def call(env)
      Thread.current[:request_id] = extract_request_id(env)
      @app.call(env)
    ensure
      RequestLocals.clear!
      Thread.current[:request_id] = nil
    end
def call(env)
      Thread.current[:request_id] = extract_request_id(env)
      @app.call(env)
    ensure
      RequestLocals.clear!
      Thread.current[:request_id] = nil
    end
Internal: Assigns the :request_id thread-local variable, and cleans up all
 the request-local variables after the request.