Rails 6 prompt to download on mobile

Question

I have a Rails 6 app where users can submit changes to a model and a confirmation email will be sent to site admins. The changes are submitted through a modal popup and once submitted the popup is replaced with another that confirms that the email has been sent.

The problem I am having is when this is done on a mobile device (I'm using an iPhone, not sure if this happens on Android), once the change is submitted another popup appears prompting me to download a file of size 0 with the name of the model being updated (it happens in both Safari and Chrome). This doesn't happen on the desktop version of the site or in the mobile emulator on the desktop, so I can't think of how I could diagnose this issue.

Here is the code being called just before the download popup appears:

<%= button_tag "Submit", type: 'submit',
                         id: 'modal-subimt',
                         class: 'btn btn-primary',
                         onClick: 'replaceModal()' %>

Here is the create function being called when the form is submitted:

def create
  ... # Setting the parameters for the model being changed
  if @model.save
    @model.send_confirmation_email()
  else
    # Irrelevant because the email gets sent
  end
end

Here is the send_confirmation_email function being called in create:

def send_confirmation_email()
  UserMailer.model_confirmation(self).deliver_now
end

And here is the model_confirmation function being called by send_confirmation_email:

def model_confirmation(model)
  @model = model
  recipient = <admin email>

  mail to: recipient, subject: "Model Confirmation"
end

Nowhere in this code can I see where I might be prompted to download a file, but alas it is happening. Any help would be appreciated on how to properly diagnose or solve this problem. Thanks!

EDIT: I changed my code so that the model would be updated without sending a confirmation email Also, the modal is no longer replaced with the new one verifying an email has been sent, and I am still having the same issue. This leads me to believe that the problem is something with the creation of the model.

EDIT 2: Previously I was creating the model and remaining on the page (with the confirmation that the email was sent). I changed my controller to redirect_to request.referer to reload the page once the change is made, and when that is done I am no longer prompted to download the empty file. Unfortunately, the way I want this to work, reloading the page isn't optimal. Is there any reason that I would be prompted for a download when updating a model without reloading the page?

SOLUTION: I was able to solve this problem by adding remote: true to the form_for line like the following:

<%= form_for(Model.new, remote: true) do |f| %>
  ...
  <%= button_tag "Submit", type: 'submit',
                           id: 'modal-subimt',
                           class: 'btn btn-primary',
                           onClick: 'replaceModal()' %>
<% end %>

I'm not sure why exactly this solved my problem though so if anyone can provide some insight that would be much appreciated!

Answer 1

The problem is related to how you instantiated the form_for. When you submit the form to a Model.new object, form_for try to infer the controller with the create method for handling it. See more how form_for works in https://apidock.com/rails/ActionView/Helpers/FormHelper/form_for

With that said, the create method is probably outputting something or nothing instead of redirecting, that's why you get a download on a mobile device and in browsers it's just an empty page because they can handle it. If there is no render on the method, Rails will answer with a 204 No Content or an empty text page. You must check your method about this.

When you use remote: true, I will quote from the docs:

:remote - If set to true, will allow the Unobtrusive JavaScript drivers to control the submit behavior. By default this behavior is an ajax submit.

So instead of reloading the page, UJS sends a XMLHttpRequest to the "backend" page, that's why you don't get a redirect. The result of the submit is treated without redirecting. But based on the result of the request the content of the page can come. So it's important that you give a response accordingly. In the links below you will find the right way to do it.

See more in these questions:

• How does ':remote => true' works in rails
• :remote => true confusion with form_for

Also, in the Rails Guides:

• https://guides.rubyonrails.org/form_helpers.html
• https://guides.rubyonrails.org/working_with_javascript_in_rails.html

This is also a good reference:

• http://www.korenlc.com/remote-true-in-rails-forms/