Handle too long dates passed to DateTime.parse

This raises an ArgumentError with a different message from the invalid
date message since Ruby 3.0.3 when the string passed is too long, as a
mitigation for CVE-2021-41817.
https://www.ruby-lang.org/en/news/2021/11/15/date-parsing-method-regexp-dos-cve-2021-41817/

In this case we should just return nil, like when the date itself is
invalid.

lib/mail/fields/common_date_field.rb

@@ -4,26 +4,32 @@
 
 module Mail
   class CommonDateField < NamedStructuredField #:nodoc:
-    def self.singular?
-      true
-    end
+    class << self
+      def singular?
+        true
+      end
 
-    def self.normalize_datetime(string)
-      if Utilities.blank?(string)
-        datetime = ::DateTime.now
-      else
-        stripped = string.to_s.gsub(/\(.*?\)/, '').squeeze(' ')
-        begin
-          datetime = ::DateTime.parse(stripped)
-        rescue ArgumentError => e
-          raise unless 'invalid date' == e.message
+      def normalize_datetime(string)
+        if Utilities.blank?(string)
+          datetime = ::DateTime.now
+        else
+          stripped = string.to_s.gsub(/\(.*?\)/, '').squeeze(' ')
+          with_invalid_date_time_error_handling do
+            datetime = ::DateTime.parse(stripped)
+          end
+        end
+
+        if datetime
+          datetime.strftime('%a, %d %b %Y %H:%M:%S %z')
+        else
+          string
         end
       end
 
-      if datetime
-        datetime.strftime('%a, %d %b %Y %H:%M:%S %z')
-      else
-        string
+      def with_invalid_date_time_error_handling(&block)
+        yield
+      rescue ArgumentError => e
+        raise unless e.message =~ /\A(invalid date|string length \(\d+\) exceeds the limit \d+)\z/
       end
     end
 
@@ -33,9 +39,9 @@ def initialize(value = nil, charset = nil)
 
     # Returns a date time object of the parsed date
     def date_time
-      ::DateTime.parse("#{element.date_string} #{element.time_string}")
-    rescue ArgumentError => e
-      raise e unless e.message == 'invalid date'
+      self.class.with_invalid_date_time_error_handling do
+        ::DateTime.parse("#{element.date_string} #{element.time_string}")
+      end
     end
 
     def default

spec/mail/fields/date_field_spec.rb

@@ -66,5 +66,11 @@
       field = Mail::DateField.new("12 Aug 2009 30:00:02 GMT")
       expect(field.date_time).to be_nil
     end
+
+    it "should handle too long invalid date" do
+      # field = Mail::DateField.new("12 Aug 2009 30:00:02 GMT")
+      field = Mail::DateField.new("Wed, 23                              Jan 2019                                               30:51:32                                                -0500")
+      expect(field.date_time).to be_nil
+    end
   end
 end