Module: PacketGen::Header::HeaderClassMethods

Included in:
ARP, Eth, ICMP, IP, IPv6, TCP, UDP
Defined in:
lib/packetgen/header/header_class_methods.rb

Defined Under Namespace

Classes: Binding

Instance Method Summary collapse

Instance Method Details

#bind_header(header_klass, args = {}) ⇒ void

This method returns an undefined value.

Bind a upper header to current class

Parameters:

  • header_klass (Class) —

    header class to bind to current class

  • args (Hash) (defaults to: {}) —

    current class field and its value when header_klass is embedded in current class



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# File 'lib/packetgen/header/header_class_methods.rb', line 19

def bind_header(header_klass, args={})
  @known_headers ||= {}
  key = args.keys.first
  @known_headers[header_klass] = Binding.new(key, args[key])
end

#define_bit_fields_on(attr, *args) ⇒ void

This method returns an undefined value.

Define a bitfield on given attribute

class MyHeader < Struct.new(:flags)

  def initialize(options={})
    super Int16.new(options[:flags])
  end

  # define a bit field on :flag attribute:
  # flag1, flag2 and flag3 are 1-bit fields
  # type and stype are 3-bit fields. reserved is a 6-bit field
  define_bit_fields_on :flags, :flag1, :flag2, :flag3, :type, 3, :stype, 3, :reserved: 6
end

A bitfield of size 1 bit defines 2 methods:

  • #field? which returns a Boolean,

  • #field= which takes and returns a Boolean.

A bitfield of more bits defines 2 methods:

  • #field which returns an Integer,

  • #field= which takes and returns an Integer.

Parameters:

  • attr (Symbol) —

    attribute name (attribute should a StructFu::Int subclass)

  • args (Array) —

    list of bitfield names. Name may be followed by bitfield size. If no size is given, 1 bit is assumed.



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# File 'lib/packetgen/header/header_class_methods.rb', line 54

def define_bit_fields_on(attr, *args)
  total_size = self.new[attr].width * 8
  idx = total_size - 1

  field = args.shift
  while field
    next unless field.is_a? Symbol
    size = if args.first.is_a? Integer
             args.shift
           else
             1
           end
    unless field == :_
      shift = idx - (size - 1)
      field_mask = (2**size - 1) << shift
      clear_mask = (2**total_size - 1) & (~field_mask & (2**total_size - 1))

      if size == 1
        class_eval <<-EOM
        def #{field}?
          val = (self[:#{attr}].to_i & #{field_mask}) >> #{shift}
          val != 0
        end
        def #{field}=(v)
          val = v ? 1 : 0
          self[:#{attr}].value = self[:#{attr}].to_i & #{clear_mask}
          self[:#{attr}].value |= val << #{shift}
        end
        EOM
      else
        class_eval <<-EOM
        def #{field}
          (self[:#{attr}].to_i & #{field_mask}) >> #{shift}
        end
        def #{field}=(v)
          self[:#{attr}].value = self[:#{attr}].to_i & #{clear_mask}
          self[:#{attr}].value |= (v & #{2**size - 1}) << #{shift}
        end
        EOM
      end
    end

    idx -= size
    field = args.shift
  end
end

#known_headers ⇒ Hash

Get knwon headers

Returns:

  • (Hash) —

    keys: header classes, values: struct with methods #key and #value



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# File 'lib/packetgen/header/header_class_methods.rb', line 27

def known_headers
  @known_headers ||= {}
end