gzuncompress

(PHP 4 >= 4.0.1, PHP 5)

gzuncompress — Uncompress a compressed string

Popis

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

This function uncompress a compressed string.

Parametre

data: The data compressed by gzcompress().
length: The maximum length of data to decode.

Vrátené hodnoty

The original uncompressed data or FALSE on error.

The function will return an error if the uncompressed data is more than 32768 times the length of the compressed input data or more than the optional parameter length .

Príklady

Example#1 gzuncompress() example


<?php
$compressed   = gzcompress('Compress me', 9);
$uncompressed = gzuncompress($compressed);
echo $uncompressed;
?>

Tiež pozri

gzwrite

gztell

Last updated: Sun, 25 Nov 2007

add a note User Contributed Notes
gzuncompress

heavyccasey at gmail dot com
07-Nov-2007 08:30


Note that gzuncompress() may not decompress some compressed strings and return a Data Error.



The problem could be that the outside compressed string has a CRC32 checksum at the end of the file instead of Adler-32, like PHP expects.



Workaround:

<?php

    function gzuncompress_crc32($data) {

         $f = tempnam('/tmp', 'gz_fix');

         file_put_contents($f, "\x1f\x8b\x08\x00\x00\x00\x00\x00" . $data);

         return file_get_contents('compress.zlib://' . $f);

    }

?>

gabriel at bumpt dot n-et
17-Sep-2007 03:08


To uncompress in PHP a string that has been compressed using MySQL's COMPRESS() function, you need to discard the first four bytes of the binary data:



<?php



  /*

   * Example:

   *

   * insert into mytable (myfield, ...) values (COMPRESS('foobar'), ...)

   *

   * then:

   */

$compressed = //...select myfield from mytable where...

  /*

   * then:

   */

$uncompressed = gzuncompress(substr($compressed, 4));

?>



Of course, you can use MySQL's UNCOMPRESS() function.

I was just providing an alternate method.

emanuele at fondani dot it
25-Nov-2006 03:21


Note that the manual states that the input parameter must be a string compressed with gzcompress(), so it is not guaranteed that it will compress ANY zlib compressed string.

I realized this while decompressing some compressed string in a pdf file. The gzuncompress() function produces a data error, but the string can be successfully decompressed with other zlib decompressors.



More info here:

http://bugs.php.net/?id=39616

chappy at citromail dot hu
13-Apr-2006 07:47


Reading an ID3v2.3+ tag it is versy useful, because these tag's frames might be compressed. Zlib compressed frame layout (ID3v2.3):



Descriptior                                                    Size

-------------------

Frameheader:

Frame id:                                                      4 bytes

Frame size (full frame size - frameheader size): 4 bytes

Frame flags:                                                  2 bytes

    The 2nd byte's 7th bit must be 1 (e.g.: %1xy00000)

Frame content decrompessed size:                   4 bytes

--------------------

Framecontent:

Compressed string                                          described in 'frame size'



<?php

$frame="[read from a mp3 file]";

$frame_id=substr($frame,0,4);

/*....*/

$cs=substr($frame,10,4);

$checksize=$cs[3]*16777216+$cs[2]*65536+$cs[1]*256+$cs[0];



$content=substr($frame,14,$contentsize);

$content=gzuncompress($content);

if(strlen($content)!=$checksize){

    echo 'Error whil uncrompessing frame data<br>';

}

echo $content;

?>

add a note

gzwrite

gztell

Last updated: Sun, 25 Nov 2007