module RLP::Decode

def consume_payload(rlp, start, type, length)


the position of the first unprocessed byte.
Returns a pair `[item, end]`, where `item` is the read item and `end` is

* `length` - the length of the payload in bytes
* `start` - the position at which to start reading
* `type` - the type of the payload (`:str` or `:list`)
* `rlp` - the rlp string to read from

Read the payload of an item from an RLP string.
# 
def consume_payload(rlp, start, type, length)
  case type
  when :str
    [rlp[start...(start+length)], start+length]
  when :list
    items = []
    next_item_start = start
    payload_end = next_item_start + length
    while next_item_start < payload_end
      item, next_item_start = consume_item rlp, next_item_start
      items.push item
    end
    raise DecodingError.new('List length prefix announced a too small length', rlp) if next_item_start > payload_end
    [items, next_item_start]
  else
    raise TypeError, 'Type must be either :str or :list'
  end
end