module RLP::Decode

def insert(rlp, index, obj)
  type, len, pos = consume_length_prefix rlp, 0
  raise DecodingError.new("Trying to insert to a non-list!", rlp) if type != :list
  beginpos = pos
  index.times do |i|
    _, _len, _pos = consume_length_prefix rlp, pos
    pos = _pos + _len
    break if _pos >= rlp.size
  end
  rlpdata = rlp[beginpos...pos] + RLP.encode(obj) + rlp[pos..-1]
  prefix = length_prefix rlpdata.size, LIST_PREFIX_OFFSET
  prefix + rlpdata
end