gistfile1.rb

class FriendsController
  def index
    @friends = @user.friends
    @friends_of_friends = slow { @user.friends_of_friends }
  end

  def import
    @result = slow { @user.friends.import(params[:big_csv]) }
  end
end

# (app/views/friends/index.html.erb)
# Your friends are <%= @friends %>
# The friends of your friends are <%= friends_of_friends %>

# (app/views/friends/import.html.erb)
# You imported <%= @result %>

# implementation idea
# @result = slow { sleep(900); "hello" } would return like a SlowString
# t0:   <%= @result %> => <span class="processing" id="slow_string_020d92ojaodisjdad">processing...</span>
# t1:   <%= @result %> => ditto
# ...
# t900: <%= @result %> => <span class="done" id="slow_string_020d92ojaodisjdad">hello</span>
#
# and there would be baked-in javascript that observed these slow strings until AJAX calls
# on them returned 200 or smth