Zlib::Deflate.new

(?::Zlib::Deflate::compression_level level, ?::Integer window_bits, ?::Integer mem_level, ?::Integer strategy) -> ::Zlib::Deflate

Zlib::Deflate.new(level=DEFAULT_COMPRESSION, window_bits=MAX_WBITS, mem_level=DEF_MEM_LEVEL, strategy=DEFAULT_STRATEGY)

ext/zlib/zlib.c View on GitHub ↗

static VALUE
rb_deflate_initialize(int argc, VALUE *argv, VALUE obj)
{
    struct zstream *z;
    VALUE level, wbits, memlevel, strategy;
    int err;

    rb_scan_args(argc, argv, "04", &level, &wbits, &memlevel, &strategy);
    TypedData_Get_Struct(obj, struct zstream, &zstream_data_type, z);

    err = deflateInit2(&z->stream, ARG_LEVEL(level), Z_DEFLATED,
                       ARG_WBITS(wbits), ARG_MEMLEVEL(memlevel),
                       ARG_STRATEGY(strategy));
    if (err != Z_OK) {
        raise_zlib_error(err, z->stream.msg);
    }
    ZSTREAM_READY(z);

    return obj;
}

Creates a new deflate stream for compression. If a given argument is nil, the default value of that argument is used.

The level sets the compression level for the deflate stream between 0 (no compression) and 9 (best compression). The following constants have been defined to make code more readable:

See www.zlib.net/manual.html#Constants for further information.

The window_bits sets the size of the history buffer and should be between 8 and 15. Larger values of this parameter result in better compression at the expense of memory usage.

The mem_level specifies how much memory should be allocated for the internal compression state. 1 uses minimum memory but is slow and reduces compression ratio while 9 uses maximum memory for optimal speed. The default value is 8. Two constants are defined:

The strategy sets the deflate compression strategy. The following strategies are available:

Zlib::DEFAULT_STRATEGY: For normal data
Zlib::FILTERED: For data produced by a filter or predictor
Zlib::FIXED: Prevents dynamic Huffman codes
Zlib::HUFFMAN_ONLY: Prevents string matching
Zlib::RLE: Designed for better compression of PNG image data

See the constants for further description.

Examples

Basic

Example

open "compressed.file", "w+" do |io|
  io << Zlib::Deflate.new.deflate(File.read("big.file"))
end

Custom compression

Example

open "compressed.file", "w+" do |compressed_io|
  deflate = Zlib::Deflate.new(Zlib::BEST_COMPRESSION,
                              Zlib::MAX_WBITS,
                              Zlib::MAX_MEM_LEVEL,
                              Zlib::HUFFMAN_ONLY)

  begin
    open "big.file" do |big_io|
      until big_io.eof? do
        compressed_io << zd.deflate(big_io.read(16384))
      end
    end
  ensure
    deflate.close
  end
end

While this example will work, for best optimization review the flags for your specific time, memory usage and output space requirements.

See also .deflate #<< #deflate also in 4.1 · 4.0 · 3.3 · 3.2 · 3.1 · 3.0

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