discourse/lib/middleware/turbo_dev.rb

# frozen_string_literal: true
module Middleware
  # Cheat and bypass Rails in development mode if the client attempts to download a static asset
  # that's already been downloaded.
  #
  # Also ensures that assets are not cached in development mode. Around Chrome 29, the behavior
  # of `must-revalidate` changed and would often not request assets that had changed.
  #
  #  To use, include in your project and add the following to development.rb:
  #
  #  require 'middleware/turbo_dev'
  #  config.middleware.insert 0, Middleware::TurboDev
  #
  class TurboDev
    def initialize(app, settings = {})
      @app = app
    end

    def call(env)
      root = "#{GlobalSetting.relative_url_root}/assets/"
      is_asset = env["REQUEST_PATH"] && env["REQUEST_PATH"].starts_with?(root)

      # hack to bypass all middleware if serving assets, a lot faster 4.5 seconds -> 1.5 seconds
      if (etag = env["HTTP_IF_NONE_MATCH"]) && is_asset
        name = env["REQUEST_PATH"][(root.length)..-1]
        etag = etag.gsub "\"", ""
        asset = Rails.application.assets.find_asset(name)
        return 304, {}, [] if asset && asset.digest == etag
      end

      status, headers, response = @app.call(env)
      headers["Cache-Control"] = "no-cache" if is_asset
      [status, headers, response]
    end
  end
end