
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; $xfl= substr($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; }
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