Made #decode_rdata client to catch errors

* lib/resolv.rb (Resolv::DNS::Message::MessageDecoder#get_rr):
  re-raise an exception from decode_rdata as DecodeError, so it
  can report them to the top in more informative way.  It was not
  reflecting on errors of data and thus breaking.  Client code
  expects `DecodeError` and knows how to handle broken messages.
  [Fix GH-1511]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57325 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/resolv.rb

@@ -1635,7 +1635,13 @@ class Resolv
           name = self.get_name
           type, klass, ttl = self.get_unpack('nnN')
           typeclass = Resource.get_class(type, klass)
-          res = self.get_length16 { typeclass.decode_rdata self }
+          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

test/resolv/test_dns.rb

@@ -205,6 +205,21 @@ class TestResolvDNS < Test::Unit::TestCase
     assert_instance_of Resolv::IPv6, Resolv::IPv6.create('::1:127.0.0.1')
   end
 
+  def test_ipv6_should_be_16
+    ref = '[rubygems:1626]'
+
+    broken_message =
+      "\0\0\0\0\0\0\0\0\0\0\0\1" \
+      "\x03ns2\bdnsimple\x03com\x00" \
+      "\x00\x1C\x00\x01\x00\x02OD" \
+      "\x00\x10$\x00\xCB\x00 I\x00\x01\x00\x00\x00\x00"
+
+    e = assert_raise_with_message(Resolv::DNS::DecodeError, /IPv6 address must be 16 bytes/, ref) do
+      Resolv::DNS::Message.decode broken_message
+    end
+    assert_kind_of(ArgumentError, e.cause)
+  end
+
   def test_too_big_label_address
     n = 2000
     m = Resolv::DNS::Message::MessageEncoder.new {|msg|