Merge 7eaa5f8 into b46f622

lib/public_suffix.rb

@@ -50,13 +50,12 @@ module PublicSuffix
   #   PublicSuffix.parse("http://www.google.com")
   #   # => PublicSuffix::DomainInvalid
   #
-  #
   # @param  [String, #to_s] name The domain name or fully qualified domain name to parse.
   # @param  [PublicSuffix::List] list The rule list to search, defaults to the default {PublicSuffix::List}
   # @param  [Boolean] ignore_private
   # @return [PublicSuffix::Domain]
   #
-  # @raise [PublicSuffix::Error]
+  # @raise [PublicSuffix::DomainInvalid]
   #   If domain is not a valid domain.
   # @raise [PublicSuffix::DomainNotAllowed]
   #   If a rule for +domain+ is found, but the rule doesn't allow +domain+.
@@ -77,7 +76,34 @@ def self.parse(name, list: List.default, default_rule: nil, ignore_private: fals
     decompose(what, rule)
   end
 
-  # Checks whether +domain+ is assigned and allowed, without actually parsing it.
+
+  # Find the registered part of the domain
+  # "The registered or registrable domain is the public suffix plus one additional label."
+  # https://publicsuffix.org/list/
+  #
+  # @param  [String, #to_s] domain
+  #   The domain name or fully qualified domain name to parse.
+  # @param  [PublicSuffix::List] list
+  #   The rule list to search, defaults to the default {PublicSuffix::List}
+  #
+  # @return [String]
+  #
+  # @raise [PublicSuffix::DomainInvalid]
+  #   If domain does not end with a public suffix according to the rule list
+  #
+  def self.registered_domain(domain, list = List.default)
+    domain = domain.to_s.downcase
+    rule   = list.find(domain)
+
+    if rule.nil? || rule.kind_of?(PublicSuffix::Rule::Wildcard)
+      raise DomainInvalid, "'#{domain}' is not a valid domain"
+    end
+
+    rule.registered_domain(domain)
+  end
+
+
+  # Checks whether +domain+ is assigned and allowed, without actually parsing it.
   #
   # This method doesn't care whether domain is a domain or subdomain.
   # The validation is performed using the default {PublicSuffix::List}.

lib/public_suffix/rule.rb

@@ -170,6 +170,27 @@ def decompose(*)
         raise NotImplementedError
       end
 
+      #
+      # @param [String, #to_s] domain
+      #   The domain string from which to extract the registered part
+      # "- The public suffix is the set of labels from the domain which match the labels of 
+      #    the prevailing rule, using the matching algorithm above.
+      #  - The registered or registrable domain is the public suffix plus one additional label."
+      #  https://publicsuffix.org/list/
+      #
+      # @return [String] registered part of domain
+      #
+      def registered_domain(domain)
+        reg_dom_len = parts.length
+        whole_parts = domain.split('.')
+        if (reg_dom_len < whole_parts.length)
+          registered_parts = whole_parts.pop(reg_dom_len + 1)
+        else
+          registered_parts = whole_parts
+        end
+        registered_parts.join('.')
+      end
+
     end
 
     # Normal represents a standard rule (e.g. com).

test/unit/public_suffix_test.rb

@@ -183,4 +183,18 @@ def test_normalize_leading_dot
     end
   end
 
+  def test_registered_domain_invalid
+    assert_throws(:dom_invalid) do
+      begin
+        PublicSuffix.registered_domain('dom.this.fake')
+      rescue PublicSuffix::DomainInvalid
+        throw :dom_invalid
+      end
+    end
+  end
+
+  def test_registered_domain
+    reg_part = PublicSuffix.registered_domain('www.example.com')
+    assert_match 'example.com', reg_part
+  end
 end