Elixir 插头 : register_before_send

Question

根据文档，Plug.Conn.register_before_send注册在发送请求之前调用的回调。以下代码仅打印“设置”消息而不打印“清理”。

defmodule MyRouter do
  use Plug.Router

  # Starts the server
  def start do
    Plug.Adapters.Cowboy.http MyRouter, []
  end

  plug :my_handle # custom plug
  plug :match
  plug :dispatch

  def my_handle(conn, _opts) do
    Plug.Conn.register_before_send(conn, fn conn -> 
      # Doesn't show up in console.
      IO.puts "== cleaning up =="
      conn
    end)
    # This is printed to the console.
    IO.puts "== setting up =="
    conn
  end

  get "/" do
    send_resp(conn, 200, "world")
  end

  match _ do
    send_resp(conn, 404, "oops")
  end
end

我从文档中遗漏了什么吗？为了使这项工作正常进行，设置是什么？提前致谢!

Answer 1

你是对的，但是你没有使用注册了 before_send 的 conn(不要忘记变量在 Elixir 中是不可变的。)

改变:

Plug.Conn.register_before_send(conn, fn conn -> 

到:

conn = Plug.Conn.register_before_send(conn, fn conn -> 

或者重写函数，使 conn 从 register_before_send 返回返回:

def my_handle(conn, _opts) do
  IO.puts "== setting up =="
  Plug.Conn.register_before_send(conn, fn conn -> 
    # Doesn't show up in console.
    IO.puts "== cleaning up =="
    conn
  end)
end