Add DomainResource class to wrap MX lookup/normalize (#32864)

app/controllers/admin/email_domain_blocks_controller.rb

@@ -58,10 +58,7 @@ module Admin
     private
 
     def set_resolved_records
-      Resolv::DNS.open do |dns|
-        dns.timeouts = 5
-        @resolved_records = dns.getresources(@email_domain_block.domain, Resolv::DNS::Resource::IN::MX).to_a
-      end
+      @resolved_records = DomainResource.new(@email_domain_block.domain).mx
     end
 
     def resource_params

app/lib/domain_resource.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class DomainResource
+  attr_reader :domain
+
+  RESOLVE_TIMEOUT = 5
+
+  def initialize(domain)
+    @domain = domain
+  end
+
+  def mx
+    Resolv::DNS.open do |dns|
+      dns.timeouts = RESOLVE_TIMEOUT
+      dns
+        .getresources(domain, Resolv::DNS::Resource::IN::MX)
+        .to_a
+        .map { |mx| mx.exchange.to_s }
+        .compact_blank
+    end
+  end
+end

app/models/user.rb

@@ -457,13 +457,7 @@ class User < ApplicationRecord
 
     # Doing this conditionally is not very satisfying, but this is consistent
     # with the MX records validations we do and keeps the specs tractable.
-    unless self.class.skip_mx_check?
-      Resolv::DNS.open do |dns|
-        dns.timeouts = 5
-
-        records = dns.getresources(domain, Resolv::DNS::Resource::IN::MX).to_a.map { |e| e.exchange.to_s }.compact_blank
-      end
-    end
+    records = DomainResource.new(domain).mx unless self.class.skip_mx_check?
 
     EmailDomainBlock.requires_approval?(records + [domain], attempt_ip: sign_up_ip)
   end

app/views/admin/email_domain_blocks/new.html.haml

@@ -30,12 +30,12 @@
             %label.batch-table__row__select.batch-table__row__select--aligned.batch-checkbox
               = f.input_field :other_domains,
                               as: :boolean,
-                              checked_value: record.exchange.to_s,
+                              checked_value: record,
                               include_hidden: false,
                               multiple: true
             .batch-table__row__content.pending-account
               .pending-account__header
-                %samp= record.exchange.to_s
+                %samp= record
                 %br
                 = t('admin.email_domain_blocks.dns.types.mx')