任意のassetsのレスポンスヘッダにService-Worker-Allowdヘッダを追加するRack Middleware

rack_sw_header.rb

class RackSwHeader
  def initialize(app, config = [])
    @app = app
    @config = config
  end

  def call(env)
    status, headers, body = @app.call env

    path = env["PATH_INFO"]
    @config.each do |entry|
      next unless path == entry[:path]
      headers["Service-Worker-Allowed"] = entry[:scope]
    end

    [status, headers, body]
  end
end