gzdecode

(PHP 5 >= 5.4.0, PHP 7)

gzdecode — Decodes a gzip compressed string

Description

string gzdecode ( string $data [, int $length ] )

This function returns a decoded version of the input data.

Parameters

data: The data to decode, encoded by gzencode().
length: The maximum length of data to decode.

Return Values

The decoded string, or FALSE if an error occurred.

User Contributed Notes

anonymous at dekho-ji dot com

2 years ago


To decode / uncompress the received HTTP POST data in PHP code, request data coming from Java / Android application via HTTP POST GZIP / DEFLATE compressed format

1) Data sent from Java Android app to PHP using DeflaterOutputStream java class and received in PHP as shown below
echo gzinflate( substr($HTTP_RAW_POST_DATA,2,-4) ) . PHP_EOL  . PHP_EOL;

2) Data sent from Java Android app to PHP using GZIPOutputStream java class and received in PHP code as shown below
echo gzinflate( substr($HTTP_RAW_POST_DATA,10,-8) ) . PHP_EOL  . PHP_EOL;

From Java Android side (API level 10+), data being sent in DEFLATE compressed format
        String body = "Lorem ipsum shizzle ma nizle";
        URL url = new URL("http://www.url.com/postthisdata.php");
        URLConnection conn = url.openConnection();
        conn.setDoOutput(true);
        conn.setRequestProperty("Content-encoding", "deflate");
        conn.setRequestProperty("Content-type", "application/octet-stream");
        DeflaterOutputStream dos = new DeflaterOutputStream(
                conn.getOutputStream());
        dos.write(body.getBytes());
        dos.flush();
        dos.close();
        BufferedReader in = new BufferedReader(new InputStreamReader(
                conn.getInputStream()));
        String decodedString = "";
        while ((decodedString = in.readLine()) != null) {
            Log.e("dump",decodedString);
        }
        in.close();

On PHP side (v 5.3.1), code for decompressing this DEFLATE data will be
    echo substr($HTTP_RAW_POST_DATA,2,-4);

From Java Android side (API level 10+), data being sent in GZIP compressed format

        String body1 = "Lorem ipsum shizzle ma nizle";
        URL url1 = new URL("http://www.url.com/postthisdata.php");
        URLConnection conn1 = url1.openConnection();
        conn1.setDoOutput(true);
        conn1.setRequestProperty("Content-encoding", "gzip");
        conn1.setRequestProperty("Content-type", "application/octet-stream");
        GZIPOutputStream dos1 = new GZIPOutputStream(conn1.getOutputStream());
        dos1.write(body1.getBytes());
        dos1.flush();
        dos1.close();
        BufferedReader in1 = new BufferedReader(new InputStreamReader(
                conn1.getInputStream()));
        String decodedString1 = "";
        while ((decodedString1 = in1.readLine()) != null) {
            Log.e("dump",decodedString1);
        }
        in1.close();

On PHP side (v 5.3.1), code for decompressing this GZIP data will be
    echo substr($HTTP_RAW_POST_DATA,10,-8);

Useful PHP code for printing out compressed data using all available formats.

$data = "Lorem ipsum shizzle ma nizle";
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
    echo chunk_split(strtoupper(bin2hex(gzcompress($data,$i))),2," ") . PHP_EOL  . PHP_EOL;
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
    echo chunk_split(strtoupper(bin2hex(gzdeflate($data,$i))),2," ") . PHP_EOL  . PHP_EOL;
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
    echo chunk_split(strtoupper(bin2hex(gzencode($data,$i,FORCE_GZIP))),2," ") . PHP_EOL  . PHP_EOL;
echo "\n\n\n";
for($i=-1;$i<=9;$i++)
    echo chunk_split(strtoupper(bin2hex(gzencode($data,$i,FORCE_DEFLATE))),2," ") . PHP_EOL  . PHP_EOL;
echo "\n\n\n";

Hope this helps. Please ThumbsUp if this saved you a lot of effort and time.

tomas at slax dot org

4 years ago


I don't have any deep knowledge in compression algorithms and formats, so I have no idea if this works the same on all platforms. But by several experiments on my Linux box I found how to get gzdecoded data without temporary files. Here it is:



<?php

function gzdecode($data)

{

   return gzinflate(substr($data,10,-8));

}

?>



That's it. Simply strip header and footer bytes and you get raw deflated data for inflation.

katzlbtjunk at hotmail dot com

8 years ago


3 more bugs found and fixed: 
1. failed to work when the gz contained a filename - FIXED
2. failed to work on 64-bit architecture (checksum) - FIXED
3. failed to work when the gz contained a comment - cannot verify. 
Returns some errors (not all!) and filename.
<?php function gzdecode($data,&$filename='',&$error='',$maxlength=null) 
{
    $len = strlen($data);
    if ($len < 18 || strcmp(substr($data,0,2),"\x1f\x8b")) {
        $error = "Not in GZIP format.";
        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) {
        $error = "Reserved bits not allowed.";
        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
        }
        $extralen = unpack("v",substr($data,8,2));
        $extralen = $extralen[1];
        if ($len - $headerlen - 2 - $extralen < 8) {
            return false;  // invalid
        }
        $extra = substr($data,10,$extralen);
        $headerlen += 2 + $extralen;
    }
    $filenamelen = 0;
    $filename = "";
    if ($flags & 8) {
        // C-style string
        if ($len - $headerlen - 1 < 8) {
            return false; // invalid
        }
        $filenamelen = strpos(substr($data,$headerlen),chr(0));
        if ($filenamelen === false || $len - $headerlen - $filenamelen - 1 < 8) {
            return false; // invalid
        }
        $filename = substr($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
        }
        $commentlen = strpos(substr($data,$headerlen),chr(0));
        if ($commentlen === false || $len - $headerlen - $commentlen - 1 < 8) {
            return false;    // Invalid header format
        }
        $comment = substr($data,$headerlen,$commentlen);
        $headerlen += $commentlen + 1;
    }
    $headercrc = "";
    if ($flags & 2) {
        // 2-bytes (lowest order) of CRC32 on header present
        if ($len - $headerlen - 2 < 8) {
            return false;    // invalid
        }
        $calccrc = crc32(substr($data,0,$headerlen)) & 0xffff;
        $headercrc = unpack("v", substr($data,$headerlen,2));
        $headercrc = $headercrc[1];
        if ($headercrc != $calccrc) {
            $error = "Header checksum failed.";
            return false;    // Bad header CRC
        }
        $headerlen += 2;
    }
    // GZIP FOOTER
    $datacrc = unpack("V",substr($data,-8,4));
    $datacrc = sprintf('%u',$datacrc[1] & 0xFFFFFFFF);
    $isize = unpack("V",substr($data,-4));
    $isize = $isize[1];
    // decompression:
    $bodylen = $len-$headerlen-8;
    if ($bodylen < 1) {
        // 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,$maxlength);
            break;
        default:
            $error = "Unknown compression method.";
            return false;
        }
    }  // zero-byte body content is allowed
    // Verifiy CRC32
    $crc   = sprintf("%u",crc32($data));
    $crcOK = $crc == $datacrc;
    $lenOK = $isize == strlen($data);
    if (!$lenOK || !$crcOK) {
        $error = ( $lenOK ? '' : 'Length check FAILED. ') . ( $crcOK ? '' : 'Checksum FAILED.');
        return false;
    }
    return $data;
}
?>

katzlbtjunk at hotmail dot com

8 years ago


Aaron G. 07-Aug-2004 03:29 posted the function gzdecode()
to gzencode comments. I FIXED the BUG: if($flags & 1) to the correct if($flags & 2)

Unfortunately the function gzencode() does NOT append a CRC so I did not notice until I tried to upload a file compressed with gzip itself.

<?php

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 & 2) {
    // 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;
}

?>

webmaster at askapache dot com

7 years ago


I have used this simple function to gzdecode gzipped files downloaded from the web.

<?php

function gzdecode($data){
  $g=tempnam('/tmp','ff');
  @file_put_contents($g,$data);
  ob_start();
  readgzfile($g);
  $d=ob_get_clean();
  return $d;
}

?>

Anonymous

1 year ago


if (!function_exists('gzdecode')) {
    function gzdecode($data)
    {
        return gzinflate(substr($data,10,-8));
    }
}

fabrizio dot rastiello at gmail dot com

2 months ago


In my case to decode correctly a GZIPOutputStream POST from Android I used 
gzinflate( substr($post,10,-8) );
and not 
gzinflate( substr($HTTP_RAW_POST_DATA,10,-8) ) . PHP_EOL  . PHP_EOL

trevize32 at gmail dot com

8 months ago


I use the following code:

function &gzdecodedata(&$data) {

    ob_start();

    readgzfile('data://application/gzip;base64,' . base64_encode($data));

    $d = ob_get_clean();

    return $d;
}

gzdecode

Description

Parameters

Return Values

See Also

User Contributed Notes