Handle multiple files through a single attachment

When setting up a form uploading multiple files through a single
attachment, mail form was discarding all attachments and sending none,
even though it could consider the form as delivered successfully.

Now we will detect multiple files and add each of them individually.

Note: the reason we are not checking for something like
`respond_to?(:each)` and instead are doing a specific `is_a?(Array)`
check, is because a single uploaded file from Rack (which we use in
our tests) also responds to the `each` method (or rather, it delegates
to the tempfile internal instance used for the upload). It appears that
the Rails uploaded file does not do it, but for increased compatibility
I decided to go with this implementation. The previous one worked
because it tried both to add multiple files and handle a single file
separately, so either one of them would work. This implementation makes
an upfront decision about one or the other path, by performing the
`is_a?` check.  I don't love these types of checks, but this seemed the
most straightforward way of doing it while keeping the code easier to
follow.

Closes #76

CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 * Add support for Rails 7.0 and Ruby 3.1 (no changes required)
+* Add support for multiple files through a single attachment. [#76, #78]
 
 # 1.9.0
 

README.md

@@ -126,6 +126,8 @@ Options:
 
 * `:attachment` - When given, expects a file to be sent and attaches
   it to the e-mail. Don't forget to set your form to multitype.
+  It also accepts multiple files through a single attachment attribute,
+  and will attach them individually to the e-mail.
 
 * `:captcha` - When true, validates the attributes must be blank.
   This is a simple way to avoid spam and the input should be hidden with CSS.

lib/mail_form/notifier.rb

@@ -12,8 +12,11 @@ def contact(resource)
 
       resource.class.mail_attachments.each do |attribute|
         value = resource.send(attribute)
-        handle_multiple_attachments value
-        add_attachment value
+        if value.is_a?(Array)
+          value.each { |attachment_file| add_attachment(attachment_file) }
+        else
+          add_attachment(value)
+        end
       end
 
       headers = resource.headers
@@ -22,17 +25,11 @@ def contact(resource)
       mail(headers)
     end
 
-    private 
-      def add_attachment(attch)
-        return unless attch.respond_to?(:read)
-        attachments[attch.original_filename] = attch.read
-      end
+    private
 
-      def handle_multiple_attachments(attchs) 
-        return unless attchs.respond_to?('each')
-        attchs.each do |attch|
-          add_attachment attch
-        end
+      def add_attachment(attachment_file)
+        return unless attachment_file.respond_to?(:read)
+        attachments[attachment_file.original_filename] = attachment_file.read
       end
   end
 end

test/mail_form_test.rb

@@ -10,8 +10,8 @@ def setup
     @advanced         = AdvancedForm.new(valid_attributes)
     @advanced.request = ActionController::TestRequest.create(Class.new)
 
-    test_file  = Rack::Test::UploadedFile.new(File.join(File.dirname(__FILE__), 'test_file.txt'))
-    @with_file = FileForm.new(name: 'José', email: 'my.email@my.domain.com', message: "Cool", file: test_file)
+    @test_file = Rack::Test::UploadedFile.new(File.join(File.dirname(__FILE__), 'test_file.txt'))
+    @with_file = FileForm.new(name: 'José', email: 'my.email@my.domain.com', message: "Cool", file: @test_file)
 
     ActionMailer::Base.deliveries = []
   end
@@ -126,6 +126,12 @@ def test_form_with_file_does_not_output_attachment_as_attribute
     assert_no_match %r[File:], first_delivery.body.to_s
   end
 
+  def test_form_with_multiple_files_includes_attachments
+    @with_file.file = [@test_file, @test_file, @test_file]
+    @with_file.deliver
+    assert_equal 3, first_delivery.attachments.size
+  end
+
   protected
 
     def first_delivery