Debug HTTP headers plug

debug_http_headers.ex

defmodule Plug.DebugHTTPHeaders do
  @moduledoc """
  Plug to debug request and response headers. Add it to TSSWeb.Endpoint before
  any other plugs to ensure you see all headers. If you add it to the router
  another plug might handle the response before this one.

  THIS IS MEANT FOR USE IN DEVELOPMENT ONLY.

  If you see this plug used in a pull request, reject it.
  """

  def init(opts) do
    opts
  end

  def call(conn, _) do
    IO.inspect(conn.req_headers, label: "Request headers")

    Plug.Conn.register_before_send(conn, fn conn ->
      IO.inspect(conn.resp_headers, label: "Response headers")

      conn
    end)
  end
end