Implement CAA resource record

This patch implements handling of CAA resource records defined by [RFC8659].

- There are no known deployment of CAA records outside of IN (Internet),
  but the RFC does not state that CAA records are class-specific.
  Thus `CAA` class is defined as a class-independent RRType.
- `CAA` class stores `flags` field (a 1-octet bitset) as an Integer.
  In this way it's easier to ensure the encoded RR is in the valid wire format.

[RFC8659]: https://datatracker.ietf.org/doc/html/rfc8659

Co-authored-by: aeris <aeris@imirhil.fr>

Author: hanazuki

lib/resolv.rb

@@ -2537,8 +2537,70 @@ class ANY < Query
         TypeValue = 255 # :nodoc:
       end
 
+      ##
+      # CAA resource record defined in RFC 8659
+      #
+      # These records identify certificate authority allowed to issue
+      # certificates for the given domain.
+
+      class CAA < Resource
+        TypeValue = 257
+
+        ##
+        # Creates a new CAA for +flags+, +tag+ and +value+.
+
+        def initialize(flags, tag, value)
+          unless (0..255) === flags
+            raise ArgumentError.new('flags must be an Integer between 0 and 255')
+          end
+          unless (1..15) === tag.bytesize
+            raise ArgumentError.new('length of tag must be between 1 and 15')
+          end
+
+          @flags = flags
+          @tag = tag
+          @value = value
+        end
+
+        ##
+        # Flags for this proprty:
+        # - Bit 0 : 0 = not critical, 1 = critical
+
+        attr_reader :flags
+
+        ##
+        # Property tag ("issue", "issuewild", "iodef"...).
+
+        attr_reader :tag
+
+        ##
+        # Property value.
+
+        attr_reader :value
+
+        ##
+        # Whether the critical flag is set on this property.
+
+        def critical?
+          flags & 0x80 != 0
+        end
+
+        def encode_rdata(msg) # :nodoc:
+          msg.put_pack('C', @flags)
+          msg.put_string(@tag)
+          msg.put_bytes(@value)
+        end
+
+        def self.decode_rdata(msg) # :nodoc:
+          flags, = msg.get_unpack('C')
+          tag = msg.get_string
+          value = msg.get_bytes
+          self.new flags, tag, value
+        end
+      end
+
       ClassInsensitiveTypes = [ # :nodoc:
-        NS, CNAME, SOA, PTR, HINFO, MINFO, MX, TXT, LOC, ANY
+        NS, CNAME, SOA, PTR, HINFO, MINFO, MX, TXT, LOC, ANY, CAA
       ]
 
       ##

test/resolv/test_resource.rb

@@ -32,3 +32,71 @@ def test_srv_no_compress
     assert_equal "\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x07example\x03com\x00\x00\x21\x00\x01\x00\x00\x00\x00\x00\x17\x00\x00\x00\x00\x00\x00\x03www\x07example\x03com\x00", m.encode, issue29
   end
 end
+
+class TestResolvResourceCAA < Test::Unit::TestCase
+  def test_caa_roundtrip
+    raw_msg = "\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x03new\x07example\x03com\x00\x01\x01\x00\x01\x00\x00\x00\x00\x00\x16\x00\x05issueca1.example.net\xC0\x0C\x01\x01\x00\x01\x00\x00\x00\x00\x00\x0C\x80\x03tbsUnknown".b
+
+    m = Resolv::DNS::Message.new(0)
+    m.add_answer('new.example.com', 0, Resolv::DNS::Resource::IN::CAA.new(0, 'issue', 'ca1.example.net'))
+    m.add_answer('new.example.com', 0, Resolv::DNS::Resource::IN::CAA.new(128, 'tbs', 'Unknown'))
+    assert_equal raw_msg, m.encode
+
+    m = Resolv::DNS::Message.decode(raw_msg)
+    assert_equal 2, m.answer.size
+    _, _, caa0 = m.answer[0]
+    assert_equal 0, caa0.flags
+    assert_equal false, caa0.critical?
+    assert_equal 'issue', caa0.tag
+    assert_equal 'ca1.example.net', caa0.value
+    _, _, caa1 = m.answer[1]
+    assert_equal true, caa1.critical?
+    assert_equal 128, caa1.flags
+    assert_equal 'tbs', caa1.tag
+    assert_equal 'Unknown', caa1.value
+  end
+
+  def test_caa_stackoverflow
+    # gathered in the wild
+    raw_msg = "\x8D\x32\x81\x80\x00\x01\x00\x0B\x00\x00\x00\x00\x0Dstackoverflow\x03com\x00\x01\x01\x00\x01\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x13\x00\x05issuecomodoca.com\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x2D\x00\x05issuedigicert.com; cansignhttpexchanges=yes\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x16\x00\x05issueletsencrypt.org\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x29\x00\x05issuepki.goog; cansignhttpexchanges=yes\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x12\x00\x05issuesectigo.com\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x17\x00\x09issuewildcomodoca.com\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x31\x00\x09issuewilddigicert.com; cansignhttpexchanges=yes\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x1A\x00\x09issuewildletsencrypt.org\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x2D\x00\x09issuewildpki.goog; cansignhttpexchanges=yes\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x16\x00\x09issuewildsectigo.com\xC0\x0C\x01\x01\x00\x01\x00\x00\x01\x2C\x00\x2D\x80\x05iodefmailto:sysadmin-team@stackoverflow.com".b
+
+    m = Resolv::DNS::Message.decode(raw_msg)
+    assert_equal 11, m.answer.size
+    _, _, caa3 = m.answer[3]
+    assert_equal 0, caa3.flags
+    assert_equal 'issue', caa3.tag
+    assert_equal 'pki.goog; cansignhttpexchanges=yes', caa3.value
+    _, _, caa8 = m.answer[8]
+    assert_equal 0, caa8.flags
+    assert_equal 'issuewild', caa8.tag
+    assert_equal 'pki.goog; cansignhttpexchanges=yes', caa8.value
+    _, _, caa10 = m.answer[10]
+    assert_equal 128, caa10.flags
+    assert_equal 'iodef', caa10.tag
+    assert_equal 'mailto:sysadmin-team@stackoverflow.com', caa10.value
+  end
+
+  def test_caa_flags
+    assert_equal 255,
+      Resolv::DNS::Resource::IN::CAA.new(255, 'issue', 'ca1.example.net').flags
+    assert_raise(ArgumentError) do
+      Resolv::DNS::Resource::IN::CAA.new(256, 'issue', 'ca1.example.net')
+    end
+
+    assert_raise(ArgumentError) do
+      Resolv::DNS::Resource::IN::CAA.new(-1, 'issue', 'ca1.example.net')
+    end
+  end
+
+  def test_caa_tag
+    assert_raise(ArgumentError, 'Empty tag should be rejected') do
+      Resolv::DNS::Resource::IN::CAA.new(0, '', 'ca1.example.net')
+    end
+
+    assert_equal '123456789012345',
+      Resolv::DNS::Resource::IN::CAA.new(0, '123456789012345', 'ca1.example.net').tag
+    assert_raise(ArgumentError, 'Tag longer than 15 bytes should be rejected') do
+      Resolv::DNS::Resource::IN::CAA.new(0, '1234567890123456', 'ca1.example.net')
+    end
+  end
+end