PHP 5.6.0 released

gzencode

(PHP 4 >= 4.0.4, PHP 5)

gzencodeCrea una stringa compressa con gzip

Descrizione

string gzencode ( string $dati [, int $livello [, int $encoding_mode ]] )

Questa funzione restituisce una versione compressa di dati compatibile con l'output del programma gzip, oppure FALSE se si verifica un errore. Il parametro opzionale livello varia da 0 (nessuna compressione) a 9 (compressione massima), se il livello di compressione non viene specificato verrà adottato quello di default della libreria zlib.

Si può anche impostare FORCE_GZIP (il default) o FORCE_DEFLATE come terzo parametro opzionale encoding_mode. Se si utilizza FORCE_DEFLATE, si ottiene una stringa compressa col DEFLATE standard di zlib (comprendente gli header zlib) dopo l'header del file gzip ma senza il checksum crc32 finale.

Nota:

livello è stato aggiunto nel PHP 4.2, prima di questa versione gzencode() aveva solo i parametri dati e (opzionale) encoding_mode.

I dati risultanti contengono gli header e la struttura adeguati per creare un file .gz standard, ad esempio:

Example #1 Creare un file gzip

<?php
    $data 
implode(""file("bigfile.txt"));
    
$gzdata gzencode($data9);
    
$fp fopen("bigfile.txt.gz""w");
    
fwrite($fp$gzdata);
    
fclose($fp);
?>

Per ulteriori informazioni sul formato dei file GZIP, consultare il documento: » GZIP file format specification version 4.3 (RFC 1952).

Vedere anche gzcompress(). gzuncompress(), gzdeflate(), gzinflate().

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User Contributed Notes 10 notes

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2
getmequick at dot com
5 years ago
NOTE:

doing like this and so on

<?php
  file_put_contents
('output.gz', gzencode( file_get_contents('input.file'),9));
?>

(complete file reading)

may cause memory overflow (Fatal error: Allowed memory size of ..), so it's better to read by parts/bytes.
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0
geompse at gmail dot com
3 years ago
Had some trouble finding the correct way to send a Content-Length header with HTTP compression.
The pitch is to use gzencode (not gzdeflaten not gzcompress).

<?php

// disable ZLIB ouput compression
ini_set('zlib.output_compression','Off');

// compress data
$gzipoutput = gzencode($output,6);

// various headers, those with # are mandatory
header('Content-Type: application/x-download');
header('Content-Encoding: gzip'); #
header('Content-Length: '.strlen($gzipoutput)); #
header('Content-Disposition: attachment; filename="myfile.name"');
header('Cache-Control: no-cache, no-store, max-age=0, must-revalidate');
header('Pragma: no-cache');

// output data
echo $gzipoutput;

?>
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0
Sam Dowling
3 years ago
this is a benchmark test of gzencode (.txt file)
----------------------------------------------
original file size = 3.29 MB (3,459,978 bytes)
compress lvl 1 = 1.09 MB (1,144,006 bytes)
compress lvl 2 = 1.06 MB (1,119,518 bytes)
compress lvl 3 = 1.03 MB (1,085,567 bytes)
compress lvl 4 = 953 KB (976,538 bytes)
compress lvl 5 = 909 KB (931,486 bytes)
compress lvl 6 = 910 KB (932,516 bytes)
compress lvl 7 = 910 KB (932,608 bytes)
compress lvl 8 = 910 KB (932,646 bytes)
compress lvl 9 = 910 KB (932,652 bytes)
----------------------------------------------
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0
gazj at nukemodified dot com
6 years ago
here is my clean up of supaplex %at% pcbkits %d0t% c0m
submission above.

function alt_gzdecode($gzdatadecode) {
  // seed with microseconds since last "whole" second.
  mt_srand((float)microtime()*1000000);
  $eh="/tmp/php-" . md5(mt_rand(0,mt_getrandmax())) . ".gz";
  if(file_exists($eh)){

  $gzf=fopen($eh,"w");
  fwrite($gzf,$gzdatadecode);
  fclose($gzf);

  $gzf = gzopen ($eh, "r");
  $gzdatadecode=gzpassthru($gzf);
  unlink($eh);

  return $gzdatadecode;
  }else{
  return 'File '.$eh.' was not found.';
  }
}
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0
henryk at ploetzli dot ch
12 years ago
Well, I was looking for a gzdecode too and didn't consider the temporary file example above to be very elegant.
However, as is noted in the very first comment: gzencode() only adds a  10 byte header.

I don't quite know what this header is supposed to be used for, but gzinflate() certainly doesn't like it, so I stripped it off:

function my_gzdecode($string) {
  $string = substr($string, 10);
  return gzinflate($string);
}

That's useful to read HTTP-Connections that were compressed by mod_gzip.
--
Henryk Pltz
Gre aus Berlin
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-1
tychay at alumni dot caltech dot edu
12 years ago
The 10 byte string in gzencode is the standard gzip header. The first two bytes (1f 8b) define the return as a gzip file, the third byte (08) means that the body is compressed using the "deflate" algorithm. The rest is padding (00)'s.

Technically, I believe one should check if the third byte is hex 08 and if so strip off the first ten bytes and last four bytes and run inflate on it. The last four bytes are file size and checksum bits.

In practice, you can get away with just stripping the first 10 bytes and running inflate on it.

Hope this helps,

terry
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-2
< supaplex %at% pcbkits %d0t% c0m >
12 years ago
I was almost discouraged when I didn't find a gzdecode() function!  However, fear not, for I'll contribute my work... :)
function alt_gzdecode($str) {
  // seed with microseconds since last "whole" second.
  mt_srand((float)microtime()*1000000);
  $eh="/tmp/php-" . md5(mt_rand(0,mt_getrandmax())) . ".gz";


  $fd=fopen($eh,"w");
  fwrite($fd,$str);
  fclose($fd);

  $fd = gzopen ($eh, "r");
  $str=gzpassthru($fd);
  unlink($eh);

  return $str;
}

It's only ugly point is that it does not check to see if the file already exists.  You may also have to adjust reference names like $str and $fd if they stomp on your code. (Sorry, but this is all you get atm! ;} )  If your conserned about a race condition, cry for a internal gzdecode() function that actualy functions...
I spent about 3 hours straight debugging this problem.  I know the input data was valid, becuase I validated it with MD5() to compare to the md5's I had made of the input data before hand.  I'm not sure whats up with gzuncompress or gzinflate, but this works in its place . . .

Enjoy!
up
-2
cbrunon at free dot fr
8 years ago
Correct is:
<?php
  file_put_contents
('output.gz', gzencode( file_get_contents('input.file'),9));
?>
up
-3
katzlbtjunk at hotmail dot com
6 years ago
Aaron G. 07-Aug-2004 03:29 posted the excellent function gzdecode() (SEE BELOW)
BUGFIX: Change: if($flags & 1) to ... if($flags & 2)

Unfortunately the function gzencode() does NOT append a CRC! So the previous version worked with output of gzencode but not with output of the gzip program itself.
up
-3
mm.. oops? - amendum (yes, tested hehe.)
12 years ago
function alt_gzdecode($str) {
  // seed with microseconds since last "whole" second
  mt_srand((float)microtime()*1000000);
  $eh="/tmp/php-" . md5(mt_rand(0,mt_getrandmax())) . ".gz";

  $fd=fopen($eh,"w");
  fwrite($fd,$str);
  fclose($fd);

  unset($str);

  $fd = gzopen ($eh, "r");
  while (1==1) {
    $s=gzread($fd,10240);
    if ("$s" == "") {
      break;
    }
    $str=$str . $s;
  }
  unlink($eh);

  return $str;
}
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