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# CLXXXVIII. Zlib Compression Functions

# 简介

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).

> 注意: 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 prefix the filename or path with `zlib:` when calling fopen(). This feature requires a C runtime library that provides the `fopencookie()` function. Up to now the GNU libc seems to be the only library that provides this feature.

> In PHP 4.3.0, `zlib:` has been changed to `compress.zlib://` to prevent ambiguities with filenames containing ':' characters. The `fopencookie()` function is not longer required. More information is available in the section about the 节 called 压缩流 于 附录 N.

# 需求

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.

# 安装

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。

> 注意: Built-in support for zlib on Windows is available with PHP 4.3.0.

# 运行时配置

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 1. Zlib Configuration Options

Name | Default | Changeable | Changelog
--- | --- | --- | ---
zlib.output_compression | "0" | PHP_INI_ALL | Available since PHP 4.0.5.
zlib.output_compression_level | "-1" | PHP_INI_ALL | Available since PHP 4.3.0.
zlib.output_handler | "" | PHP_INI_ALL | Available since PHP 4.3.0.

有关 PHP_INI_* 常量进一步的细节与定义参见附录 H。

以下是配置选项的简要解释。

`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).

  > 注意: 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.

# 资源类型

This extension defines a file pointer resource returned by gzopen().

# 预定义常量

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)

`FORCE_DEFLATE` (integer)

# 范例

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

例 1. Small Zlib Example

`<?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";
// open file for writing with maximum compression
$zp = gzopen($filename, "w9");
// write string to file
gzwrite($zp, $s);
// close file
gzclose($zp);
// open file for reading
$zp = gzopen($filename, "r");
// read 3 char
echo gzread($zp, 3);
// output until end of the file and close it.
gzpassthru($zp);
gzclose($zp);
echo "\n";
// open file and print content (the 2nd time).
if (readgzfile($filename) != strlen($s)) {
echo "Error with zlib functions!";
}
unlink($filename);
echo "</pre>\n</body>\n</html>\n";
?>`

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