CLXIV. Zlib Compression Functions


This module enables you to transparently read and write gzip (.gz) compressed files, through versions of most of the filesystem functions which work with gzip-compressed files (and uncompressed files, too, but not with sockets).

注: Version 4.0.4 introduced a fopen-wrapper for .gz-files, so that you can use a special 'zlib:' URL to access compressed files transparently using the normal f*() file access functions if you prepend the filename or path with a 'zlib:' prefix when calling fopen().

In version 4.3.0, this special prefix has been changed to 'zlib://' to prevent ambiguities with filenames containing ':'.

This feature requires a C runtime library that provides the fopencookie() function. To my current knowledge the GNU libc is the only library that provides this feature.


This module uses the functions of zlib by Jean-loup Gailly and Mark Adler. You have to use a zlib version >= 1.0.9 with this module.


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

PHP 的 Windows 版本已经内置该扩展模块的支持。无需加载任何附加扩展库即可使用这些函数。

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


这些函数的行为受 php.ini 的影响。

The zlib extension offers the option to transparently compress your pages on-the-fly, if the requesting browser supports this. Therefore there are three options in the configuration file php.ini.

表格 1. Zlib Configuration Options

zlib.output_compression"0"PHP_INI_ALLAvailable since PHP 4.0.5.
zlib.output_compression_level"-1"PHP_INI_ALLAvailable since PHP 4.3.0.
zlib.output_handler""PHP_INI_ALLAvailable since PHP 4.3.0.
有关 PHP_INI_* 常量进一步的细节与定义参见附录 G


zlib.output_compression boolean/integer

Whether to transparently compress pages. If this option is set to "On" in php.ini or the Apache configuration, pages are compressed if the browser sends an "Accept-Encoding: gzip" or "deflate" header. "Content-Encoding: gzip" (respectively "deflate") and "Vary: Accept-Encoding" headers are added to the output. In runtime, it can be set only before sending any output.

This option also accepts integer values instead of boolean "On"/"Off", using this you can set the output buffer size (default is 4KB).

注: output_handler must be empty if this is set 'On' ! Instead you must use zlib.output_handler.

zlib.output_compression_level integer

Compression level used for transparent output compression.

zlib.output_handler string

You cannot specify additional output handlers if zlib.output_compression is activated here. This setting does the same as output_handler but in a different order.




以下常量由本扩展模块定义,因此只有在本扩展模块被编译到 PHP 中,或者在运行时被动态加载后才有效。

FORCE_GZIP (integer)



This example opens a temporary file and writes a test string to it, then it prints out the content of this file twice.

例子 1. Small Zlib Example


= tempnam('/tmp', 'zlibtest') . '.gz';
$s = "Only a test, test, test, test, test, test, test, test!\n";

// open file for writing with maximum compression
$zp = gzopen($filename, "w9");

// write string to file
gzwrite($zp, $s);

// close file

// open file for reading
$zp = gzopen($filename, "r");

// read 3 char
echo gzread($zp, 3);

// output until end of the file and close it.


// open file and print content (the 2nd time).
if (readgzfile($filename) != strlen($s)) {
"Error with zlib functions!";

gzclose -- Close an open gz-file pointer
gzcompress -- Compress a string
gzdeflate -- Deflate a string
gzencode -- Create a gzip compressed string
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 -- 别名 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

add a note add a note User Contributed Notes
anzenews at volja dot net
27-Jul-2006 09:59
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 04:49
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
24-May-2006 01:34
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-Sep-2005 09:45
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-Aug-2005 11:27
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
04-Jul-2005 12:45
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 09:08
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.
08-Oct-2004 08:32
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-Jul-2004 11:03
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 06:44
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 10:52
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
21-May-2004 02:38
 * @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-May-2004 10:04
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-Nov-2003 08:02
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-May-2003 08:10
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-Mar-2003 11:47
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
13-Feb-2003 06:06
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-Apr-2001 09:02
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.