Improve e-mail MX validator and add tests (#9489)

spec/validators/email_mx_validator_spec.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe EmailMxValidator do
+  describe '#validate' do
+    let(:user) { double(email: 'foo@example.com', errors: double(add: nil)) }
+
+    it 'adds an error if there are no DNS records for the e-mail domain' do
+      resolver = double
+
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::MX).and_return([])
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::A).and_return([])
+      allow(resolver).to receive(:timeouts=).and_return(nil)
+      allow(Resolv::DNS).to receive(:open).and_yield(resolver)
+
+      subject.validate(user)
+      expect(user.errors).to have_received(:add)
+    end
+
+    it 'adds an error if a MX record exists but does not lead to an IP' do
+      resolver = double
+
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::MX).and_return([double(exchange: 'mail.example.com')])
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::A).and_return([])
+      allow(resolver).to receive(:getresources).with('mail.example.com', Resolv::DNS::Resource::IN::A).and_return([])
+      allow(resolver).to receive(:timeouts=).and_return(nil)
+      allow(Resolv::DNS).to receive(:open).and_yield(resolver)
+
+      subject.validate(user)
+      expect(user.errors).to have_received(:add)
+    end
+
+    it 'adds an error if the A record is blacklisted' do
+      EmailDomainBlock.create!(domain: '1.2.3.4')
+      resolver = double
+
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::MX).and_return([])
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::A).and_return([double(address: '1.2.3.4')])
+      allow(resolver).to receive(:timeouts=).and_return(nil)
+      allow(Resolv::DNS).to receive(:open).and_yield(resolver)
+
+      subject.validate(user)
+      expect(user.errors).to have_received(:add)
+    end
+
+    it 'adds an error if the MX record is blacklisted' do
+      EmailDomainBlock.create!(domain: '2.3.4.5')
+      resolver = double
+
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::MX).and_return([double(exchange: 'mail.example.com')])
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::A).and_return([])
+      allow(resolver).to receive(:getresources).with('mail.example.com', Resolv::DNS::Resource::IN::A).and_return([double(address: '2.3.4.5')])
+      allow(resolver).to receive(:timeouts=).and_return(nil)
+      allow(Resolv::DNS).to receive(:open).and_yield(resolver)
+
+      subject.validate(user)
+      expect(user.errors).to have_received(:add)
+    end
+
+    it 'adds an error if the MX hostname is blacklisted' do
+      EmailDomainBlock.create!(domain: 'mail.example.com')
+      resolver = double
+
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::MX).and_return([double(exchange: 'mail.example.com')])
+      allow(resolver).to receive(:getresources).with('example.com', Resolv::DNS::Resource::IN::A).and_return([])
+      allow(resolver).to receive(:getresources).with('mail.example.com', Resolv::DNS::Resource::IN::A).and_return([double(address: '2.3.4.5')])
+      allow(resolver).to receive(:timeouts=).and_return(nil)
+      allow(Resolv::DNS).to receive(:open).and_yield(resolver)
+
+      subject.validate(user)
+      expect(user.errors).to have_received(:add)
+    end
+  end
+end