Add support for conditional intercepts

Author: studzien

lib/phoenix/channel.ex

@@ -521,14 +521,18 @@ defmodule Phoenix.Channel do
   """
   defmacro intercept(events) do
     quote do
-      @phoenix_intercepts unquote(events)
+      @phoenix_intercepts Map.new(unquote(events),
+        fn {event, predicate} -> {event, predicate}
+           event -> {event, true}
+      end)
     end
   end
 
   @doc false
   def __on_definition__(env, :def, :handle_out, [event, _payload, _socket], _, _)
       when is_binary(event) do
-    unless event in Module.get_attribute(env.module, :phoenix_intercepts) do
+    intercepts = Module.get_attribute(env.module, :phoenix_intercepts)
+    unless event in Map.keys(intercepts) do
       IO.write(
         "#{Path.relative_to(env.file, File.cwd!())}:#{env.line}: [warning] " <>
           "An intercept for event \"#{event}\" has not yet been defined in #{env.module}.handle_out/3. " <>

lib/phoenix/channel/server.ex

@@ -89,8 +89,14 @@ defmodule Phoenix.Channel.Server do
       {pid, _}, cache when pid == from ->
         cache
 
-      {pid, {:fastlane, fastlane_pid, serializer, event_intercepts}}, cache ->
-        if event in event_intercepts do
+      {pid, {:fastlane, fastlane_pid, serializer, socket, event_intercepts}}, cache ->
+        intercept? = case Map.get(event_intercepts, event) do
+          true -> true
+          predicate when is_function(predicate, 1) -> predicate.(socket)
+          _ -> false
+        end
+
+        if intercept? do
           send(pid, msg)
           cache
         else
@@ -433,7 +439,7 @@ defmodule Phoenix.Channel.Server do
     end
 
     Process.monitor(transport_pid)
-    fastlane = {:fastlane, transport_pid, serializer, channel.__intercepts__()}
+    fastlane = {:fastlane, transport_pid, serializer, socket, channel.__intercepts__()}
     PubSub.subscribe(pubsub_server, topic, metadata: fastlane)
 
     {:noreply, %{socket | joined: true}}

test/phoenix/test/channel_test.exs

@@ -29,7 +29,9 @@ defmodule Phoenix.Test.ChannelTest do
   defmodule Channel do
     use Phoenix.Channel
 
-    intercept ["stop"]
+    intercept ["stop", {"intercept", &Channel.intercept_predicate/1}]
+
+    def intercept_predicate(socket), do: socket.assigns[:intercept]
 
     def join("foo:ok", _, socket) do
       {:ok, socket}
@@ -62,6 +64,10 @@ defmodule Phoenix.Test.ChannelTest do
       {:ok, socket}
     end
 
+    def join("foo:intercept", payload, socket) do
+      {:ok, assign(socket, :intercept, payload["intercept"])}
+    end
+
     def handle_in("broadcast", broadcast, socket) do
       broadcast_from!(socket, "broadcast", broadcast)
       {:noreply, socket}
@@ -102,6 +108,12 @@ defmodule Phoenix.Test.ChannelTest do
       {:stop, :shutdown, :ok, socket}
     end
 
+    def handle_out("intercept", payload, socket) do
+      payload = Map.put(payload, "intercepted", true)
+      push(socket, "intercept", payload)
+      {:noreply, socket}
+    end
+
     def handle_out("stop", _payload, socket) do
       {:stop, :shutdown, socket}
     end
@@ -435,6 +447,18 @@ defmodule Phoenix.Test.ChannelTest do
     assert_graceful_exit(pid)
   end
 
+  test "broadcast is intercepted when socket predicate returns true" do
+    {:ok, _, socket} = subscribe_and_join(socket(UserSocket), Channel, "foo:intercept", %{"intercept" => true})
+    broadcast_from!(socket, "intercept", %{"intercepted" => false})
+    assert_push "intercept", %{"intercepted" => true}
+  end
+
+  test "broadcast isn't intercepted when socket predicate returns false" do
+    {:ok, _, socket} = subscribe_and_join(socket(UserSocket), Channel, "foo:intercept")
+    broadcast_from!(socket, "intercept", %{"intercepted" => false})
+    assert_push "intercept", %{"intercepted" => false}
+  end
+
   ## handle_info
 
   test "handles messages and stops" do