Simple e-mail service with Rails - Part 6: Sending Replies

Now that we can see Topics, there’s one last thing that’s missing. We can track replies, but there’s no way to send a reply. Technically, sending a reply should be opposite process as receiving one, so let’s get started!

TLDR: You can find the code in this GitHub repository. Every part has a corresponding commit.

We can start with a button this time. I personally added option to reply to each Message in a Topic. For that, we add link to a new Message, but this time, we also pass message_id so we know to which Message we want to reply to.

    <%= link_to 'Reply', new_message_path(reply_to_id: message.id), class: "rounded-lg py-3 px-5 bg-gray-100 inline-block font-medium" %>

Replying to an email is simply reversing from and to. It’s also common to prepend Re: to the original subject.

  # ...

  def new
    @message = Message.new

    if params[:reply_to_id].present?
      reply_to = Message.find(params[:reply_to_id])
      @message.reply_to = reply_to # we also have to save reference to original Message
      @message.subject = "Re: #{reply_to.subject}"
      @message.to = reply_to.from
      @message.from = reply_to.to
      @message.cc = reply_to.cc
    end
  end

  # ...

This change prefill new Message object with all reply related data. We also set reference to Message this new one is a reply to. As we need the reply_to value to be part to the HTML form, incidentally being passed in form data to the create method, we have to do few minor changes.

<%= form_with(model: message, class: "contents") do |form| %>
  <%= form.hidden_field :reply_to_id %>

We have to add new hidden field to the form which will include id of a Message we are replying to. We also have to allow reply_to_id as a valid param for a Message. This we can do by updating existing message_params method in the MessagesController.

class MessagesController < ApplicationController
    # ...

    def message_params
      params.require(:message).permit(:subject, :from, :to, :cc, :bcc, :content, :reply_to_id, attachments: [])
    end

    # ...
end

Right now, if you try to send a new reply, email will be delivered and new Message record will also include reply_to association to another Message. That could be enough, but if you remember from reply tracking part, we tracked replies by reading a message_id from the Mail object. It’d be a good idea to also pass message_id of a Message we are trying to send a reply to, so we make tracking of replies possible for receiver of the reply too.

class MessageMailer < ApplicationMailer
  def send_message(message_id)
    # ...

    if @message.reply_to.present?
      headers['In-Reply-To'] = @message.reply_to.message_id
    end

    mail subject: ...

And that’s it. This simple change ensures we are including correct header to mark email as a reply to another email.

This part was fairly short and simple, but our app currently looks like a mess unless you did some styling on your own. I won’t include changes in the text, but I’ll add one extra commit with few UX changes and my attempt to styling.