You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: packet.rb
    path of file: ./repos/metasploit-framework/lib/rex/proto/drda
    
    the code of the file until where you have to start completion: # -*- coding: binary -*-


module Rex
module Proto
module DRDA::Packet

class Error < StandardError; end
class RespError < Error; end

# See:
# http://publib.
    
  def read(str="")
    raise DRDA::Error, "Input isn't a String." if !str.kind_of? String
    raise DRDA::RespError, "DDM_PARAM is too short" if str.size < 4
    (self[:length], self[:codepoint]) =
      str.unpack("nn")
    raise DRDA::RespError, "DDM_PARAM Length is too short" if self[:length] < 4
    rest = str[4,self[:length]-4] # If it's negative or whatever, it'll end up as "".
    self[:payload] = rest.to_s[0,self[:length]-4]
    return self
  end