Compression Filters
While the Compression Wrappers provide a way of creating gzip and bz2 compatible files on the local filesystem, they do not provide a means for generalized compression over network streams, nor do they provide a means to begin with a non-compressed stream and transition to a compressed one. For this, a compression filter may be applied to any stream resource at any time.
Note: Compression filters do not generate headers and trailers used by command line utilities such as gzip. They only compress and decompress the payload portions of compressed data streams.
zlib.deflate (compression) and
zlib.inflate (decompression) are implementations of
the compression methods described in » RFC 1951.
The deflate filter takes up to three parameters passed as
an associative array.
level describes the compression
strength to use (1-9). Higher numbers will generally yield smaller payloads at
the cost of additional processing time. Two special compression levels also exist:
0 (for no compression at all), and -1 (zlib internal default -- currently 6).
window is the base-2 log of the compression loopback window size.
Higher values (up to 15 -- 32768 bytes) yield better compression at a cost of memory,
while lower values (down to 9 -- 512 bytes) yield worse compression in a smaller memory footprint.
Default window size is currently 15.
memory is a scale indicating how much work memory should be allocated.
Valid values range from 1 (minimal allocation) to 9 (maximum allocation). This memory allocation
affects speed only and does not impact the size of the generated payload.
Note: Because compression level is the most commonly used parameter, it may be alternatively provided as a simple integer value (rather than an array element).
zlib.* compression filters are available with PHP as of version 5.1.0 if zlib support is enabled. They are also available as a backport in version 5.0.x by installing the » zlib_filter package from » PECL.
Example #1 zlib.deflate and 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";
/* Use readfile and zlib.inflate to decompress on the fly */
readfile('php://filter/zlib.inflate/resource=test.deflated');
/* Generates output:
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.
*/
?>
Example #2 zlib.deflate simple
<?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";
$fp = fopen('test.deflated', 'w');
/* Here "6" indicates compression level 6 */
stream_filter_append($fp, 'zlib.deflate', STREAM_FILTER_WRITE, 6);
fwrite($fp, $original_text);
fclose($fp);
echo "The compressed file is " . filesize('test.deflated') . " bytes long.\n";
/* Generates output:
The original text is 70 characters long.
The compressed file is 56 bytes long.
*/
?>
bzip2.compress and
bzip2.decompress
work in the same manner as the zlib filters described above.
The bzip2.compress filter accepts up to two parameters given as
elements of an associative array:
blocks is an integer value
from 1 to 9 specifying the number of 100kbyte blocks of memory to allocate for
workspace.
work is also an integer value ranging from
0 to 250 indicating how much effort to expend using the normal compression method
before falling back on a slower, but more reliable method. Tuning this parameter
effects only compression speed. Neither size of compressed output nor memory usage
are changed by this setting. A work factor of 0 instructs the bzip library to use
an internal default.
The bzip2.decompress filter only accepts one parameter,
which can be passed as either an ordinary boolean value, or as the
small element of an associative array.
small, when set to a TRUE value, instructs the bzip library
to perform decompression in a minimal memory footprint at the cost of speed.
bzip2.* compression filters are available with PHP as of version 5.1.0 if bz2 support is enabled. They are also available as a backport in version 5.0.x by installing the » bz2_filter package from » PECL.
Example #3 bzip2.compress and 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";
/* Generates output:
The original text is 3288 characters long.
The compressed file is 1488 bytes long.
*/
?>
Vertaling niet beschikbaar
De PHP-handleiding is nog niet in het Nederlands vertaald, dus het scherm is in het Engels. Als u wilt, kunt u het ook in het Frans of in het Duits raadplegen.
Als je de moed voelt, kun je je vertaling aanbieden ;-)
Nederlandse vertaling
U hebt gevraagd om deze site in het Nederlands te bezoeken. Voor nu wordt alleen de interface vertaald, maar nog niet alle inhoud.Als je me wilt helpen met vertalingen, is je bijdrage welkom. Het enige dat u hoeft te doen, is u op de site registreren en mij een bericht sturen waarin u wordt gevraagd om u toe te voegen aan de groep vertalers, zodat u de gewenste pagina's kunt vertalen. Een link onderaan elke vertaalde pagina geeft aan dat u de vertaler bent en heeft een link naar uw profiel.
Bij voorbaat dank.
Document heeft de 30/01/2003 gemaakt, de laatste keer de 26/10/2018 gewijzigd
Bron van het afgedrukte document:https://www.gaudry.be/nl/php-rf-filters.compression.html
De infobrol is een persoonlijke site waarvan de inhoud uitsluitend mijn verantwoordelijkheid is. De tekst is beschikbaar onder CreativeCommons-licentie (BY-NC-SA). Meer info op de gebruiksvoorwaarden en de auteur.
Referenties
Deze verwijzingen en links verwijzen naar documenten die geraadpleegd zijn tijdens het schrijven van deze pagina, of die aanvullende informatie kunnen geven, maar de auteurs van deze bronnen kunnen niet verantwoordelijk worden gehouden voor de inhoud van deze pagina.
De auteur Deze site is als enige verantwoordelijk voor de manier waarop de verschillende concepten, en de vrijheden die met de referentiewerken worden genomen, hier worden gepresenteerd. Vergeet niet dat u meerdere broninformatie moet doorgeven om het risico op fouten te verkleinen.
