metasploit-framework/lib/bit-struct/text-field.rb

class BitStruct
  # Class for null-terminated printable text strings.
  # Declared with BitStruct.text.
  class TextField < Field
    # Used in describe.
    def self.class_name
      @class_name ||= "text"
    end

    def add_accessors_to(cl, attr = name) # :nodoc:
      unless offset % 8 == 0
        raise ArgumentError,
          "Bad offset, #{offset}, for #{self.class} #{name}." +
          " Must be multiple of 8."
      end
      
      unless length % 8 == 0
        raise ArgumentError,
          "Bad length, #{length}, for #{self.class} #{name}." +
          " Must be multiple of 8."
      end
      
      offset_byte = offset / 8
      length_byte = length / 8
      last_byte = offset_byte + length_byte - 1
      byte_range = offset_byte..last_byte
      val_byte_range = 0..length_byte-1

      cl.class_eval do
        define_method attr do ||
          self[byte_range].sub(/\0*$/, "").to_s
        end

        define_method "#{attr}=" do |val|
          val = val.to_s
          if val.length < length_byte
            val += "\0" * (length_byte - val.length)
          end
          self[byte_range] = val[val_byte_range]
        end
      end
    end
  end
end