Last updated: Wed, 26 Oct 2005

CLXIX. Funzioni di compressione Zlib

Introduzione

questo modulo permette di leggere e scrivere in modo trasparente i file compressi con gzip (.gz), attraverso versioni di molte delle funzioni del filesystem in grado di operare su file compressi con gzip (ed anche su file non compressi, ma non con i socket).

Nota: La versione 4.0.4 ha introdotto un wrapper di fopen per i file .gz, che permette di usare una speciale URL 'zlib:' per accedere ai file compressi utilizzando le normali funzioni di accesso ai file [ f*() ], semplicemente anteponendo al nome del file o percorso il prefisso 'zlib:' nella chiamata a fopen().
Nella versione 4.3.0, questo prefisso è stato cambiato in 'zlib://' per evitare ambiguità con i nomi di file contenenti il carattere ':'.
Questa funzionalità richiedere una libreria di runtime C che fornisca la funzione fopencookie(). Al momento sembra che la GNU libc sia l'unica libreria a fornire questa funzionalità.

Requisiti

Questo modulo usa le funzioni di zlib di Jean-loup Gailly e Mark Adler. Si deve utilizzare una versione >= 1.0.9 con questo modulo.

Installazione

Zlib support in PHP is not enabled by default. You will need to configure PHP --with-zlib[=DIR]

La versione per Windows di PHP ha già compilato il supporto per questo modulo. Non occorre caricare alcun modulo addizionale per potere utilizzare queste funzioni.

Nota: Builtin support for zlib on Windows is available with PHP 4.3.0.

Configurazione di Runtime

Il comportamento di queste funzioni è influenzato dalle impostazioni di php.ini.

L'estensione zlib permette di comprimere in modo trasparente le pagine on-the-fly, se il browser supporta questa funzionalità. Quindi ci sono due opzioni nel file di configurazione php.ini.

Tabella 1. Opzioni di configurazione di Zlib

Nome	Default	Configurabile in
zlib.output_compression	"Off"	PHP_INI_ALL
zlib.output_compression_level	"-1"	PHP_INI_ALL
zlib.output_handler	""	PHP_INI_ALL

Per ulteriori dettagli e definizioni delle costanti PHP_INI_* vedere ini_set().

Breve descrizione dei parametri di configurazione.

zlib.output_compression boolean/integer

Decide se comprimere le agine in maniera trasparente. Se questa opzione è impostata a "On" in php.ini o nella configurazione di Apache, le pagine vengono compresse se il browser invia un header "Accept-Encoding: gzip" o "deflate". Gli header "Content-Encoding: gzip" (oppure "deflate") e "Vary: Accept-Encoding" sono aggiunti all'output.

Questa opzione accetta anche valori interi oltre ai booleani "On"/"Off", in questo modo è possibile impostare la dimensione del buffer (il default è 4KB).

Nota: output_handler deve essere vuoto se quest opzione è 'On' ! Altrimenti occorre utilizzare zlib.output_handler.

zlib.output_compression_level integer

Livello di compressione utilizzato per la compressione trasparente dell'output.

zlib.output_handler string

Non si possino specificare ulteriori handler dell'output se zlib.output_compression è attivo. Questa impostazione è come output_handler ma con un ordine differente.

Tipi di risorse

Questa estensione non definisce alcun tipo di risorsa.

Costanti predefinite

Queste costanti sono definite da questa estensione e sono disponibili solo se l'estensione è stata compilata nel PHP o se è stata caricata dinamicamente a runtime.

FORCE_GZIP (integer)
FORCE_DEFLATE (integer)

Esempi

Questo esempio apre un file temporaneo e vi scrive una stringa di prova, quindi stampa il contenuto del file due volte.

Esempio 1. Esempio di Zlib


<?php



$filename = tempnam('/tmp', 'zlibtest') . '.gz';

echo "<html>\n<head></head>\n<body>\n<pre>\n";

$s = "Only a test, test, test, test, test, test, test, test!\n";



// apre il file in scrittura con la massima compressione

$zp = gzopen($filename, "w9");



// scrive la stringa sul file

gzwrite($zp, $s);



// chiude il file

gzclose($zp);



// apre il file in lettura

$zp = gzopen($filename, "r");



// legge 3 caratteri

echo gzread($zp, 3);



// stampa fino alla fine del file e lo chiude

gzpassthru($zp);

gzclose($zp);



echo "\n";



// apre il file e stampa il contenuto (la seconda volta)

if (readgzfile($filename) != strlen($s)) {

        echo "Errore nelle funzioni zlib!";

}

unlink($filename);

echo "</pre>\n</body>\n</html>\n";



?>

Sommario
gzclose -- Chiude un puntatore a file gz
gzcompress -- Comprime una stringa col metodo COMPRESS
gzdeflate -- Comprime una stringa con il metodo DEFLATE
gzencode -- Crea una stringa compressa con gzip
gzeof -- Test for end-of-file on a gz-file pointer
gzfile -- Read entire gz-file into an array
gzgetc -- Get character from gz-file pointer
gzgets -- Get line from file pointer
gzgetss -- Get line from gz-file pointer and strip HTML tags
gzinflate -- Inflate a deflated string
gzopen -- Open gz-file
gzpassthru -- Output all remaining data on a gz-file pointer
gzputs -- Alias di gzwrite()
gzread -- Binary-safe gz-file read
gzrewind -- Rewind the position of a gz-file pointer
gzseek -- Seek on a gz-file pointer
gztell -- Tell gz-file pointer read/write position
gzuncompress -- Uncompress a compressed string
gzwrite -- Binary-safe gz-file write
readgzfile -- Output a gz-file
zlib_get_coding_type -- Returns the coding type used for output compression

gzclose

zip_read

Last updated: Wed, 26 Oct 2005

add a note User Contributed Notes
Funzioni di compressione Zlib

Brian
25-Jun-2007 11:58


If you have zlib.output_compression set to on when your script starts (in php.ini or via apache directive), then you disable it at runtime using ini_set() before producing output, your output will still be buffered!  Even if you call ob_implicit_flush().



If you want unbuffered output, you must disable zlib.output_compression before your script starts (as well as mod_gzip of course, if you have both installed).



This behaviour experienced on Server: Apache/1.3.33 (Debian GNU/Linux) mod_gzip/1.3.26.1a PHP/4.3.10-18

anzenews at volja dot net
27-Jul-2006 06:59


php at seven dot net dot nz: 

Have you been using register_shutdown_function() that outputs something? If yes, some of the output was not encoded and IE6 is less than forgiving about that. In my case it was reloading the page and sometimes showing a blank page. So IE6 does get invalid stream, bug is not bogus, only description is not good enough. 



jpleveille at webgraphe dot com:

In PHP 4.4.2 register_shutdown_function() DOES output whatever you wish, but it is not encoded with the rest of the document. Which is even worse as you get a bug that is difficult / impossible to track down.

php at seven dot net dot nz
07-Jul-2006 01:49


zlib.output_compression has caused problems for me in IE 6, when pages are sometimes not displayed. This could be difficult to track down and PHP have no intention of fixing it, so hopefully you find this note in a search if it happens to you.



http://bugs.php.net/bug.php?id=38026

Arne dot Heizmann at csr dot com
23-May-2006 10:34


PHP Version 5.1.4 here. What Bob said is correct even in this version (newest at the time of writing). You can't enable zlib.output_compression via ini_set(). You have to use php.ini.

Bob
19-Sep-2005 06:45


Contrary to what the documentation says, I've been unable to get zlib.output_compression to work via ini_set() (Even though I put it at the very beginning of the file before any output was sent) as of php 4.3.11.  While it does get set to true, it will not actually do anything. Which means if you don't set this via php.ini or Apache configuration it's a no-go. I have to use ob_start("ob_gzhandler"); instead.

djmaze(AT)dragonflycms(.)org
27-Aug-2005 08:27


If you need to compress data and send it as "Content-disposition: attachment" and on-the-fly to the client due to the size for example (40Mb) here's a dirty trick using ob_gzhandler()



Keep in mind that $str is the content to output.



When you start the output call



<?php

echo ob_gzhandler($str, PHP_OUTPUT_HANDLER_START);

?>



Then to output any further content



<?php

echo ob_gzhandler($str, PHP_OUTPUT_HANDLER_CONT);

?>



And to close the output



<?php

echo ob_gzhandler('', PHP_OUTPUT_HANDLER_END);

exit;

?>



Only tested on Apache 1.3.33 with PHP 5.0.4

ghassler at speakeasy dot net
03-Jul-2005 09:45


I tested all the compression levels against a 22k page and here are the results I got (in bytes):



off = 22549

1 = 4297

2 = 4279

3 = 4264

4 = 4117

5 = 4097

6 = 4063

7 = 4011

8 = 3998

9 = 3996



Looks like the best bets for zlib.output_compression_level is 1 or 5.  The default of 6 is probably OK too.  Don't know what the CPU usage difference is between them all though.

jpleveille at webgraphe dot com
10-Jun-2005 06:08


register_shutdown_function() (http://www.php.net/register_shutdown_function) won't output anything if you use zlib.output_compression.



Shutdown function is called after closing all opened output buffers thus, for example, its output will not be compressed if zlib.output_compression is enabled.

admin_at_commandline_dot_ch
08-Oct-2004 05:32


My gzip function.



This function read, compress and writhe only small chunks at one time, this way you can compress big files without memory problems...



<?php

function gzip($src, $level = 5, $dst = false){

    if($dst == false){

        $dst = $src.".gz";

    }

    if(file_exists($src)){

        $filesize = filesize($src);

        $src_handle = fopen($src, "r");

        if(!file_exists($dst)){

            $dst_handle = gzopen($dst, "w$level");

            while(!feof($src_handle)){

                $chunk = fread($src_handle, 2048);

                gzwrite($dst_handle, $chunk);

            }

            fclose($src_handle);

            gzclose($dst_handle);

            return true;

        } else {

            error_log("$dst already exists");

        }

    } else {

        error_log("$src doesn't exist");

    }

    return false;

}

?>

gem at rellim dot com
13-Jul-2004 08:03


Run, do not walk, run, to add this to your Apache config file:



php_flag zlib.output_compression On

php_value zlib.output_compression_level 5



I just tried this and achieved 10x and 15x speed inprovement on

some mature php pages.  Pages I have been seating over to make 5% gains on.  I use microtime() on critical pages to help me track page speed and that confirms the speed improvement.  The php page takes a timestamp at the beginning and end, then logs the page duration.  So any IP transmission effects are not included.  There is

a clear subjective difference to the user.



The test system was PHP 4.3.6, Apache 2.0.49 over Linux 2.4.

As always YMMV.

zigazou at free dot fr
12-Jun-2004 03:44


If you use "zlib.output_compression = On" in your php.ini file, and activates output buffering (ob_start), don't output this header :

header('Content-Length: '.ob_get_length());



This is because ob_get_length() will return the uncompressed size while zlib will compress the output. Thus your browser will get confused waiting for extra data that will never come.

xorinox at tiscali dot ch
04-Jun-2004 07:52


Have a look to this extended version :)



<?php



function compress( $srcFileName, $dstFileName )

{

    // getting file content

    $fp = fopen( $srcFileName, "r" );

    $data = fread ( $fp, filesize( $srcFileName ) );

    fclose( $fp );

    

    // writing compressed file

    $zp = gzopen( $dstFileName, "w9" );

    gzwrite( $zp, $data );

    gzclose( $zp );

}



function uncompress( $srcFileName, $dstFileName, $fileSize )

{

    // getting content of the compressed file

    $zp = gzopen( $srcFileName, "r" );

    $data = fread ( $zp, $fileSize );

    gzclose( $zp );

    

    // writing uncompressed file

    $fp = fopen( $dstFileName, "w" );

    fwrite( $fp, $data );

    fclose( $fp );

}



compress( "tmp/supportkonzept.rtf", "tmp/_supportkonzept.rtf.gz" );

uncompress( "tmp/_supportkonzept.rtf.gz", "tmp/_supportkonzept.rtf", filesize( "tmp/supportkonzept.rtf" ) );



?>

ec10 at gmx dot net
20-May-2004 11:38


/**

 * @return bool

 * @param string $in

 * @param string $out

 * @param string $param = "1"

 * @desc compressing the file with the zlib-extension

*/

function gzip ($in, $out, $param="1")

{

    if (!file_exists ($in) || !is_readable ($in))

        return false;

    if ((!file_exists ($out) && !is_writable (dirname ($out)) || (file_exists($out) && !is_writable($out)) ))

        return false;

    

    $in_file = fopen ($in, "rb");

    if (!$out_file = gzopen ($out, "wb".$param)) {

        return false;

    }

    

    while (!feof ($in_file)) {

        $buffer = fgets ($in_file, 4096);

        gzwrite ($out_file, $buffer, 4096);

    }



    fclose ($in_file);

    gzclose ($out_file);

    

    return true;

}



/**

 * @return bool

 * @param string $in

 * @param string $out

 * @desc uncompressing the file with the zlib-extension

*/

function gunzip ($in, $out)

{

    if (!file_exists ($in) || !is_readable ($in))

        return false;

    if ((!file_exists ($out) && !is_writable (dirname ($out)) || (file_exists($out) && !is_writable($out)) ))

        return false;



    $in_file = gzopen ($in, "rb");

    $out_file = fopen ($out, "wb");



    while (!gzeof ($in_file)) {

        $buffer = gzread ($in_file, 4096);

        fwrite ($out_file, $buffer, 4096);

    }

 

    gzclose ($in_file);

    fclose ($out_file);

    

    return true;

}

spam at wildpeaks dot com
13-May-2004 07:04


For decompressing, i modified a function posted earlier (that way $string doesn't have a big size that may be beyond the memory limit if the gzipped file is big) :



function file_ungzip($fromFile, $toFile) {

    $zp = @gzopen($fromFile, "r");

    $fp = @fopen($toFile, "w");

    while(!@gzeof($zp)) {$string = @gzread($zp, 4096); @fwrite($fp, $string, strlen($string));}

    @gzclose($zp);

    @fclose($fp);

}

thivierr at telus dot net
17-Nov-2003 04:02


I found the absolute easiest way to read a gzip file is as follows:



echo file_get_contents("compress.zlib:///myphp/test.txt.gz");



To create a gzip file:

file_put_contents("compress.zlib:///myphp/test.txt.gz","Put this in the file\r\n");



Things to note about this:

-The best prefix to use is "compress.zlib", not "zlib"

-If you wish to specify a path starting in the root path, you actually end up with three slashes.  The above path corresponds to "/myphp/test.txt" on unix, and "c:\myphp\test.txt" on Windows (if C: is the current drive).  I tested it just on Windows.

-Compression and decompression both use the same prefix of "compress.zlib://" (plus one more slash to get a root dir).

-I'm using 5.0, so I'm not 100% sure which behaviour started in which version.

chris at mad-teaparty dot com
27-May-2003 05:10


Nice function. I did it the other way round:



function uncompress($srcName, $dstName) {

   $zp = gzopen($srcName, "r");

   while(!gzeof($zp))

        $string .= gzread($zp, 4096);

   gzclose($zp);



   $fp = fopen($dstName, "w");

   fwrite($fp, $string, strlen($string));

   fclose($fp);

}



uncompress("./myfile.txt.gz", "./myfile.txt");



A shorter approach would be:



function uncompress($srcName, $dstName) {

  $string = implode("", gzfile($srcName));

  $fp = fopen($dstName, "w");

  fwrite($fp, $string, strlen($string));

  fclose($fp);

}

devcontact at tech-island dot com
24-Mar-2003 07:47


The method of first reading the source file and then passing its content to the gzip function instead of simply the source and destination filename was a bit confusing for me.



So I have written a simple funtion you can use to compress files in the gzip format (gzip is readable by winzip like .zip files)



function compress($srcName, $dstName)

{

  $fp = fopen($srcName, "r");

  $data = fread ($fp, filesize($srcName));

  fclose($fp);



  $zp = gzopen($dstName, "w9");

  gzwrite($zp, $data);

  gzclose($zp);

}



// Compress a file

compress("/web/myfile.dat", "/web/myfile.gz");

mlevy at rgj dot com
12-Feb-2003 02:06


If you turn zlib.output_compression_level on, be advised that you shouldn't try to flush() the output in your scripts. PHP will add the gzip header but send the output uncompressed, which plays havoc with Mozilla. IE seems to handle it, though.

monte at ispi dot net
18-Apr-2001 06:02


An alternate way to handle gzip compression is to let the mod_gzip module of apache handle it. This seems to contradict the tutorial on phpbuilder.com saying that it won't compress php (or any dynamic) output, but mod_gzip as of version 1.3.17.1a works well for me.





Here is an example of an httpd.conf setup:





<IfModule mod_gzip.c>


mod_gzip_on                 Yes


mod_gzip_dechunk            Yes


mod_gzip_minimum_file_size  300


mod_gzip_maximum_file_size  0


mod_gzip_maximum_inmem_size 100000


mod_gzip_keep_workfiles     No


mod_gzip_temp_dir           /tmp


mod_gzip_item_include       file \.html$


mod_gzip_item_include       file \.jsp$


mod_gzip_item_include       file \.php$


mod_gzip_item_include       file \.pl$


mod_gzip_item_include       mime ^text/.*


mod_gzip_item_include       mime ^application/x-httpd-php


mod_gzip_item_include       mime ^httpd/unix-directory$


mod_gzip_item_include       handler ^perl-script$


mod_gzip_item_include       handler ^server-status$


mod_gzip_item_include       handler ^server-info$


mod_gzip_item_exclude       mime ^image/.*


</IfModule>





This will automatically compress all output of your files with the .php extention or the x-httpd-php mime type. Be sure to have dechunk set to Yes.

add a note

gzclose

zip_read

Last updated: Wed, 26 Oct 2005