Allow to not block the channel supervisor on join

lib/phoenix/channel/server.ex

@@ -39,9 +39,25 @@ defmodule Phoenix.Channel.Server do
 
     case PoolSupervisor.start_child(socket.endpoint, socket.handler, from, args) do
       {:ok, :undefined} ->
-        receive do: ({^ref, reply} -> {:error, reply})
+        receive do: ({^ref, {:error, reply}} -> {:error, reply})
+
       {:ok, pid} ->
-        receive do: ({^ref, reply} -> {:ok, reply, pid})
+        mon_ref = Process.monitor(pid)
+
+        receive do
+          {^ref, {:ok, reply}} ->
+            Process.demonitor(mon_ref, [:flush])
+            {:ok, reply, pid}
+
+          {^ref, {:error, reply}} ->
+            Process.demonitor(mon_ref, [:flush])
+            {:error, reply}
+
+          {:DOWN, ^mon_ref, _, _, reason} ->
+            Logger.error fn -> Exception.format_exit(reason) end
+            {:error, %{reason: "join crashed"}}
+        end
+
       {:error, reason} ->
         Logger.error fn -> Exception.format_exit(reason) end
         {:error, %{reason: "join crashed"}}
@@ -207,7 +223,7 @@ defmodule Phoenix.Channel.Server do
         init(socket, channel, topic, reply, from)
       {:error, reply} ->
         log_join socket, topic, fn -> "Replied #{topic} :error" end
-        GenServer.reply(from, reply)
+        GenServer.reply(from, {:error, reply})
         :ignore
       other ->
         raise """
@@ -238,7 +254,7 @@ defmodule Phoenix.Channel.Server do
     PubSub.subscribe(pubsub_server, topic, link: true, fastlane: fastlane)
 
     log_join socket, topic, fn -> "Replied #{topic} :ok" end
-    GenServer.reply(from, reply)
+    GenServer.reply(from, {:ok, reply})
     {:ok, %{socket | joined: true}}
   end
 

lib/phoenix/socket.ex

@@ -138,9 +138,9 @@ defmodule Phoenix.Socket do
       {auth_payload, from, socket}
 
   A custom channel implementation MUST invoke
-  `GenServer.reply(from, reply_payload)` during its initialization
-  with a custom `reply_payload` that will be sent as a reply to the
-  client. Failing to do so will block the socket forever.
+  `GenServer.reply(from, {:ok | :error, reply_payload})` during its
+  initialization with a custom `reply_payload` that will be sent as
+  a reply to the client. Failing to do so will block the socket forever.
 
   A custom channel receives `Phoenix.Socket.Message` structs as regular
   messages from the transport. Replies to those messages and custom

test/phoenix/integration/websocket_channels_test.exs

@@ -70,12 +70,13 @@ defmodule Phoenix.Integration.WebSocketChannelsTest do
     def init({payload, from, socket}) do
       case payload["action"] do
         "ok" ->
-          GenServer.reply(from, %{"action" => "ok"})
+          GenServer.reply(from, {:ok, %{"action" => "ok"}})
           {:ok, socket}
 
         "ignore" ->
-          GenServer.reply(from, %{"action" => "ignore"})
-          :ignore
+          GenServer.reply(from, {:error, %{"action" => "ignore"}})
+          send(self(), :stop)
+          {:ok, socket}
 
         "error" ->
           raise "oops"
@@ -86,6 +87,10 @@ defmodule Phoenix.Integration.WebSocketChannelsTest do
       send socket.transport_pid, {:socket_close, self(), :shutdown}
       {:stop, :shutdown, socket}
     end
+
+    def handle_info(:stop, socket) do
+      {:stop, :shutdown, socket}
+    end
   end
 
   defmodule UserSocketConnectInfo do