• List of Available Filters
  • Compression Filters

  • Compression Filters
  • Compression Filters

    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

    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

    = array('level' => 6'window' => 15'memory' => 9);

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

    $fp fopen('test.deflated''w');

    echo "The compressed file is " filesize('test.deflated') . " bytes long.\n";
    "The original text was:\n";
    /* Use readfile and zlib.inflate to decompress on the fly */

    /* 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

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

    $fp fopen('test.deflated''w');
    /* Here "6" indicates compression level 6 */

    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

    = array('blocks' => 9'work' => 0);

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

    $fp fopen('LICENSE.compressed''w');

    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.