Allow private zones with an SOA to satisfy apex_domain?

lib/github-pages-health-check/domain.rb

@@ -164,8 +164,11 @@ def valid_domain?
       # Is this domain an apex domain, meaning a CNAME would be innapropriate
       def apex_domain?
         return @apex_domain if defined?(@apex_domain)
+
         return unless valid_domain?
 
+        return true if dns_zone_soa?
+
         # PublicSuffix.domain pulls out the apex-level domain name.
         # E.g. PublicSuffix.domain("techblog.netflix.com") # => "netflix.com"
         # It's aware of multi-step top-level domain names:
@@ -177,6 +180,14 @@ def apex_domain?
                             :ignore_private => true) == unicode_host
       end
 
+      def dns_zone_soa?
+        return @soa_records if defined?(@soa_records)
+        return false unless dns?
+
+        soa_records = dns.select { |answer| answer.type == Dnsruby::Types::SOA }
+        soa_records.any?
+      end
+
       # Should the domain use an A record?
       def should_be_a_record?
         !pages_io_domain? && (apex_domain? || mx_records_present?)
@@ -278,7 +289,8 @@ def proxied?
         Dnsruby::Types::A,
         Dnsruby::Types::AAAA,
         Dnsruby::Types::CNAME,
-        Dnsruby::Types::MX
+        Dnsruby::Types::MX,
+        Dnsruby::Types::SOA
       ].freeze
 
       # Returns an array of DNS answers

spec/github_pages_health_check/domain_spec.rb

@@ -23,6 +23,9 @@
   let(:caa_packet) do
     Dnsruby::RR.create("#{domain}. 1000 IN CAA 0 issue #{caa_domain.inspect}")
   end
+  let(:soa_packet) do
+    Dnsruby::RR.create("#{domain}. 1000 IN SOA ns.example.com. #{domain.inspect}")
+  end
 
   context "constructor" do
     it "can handle bare domains" do
@@ -257,6 +260,17 @@
         end
       end
 
+      ["private.dns.zone"].each do |soa_domain|
+        context "given #{soa_domain}" do
+          before(:each) { allow(subject).to receive(:dns) { [soa_packet] } }
+          let(:domain) { soa_domain }
+
+          it "allows child zones with an SOA to be an Apex" do
+            expect(subject.should_be_a_record?).to be_truthy
+          end
+        end
+      end
+
       context "a domain with an MX record" do
         let(:domain) { "blog.parkermoore.de" }
         before(:each) do