emails: automatically fix typos in email addresses.

Try to automatically fix various kind of typos and common mistakes in
email addresses when a user creates a new account. It's common for users
to signup with addresses like `name@gmai.com`, which leads to bounces
when we try to send the welcome email.

app/logical/danbooru/email_address.rb

@@ -0,0 +1,130 @@
+# frozen_string_literal: true
+
+# A utility class that represents an email address. A wrapper around Mail::Address
+# that adds extra utility methods for normalizing and validating email addresses.
+#
+# @see https://www.rubydoc.info/gems/mail/Mail/Address
+# @see app/logical/email_address_type.rb
+# @see config/initializers/types.rb
+module Danbooru
+  class EmailAddress
+    class Error < StandardError; end
+
+    # https://www.regular-expressions.info/email.html
+    EMAIL_REGEX = /\A[a-z0-9._%+-]+@(?:[a-z0-9][a-z0-9-]{0,61}\.)+[a-z]{2,}\z/i
+
+    # @return [String] The original email address as a string.
+    attr_reader :address
+
+    # @return [Mail::Address] The parsed email address.
+    attr_reader :parsed_address
+
+    delegate :local, to: :parsed_address
+    alias_method :name, :local
+    alias_method :to_s, :address
+
+    # Parse a string into an email address, or raise an exception if the string is not a syntactically valid address.
+    #
+    # @param string [String, Danbooru::EmailAddress]
+    def initialize(string)
+      raise Error, "#{string} is not a valid email address" if !string.match?(EMAIL_REGEX)
+
+      @address = string.to_s
+      @parsed_address = Mail::Address.new(parsed_address)
+    end
+
+    # Parse a string into an email address, or return nil if the string is not a syntactically valid email address.
+    #
+    # @param url [String, Danbooru::EmailAddress]
+    # @return [Danbooru::EmailAddress]
+    def self.parse(address)
+      new(address)
+    rescue Error
+      nil
+    end
+
+    # Parse a string into an email address while attempting to fix common typos and mistakes, or return
+    # nil if the string can't be normalized into a valid email address.
+    #
+    # @param address [String]
+    # @return [Danbooru::EmailAddress]
+    def self.normalize(address)
+      address = address.gsub(/[[:space:]]+/, " ").strip
+
+      address = address.gsub(/[\\\/]$/, '') # @qq.com\ -> @qq.com, @web.de/ -> @web.de
+      #address = address.gsub(/,/, ".") # foo,bar@gmail.com -> foo.bar@gmail.com | @gmail,com -> @gmail.com
+      address = address.gsub(/^https?:\/\/(www\.)?/i, "") # https://xxx@gmail.com -> xxx@gmail.com
+      address = address.gsub(/^mailto:/i, "") # mailto:foo@gmail.com -> foo@gmail.com
+      address = address.gsub(/.* <(.*)>$/, '\1') # foo <bar@gmail.com> -> bar@gmail.com
+      address = address.gsub(/@\./, "@") # @.gmail.com -> @gmail.com
+      address = address.gsub(/@com$/i, ".com") # @gmail@com -> @gmail.com
+      address = address.gsub(/\.co,$/i, '.com') # @gmail.co, -> @gmail.com
+      address = address.gsub(/\.com.$/i, '.com') # @gmail.com, -> @gmail.com
+      address = address.gsub(/\.con$/i, '.com') # @gmail.con -> @gmail.com
+      address = address.gsub(/\.\.com$/i, '.com') # @gmail..com -> @gmail.com
+
+      # @gmail -> @gmail.com
+      address = address.gsub(/@gmai$/i, "@gmail.com")
+      address = address.gsub(/@gmail$/i, "@gmail.com")
+      address = address.gsub(/@yahoo$/i, "@yahoo.com")
+      address = address.gsub(/@hotmai$/i, "@hotmail.com")
+      address = address.gsub(/@hotmail$/i, "@hotmail.com")
+      address = address.gsub(/@hot[^m]ail$/i, "@hotmail.com")
+      address = address.gsub(/@live$/i, "@live.com")
+
+      address = address.gsub(/@.gmail\.com$/i, "@gmail.com") # @-gmail.com -> @gmail.com
+      address = address.gsub(/@g.ail\.com$/i, "@gmail.com") # @g,ail.com -> @gmail.com
+      address = address.gsub(/@gmail\.co.$/i, "@gmail.com") # @gmail.co, -> @gmail.com
+      address = address.gsub(/@gamil\.com$/i, "@gmail.com") # @gamil.com -> @gmail.com
+      address = address.gsub(/@gnail\.com$/i, "@gmail.com") # @gnail.com -> @gmail.com
+      address = address.gsub(/@gmail\.co$/i, "@gmail.com") # @gmail.co -> @gmail.com
+      address = address.gsub(/@gmai.\.com$/i, "@gmail.com") # @gmai;.com -> @gmail.com
+      address = address.gsub(/@gmai\.com$/i, "@gmail.com") # @gmai.com -> @gmail.com
+      address = address.gsub(/@gmai\.co$/i, "@gmail.com") # @gmai.co -> @gmail.com
+      address = address.gsub(/@hotmai\.com$/i, "@hotmail.com") # @hotmai.com -> @hotmail.com
+      address = address.gsub(/@hot.ail\.com$/i, "@hotmail.com") # @hot.ail.com -> @hotmail.com
+      address = address.gsub(/@hot.mail\.com$/i, "@hotmail.com") # @hot,mail.com -> @hotmail.com
+      address = address.gsub(/@hanm.ail\.net$/i, "@hanmail.net") # @hanmiail.net -> @hanmail.net
+
+      address = address.gsub(/@(gmail|yahoo|hotmail|outlook|live).com$/i, '@\1.com') # @gmail,com -> @gmail.com
+      address = address.gsub(/@(gmail|yahoo|hotmail|outlook|live)com$/i, '@\1.com') # @gmailcom -> @gmail.com
+
+      address = address.gsub(/@([a-z]+)\.com@\1\.com$/i, '@\1.com') # @gmail.com@gmail.com -> @gmail.com
+      address = address.gsub(/@([a-z]+)@\1\.com$/i, '@\1.com') # @gmail@gmail.com -> @gmail.com
+
+      address = address.gsub(/(@.*)$/) { $1.downcase } # @Gmail.com -> @gmail.com
+
+      parse(address)
+    end
+
+    # @return [Danbooru::EmailAddress] The email address, normalized to fix typos.
+    def normalized_address
+      Danbooru::EmailAddress.normalize(address)
+    end
+
+    # @return [PublicSuffix::Domain] The domain part of the email address.
+    def domain
+      @domain ||= PublicSuffix.parse(parsed_address.domain)
+    rescue PublicSuffix::DomainNotAllowed
+      nil
+    end
+
+    def as_json
+      to_s
+    end
+
+    def inspect
+      "#<Danbooru::EmailAddress #{to_s}>"
+    end
+
+    def ==(other)
+      self.class == other.class && to_s == other.to_s
+    end
+
+    def hash
+      to_s.hash
+    end
+
+    alias_method :eql?, :==
+  end
+end

app/logical/email_address_type.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# Define a custom email address type that allows models to declare attributes of type Danbooru::EmailAddress.
+#
+# @see app/logical/danbooru/email_address.rb
+# @see config/initializers/types.rb
+# @see https://www.bigbinary.com/blog/rails-5-attributes-api
+# @see https://api.rubyonrails.org/classes/ActiveModel/Type/Value.html
+class EmailAddressType < ActiveRecord::Type::Value
+  # Cast a String (or nil) value from the database to a Danbooru::EmailAddress object.
+  #
+  # @param value [String] the email address from the database
+  # @return [Danbooru::EmailAddress]
+  def cast(value)
+    return nil if value.blank?
+    super(Danbooru::EmailAddress.new(value))
+  rescue Danbooru::EmailAddress::Error
+    nil
+  end
+
+  # Serialize a Danbooru::EmailAddress to a String for the database.
+  #
+  # @param value [Danbooru::EmailAddress] the email address object
+  # @return [String]
+  def serialize(value)
+    return value.to_s if value.is_a?(Danbooru::EmailAddress)
+    super value
+  end
+end

app/models/email_address.rb

@@ -3,8 +3,11 @@
 class EmailAddress < ApplicationRecord
   belongs_to :user, inverse_of: :email_address
 
-  validates :address, presence: true, confirmation: true, format: { with: EmailValidator::EMAIL_REGEX }
-  validates :normalized_address, uniqueness: true
+  attribute :address
+  attribute :normalized_address
+
+  validates :address, presence: true, format: { message: "is invalid", with: EmailValidator::EMAIL_REGEX }
+  validates :normalized_address, presence: true, uniqueness: true
   validates :user_id, uniqueness: true
   validate :validate_deliverable, on: :deliverable
 
@@ -17,6 +20,7 @@ class EmailAddress < ApplicationRecord
   end
 
   def address=(value)
+    value = Danbooru::EmailAddress.normalize(value)&.to_s || value
     self.normalized_address = EmailValidator.normalize(value) || address
     super
   end

config/initializers/types.rb

@@ -1,3 +1,4 @@
 Rails.application.reloader.to_prepare do
   ActiveRecord::Type.register(:ip_address, IpAddressType)
+  ActiveRecord::Type.register(:email_address, EmailAddressType)
 end

config/locales/en.yml

@@ -69,6 +69,7 @@ en:
         uploader: "You"
         uploader_id: "You"
       user/email_address:
+        address: "Email address"
         normalized_address: "Email address"
       user_feedback:
         creator: "You"

test/unit/email_address_test.rb

@@ -12,29 +12,32 @@ class EmailAddressTest < ActiveSupport::TestCase
       should allow_value("foo+bar@gmail.com").for(:address)
       should allow_value("foo@foo.bar.com").for(:address)
 
-      should_not allow_value("foo@gmail.com ").for(:address)
-      should_not allow_value(" foo@gmail.com").for(:address)
-      should_not allow_value("foo@-gmail.com").for(:address)
-      should_not allow_value("foo@.gmail.com").for(:address)
-      should_not allow_value("foo@gmail").for(:address)
-      should_not allow_value("foo@gmail.").for(:address)
-      should_not allow_value("foo@gmail,com").for(:address)
-      should_not allow_value("foo@gmail.com.").for(:address)
-      should_not allow_value("foo@gmail.co,").for(:address)
+      should_not allow_value("foo@example").for(:address)
       should_not allow_value("fooqq@.com").for(:address)
-      should_not allow_value("foo@gmail..com").for(:address)
-      should_not allow_value("foo@gmailcom").for(:address)
-      should_not allow_value("mailto:foo@gmail.com").for(:address)
       should_not allow_value('foo"bar"@gmail.com').for(:address)
       should_not allow_value('foo<bar>@gmail.com').for(:address)
-      should_not allow_value("foo@gmail.com@gmail.com").for(:address)
-      should_not allow_value("foo@g,ail.com").for(:address)
-      should_not allow_value("foo@gmai;.com").for(:address)
-      should_not allow_value("foo@gmail@com").for(:address)
-      should_not allow_value("foo@gmail.c").for(:address)
       should_not allow_value("foo@foo.-bar.com").for(:address)
       should_not allow_value("foo@127.0.0.1").for(:address)
       should_not allow_value("foo@localhost").for(:address)
     end
+
+    should "fix typos" do
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail.com ").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: " foo@gmail.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail.com\n").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@-gmail.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@.gmail.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail,com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail.com.").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail.co,").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail..com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmailcom").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "mailto:foo@gmail.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail.com@gmail.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@g,ail.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmai;.com").address.to_s)
+      assert_equal("foo@gmail.com", EmailAddress.new(address: "foo@gmail@com").address.to_s)
+    end
   end
 end