How Rails Turns a Controller Action Into Response

In the last article, we looked at the code Rails can run before your controller action. Now the action finally gets its turn. It can load records, check state, create something, enqueue work, assign instance variables, choose a format, or decide the user should be somewhere else entirely. But after all that Ruby code runs, Rails still owes the outside world the same primitive output: an HTTP response. HTTP doesn’t know about controller actions. It does not know about @user, current_user, service objects, partials, or Active Record.