[ruby/resolv] 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

https://github.com/ruby/resolv/commit/cfc4de75e3

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

1 files changed, 63 insertions, 1 deletions

diff --git a/lib/resolv.rb b/lib/resolv.rb
index 1363d49dc4..b585b10ca9 100644
--- a/lib/resolv.rb
+++ b/lib/resolv.rb
@@ -2537,8 +2537,70 @@ class Resolv
         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
       ]
 
       ##