class Zlib::Deflate
Zlib::Deflate
is the class for compressing data. See Zlib::ZStream
for more information.
Public Class Methods
Compresses the given string
. Valid values of level are Zlib::NO_COMPRESSION, Zlib::BEST_SPEED, Zlib::BEST_COMPRESSION, Zlib::DEFAULT_COMPRESSION, or an integer from 0 to 9.
This method is almost equivalent to the following code:
def deflate(string, level) z = Zlib::Deflate.new(level) dst = z.deflate(string, Zlib::FINISH) z.close dst end
See also Zlib.inflate
static VALUE rb_deflate_s_deflate(int argc, VALUE *argv, VALUE klass) { struct zstream z; VALUE src, level, dst, args[2]; int err, lev; rb_scan_args(argc, argv, "11", &src, &level); lev = ARG_LEVEL(level); StringValue(src); zstream_init_deflate(&z); err = deflateInit(&z.stream, lev); if (err != Z_OK) { raise_zlib_error(err, z.stream.msg); } ZSTREAM_READY(&z); args[0] = (VALUE)&z; args[1] = src; dst = rb_ensure(deflate_run, (VALUE)args, zstream_ensure_end, (VALUE)&z); return dst; }
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:
-
Zlib::DEFAULT_COMPRESSION
-
Zlib::NO_COMPRESSION
-
Zlib::BEST_SPEED
-
Zlib::BEST_COMPRESSION
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:
-
Zlib::DEF_MEM_LEVEL
-
Zlib::MAX_MEM_LEVEL
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¶ ↑
open "compressed.file", "w+" do |io| io << Zlib::Deflate.new.deflate(File.read("big.file")) end
Custom compression¶ ↑
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.
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; }
Public Instance Methods
Inputs string
into the deflate stream just like Zlib::Deflate#deflate
, but returns the Zlib::Deflate
object itself. The output from the stream is preserved in output buffer.
static VALUE rb_deflate_addstr(VALUE obj, VALUE src) { do_deflate(get_zstream(obj), src, Z_NO_FLUSH); return obj; }
Inputs string
into the deflate stream and returns the output from the stream. On calling this method, both the input and the output buffers of the stream are flushed. If string
is nil, this method finishes the stream, just like Zlib::ZStream#finish
.
If a block is given consecutive deflated chunks from the string
are yielded to the block and nil
is returned.
The flush
parameter specifies the flush mode. The following constants may be used:
- Zlib::NO_FLUSH
-
The default
- Zlib::SYNC_FLUSH
-
Flushes the output to a byte boundary
- Zlib::FULL_FLUSH
-
SYNC_FLUSH + resets the compression state
- Zlib::FINISH
-
Pending input is processed, pending output is flushed.
See the constants for further description.
static VALUE rb_deflate_deflate(int argc, VALUE *argv, VALUE obj) { struct zstream *z = get_zstream(obj); VALUE src, flush; rb_scan_args(argc, argv, "11", &src, &flush); do_deflate(z, src, ARG_FLUSH(flush)); return zstream_detach_buffer(z); }
This method is equivalent to deflate('', flush)
. This method is just provided to improve the readability of your Ruby program. If a block is given chunks of deflate output are yielded to the block until the buffer is flushed.
See Zlib::Deflate#deflate
for detail on the flush
constants NO_FLUSH, SYNC_FLUSH, FULL_FLUSH and FINISH.
static VALUE rb_deflate_flush(int argc, VALUE *argv, VALUE obj) { struct zstream *z = get_zstream(obj); VALUE v_flush; int flush; rb_scan_args(argc, argv, "01", &v_flush); flush = FIXNUMARG(v_flush, Z_SYNC_FLUSH); if (flush != Z_NO_FLUSH) { /* prevent Z_BUF_ERROR */ zstream_run(z, (Bytef*)"", 0, flush); } return zstream_detach_buffer(z); }
Duplicates the deflate stream.
static VALUE rb_deflate_init_copy(VALUE self, VALUE orig) { struct zstream *z1, *z2; int err; TypedData_Get_Struct(self, struct zstream, &zstream_data_type, z1); z2 = get_zstream(orig); if (z1 == z2) return self; err = deflateCopy(&z1->stream, &z2->stream); if (err != Z_OK) { raise_zlib_error(err, 0); } z1->input = NIL_P(z2->input) ? Qnil : rb_str_dup(z2->input); z1->buf = NIL_P(z2->buf) ? Qnil : rb_str_dup(z2->buf); z1->flags = z2->flags; return self; }
Changes the parameters of the deflate stream to allow changes between different types of data that require different types of compression. Any unprocessed data is flushed before changing the params.
See Zlib::Deflate.new
for a description of level
and strategy
.
static VALUE rb_deflate_params(VALUE obj, VALUE v_level, VALUE v_strategy) { struct zstream *z = get_zstream(obj); int level, strategy; int err; uInt n; long filled; level = ARG_LEVEL(v_level); strategy = ARG_STRATEGY(v_strategy); n = z->stream.avail_out; err = deflateParams(&z->stream, level, strategy); filled = n - z->stream.avail_out; while (err == Z_BUF_ERROR) { rb_warning("deflateParams() returned Z_BUF_ERROR"); zstream_expand_buffer(z); rb_str_set_len(z->buf, RSTRING_LEN(z->buf) + filled); n = z->stream.avail_out; err = deflateParams(&z->stream, level, strategy); filled = n - z->stream.avail_out; } if (err != Z_OK) { raise_zlib_error(err, z->stream.msg); } rb_str_set_len(z->buf, RSTRING_LEN(z->buf) + filled); return Qnil; }
Sets the preset dictionary and returns string
. This method is available just only after Zlib::Deflate.new
or Zlib::ZStream#reset
method was called. See zlib.h for details.
Can raise errors of Z_STREAM_ERROR if a parameter is invalid (such as NULL dictionary) or the stream state is inconsistent, Z_DATA_ERROR if the given dictionary doesn’t match the expected one (incorrect adler32 value)
static VALUE rb_deflate_set_dictionary(VALUE obj, VALUE dic) { struct zstream *z = get_zstream(obj); VALUE src = dic; int err; StringValue(src); err = deflateSetDictionary(&z->stream, (Bytef*)RSTRING_PTR(src), RSTRING_LENINT(src)); if (err != Z_OK) { raise_zlib_error(err, z->stream.msg); } return dic; }