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# CXLI. Zlib Compression Functions

# 介紹

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.

# 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.

# 安裝

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

Windows 版本的 PHP 已內建此延伸的支援﹐所以你毋須再載入附加的延伸來使用這些功能。

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

# 執行時期組態

`php.ini`中的設定會影響這些函數的行為。

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

Name | Default | Changeable
--- | --- | ---
zlib.output_compression | "Off" | PHP_INI_ALL
zlib.output_compression_level | "-1" | PHP_INI_ALL
zlib.output_handler | "" | PHP_INI_ALL

For further details and definitions of the PHP_INI_* constants, see the 附錄 H.

這裡為簡短的結構指令說明。

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.

  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.

# 資源類型

這個延伸沒有定義任何資源。

# 預先定義常數

以下的常數由此延伸定義，只在這個延伸被編譯成PHP或實行時期被動態載入時有效。

`FORCE_GZIP` (integer)

`FORCE_DEFLATE` (integer)

# 範例

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

範例 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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