Class: Resolv::DNS::Message::MessageDecoder

Inherits:
Object
  • Object
show all
Defined in:
lib/resolv.rb

Overview

:nodoc:

Instance Method Summary collapse

Constructor Details

#initialize(data) {|_self| ... } ⇒ MessageDecoder

Returns a new instance of MessageDecoder.

Yields:

  • (_self)

Yield Parameters:



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# File 'lib/resolv.rb', line 1758

def initialize(data)
  @data = data
  @index = 0
  @limit = data.bytesize
  yield self
end

Instance Method Details

#get_bytes(len = @limit - @index) ⇒ Object

Raises:



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# File 'lib/resolv.rb', line 1783

def get_bytes(len = @limit - @index)
  raise DecodeError.new("limit exceeded") if @limit < @index + len
  d = @data.byteslice(@index, len)
  @index += len
  return d
end

#get_label ⇒ Object 



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# File 'lib/resolv.rb', line 1875

def get_label
  return Label::Str.new(self.get_string)
rescue ArgumentError => e
  # A length octet of 64..191 is reserved rather than a label length,
  # but this decoder used to read it as one. [RFC 1035 4.1.4] Report it
  # the way the rest of a malformed message is reported.
  raise DecodeError.new(e.message)
end

#get_labels ⇒ Object 



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# File 'lib/resolv.rb', line 1840

def get_labels
  prev_index = @index
  save_index = nil
  d = []
  # size counts the encoded form, so it starts at 1 for the root
  # label's terminating zero octet. [RFC 1035 3.1]
  size = 1
  while true
    raise DecodeError.new("limit exceeded") if @limit <= @index
    case @data.getbyte(@index)
    when 0
      @index += 1
      if save_index
        @index = save_index
      end
      return d
    when 192..255
      idx = self.get_unpack('n')[0] & 0x3fff
      if prev_index <= idx
        raise DecodeError.new("non-backward name pointer")
      end
      prev_index = idx
      if !save_index
        save_index = @index
      end
      @index = idx
    else
      l = self.get_label
      d << l
      size += 1 + l.string.bytesize
      raise DecodeError.new("name label data exceed 255 octets") if size > 255
    end
  end
end

#get_length16 ⇒ Object 



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# File 'lib/resolv.rb', line 1769

def get_length16
  len, = self.get_unpack('n')
  save_limit = @limit
  @limit = @index + len
  d = yield(len)
  if @index < @limit
    raise DecodeError.new("junk exists")
  elsif @limit < @index
    raise DecodeError.new("limit exceeded")
  end
  @limit = save_limit
  return d
end

#get_list ⇒ Object 



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# File 'lib/resolv.rb', line 1828

def get_list
  [].tap do |values|
    while @index < @limit
      values << yield
    end
  end
end

#get_name ⇒ Object 



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# File 'lib/resolv.rb', line 1836

def get_name
  return Name.new(self.get_labels)
end

#get_question ⇒ Object 



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# File 'lib/resolv.rb', line 1884

def get_question
  name = self.get_name
  type, klass = self.get_unpack("nn")
  return name, Resource.get_class(type, klass)
end

#get_rr ⇒ Object 



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# File 'lib/resolv.rb', line 1890

def get_rr
  name = self.get_name
  type, klass, ttl = self.get_unpack('nnN')
  typeclass = Resource.get_class(type, klass)
  res = self.get_length16 do
    begin
      typeclass.decode_rdata self
    rescue => e
      raise DecodeError, e.message, e.backtrace
    end
  end
  res.instance_variable_set :@ttl, ttl
  return name, ttl, res
end

#get_string ⇒ Object

Raises:



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# File 'lib/resolv.rb', line 1811

def get_string
  raise DecodeError.new("limit exceeded") if @limit <= @index
  len = @data.getbyte(@index)
  raise DecodeError.new("limit exceeded") if @limit < @index + 1 + len
  d = @data.byteslice(@index + 1, len)
  @index += 1 + len
  return d
end

#get_string_list ⇒ Object 



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# File 'lib/resolv.rb', line 1820

def get_string_list
  strings = []
  while @index < @limit
    strings << self.get_string
  end
  strings
end

#get_unpack(template) ⇒ Object

Raises:



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# File 'lib/resolv.rb', line 1790

def get_unpack(template)
  len = 0
  template.each_byte {|byte|
    byte = "%c" % byte
    case byte
    when ?c, ?C
      len += 1
    when ?n
      len += 2
    when ?N
      len += 4
    else
      raise StandardError.new("unsupported template: '#{byte.chr}' in '#{template}'")
    end
  }
  raise DecodeError.new("limit exceeded") if @limit < @index + len
  arr = @data.unpack("@#{@index}#{template}")
  @index += len
  return arr
end

#inspect ⇒ Object 



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# File 'lib/resolv.rb', line 1765

def inspect
  "\#<#{self.class}: #{@data.byteslice(0, @index).inspect} #{@data.byteslice(@index..-1).inspect}>"
end