Class: PacketGen::Types::Fields Abstract

Inherits:
Object
  • Object
show all
Defined in:
lib/packetgen/types/fields.rb

Overview

This class is abstract.

Set of fields

This class is a base class to define headers or anything else with a binary format containing multiple fields.

Basics

A Fields subclass is generaly composed of multiple binary fields. These fields have each a given type. All types from PacketGen::Types module are supported, and all Fields subclasses may also be used as field type.

To define a new subclass, it has to inherit from Fields. And some class methods have to be used to declare attributes/fields:

class MyBinaryStructure < PacketGen::Types::Fields
  # define a first Int8 attribute, with default value: 1
  define_field :attr1, PacketGen::Types::Int8, default: 1
  #define a second attribute, of kind Int32
  define_field :attr2, PacketGen::Types::Int32
end

These defintions create 4 methods: #attr1, #attr1=, #attr2 and #attr2=. All these methods take and/or return Integers.

Fields may also be accessed through #[] ans #[]=. These methods give access to type object:

mybs = MyBinaryStructure.new
mybs.attr1     # => Integer
mybs[:attr1]   # => PacketGen::Types::Int8

#initialize accepts an option hash to populate attributes. Keys are attribute name symbols, and values are those expected by writer accessor.

#read is able to populate object from a binary string.

#to_s returns binary string from object.

Add Fields

Fields.define_field adds a field to Fields subclass. A lot of field types may be defined: integer types, string types (to handle a stream of bytes). More complex field types may be defined using others Fields subclasses:

# define a 16-bit little-endian integer field, named type
define_field :type, PacketGen::Types::Int16le
# define a string field
define_field :body, PacketGen::Types::String
# define afield using a complex type (Fields subclass)
define_field :mac_addr, PacketGen::Eth::MacAddr

This example creates six methods on our Fields subclass: #type, #type=, #body, #body=, #mac_addr and #mac_addr=.

Fields.define_field has many options (third optional Hash argument):

  • :default gives default field value. It may be a simple value (an Integer for an Int field, for example) or a lambda,

  • :builder to give a builder/constructor lambda to create field. The lambda takes one argument: Fields subclass object owning field,

  • :optional to define this field as optional. This option takes a lambda parameter used to say if this field is present or not,

  • :enum to define Hash enumeration for an Enum type.

For example:

# 32-bit integer field defaulting to 1
define_field :type, PacketGen::Types::Int32, default: 1
# 16-bit integer field, created with a random value. Each instance of this
# object will have a different value.
define_field :id, PacketGen::Types::Int16, default: ->{ rand(65535) }
# a size field
define_field :body_size, PacketGen::Types::Int16
# String field which length is taken from body_size field
define_field :body, PacketGen::Types::String, builder: ->(obj, type) { type.new('', length_from: obj[:body_size]) }
# 16-bit enumeration type. As :default not specified, default to first value of enum
define_field :type_class, PacketGen::Types::Int16Enum, enum: { 'class1' => 1, 'class2' => 2}
# optional field. Only present if another field has a certain value
define_field :opt1, PacketGen::Types::Int16, optional: ->(h) { h.type == 42 }

Fields.define_field_before and Fields.define_field_after are also defined to relatively create a field from anoher one (for example, when adding a field in a subclass).

Generating bit fields

Fields.define_bit_fields_on creates a bit field on a previuously declared integer field. For example, frag field in IP header:

define_field :frag, Types::Int16, default: 0
define_bit_fields_on :frag, :flag_rsv, :flag_df, :flag_mf, :fragment_offset, 13

This example generates methods:

  • #frag and #frag= to access frag field as a 16-bit integer,

  • #flag_rsv?, #flag_rsv=, #flag_df?, #flag_df=, #flag_mf? and #flag_mf= to access Boolean RSV, MF and DF flags from frag field,

  • #fragment_offset and #fragment_offset= to access 13-bit integer fragment offset subfield from frag field.

Author:

  • Sylvain Daubert

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(options = {}) ⇒ Fields

Create a new header object

Parameters:



346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
 
# File 'lib/packetgen/types/fields.rb', line 346

def initialize(options={})
  @fields = {}
  @optional_fields = {}

  self.class.class_eval { @field_defs }.each do |field, ary|
    type, default, builder, optional, enum, field_options = ary
    default = default.to_proc.call(self) if default.is_a?(Proc)
    @fields[field] = if builder
                       builder.call(self, type)
                     elsif enum
                       type.new(enum)
                     elsif !field_options.empty?
                       type.new(field_options)
                     else
                       type.new
                     end

    value = options[field] || default
    if value.class <= type
      @fields[field] = value
    elsif type < Types::Enum
      case value
      when ::String
        @fields[field].value = value
      else
        @fields[field].read(value)
      end
    elsif type < Types::Int
      @fields[field].read(value)
    elsif type <= Types::String
      @fields[field].read(value)
    elsif @fields[field].respond_to? :from_human
      @fields[field].from_human(value)
    end

    @optional_fields[field] = optional if optional
  end
  self.class.class_eval { @bit_fields }.each do |_, hsh|
    hsh.each_key do |bit_field|
      self.send "#{bit_field}=", options[bit_field] if options[bit_field]
    end
  end
end

Class Method Details

.define_bit_fields_on(attr, *args) ⇒ void

This method returns an undefined value.

Define a bitfield on given attribute

class MyHeader < PacketGen::Types::Fields
  define_field :flags, Types::Int16
  # 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, 7
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 be a Int subclass)

  • args (Array) —

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

Raises:

  • (ArgumentError) 


270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
 
# File 'lib/packetgen/types/fields.rb', line 270

def self.define_bit_fields_on(attr, *args)
  attr_def = @field_defs[attr]
  raise ArgumentError, "unknown #{attr} field" if attr_def.nil?

  type = attr_def.first
  unless type < Types::Int
    raise TypeError, "#{attr} is not a PacketGen::Types::Int"
  end

  total_size = type.new.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 "        def \#{field}?\n          val = (self[:\#{attr}].to_i & \#{field_mask}) >> \#{shift}\n          val != 0\n        end\n        def \#{field}=(v)\n          val = v ? 1 : 0\n          self[:\#{attr}].value = self[:\#{attr}].to_i & \#{clear_mask}\n          self[:\#{attr}].value |= val << \#{shift}\n        end\n        METHODS\n      else\n        class_eval <<-METHODS\n        def \#{field}\n          (self[:\#{attr}].to_i & \#{field_mask}) >> \#{shift}\n        end\n        def \#{field}=(v)\n          self[:\#{attr}].value = self[:\#{attr}].to_i & \#{clear_mask}\n          self[:\#{attr}].value |= (v & \#{2**size - 1}) << \#{shift}\n        end\n        METHODS\n      end\n\n      @bit_fields[attr] = {} if @bit_fields[attr].nil?\n      @bit_fields[attr][field] = size\n    end\n\n    idx -= size\n    field = args.shift\n  end\nend\n"

.define_field(name, type, options = {}) ⇒ void

This method returns an undefined value.

Define a field in class

class BinaryStruct < PacketGen::Types::Fields
  # 8-bit value
  define_field :value1, Types::Int8
  # 16-bit value
  define_field :value2, Types::Int16
  # specific class, may use a specific constructor
  define_field :value3, MyClass, builder: ->(obj, type) { type.new(obj) }
end

bs = BinaryStruct.new
bs[value1]   # => Types::Int8
bs.value1    # => Integer

Parameters:

  • name (Symbol) —

    field name

  • type (Object) —

    class or instance

  • options (Hash) (defaults to: {}) —

    Unrecognized options are passed to object builder if :builder option is not set.

Options Hash (options):

  • :default (Object) —

    default value. May be a proc. This lambda take one argument: the caller object.

  • :builder (Lambda) —

    lambda to construct this field. Parameters to this lambda is the caller object and the field type class.

  • :optional (Lambda) —

    define this field as optional. Given lambda is used to known if this field is present or not. Parameter to this lambda is the being defined Field object.

  • :enum (Hash) —

    mandatory option for an Enum type. Define enumeration: hash’s keys are String, and values are Integer.



148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
 
# File 'lib/packetgen/types/fields.rb', line 148

def self.define_field(name, type, options={})
  define = []
  if type < Types::Enum
    define << "def #{name}; self[:#{name}].to_i; end"
    define << "def #{name}=(val) self[:#{name}].value = val; end"
  elsif type < Types::Int
    define << "def #{name}; self[:#{name}].to_i; end"
    define << "def #{name}=(val) self[:#{name}].read val; end"
  elsif type.instance_methods.include?(:to_human) &&
        type.instance_methods.include?(:from_human)
    define << "def #{name}; self[:#{name}].to_human; end"
    define << "def #{name}=(val) self[:#{name}].from_human val; end"
  else
    define << "def #{name}; self[:#{name}]; end\n"
    define << "def #{name}=(val) self[:#{name}].read val; end"
  end

  define.delete(1) if type.instance_methods.include? "#{name}=".to_sym
  define.delete(0) if type.instance_methods.include? name
  class_eval define.join("\n")
  @field_defs[name] = [type, options.delete(:default),
                       options.delete(:builder),
                       options.delete(:optional),
                       options.delete(:enum),
                       options]
  @ordered_fields << name
end

.define_field_after(other, name, type, options = {}) ⇒ void

This method returns an undefined value.

Define a field, after another one

Parameters:

  • other (Symbol, nil) —

    field name to create a new one after. If nil, new field is appended.

  • name (Symbol) —

    field name to create

  • type (Object) —

    class or instance

  • options (Hash) (defaults to: {}) —

    See define_field.

Raises:

  • (ArgumentError)

See Also:



203
204
205
206
207
208
209
210
211
212
 
# File 'lib/packetgen/types/fields.rb', line 203

def self.define_field_after(other, name, type, options={})
  define_field name, type, options
  return if other.nil?

  @ordered_fields.delete name
  idx = @ordered_fields.index(other)
  raise ArgumentError, "unknown #{other} field" if idx.nil?

  @ordered_fields[idx + 1, 0] = name
end

.define_field_before(other, name, type, options = {}) ⇒ void

This method returns an undefined value.

Define a field, before another one

Parameters:

  • other (Symbol, nil) —

    field name to create a new one before. If nil, new field is appended.

  • name (Symbol) —

    field name to create

  • type (Object) —

    class or instance

  • options (Hash) (defaults to: {}) —

    See define_field.

Raises:

  • (ArgumentError)

See Also:



184
185
186
187
188
189
190
191
192
193
 
# File 'lib/packetgen/types/fields.rb', line 184

def self.define_field_before(other, name, type, options={})
  define_field name, type, options
  return if other.nil?

  @ordered_fields.delete name
  idx = @ordered_fields.index(other)
  raise ArgumentError, "unknown #{other} field" if idx.nil?

  @ordered_fields[idx, 0] = name
end

.delete_field(name) ⇒ void

Deprecated.

Use remove_field instead.

This method returns an undefined value.

Delete a previously defined field

Parameters:

  • name (Symbol)

Since:

  • 2.8.4 deprecated



230
231
232
233
 
# File 'lib/packetgen/types/fields.rb', line 230

def self.delete_field(name)
  Deprecation.deprecated(self, __method__, 'remove_field', klass_method: true)
  remove_field name
end

.inherited(klass) ⇒ void

This method returns an undefined value.

On inheritage, create @field_defs class variable

Parameters:

  • klass (Class) 


107
108
109
110
111
112
113
114
115
116
117
118
119
 
# File 'lib/packetgen/types/fields.rb', line 107

def self.inherited(klass)
  field_defs = {}
  @field_defs.each do |k, v|
    field_defs[k] = v.clone
  end
  ordered = @ordered_fields.clone
  bf = @bit_fields.clone
  klass.class_eval do
    @ordered_fields = ordered
    @field_defs = field_defs
    @bit_fields = bf
  end
end

.remove_bit_fields_on(attr) ⇒ void

This method returns an undefined value.

Remove all bit fields defined on attr

Parameters:

  • attr (Symbol) —

    attribute defining bit fields

Since:

  • 2.8.4



333
334
335
336
337
338
339
340
341
 
# File 'lib/packetgen/types/fields.rb', line 333

def self.remove_bit_fields_on(attr)
  fields = @bit_fields.delete(attr)
  return if fields.nil?

  fields.each do |field, size|
    undef_method "#{field}="
    undef_method(size == 1 ? "#{field}?" : "#{field}")
  end
end

.remove_field(name) ⇒ void

This method returns an undefined value.

Remove a previously defined field

Parameters:

  • name (Symbol)

Since:

  • 2.8.4



218
219
220
221
222
223
 
# File 'lib/packetgen/types/fields.rb', line 218

def self.remove_field(name)
  @ordered_fields.delete name
  @field_defs.delete name
  undef_method name
  undef_method "#{name}="
end

.update_field(field, options) ⇒ void

This method returns an undefined value.

Update a previously defined field

Parameters:

  • field (Symbol) —

    field name to create

  • options (Hash) —

    See define_field.

Raises:

  • (ArgumentError) —

    unknown field

See Also:

Since:

  • 2.8.4



241
242
243
244
245
246
247
248
249
 
# File 'lib/packetgen/types/fields.rb', line 241

def self.update_field(field, options)
  raise ArgumentError, "unkown #{field} field for #{self}" unless @field_defs.key?(field)

  @field_defs[field][1] = options.delete(:default) if options.key?(:default)
  @field_defs[field][2] = options.delete(:builder) if options.key?(:builder)
  @field_defs[field][3] = options.delete(:optional) if options.key?(:optional)
  @field_defs[field][4] = options.delete(:enum) if options.key?(:enum)
  @field_defs[field][5].merge!(options)
end

Instance Method Details

#[](field) ⇒ Object

Get field object

Parameters:

  • field (Symbol)

Returns:

  • (Object) 


393
394
395
 
# File 'lib/packetgen/types/fields.rb', line 393

def [](field)
  @fields[field]
end

#[]=(field, obj) ⇒ Object

Set field object

Parameters:

  • field (Symbol)
  • obj (Object)

Returns:

  • (Object) 


401
402
403
 
# File 'lib/packetgen/types/fields.rb', line 401

def []=(field, obj)
  @fields[field] = obj
end

#bits_on(field) ⇒ Hash?

Get bit fields definition for given field.

Parameters:

  • field (Symbol) —

    defining bit fields

Returns:

  • (Hash, nil) —

    keys: bit fields, values: their size in bits

Since:

  • 2.8.3



552
553
554
 
# File 'lib/packetgen/types/fields.rb', line 552

def bits_on(field)
  self.class.class_eval { @bit_fields }[field]
end

#body=(value) ⇒ void

This method returns an undefined value.

Used to set body as value of body object.

Parameters:

Raises:

  • (BodyError) —

    no body on given object

  • (ArgumentError) —

    cannot cram body in :body field



510
511
512
513
514
515
516
517
518
519
520
521
522
523
 
# File 'lib/packetgen/types/fields.rb', line 510

def body=(value)
  raise BodyError, 'no body field' unless @fields.key? :body

  case body
  when ::String
    self[:body].read value
  when Int, Fields
    self[:body] = value
  when NilClass
    self[:body] = Types::String.new.read('')
  else
    raise ArgumentError, "Can't cram a #{body.class} in a :body field"
  end
end

#fields ⇒ Array<Symbol>

Get all field names

Returns:



407
408
409
 
# File 'lib/packetgen/types/fields.rb', line 407

def fields
  @ordered_fields ||= self.class.class_eval { @ordered_fields }
end

#force_binary(str) ⇒ String

Force str to binary encoding

Parameters:

Returns:



528
529
530
 
# File 'lib/packetgen/types/fields.rb', line 528

def force_binary(str)
  PacketGen.force_binary(str)
end

#inspect ⇒ String

Common inspect method for headers

Returns:



475
476
477
478
479
480
481
482
483
484
 
# File 'lib/packetgen/types/fields.rb', line 475

def inspect
  str = Inspect.dashed_line(self.class, 1)
  fields.each do |attr|
    next if attr == :body
    next unless present?(attr)

    str << Inspect.inspect_attribute(attr, self[attr], 1)
  end
  str
end

#is_optional?(field) ⇒ Boolean

Deprecated.

Use #optional? instead.

Returns:

  • (Boolean) 


423
424
425
426
 
# File 'lib/packetgen/types/fields.rb', line 423

def is_optional?(field)
  Deprecation.deprecated(self.class, __method__, 'optional?', klass_method: true)
  optional? field
end

#is_present?(field) ⇒ Boolean

Say if an optional field is present

Returns:

  • (Boolean) 


438
439
440
441
 
# File 'lib/packetgen/types/fields.rb', line 438

def is_present?(field)
  Deprecation.deprecated(self.class, __method__, 'present?', klass_method: true)
  present? field
end

#offset_of(field) ⇒ Integer

Get offset of given field in PacketGen::Types::Fields structure.

Parameters:

  • field (Symbol)

Returns:

  • (Integer)

Raises:

  • (ArgumentError) —

    unknown field



536
537
538
539
540
541
542
543
544
545
546
 
# File 'lib/packetgen/types/fields.rb', line 536

def offset_of(field)
  raise ArgumentError, "#{field} is an unknown field of #{self.class}" unless @fields.include?(field)

  offset = 0
  fields.each do |f|
    break offset if f == field
    next unless present?(f)

    offset += self[f].sz
  end
end

#optional?(field) ⇒ Boolean

Say if this field is optional

Returns:

  • (Boolean) 


418
419
420
 
# File 'lib/packetgen/types/fields.rb', line 418

def optional?(field)
  @optional_fields.key? field
end

#optional_fields ⇒ Object

Get all optional field name



412
413
414
 
# File 'lib/packetgen/types/fields.rb', line 412

def optional_fields
  @optional_fields.keys
end

#present?(field) ⇒ Boolean

Say if an optional field is present

Returns:

  • (Boolean) 


430
431
432
433
434
 
# File 'lib/packetgen/types/fields.rb', line 430

def present?(field)
  return true unless optional?(field)

  @optional_fields[field].call(self)
end

#read(str) ⇒ Fields

Populate object from a binary string

Parameters:

Returns:



446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
 
# File 'lib/packetgen/types/fields.rb', line 446

def read(str)
  return self if str.nil?

  force_binary str
  start = 0
  fields.each do |field|
    next unless present?(field)

    obj = nil
    if self[field].respond_to? :width
      width = self[field].width
      obj = self[field].read str[start, width]
      start += width
    elsif self[field].respond_to? :sz
      obj = self[field].read str[start..-1]
      size = self[field].sz
      start += size
    else
      obj = self[field].read str[start..-1]
      start = str.size
    end
    self[field] = obj unless obj == self[field]
  end

  self
end

#sz ⇒ nteger

Size of object as binary string

Returns:

  • (nteger) 


495
496
497
 
# File 'lib/packetgen/types/fields.rb', line 495

def sz
  to_s.size
end

#to_h ⇒ Hash

Return object as a hash

Returns:

  • (Hash) —

    keys: attributes, values: attribute values



501
502
503
 
# File 'lib/packetgen/types/fields.rb', line 501

def to_h
  Hash[fields.map { |f| [f, @fields[f].to_human] }]
end

#to_s ⇒ String

Return object as a binary string

Returns:



488
489
490
491
 
# File 'lib/packetgen/types/fields.rb', line 488

def to_s
  fields.select { |f| present?(f) }
        .map! { |f| force_binary @fields[f].to_s }.join
end