Add dns_nameserver option for mx checking

README.md

@@ -51,12 +51,18 @@ To validate strictly that the domain has an MX record:
 ```ruby
 validates :email, 'valid_email_2/email': { strict_mx: true }
 ```
-`strict_mx` and `mx` both default to a 5 second timeout for DNS lookups.  To
-override this timeout, specify a `dns_timeout` option:
+`strict_mx` and `mx` both default to a 5 second timeout for DNS lookups.  
+To override this timeout, specify a `dns_timeout` option:
 ```ruby
 validates :email, 'valid_email_2/email': { strict_mx: true, dns_timeout: 10 }
 ```
 
+Any checks that require DNS resolution will use the default `Resolv::DNS` nameservers for DNS lookups.  
+To override these, specify a `dns_nameserver` option:
+```ruby
+validates :email, 'valid_email_2/email': { mx: true, dns_nameserver: ['8.8.8.8', '8.8.4.4'] }
+```
+
 To validate that the domain is not a disposable email (checks domain and MX server):
 ```ruby
 validates :email, 'valid_email_2/email': { disposable: true }

lib/valid_email2/address.rb

@@ -20,11 +20,14 @@ def self.prohibited_domain_characters_regex=(val)
       @prohibited_domain_characters_regex = val
     end
 
-    def initialize(address, dns_timeout = 5)
+    def initialize(address, dns_timeout = 5, dns_nameserver = nil)
       @parse_error = false
       @raw_address = address
       @dns_timeout = dns_timeout
 
+      @resolv_config = Resolv::DNS::Config.default_config_hash
+      @resolv_config[:nameserver] = dns_nameserver if dns_nameserver
+
       begin
         @address = Mail::Address.new(address)
       rescue Mail::Field::ParseError
@@ -134,7 +137,7 @@ def address_contain_emoticons?(email)
     end
 
     def mx_servers
-      @mx_servers ||= Resolv::DNS.open do |dns|
+      @mx_servers ||= Resolv::DNS.open(@resolv_config) do |dns|
         dns.timeouts = @dns_timeout
         dns.getresources(address.domain, Resolv::DNS::Resource::IN::MX)
       end
@@ -145,7 +148,7 @@ def null_mx?
     end
 
     def mx_or_a_servers
-      @mx_or_a_servers ||= Resolv::DNS.open do |dns|
+      @mx_or_a_servers ||= Resolv::DNS.open(@resolv_config) do |dns|
         dns.timeouts = @dns_timeout
         (mx_servers.any? && mx_servers) ||
           dns.getresources(address.domain, Resolv::DNS::Resource::IN::A)

lib/valid_email2/email_validator.rb

@@ -5,14 +5,14 @@
 module ValidEmail2
   class EmailValidator < ActiveModel::EachValidator
     def default_options
-      { disposable: false, mx: false, strict_mx: false, disallow_subaddressing: false, multiple: false, dns_timeout: 5 }
+      { disposable: false, mx: false, strict_mx: false, disallow_subaddressing: false, multiple: false, dns_timeout: 5, dns_nameserver: nil }
     end
 
     def validate_each(record, attribute, value)
       return unless value.present?
       options = default_options.merge(self.options)
 
-      addresses = sanitized_values(value).map { |v| ValidEmail2::Address.new(v, options[:dns_timeout]) }
+      addresses = sanitized_values(value).map { |v| ValidEmail2::Address.new(v, options[:dns_timeout], options[:dns_nameserver]) }
 
       error(record, attribute) && return unless addresses.all?(&:valid?)
 

spec/valid_email2_spec.rb

@@ -23,6 +23,22 @@ class TestUserStrictMX < TestModel
   validates :email, 'valid_email_2/email': { strict_mx: true }
 end
 
+class TestUserMXDnsTimeout < TestModel
+  validates :email, 'valid_email_2/email': { mx: true, dns_timeout: 10 }
+end
+
+class TestUserMXDnsFailingTimeout < TestModel
+  validates :email, 'valid_email_2/email': { mx: true, dns_timeout: Float::MIN }
+end
+
+class TestUserMXDnsNameserver < TestModel
+  validates :email, 'valid_email_2/email': { mx: true, dns_nameserver: ['8.8.8.8', '8.8.4.4'] }
+end
+
+class TestUserMXDnsFailingNameserver < TestModel
+  validates :email, 'valid_email_2/email': { mx: true, dns_timeout: 0.1, dns_nameserver: '1.0.0.0' }
+end
+
 class TestUserDisallowDisposable < TestModel
   validates :email, 'valid_email_2/email': { disposable: true }
 end
@@ -292,6 +308,94 @@ def set_whitelist
     end
   end
 
+  describe "with mx validation and dns not hitting timeout" do
+    it "is valid if mx records are found" do
+      user = TestUserMXDnsTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_truthy
+    end
+
+    it "is valid if A records are found" do
+      user = TestUserMXDnsTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_truthy
+    end
+
+    it "is invalid if no mx records are found" do
+      user = TestUserMXDnsTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is invalid if a null mx is found" do
+      user = TestUserMXDnsTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+  end
+
+  describe "with mx validation and dns hitting timeout" do
+    it "is never valid even if mx records exist" do
+      user = TestUserMXDnsFailingTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is never valid even A records exist" do
+      user = TestUserMXDnsFailingTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is invalid if no mx records exist" do
+      user = TestUserMXDnsFailingTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is invalid if a null mx exists" do
+      user = TestUserMXDnsFailingTimeout.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+  end
+
+  describe "with mx validation and dns nameserver" do
+    it "is valid if mx records are found" do
+      user = TestUserMXDnsNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_truthy
+    end
+
+    it "is valid if A records are found" do
+      user = TestUserMXDnsNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_truthy
+    end
+
+    it "is invalid if no mx records are found" do
+      user = TestUserMXDnsNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is invalid if a null mx is found" do
+      user = TestUserMXDnsNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+  end
+
+  describe "with mx validation and failing dns nameserver" do
+    it "is never valid even if mx records exist" do
+      user = TestUserMXDnsFailingNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is never valid even A records exist" do
+      user = TestUserMXDnsFailingNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is invalid if no mx records exist" do
+      user = TestUserMXDnsFailingNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+
+    it "is invalid if a null mx exists" do
+      user = TestUserMXDnsFailingNameserver.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
+  end
+
   describe "with dotted validation" do
     it "is valid when address does not contain dots" do
       user = TestUserDotted.new(email: "[email protected]")