Emit {:plug_conn, :sent} on responses

Author: josevalim

lib/plug/cowboy/conn.ex

@@ -2,6 +2,8 @@ defmodule Plug.Cowboy.Conn do
   @behaviour Plug.Conn.Adapter
   @moduledoc false
 
+  @already_sent {:plug_conn, :sent}
+
   def conn(req) do
     %{
       path: path,
@@ -14,7 +16,7 @@ defmodule Plug.Cowboy.Conn do
     } = req
 
     %Plug.Conn{
-      adapter: {__MODULE__, req},
+      adapter: {__MODULE__, Map.put(req, :plug_pid, self())},
       host: host,
       method: method,
       owner: self(),
@@ -33,6 +35,7 @@ defmodule Plug.Cowboy.Conn do
     req = to_headers_map(req, headers)
     status = Integer.to_string(status) <> " " <> Plug.Conn.Status.reason_phrase(status)
     req = :cowboy_req.reply(status, %{}, body, req)
+    send(req.plug_pid, @already_sent)
     {:ok, nil, req}
   end
 
@@ -49,13 +52,15 @@ defmodule Plug.Cowboy.Conn do
     body = {:sendfile, offset, length, path}
     req = to_headers_map(req, headers)
     req = :cowboy_req.reply(status, %{}, body, req)
+    send(req.plug_pid, @already_sent)
     {:ok, nil, req}
   end
 
   @impl true
   def send_chunked(req, status, headers) do
     req = to_headers_map(req, headers)
     req = :cowboy_req.stream_reply(status, %{}, req)
+    send(req.plug_pid, @already_sent)
     {:ok, nil, req}
   end