Fix domain_is_in? for deeply nested subdomain

lib/valid_email2/address.rb

@@ -29,11 +29,12 @@ def self.permitted_multibyte_characters_regex=(val)
       @permitted_multibyte_characters_regex = val
     end
 
-    def initialize(address, dns_timeout = 5, dns_nameserver = nil)
+    def initialize(address, dns_timeout = 5, dns_nameserver = nil, domain_hierarchy_max_depth: 3)
       @parse_error = false
       @raw_address = address
       @dns_timeout = dns_timeout
       @dns_nameserver = dns_nameserver
+      @domain_hierarchy_max_depth = domain_hierarchy_max_depth
 
       begin
         @address = Mail::Address.new(address)
@@ -119,10 +120,16 @@ def domain_is_in?(domain_list)
       address_domain = address.domain.downcase
       return true if domain_list.include?(address_domain)
 
-      i = address_domain.index('.')
-      return false unless i
+      tokens = address_domain.split('.')
+      return false if tokens.length < 3
 
-      domain_list.include?(address_domain[(i + 1)..-1])
+      max_depth = [@domain_hierarchy_max_depth, tokens.length].min
+      (2..max_depth).each do |depth|
+        partial_domain = tokens.last(depth).join('.')
+        return true if domain_list.include?(partial_domain)
+      end
+
+      return false
     end
 
     def mx_server_is_in?(domain_list)

spec/address_spec.rb

@@ -56,6 +56,53 @@
     end
   end
 
+  describe "#disposable_domain?" do
+    let(:domain_hierarchy_max_depth) { 10 }
+
+    context "when the disposable domain does not have subdomains" do
+      let(:disposable_domain) { ValidEmail2.disposable_emails.find { |domain| domain.count(".") == 1 } }
+
+      it "is true if the domain is in the disposable_emails list" do
+        address = described_class.new("foo@#{disposable_domain}", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq true
+      end
+
+      it "is true if the domain is a subdomain of a disposable domain" do
+        address = described_class.new("foo@sub.#{disposable_domain}", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq true
+      end
+
+      it "is true if the domain is a deeply nested subdomain of a disposable domain" do
+        address = described_class.new("[email protected].#{disposable_domain}", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq true
+      end
+
+      it "is false if the domain is not in the disposable_emails list" do
+        address = described_class.new("[email protected]", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq false
+      end
+    end
+
+    context "when the disposable domain has subdomains" do
+      let(:disposable_domain) { ValidEmail2.disposable_emails.find { |domain| domain.count(".") > 1 } }
+
+      it "is true if the domain is in the disposable_emails list" do
+        address = described_class.new("foo@#{disposable_domain}", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq true
+      end
+
+      it "is true if the domain is a subdomain of a disposable domain" do
+        address = described_class.new("foo@sub.#{disposable_domain}", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq true
+      end
+
+      it "is true if the domain is a deeply nested subdomain of a disposable domain" do
+        address = described_class.new("[email protected].#{disposable_domain}", nil, nil, domain_hierarchy_max_depth:)
+        expect(address.disposable_domain?).to eq true
+      end
+    end
+  end
+
   describe "caching" do
     let(:email_address) { "[email protected]" }
     let(:email_instance) { described_class.new(email_address) }
@@ -181,7 +228,7 @@
             email_instance.valid_strict_mx?
           end
 
-          it "calls the the MX servers lookup" do    
+          it "calls the the MX servers lookup" do
             email_instance.valid_strict_mx?
 
             expect(Resolv::DNS).to have_received(:open).once
@@ -308,8 +355,8 @@
             stub_const("ValidEmail2::DnsRecordsCache::MAX_CACHE_SIZE", 0)
           end
 
-          it "prunes the cache" do 
-            expect(dns_records_cache_instance).to receive(:prune_cache).once 
+          it "prunes the cache" do
+            expect(dns_records_cache_instance).to receive(:prune_cache).once
 
             email_instance.valid_mx?
           end
@@ -331,7 +378,7 @@
             end
           end
         end
-      end    
+      end
     end
   end
 end