[ruby/resolv] Implement dohpath SvcParam

(https://github.com/ruby/resolv/pull/33)

* Implement dohpath SvcParam [RFC 9461]

This patch implements "dohpath" SvcParam proposed in
[draft-ietf-add-svcb-dns-08]. This parameter specifies a URI template
for the :path used in DNS-over-HTTPS requests.

"dohpath" is employed by [DDR], also a to-be-published Proposed Standard
that specifies how to upgrade DNS transport to a more secure one, i.d.,
DNS-over-TLS or DNS-over-HTTPS. DDR is deployed in the public DNS
resolvers including Cloudflare DNS, Google Public DNS, and Quad9.

[RFC 9461]: https://datatracker.ietf.org/doc/rfc9461/
[DDR]: https://datatracker.ietf.org/doc/draft-ietf-add-ddr/

da9c023539

Co-authored-by: Sorah Fukumori <her@sorah.jp>

lib/resolv.rb

@@ -2027,6 +2027,35 @@ class Resolv
         end
       end
 
+      ##
+      # "dohpath" SvcParam -- DNS over HTTPS path template [RFC9461]
+
+      class DoHPath < SvcParam
+        KeyName = :dohpath
+        KeyNumber = 7
+        ClassHash[KeyName] = ClassHash[KeyNumber] = self # :nodoc:
+
+        ##
+        # URI template for DoH queries.
+
+        attr_reader :template
+
+        ##
+        # Initialize "dohpath" ScvParam.
+
+        def initialize(template)
+          @template = template.encode('utf-8')
+        end
+
+        def encode(msg) # :nodoc:
+          msg.put_bytes(@template)
+        end
+
+        def self.decode(msg) # :nodoc:
+          template = msg.get_bytes.force_encoding('utf-8')
+          return self.new(template)
+        end
+      end
     end
 
     ##