decoder.rb

encoded_in = "\x00\x00\x00\x03aaa\x00\x00\x00\x06Binary\x02\x00\x00\x00\fP\x00\x84A\xEB\xF9~?\x966\xE7\x8A\x00\x00\x00\x03ccc\x00\x00\x00\x06String\x01\x00\x00\x00\x04test\x00\x00\x00\x03zzz\x00\x00\x00\x06Number\x01\x00\x00\x00\a0230.01\x00\x00\x00\x10\xC3\xB6ther_encodings\x00\x00\x00\x06String\x01\x00\x00\x00\x05T\xC3\xBCst"

class EncodedMessage
  attr_accessor :data
  attr_accessor :md5

  def initialize(data, md5)
    @data = [data].pack('a*')
    @md5 = md5
    # TODO(fg) verify md5
  end

  def decode
    attributes = []
    decoder = Decoder.new(@data)
    while !decoder.empty do
      attribute = Attribute.new
      attribute.decode(decoder)
      attributes << attribute
    end
    return DecodedMessage.new(attributes)
  end
end

class DecodedMessage
  attr_accessor :attributes

  def initialize(attributes)
    @attributes = attributes
  end

  def encode()
    encoder = Encoder.new
    
    @attributes.each do |attribute|
      attribute.encode(encoder)
    end

    # TODO calculate md5
    md5 = "123"
    return EncodedMessag.new(encoder.data, md5)
  end
end

class Attribute
  attr_accessor :name
  attr_accessor :type
  attr_accessor :value_type
  attr_accessor :value

  def decode(decoder)
    @name = decoder.var_string
    @type = decoder.var_string
    @value_type = decoder.num_8
    @value = decoder.var_string
  end

  def encode(encoder)
    encoder.var_string(@name)
    encoder.var_string(@type)
    encoder.num_8(@value_type)
    encoder.var_string(@value)
  end
end
    

class Decoder
  attr_accessor :data

  def initialize(data)
    @data = data
  end

  def var_string()
    l = @data.unpack('L>')[0]
    @data = @data.byteslice(4..-1)
    s = @data.unpack('a'+String(l))[0]
    @data = @data.byteslice(l..-1)
    return s
  end

  def num_8()
    n = @data.unpack('C')[0]
    @data = @data.byteslice(1..-1)
    return n
  end

  def empty()
    return @data.bytesize == 0
  end
end

class Encoder
  attr_accessor :data

  def initialize()
    @data = ""
  end

  def var_string(s)
    @data += [s.bytesize].pack('L>*')
    @data += [s].pack('a*')
  end

  def num_8(n)
    @data += [n].pack('C')
  end
end

def hex(s)
  s.each_byte.map { |b| b.to_s(16) }.join(' ')
end

em = EncodedMessage.new(encoded_in, "abc")
p(em.data)
p(em)
dm = em.decode()
p(dm)
encoded_out = dm.encode()
p(encoded_out)
p(em.data == encoded_out)