simple-json-pack

Pack and unpack JSON files

Introduction

A quick search on NPM reveals lots of JSON compression related projects. Each with different trade-offs. This compressor has the following goals:

• The code is simple to use, understand and simple to add to your own projects. This simplity allows for creating simple client decoders in languages other than JavaScript.
• Compressed JSON files remain JSON compatible on output

How it works

Simple JSON Pack works by scanning a JSON file and creating a tokenization dictionary. The dictionary is then embedded in the output (packed) JSON so its availble for use by another decoder.

This approach offers the opportunty of removing the dictionary from the target JSON output, whereby further reducing the file size. In this use case you would just have the dictionary available on the receiving end. This allows for smaller payloads in storage and transmission. This is completly optional - but possible.

Command line

There's an included command line program called sjp. If you'd like to use the code directly in your own projects then just use the simple-json-pack.js. The sjp serves as a working example.

You can install sjp has a global command:

$ npm install -g simple-json-pack
$ sjp --help

Help options

$ sjp --help
SJP - Simple JSON Pack
Usage: sjp [options]

Options:
  -v, --version          output the version number
  -p, --pack             perform packing
  -u, --unpack           perform unpacking
  -i, --input <file>     input filename
  -o, --output <file>    output filename
  -e, --exclude <items>  exclusion list
  -v, --version          display version
  -d, --debug            output prettified JSON for easier debugging
  -h, --help             output usage information

Compress (pack)

Use the -p option with the -i option to specify a file:

$ sjp -p -i ./tests/game.json
SJP - Simple JSON Pack
./tests/game.json file size in bytes: 24110
./tests/game.json.out file size in bytes: 12379
resulting compression: 49%

$ sjp -p -i ./tests/github.json
SJP - Simple JSON Pack
./tests/github.json file size in bytes: 71547
./tests/github.json.out file size in bytes: 48165
resulting compression: 33%

Decompress (unpack)

Use the -u option with the -i option to specify an input file and the -o option to specify a destination output file.

$ sjp -u -i ./tests/game.json.out -o ./tests/game2.json

Excluding keys

You can exclude named JSON keys by specifying them in an exclusion list using the -e/--exclude

$ sjp -p -e "comments","frame" -i ./tests/game.json

When using excludes make sure that you don't have spaces between entries

Debug

You can generate output files which are JSON prettifed for debugging purposes by using the -d/--debug flag.