deft4j

WIP deflate toolkit for Java.

deft4j is a (very inefficient) deflate stream parser and optimiser.

It has support for parsing and writing ZIP, GZip, ZLib, and PNG files (including APNG and most deflate compressed PNG chunks).

deft4j implements a few deflate stream optimisations:

• If the encoded size of a backref is larger than the equivalent sequence of literals, and the literals are able to be encoded by the huffman codes a block uses, it replaces the backref with literals.
• Similarly, if a RLE instruction in a dynamic tree header is larger than the equivalent sequence of literals, it replaces the instruction with literals.
• Dynamic headers are re-encoded with various strategies.
• Type 2 blocks are tested to see if they would be smaller when encoded as type 1 blocks.
• Trailing zero-length codelength lengths are removed from dynamic headers.
• Empty blocks are removed.
• Type 1 & 2 blocks are tested to see if they would be smaller when encoded as type 0 blocks.

Future work includes:

• Merging type 0 and 1 blocks, as well as type 2 blocks which have the same huffman trees.
• Improvements to header re-encoding.
• Backref replacement when the symbol is not already able to be encoded.

deft4j also includes options for recompressing files with various libraries, including CafeUndZopfli.

Usage

deft4j is currently available as a command line application:

Usage: deft4j optimise [-hrV] [-f=<format>] [-m=<recompressMode>] <inputFile>
                       <outputFile>
Deflate stream optimiser
      <inputFile>         The file to optimise
      <outputFile>        The optimised file
  -f, --format=<format>   File format
  -h, --help              Show this help message and exit.
  -m, --mode, --recompress-mode=<recompressMode>
                          Enable various levels of recompression. Valid values:
                            NONE, CHEAP, ZOPFLI, ZOPFLI_EXTENSIVE,
                            ZOPFLI_VERY_EXTENSIVE
  -r, --raw               Ignore file format, treat input as a raw deflate
                            stream
  -V, --version           Print version information and exit.

Credits

The code for parsing and writing deflate streams is based on hwzip, which is in the public domain. The code for Huffman encoding and decoding is largely from deflate-impl, which is licensed under the MIT license.

License

All original code is licensed under the BSD Zero Clause License. The code for Huffman encoding and decoding is licensed under its original terms of the MIT license.