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gzuncompress

(PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

gzuncompress — Decomprime una stringa compressa

Descrizione

gzuncompress(string $data, int $length = 0): string

Questa funzione decomprime una stringa compressa.

Elenco dei parametri

data: Il dato compresso dalla funzione gzcompress().
length: La lunghezza massima del dato da decomprimere.

Valori restituiti

Il dato originale decompresso oppure false in caso di errore.

La funzione ritornerà un errore se il dato decompresso è più di 32768 volte la lunghezza dell'input compresso data oppure se è maggiore del parametro opzionale length.

Esempi

Example #1 Esempio gzuncompress()

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

Vedere anche:

gzcompress() - Comprime una stringa
gzinflate() - Inflate a deflated string
gzdeflate() - Comprime una stringa
gzencode() - Crea una stringa compressa con gzip

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User Contributed Notes 7 notes

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heavyccasey at gmail dot com ¶

17 years ago


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);
    }
?>

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anonymous at dekho-ji dot com ¶

11 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.

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MagicalTux at php dot net ¶

13 years ago


Hi, I got an alternative for those zipped strings that gzuncompress() cannot extract.

It is a bit better than previous options as it do not create any temporary files, but it has to encode the string in base64, meaning it won't be as fast as a native equivalent (which is probably going to be gzdecode())

<?php
if (!function_exists('gzdecode')) {
    function gzdecode($string) { // no support for 2nd argument
        return file_get_contents('compress.zlib://data:who/cares;base64,'. base64_encode($string));
    }
}
?>

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gabriel at bumpt dot n-et ¶

17 years ago


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.

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chappy at citromail dot hu ¶

18 years ago


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;
?>

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squeegee ¶

15 years ago


One way to uncompress zlib-compressed data that is in a file without first reading in the file and then gzuncompressing it (maybe you have memory problems doing it that way) is to compile the zpipe.c program from zlib ( http://www.zlib.net/zpipe.c )...

on linux, etc:

# gcc -lz -o zpipe zpipe.c

# cp zpipe /usr/local/bin 

Then do this

<?php

$uncompressed = shell_exec("cat $compressed_file | zpipe -d");

?>

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emanuele at fondani dot it ¶

18 years ago


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

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