Rails example to log session as LTSV (Labeled Tab-separated Values)

config_application.rb

class Application < Rails::Application
  config.middleware.use LtsvRequestLogger
end

ltsv_request_logger.rb

class LtsvRequestLogger
  def initialize(env)
    @app = app
  end
  
  def call(env)
    @app.call(env).tap do |(status, headers, body)|
      log_session(ActionDispatch::Request.new(env), ActionDispatch::Response.new(status, headers, body))
    end
  end
  
  def log_session(request, response)
    stash = {
      method: request.request_method,
      status: response.status,
      uri: request.filtered_path,
      host: request.ip,
      ua: request.user_agent,
    }
    
    stash[:referer] = request.referer unless request.referer.blank?
    stash[:runtime] = response['X-Runtime'] unless response['X-Runtime'].blank?
    
    Rails.logger.info(stash.each_entry.map {|(key, value)| "#{key}:#{value}" }.join("\t") + "\t")
  end
end

I've swapped Rails::Rack::Logger for this middleware.