How to do it...

1. Open the service object we created in the previous recipe. We'll modify the service object to be able to call an external microservice responsible for managing attachments. For the sake of simplicity, we'll use an HTTP client that is provided in the Ruby standard library. The service object should be in the app/services/attachments_service.rb file:

class AttachmentsService

  BASE_URI = "http://attachment-service.yourorg.example.com/"

  def upload(message_id, user_id, file_name, data, media_type)
    body = {
      user_id: user_id,
      file_name: file_name,
      data: StringIO.new(Base64.decode64(params[:file]
      [:data]), 'rb'),
      message: message_id,
      media_type: media_type
    }.to_json
    uri = URI("#{BASE_URI}attachment")
    headers = { "Content-Type" => "application/json" }
    Net::HTTP.post(uri, body, headers)
  end

end

2. Open the attachments_controller.rb file, located in pichat/app/controllers/, and look at the following create action. Because of the refactoring work done in the previous chapter, we require only a small change to make the controller work with our new service object:

class AttachmentsController < ApplicationController
  # POST /messages/:message_id/attachments
  def create
    service = AttachmentService.new
    response = service.upload(params[:message_id], current_user.id,
     params[:file][:name], params[:file][:data], 
     params[:media_type])
    json_response(response.body, response.code)
  end
  # ...
end