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Robin Skoglund
5.04.2008 2:39
ini_set('zlib.output_compression', 'On') doesn't work

It says that zlib.output_compression is PHP_INI_ALL changable, but in my case at least, this is not true. When using ini_set('zlib.output_compression', 'On') runtime, phpinfo() states that zlib.output_compression is enabled, yet there is no compression.

Since I don't want to enable zlib.ouput_compression for all sites in php.ini, my solution was to enable it in apache conf (.htaccess should work as well) with the line:
php_flag zlib.output_compression on

Just spent hours figuring this out, so I hope it helps other people.

Btw, I'm using Apache/2.2.4 (Ubuntu) PHP/5.2.3-1ubuntu6.3.
26.06.2007 8:58
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/ PHP/4.3.10-18
anzenews at volja dot net
27.07.2006 15:59
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
7.07.2006 10:49
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.
Arne dot Heizmann at csr dot com
23.05.2006 19:34
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.
19.09.2005 15:45
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.
27.08.2005 17:27
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

echo ob_gzhandler($str, PHP_OUTPUT_HANDLER_START);

Then to output any further content

echo ob_gzhandler($str, PHP_OUTPUT_HANDLER_CONT);

And to close the output

echo ob_gzhandler('', PHP_OUTPUT_HANDLER_END);

Only tested on Apache 1.3.33 with PHP 5.0.4
ghassler at speakeasy dot net
3.07.2005 18:45
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
10.06.2005 15:08
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.
8.10.2004 14:32
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...

function gzip($src, $level = 5, $dst = false){
$dst == false){
$dst = $src.".gz";
$filesize = filesize($src);
$src_handle = fopen($src, "r");
$dst_handle = gzopen($dst, "w$level");
$chunk = fread($src_handle, 2048);
gzwrite($dst_handle, $chunk);
        } else {
error_log("$dst already exists");
    } else {
error_log("$src doesn't exist");
gem at rellim dot com
14.07.2004 5:03
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
12.06.2004 12:44
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
4.06.2004 16:52
Have a look to this extended version :)


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 );

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
20.05.2004 20:38
 * @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
14.05.2004 4:04
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));}
thivierr at telus dot net
17.11.2003 13:02
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
28.05.2003 2:10
Nice function. I did it the other way round:

function uncompress($srcName, $dstName) {
   $zp = gzopen($srcName, "r");
        $string .= gzread($zp, 4096);

   $fp = fopen($dstName, "w");
   fwrite($fp, $string, strlen($string));

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));
devcontact at tech-island dot com
24.03.2003 16:47
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));

  $zp = gzopen($dstName, "w9");
  gzwrite($zp, $data);

// Compress a file
compress("/web/myfile.dat", "/web/myfile.gz");
mlevy at rgj dot com
12.02.2003 23:06
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
19.04.2001 3:02
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 saying that it won't compress php (or any dynamic) output, but mod_gzip as of version 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/.*

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.

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