gzuncompress

(PHP 4 >= 4.0.1, PHP 5)

gzuncompress — Descomprime una cadena comprimida

Descripción

string gzuncompress ( string $datos [, int $longitud ] )

Esta función descomprime una cadena comprimida.

Lista de parámetros

datos: Los datos comprimidos por gzcompress().
longitud: La longitud máxima a decodificar o descomprimir.

Valores retornados

Los datos originales sin compresió o FALSE en error.

La función regresará un error si los datos sin comprimir son mas que 32768 veces la longitud de los datos de entrada, o mayor al parámetro opcional longitud .

Ejemplos

Example #1 Ejemplo de gzuncompress()


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

Ver también

gzwrite

gztell

Last updated: Fri, 18 Jul 2008

add a note User Contributed Notes
gzuncompress

heavyccasey at gmail dot com
08-Nov-2007 05:30


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
18-Sep-2007 12:08


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 12:21


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 04:47


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: Fri, 18 Jul 2008