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    gzcompress

    (PHP 4 >= 4.0.1, PHP 5, PHP 7, PHP 8)

    gzcompress — 文字列を圧縮する

    説明

    gzcompress(string $data, int $level = -1, int $encoding = ZLIB_ENCODING_DEFLATE): string|false

    この関数は、ZLIB データフォーマットを用いて 与えられた文字列を圧縮します。

    ZLIB 圧縮アルゴリズムについての詳細は、 "» ZLIB Compressed Data Format Specification version 3.3" (RFC 1950) を参照ください。

    注意:

    これは、いくつかのヘッダデータを有する gzip 圧縮と同じでは ありません。 gzip圧縮については、gzencode()を参照ください。

    パラメータ

    data

    圧縮するデータ

    level

    圧縮レベル。0 で圧縮無し、9 で最大限の圧縮を指定できます。

    -1 を指定すると、zlib ライブラリのデフォルトを使います。デフォルトは 6 です。

    encoding

    定数 ZLIB_ENCODING_* のいずれか。

    戻り値

    圧縮された文字列、もしくはエラーの場合 false 。

    例

    例1 gzcompress() の例

    <?php
    $compressed     = gzcompress('Compress me', 9);
    echo     $compressed;
    ?>

    参考

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    User Contributed Notes 2 notes

    up
    7
    @boas.anthro.mnsu.edu
    24 years ago
    No, it doesn't return gzip compressed data -- specifically, the CRC is messed up. However, after massaging the output a lot, I have come up with a solution. I also commented it a lot, pointing out odd things.

    <?php
    // Start the output buffer
    ob_start();
    ob_implicit_flush(0);

    // Output stuff here...

    // Get the contents of the output buffer
    $contents = ob_get_contents();
    ob_end_clean();

    // Tell the browser that they are going to get gzip data
    // Of course, you already checked if they support gzip or x-gzip
    // and if they support x-gzip, you'd change the header to say
    // x-gzip instead, right?
    header("Content-Encoding: gzip");

    // Display the header of the gzip file
    // Thanks ck@medienkombinat.de!
    // Only display this once
    echo "\x1f\x8b\x08\x00\x00\x00\x00\x00";

    // Figure out the size and CRC of the original for later
    $Size = strlen($contents);
    $Crc = crc32($contents);

    // Compress the data
    $contents = gzcompress($contents, 9);

    // We can't just output it here, since the CRC is messed up.
    // If I try to "echo $contents" at this point, the compressed
    // data is sent, but not completely. There are four bytes at
    // the end that are a CRC. Three are sent. The last one is
    // left in limbo. Also, if we "echo $contents", then the next
    // byte we echo will not be sent to the client. I am not sure
    // if this is a bug in 4.0.2 or not, but the best way to avoid
    // this is to put the correct CRC at the end of the compressed
    // data. (The one generated by gzcompress looks WAY wrong.)
    // This will stop Opera from crashing, gunzip will work, and
    // other browsers won't keep loading indefinately.
    //
    // Strip off the old CRC (it's there, but it won't be displayed
    // all the way -- very odd)
    $contents = substr($contents, 0, strlen($contents) - 4);

    // Show only the compressed data
    echo $contents;

    // Output the CRC, then the size of the original
    gzip_PrintFourChars($Crc);
    gzip_PrintFourChars($Size);


    // Done. You can append further data by gzcompressing
    // another string and reworking the CRC and Size stuff for
    // it too. Repeat until done.


    function gzip_PrintFourChars($Val)
    {
    for (    $i = 0; $i < 4; $i ++)
    {
    echo     chr($Val % 256);
    $Val = floor($Val / 256);
    }
    }
    ?>
    up
    3
    detain at interserver dot net
    7 years ago
    gzipped strings include header/metadata you can use to determine if a string is gzipped or not , but since gzcompress does not include that I found myself needing a way to determine if a string was compressed or not. After some research (and then improvements) i came up with this:

    /**
    * determines if a string is a gzipped string supporting strings
    * encoded with either gzencode or gzcompress
    *
    * @param string $string the string to check for compression
    * @return bool whether or not the string was compmressed
    */
    function is_gzipped($string) {
    return mb_strpos($string, "\x1f\x8b\x08", 'US-ASCII') === 0 && @gzuncompress($string) !== FALSE;
    }
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