pjson.rb

#! /usr/bin/ruby

LBRACE = '{'
RBRACE = '}'
LBRACKET = '['
RBRACKET = ']'
COMMA = ','
COLON = ':'
WHITESPACE = /\s/


# Very naively prints formatted JSON from a stream.
# This doesn't handle Strings or escapes or any other stuff like that.
#
# Usage:
#  ruby pjson.rb minified.json
#  curl http://example.com/index.json | ruby pjson.rb
class PJson
  def initialize(input = ARGF, output = $stdout)
    @input = input
    @output = output

    @stack = []
    @buffer = ''
  end

  attr_reader :buffer, :stack

  def format!
    ARGF.each_char do |char|
      case char
      when WHITESPACE
        # ignore
      when LBRACE, LBRACKET
        buffer << char
        print
        stack.push char
      when RBRACE, RBRACKET
        print
        stack.pop
        buffer << char
      when COLON
        buffer << ': '
      when COMMA
        buffer << char
        print
      else
        buffer << char
      end
    end

    print
  end

  def print
    return if buffer.empty?

    padding = ('  ' * stack.length)
    $stdout.puts (padding << buffer)
    buffer.clear
  end
end


PJson.new.format! if $0 == __FILE__