PHP: 压缩过滤器

压缩过滤器

虽然压缩封装协议提供了在本地文件系统中创建 gzip 和 bz2 兼容文件的方法，但不代表可以在网络的流中提供通用压缩的意思，也不代表可以将一个非压缩的流转换成一个压缩流。对此，压缩过滤器可以在任何时候应用于任何流资源。

注意: 压缩过滤器不产生命令行工具如 gzip 的头和尾信息。只是压缩和解压数据流中的有效载荷部分。

zlib.deflate 和 zlib.inflate

zlib.deflate（压缩）和 zlib.inflate（解压）实现了定义与 » RFC 1951 的压缩算法。 deflate 过滤器可以接受以一个关联数组传递的最多三个参数。 level定义了压缩强度（1-9）。数字更高通常会产生更小的载荷，但要消耗更多的处理时间。存在两个特殊压缩等级：0（完全不压缩）和 -1（zlib 内部默认值，目前是 6）。 window是压缩回溯窗口大小，以二的次方表示。更高的值（大到 15 —— 32768 字节）产生更好的压缩效果但消耗更多内存，低的值（低到 9 —— 512 字节）产生产生较差的压缩效果但内存消耗低。目前默认的 window 大小是 15。 memory用来指示要分配多少工作内存。合法的数值范围是从 1（最小分配）到 9（最大分配）。内存分配仅影响速度，不会影响生成的载荷的大小。

注意: 因为最常用的参数是压缩等级，也可以提供一个整数值作为此参数（而不用数组）。

在激活 zlib 的前提下可以使用 zlib.* 压缩过滤器。

示例 #1 zlib.deflate 和 zlib.inflate

<?php
$params = array('level' => 6, 'window' => 15, 'memory' => 9);

$original_text = "This is a test.\nThis is only a test.\nThis is not an important string.\n";
echo "The original text is " . strlen($original_text) . " characters long.\n";

$fp = fopen('test.deflated', 'w');
stream_filter_append($fp, 'zlib.deflate', STREAM_FILTER_WRITE, $params);
fwrite($fp, $original_text);
fclose($fp);

echo "The compressed file is " . filesize('test.deflated') . " bytes long.\n";
echo "The original text was:\n";
/* 使用 readfile 和 zlib.inflate 即时解压缩 */
readfile('php://filter/zlib.inflate/resource=test.deflated');

/* 生成的输出：

The original text is 70 characters long.
The compressed file is 56 bytes long.
The original text was:
This is a test.
This is only a test.
This is not an important string.

 */
?>

示例 #2 zlib.deflate 简单参数用法

<?php
$original_text = "This is a test.\nThis is only a test.\nThis is not an important string.\n";
echo "The original text is " . strlen($original_text) . " characters long.\n";

$fp = fopen('test.deflated', 'w');
/* 这里的 “6” 代表压缩级别为 6 */
stream_filter_append($fp, 'zlib.deflate', STREAM_FILTER_WRITE, 6);
fwrite($fp, $original_text);
fclose($fp);

echo "The compressed file is " . filesize('test.deflated') . " bytes long.\n";

/* 生成的输出：

The original text is 70 characters long.
The compressed file is 56 bytes long.

 */
?>

bzip2.compress 和 bzip2.decompress

bzip2.compress 和 bzip2.decompress 工作的方式与上面讲的 zlib 过滤器相同。 bzip2.compress 过滤器接受以一个关联数组给出的最多两个参数： blocks 是从 1 到 9 的整数值，指定分配多少个 100K 字节的内存块作为工作区。 work 是 0 到 250 的整数值，指定在退回到一个慢一些，但更可靠的算法之前做多少次常规压缩算法的尝试。调整此参数仅影响到速度，压缩输出和内存使用都不受此设置的影响。将此参数设为 0 指示 bzip 库使用内部默认算法。 bzip2.decompress 过滤器仅接受一个参数，可以用普通的布尔值传递，或者用一个关联数组中的 small 单元传递。当 small 设为 &true; 值时，指示 bzip 库用最小的内存占用来执行解压缩，代价是速度会慢一些。

在激活 bz2 支持的前提下可以使用 bzip2.* 压缩过滤器。

示例 #3 bzip2.compress 和 bzip2.decompress

<?php
$param = array('blocks' => 9, 'work' => 0);

echo "The original file is " . filesize('LICENSE') . " bytes long.\n";

$fp = fopen('LICENSE.compressed', 'w');
stream_filter_append($fp, 'bzip2.compress', STREAM_FILTER_WRITE, $param);
fwrite($fp, file_get_contents('LICENSE'));
fclose($fp);

echo "The compressed file is " . filesize('LICENSE.compressed') . " bytes long.\n";

/* 生成的输出：

The original file is 3288 bytes long.
The compressed file is 1488 bytes long.

 */
?>

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User Contributed Notes 4 notes

down

Anonymous ¶

9 years ago


To read a gzip encoded stream from http
<?php
$opts = [
    "http" => [
        "method" => "GET",
        "header" => [ "Accept-Encoding: gzip" ],
    ]
];
$ctx = stream_context_create($opts);
$f = fopen("http://php.net", "r", false, $ctx);
// check  stream_get_meta_data($f)["wrapper_data"] has "Content-Encoding: gzip"
stream_filter_append($f, "zlib.inflate", STREAM_FILTER_READ, ["window" => 30]);
echo stream_get_contents($f); // any stream processing
fclose($f);

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Anonymous ¶

3 years ago


To use the zlib.inflate filter with data originally written using gzcompress() or zlib.deflate, set the window option to 15 as outlined here: https://bugs.php.net/bug.php?id=68556

<?php
$fh = fopen(file_name, 'rb');
stream_filter_append($fh, 'zlib.inflate', STREAM_FILTER_READ, ['window' => 15]);
$contents = stream_get_contents($fh);
fclose($fh);

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bohwaz ¶

6 years ago


Please note that there is currently a bug in this feature. ftell(), fseek() and fstat() functions cannot be used. Writing to a stream after using this function will not change the stream position as it should.

See bug: https://bugs.php.net/bug.php?id=49874

Also the zlib filters don't work with php://temp, php://memory and php://input streams, nothing is outputted to those streams.

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-1

TingSong ¶

1 year ago


To decompress a gzipped stream:

<?php
$stream = fopen('https://example.com/some/file.txt.gz', 'rb');
stream_filter_append($stream, 'zlib.inflate', STREAM_FILTER_READ, ['window' => 15+16]);

// read the decompressed line directly
$line = fgets($stream);

// process the lines
?>

As the doc of zlib https://www.zlib.net/manual.html#Advanced

The 'window' parameter between 8 and 15 specified the window size from 2⁸ to 2¹⁵ bytes. It can be added by 16 for wrapping with gzip header and trailer instead of zlib wrapper.

And, window could be -8..-15 for unwrapping RAW deflate data.

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