Is the RLP protocol supposed to decode the same values that were encoded?

Question

I'm using a Ruby RLP library to encode one value and then decode it. However, I'm getting different values for encoding and decoding:

require 'rlp'                                                                                           

class Transaction                                                                                       
  include RLP::Sedes::Serializable                                                                      

  set_serializable_fields(                                                                              
    to: RLP::Sedes::Binary.fixed_length(20, allow_empty: true)                                          
  )                                                                                                     

  def initialize(*args)                                                                                 
    fields = parse_field_args(args)                                                                     
    fields[:to] = [fields[:to]].pack('H*')                                                              

    serializable_initialize(fields)                                                                     
  end                                                                                                   

  def encoded                                                                                           
    RLP.encode(self)                                                                                    
  end                                                                                                   

  def self.decode(data_in)                                                                              
    deserialize(RLP.decode(data_in))                                                                    
  end                                                                                                   
end                                                                                                     

recipient = "6ba381ce15b19c7e44b8603ad7e698059c09a39b"                                                  
tx = Transaction.new(recipient)                                                                         

puts "Should decode to #{recipient}"                                                                    
puts "Actually decodes to #{Transaction.decode(tx.encoded).to.unpack('H*').first}"

Running it, the decoded value is actually 431e51ced80a7685c93b, instead of the inputed value. This doesn't even seem to be related to what was encoded.

Is the library at fault here? I'm using this library: https://github.com/cryptape/ruby-rlp

Answer 1

Yes, it is always the same and you can go back and forth.

require "eth"

recipient = "6ba381ce15b19c7e44b8603ad7e698059c09a39b"                                                  
# => "6ba381ce15b19c7e44b8603ad7e698059c09a39b"

encoded = Eth::Rlp.encode "6ba381ce15b19c7e44b8603ad7e698059c09a39b"
# => "\xA86ba381ce15b19c7e44b8603ad7e698059c09a39b"

decoded = Eth::Rlp.decode encoded
# => "6ba381ce15b19c7e44b8603ad7e698059c09a39b"

decoded === recipient
# => true

If you are trying to build a transaction serializer in Ruby, take a look at the eth gem.