Module: ZipTricks::BlockDeflate
- Defined in:
- lib/zip_tricks/block_deflate.rb
Overview
Permits Deflate compression in independent blocks. The workflow is as follows:
- Run every block to compress through deflate_chunk, remove the header, footer and adler32 from the result
- Write out the compressed block bodies (the ones deflate_chunk returns)to your output, in sequence
- Write out the footer (\03\00)
The resulting stream is guaranteed to be handled properly by all zip unarchiving tools, including the BOMArchiveHelper/ArchiveUtility on OSX.
You could also build a compressor for Rubyzip using this module quite easily, even though this is outside the scope of the library.
When you deflate the chunks separately, you need to write the end marker yourself (using write_terminator
).
If you just want to deflate a large IO's contents, use deflate_in_blocks_and_terminate
to have the end marker
written out for you.
Constant Summary collapse
- DEFAULT_BLOCKSIZE =
1024*1024*5
- END_MARKER =
[3, 0].pack("C*")
- VALID_COMPRESSIONS =
Zlib::NO_COMPRESSION..
(Zlib::DEFAULT_COMPRESSION..Zlib::BEST_COMPRESSION).to_a.freeze
Class Method Summary collapse
-
.deflate_chunk(bytes, level: Zlib::DEFAULT_COMPRESSION) ⇒ String
Compress a given binary string and flush the deflate stream at byte boundary.
-
.deflate_in_blocks(input_io, output_io, level: Zlib::DEFAULT_COMPRESSION, block_size: DEFAULT_BLOCKSIZE) ⇒ Fixnum
Compress the contents of input_io into output_io, in blocks of block_size.
-
.deflate_in_blocks_and_terminate(input_io, output_io, level: Zlib::DEFAULT_COMPRESSION, block_size: DEFAULT_BLOCKSIZE) ⇒ Fixnum
Compress the contents of input_io into output_io, in blocks of block_size.
-
.write_terminator(output_io) ⇒ Fixnum
Write the end marker (\x3\x0) to the given IO.
Class Method Details
.deflate_chunk(bytes, level: Zlib::DEFAULT_COMPRESSION) ⇒ String
Compress a given binary string and flush the deflate stream at byte boundary. The returned string can be spliced into another deflate stream.
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# File 'lib/zip_tricks/block_deflate.rb', line 37 def self.deflate_chunk(bytes, level: Zlib::DEFAULT_COMPRESSION) raise "Invalid Zlib compression level #{level}" unless VALID_COMPRESSIONS.include?(level) z = Zlib::Deflate.new(level) compressed_blob = z.deflate(bytes, Zlib::SYNC_FLUSH) compressed_blob << z.finish z.close # Remove the header (2 bytes), the [3,0] end marker and the adler (4 bytes) compressed_blob[2...-6] end |
.deflate_in_blocks(input_io, output_io, level: Zlib::DEFAULT_COMPRESSION, block_size: DEFAULT_BLOCKSIZE) ⇒ Fixnum
Compress the contents of input_io into output_io, in blocks of block_size. Align the parts so that they can be concatenated later. Will not write the deflate end marker (\x3\x0) so more parts can be written later and succesfully read back in provided the end marker wll be written.
output_io
can also be a Streamer to expedite ops.
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# File 'lib/zip_tricks/block_deflate.rb', line 80 def self.deflate_in_blocks(input_io, output_io, level: Zlib::DEFAULT_COMPRESSION, block_size: DEFAULT_BLOCKSIZE) bytes_written = 0 while block = input_io.read(block_size) deflated = deflate_chunk(block, level: level) output_io << deflated bytes_written += deflated.bytesize end bytes_written end |
.deflate_in_blocks_and_terminate(input_io, output_io, level: Zlib::DEFAULT_COMPRESSION, block_size: DEFAULT_BLOCKSIZE) ⇒ Fixnum
Compress the contents of input_io into output_io, in blocks
of block_size. Aligns the parts so that they can be concatenated later.
Writes deflate end marker (\x3\x0) into output_io
as the final step, so
the contents of output_io
can be spliced verbatim into a ZIP archive.
Once the write completes, no more parts for concatenation should be written to the same stream.
output_io
can also be a Streamer to expedite ops.
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# File 'lib/zip_tricks/block_deflate.rb', line 63 def self.deflate_in_blocks_and_terminate(input_io, output_io, level: Zlib::DEFAULT_COMPRESSION, block_size: DEFAULT_BLOCKSIZE) bytes_written = deflate_in_blocks(input_io, output_io, level: level, block_size: block_size) bytes_written + write_terminator(output_io) end |
.write_terminator(output_io) ⇒ Fixnum
Write the end marker (\x3\x0) to the given IO.
output_io
can also be a Streamer to expedite ops.
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# File 'lib/zip_tricks/block_deflate.rb', line 26 def self.write_terminator(output_io) output_io << END_MARKER END_MARKER.bytesize end |