Module: Net::DNS::Names

Included in:
Packet, Question, RR
Defined in:
lib/net/dns/names.rb

Defined Under Namespace

Classes: Error, ExpandError

Constant Summary collapse

INT16SZ = 
2

Instance Method Summary collapse

Instance Method Details

#dn_comp(name, offset, compnames) ⇒ Object 



86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
 
# File 'lib/net/dns/names.rb', line 86

def dn_comp(name,offset,compnames)
  names = {}
  ptr = 0
  str = ""
  arr = names_array(name)
  arr.each do |entry|
    if compnames.has_key?(entry)
      ptr = 0xC000 | compnames[entry]
      str += [ptr].pack("n")
      offset += INT16SZ
      break
    else
      len = entry.unpack("C")[0]
      elem = entry[1..len]
      str += [len,elem].pack("Ca*")
      names.update({"#{entry}" => offset})
      offset += len
    end
  end
  return str,offset,names
end

#dn_expand(packet, offset) ⇒ Object

Expand a compressed name in a DNS Packet object. Please see RFC1035 for an explanation of how the compression in DNS packets works, how may it be useful and how should be handled.

This method accept two parameters: a raw packet data and an offset, which indicates the point in the packet in which the parsing has arrived.



26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
 
# File 'lib/net/dns/names.rb', line 26

def dn_expand(packet,offset)
  name = ""
  packetlen = packet.size
  while true
    raise ExpandError, "Offset is greater than packet length!" if packetlen < (offset+1)
    len = packet.unpack("@#{offset} C")[0]

    if len == 0
      offset += 1
      break
    elsif (len & 0xC0) == 0xC0
      raise ExpandError, "Packet ended before offset expand" if packetlen < (offset+INT16SZ)
      ptr = packet.unpack("@#{offset} n")[0]
      ptr &= 0x3FFF
      name2 = dn_expand(packet,ptr)[0]
      raise ExpandError, "Packet is malformed!" if name2 == nil
      name += name2
      offset += INT16SZ
      break
    else
      offset += 1
      raise ExpandError, "No expansion found" if packetlen < (offset+len)
      elem = packet[offset..offset+len-1]
      name += "#{elem}."
      offset += len
    end
  end
  [name, offset] # name.chomp(".") if trailing dot has to be omitted
end

#names_array(name) ⇒ Object 



72
73
74
75
76
77
78
79
80
81
82
83
84
 
# File 'lib/net/dns/names.rb', line 72

def names_array(name)
  arr = name.split(".")
  ar = []
  string = ""
  arr.size.times do |i|
    x = i+1
    elem = arr[-x]
    len = elem.size
    string = ((string.reverse)+([len,elem].pack("Ca*")).reverse).reverse
    ar.unshift(string)
  end
  return ar
end

#pack_name(name) ⇒ Object 



56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
 
# File 'lib/net/dns/names.rb', line 56

def pack_name(name)
  if name.size > 255
    raise ArgumentError, "Name may not exceed 255 chars"
  end
  arr = name.split(".")
  str = ""
  arr.each do |elem|
    if elem.size > 63
      raise ArgumentError, "Label may not exceed 63 chars"
    end
    str += [elem.size,elem].pack("Ca*")
  end
  str += [0].pack("C")
  str
end

#valid?(name) ⇒ Boolean

Returns:

  • (Boolean) 


108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
 
# File 'lib/net/dns/names.rb', line 108

def valid?(name)
  return false if name.length < 1 or name.length > 255

  return true if name == '.' # the root domain is the only valid domain that begins with a dot

  parts = name.split('.', -1)
  parts.delete_at(parts.length-1) if parts.last.empty? # the domain may end with a dot

  parts.each do |part|
    if not part =~ /^[a-z0-9]([-a-z0-9]*[a-z0-9])?$/i or part.length < 1 or part.length > 63
      return false
    end
  end

  return true
end