PHP中实现GZIP解压缩函数

luinstein

3. function gzdecode($data) {
4.   $len = strlen($data);
5.   if ($len < 18 || strcmp(substr($data,0,2),\"x1fx8b\")) {
6.    return null;  // Not GZIP format (See RFC 1952)
7.   }
8.   $method = ord(substr($data,2,1));  // Compression method
9.   $flags  = ord(substr($data,3,1));  // Flags
10.   if ($flags & 31 != $flags) {
11.    // Reserved bits are set -- NOT ALLOWED by RFC 1952
12.    return null;
13.   }
14.   // NOTE: $mtime may be negative (PHP integer limitations)
15.   $mtime = unpack(\"V\", substr($data,4,4));
16.   $mtime = $mtime[1];
17.   $xfl  = substr($data,8,1);
18.   $os    = substr($data,8,1);
19.   $headerlen = 10;
20.   $extralen  = 0;
21.   $extra    = \"\";
22.   if ($flags & 4) {
23.    // 2-byte length prefixed EXTRA data in header
24.    if ($len - $headerlen - 2 < 8) {
25.      return false;    // Invalid format
26.    }
27.    $extralen = unpack(\"v\",substr($data,8,2));
28.    $extralen = $extralen[1];
29.    if ($len - $headerlen - 2 - $extralen < 8) {
30.      return false;    // Invalid format
31.    }
32.    $extra = substr($data,10,$extralen);
33.    $headerlen += 2 + $extralen;
34.   }
36.   $filenamelen = 0;
37.   $filename = \"\";
38.   if ($flags & 8) {
39.    // C-style string file NAME data in header
40.    if ($len - $headerlen - 1 < 8) {
41.      return false;    // Invalid format
42.    }
43.    $filenamelen = strpos(substr($data,8+$extralen),chr(0));
44.    if ($filenamelen === false || $len - $headerlen - $filenamelen - 1 < 8) {
45.      return false;    // Invalid format
46.    }
47.    $filename = substr($data,$headerlen,$filenamelen);
48.    $headerlen += $filenamelen + 1;
49.   }
51.   $commentlen = 0;
52.   $comment = \"\";
53.   if ($flags & 16) {
54.    // C-style string COMMENT data in header
55.    if ($len - $headerlen - 1 < 8) {
56.      return false;    // Invalid format
57.    }
58.    $commentlen = strpos(substr($data,8+$extralen+$filenamelen),chr(0));
59.    if ($commentlen === false || $len - $headerlen - $commentlen - 1 < 8) {
60.      return false;    // Invalid header format
61.    }
62.    $comment = substr($data,$headerlen,$commentlen);
63.    $headerlen += $commentlen + 1;
64.   }
66.   $headercrc = \"\";
67.   if ($flags & 1) {
68.    // 2-bytes (lowest order) of CRC32 on header present
69.    if ($len - $headerlen - 2 < 8) {
70.      return false;    // Invalid format
71.    }
72.    $calccrc = crc32(substr($data,0,$headerlen)) & 0xffff;
73.    $headercrc = unpack(\"v\", substr($data,$headerlen,2));
74.    $headercrc = $headercrc[1];
75.    if ($headercrc != $calccrc) {
76.      return false;    // Bad header CRC
77.    }
78.    $headerlen += 2;
79.   }
81.   // GZIP FOOTER - These be negative due to PHP\'s limitations
82.   $datacrc = unpack(\"V\",substr($data,-8,4));
83.   $datacrc = $datacrc[1];
84.   $isize = unpack(\"V\",substr($data,-4));
85.   $isize = $isize[1];
87.   // Perform the decompression:
88.   $bodylen = $len-$headerlen-8;
89.   if ($bodylen < 1) {
90.    // This should never happen - IMPLEMENTATION BUG!
91.    return null;
92.   }
93.   $body = substr($data,$headerlen,$bodylen);
94.   $data = \"\";
95.   if ($bodylen > 0) {
96.    switch ($method) {
97.      case 8:
98.        // Currently the only supported compression method:
99.        $data = gzinflate($body);
100.        break;
101.      default:
102.        // Unknown compression method
103.        return false;
104.    }
105.   } else {
106.    // I\'m not sure if zero-byte body content is allowed.
107.    // Allow it for now...  Do nothing...
108.   }
110.   // Verifiy decompressed size and CRC32:
111.   // NOTE: This may fail with large data sizes depending on how
112.   //      PHP\'s integer limitations affect strlen() since $isize
113.   //      may be negative for large sizes.
114.   if ($isize != strlen($data) || crc32($data) != $datacrc) {
115.    // Bad format!  Length or CRC doesn\'t match!
116.    return false;
117.   }
118.   return $data;
119. }

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