Ruby JSON-to-CBOR converter, also intended to demonstrate an issue

jcbor.rb

# Written by Peter O. in 2014.
# Any copyright is dedicated to the Public Domain.
# http://creativecommons.org/publicdomain/zero/1.0/
#
# If you like this, you should donate to Peter O.
# at: http://upokecenter.com/d/

require 'json'

module JCBOR

private

def self._length2cbor(len, mtype, output)
  raise "error writing" if len<0
  ax=len
      if ax<24
        output << [mtype|ax].pack("C")
      elsif ax<256
        output << [mtype|0x18, ax].pack("CC")
      elsif ax<65536
        output << [mtype|0x19, ax].pack("Cn")
      elsif ax<=0xFFFFFFFF
        output << [mtype|0x1A, ax].pack("CN")
      elsif ax<=0xFFFFFFFFFFFFFFFF
        hi=(ax>>32)&0xFFFFFFFF
        lo=(ax)&0xFFFFFFFF
        output << [mtype|0x1B, hi, lo].pack("CN*")
      else
        raise "length bigger than supported"
      end
end

def self._json2cbor(x, output)
  if x==false
    output << 0xF4.chr
    return
  elsif x==true
    output << 0xF5.chr
    return
  elsif x==nil
    output << 0xF6.chr
    return
  elsif x.is_a?(Numeric)
    if x.to_i==x
      ax=(x<0) ? (-x)-1 : x
      mtype=(x<0) ? 0x20 : 0
      if ax<24
        output << [mtype|ax].pack("C")
      elsif ax<256
        output << [mtype|0x18, ax].pack("CC")
      elsif ax<65536
        output << [mtype|0x19, ax].pack("Cn")
      elsif ax<=0xFFFFFFFF
        output << [mtype|0x1A, ax].pack("CN")
      else
        output << [0xFB, x.to_f].pack("CG")
      end
    else
      output << [0xFB, x.to_f].pack("CG")
    end
  elsif x.is_a?(String)
    x2=x.encode("UTF-8")
    self._length2cbor(x2.bytesize,0x60,output)
    output << x2
  elsif x.is_a?(Hash)
    self._length2cbor(x.length,0xa0,output)
    x.keys.each{|item| 
      self._json2cbor(item,output) 
      self._json2cbor(x[item],output) 
    }
  elsif x.is_a?(Array)
    self._length2cbor(x.length,0x80,output)
    x.each{|item| self._json2cbor(item,output) }
  else
    raise "unsupported object"
  end
end

public

def self.json2cbor(x, output)
  if !x[/\A\ufeff?\s*[\[\{]/]
    # Unfortunately, JSON.parse doesn't accept non-object,
    # non-array strings, as are now allowed in the latest JSON RFC,
    # so we use this workaround
    json=JSON.parse("["+x+"]")
    self._json2cbor(json[0],output)
  else
    json=JSON.parse(x)
    self._json2cbor(json,output)
  end
end

end

# Generate a fake document as a demonstration
x=[]
for i in 0...1000
  y={}
  y["item1"]="itemitemitemitem"
  y["item2"]=true
  y["item3"]=999999999
  y["item4"]="itemitemitemitem"
  y["item5"]=["itemitemitemitem"]
  x.push(y)
end
json=JSON.generate(x)
File.open("document.cbor","wb"){|f|
 JCBOR.json2cbor(json,f)
}