Add support for clients-only outputs (#1810)

lib/livebook/runtime/evaluator/io_proxy.ex

@@ -234,6 +234,12 @@ defmodule Livebook.Runtime.Evaluator.IOProxy do
     {:ok, state}
   end
 
+  defp io_request({:livebook_put_output_to_clients, output}, state) do
+    state = flush_buffer(state)
+    send(state.send_to, {:runtime_evaluation_output_to_clients, state.ref, output})
+    {:ok, state}
+  end
+
   defp io_request({:livebook_get_input_value, input_id}, state) do
     input_cache =
       Map.put_new_lazy(state.input_cache, input_id, fn ->

lib/livebook/session.ex

@@ -1307,9 +1307,12 @@ defmodule Livebook.Session do
         send(client_pid, {:operation, operation})
 
         # Keep track of assets infos, so we can look them up when fetching
-        for assets_info <- Cell.find_assets_in_output(output), reduce: state do
-          state -> put_in(state.client_id_with_assets[client_id][assets_info.hash], assets_info)
-        end
+        new_asset_infos =
+          for assets_info <- Cell.find_assets_in_output(output),
+              into: %{},
+              do: {assets_info.hash, assets_info}
+
+        update_in(state.client_id_with_assets[client_id], &Map.merge(&1, new_asset_infos))
       else
         state
       end
@@ -1317,6 +1320,27 @@ defmodule Livebook.Session do
     {:noreply, state}
   end
 
+  def handle_info({:runtime_evaluation_output_to_clients, cell_id, output}, state) do
+    operation = {:add_cell_evaluation_output, @client_id, cell_id, output}
+    broadcast_operation(state.session_id, operation)
+
+    # Keep track of assets infos, so we can look them up when fetching
+    new_asset_infos =
+      for assets_info <- Cell.find_assets_in_output(output),
+          into: %{},
+          do: {assets_info.hash, assets_info}
+
+    state =
+      update_in(
+        state.client_id_with_assets,
+        &Map.new(&1, fn {client_id, asset_infos} ->
+          {client_id, Map.merge(asset_infos, new_asset_infos)}
+        end)
+      )
+
+    {:noreply, state}
+  end
+
   def handle_info({:runtime_evaluation_response, cell_id, response, metadata}, state) do
     {memory_usage, metadata} = Map.pop(metadata, :memory_usage)
     operation = {:add_cell_evaluation_response, @client_id, cell_id, response, metadata}

test/livebook_web/live/session_live_test.exs

@@ -496,6 +496,31 @@ defmodule LivebookWeb.SessionLiveTest do
       {:ok, view, _} = live(conn, ~p"/sessions/#{session.id}")
       refute render(view) =~ "line 1"
     end
+
+    test "clients-only output is sent to all targets, but not reflected in session",
+         %{conn: conn, session: session} do
+      user1 = build(:user, name: "Jake Peralta")
+      Session.register_client(session.pid, self(), user1)
+
+      Session.subscribe(session.id)
+      evaluate_setup(session.pid)
+
+      section_id = insert_section(session.pid)
+      cell_id = insert_text_cell(session.pid, section_id, :code)
+
+      Session.queue_cell_evaluation(session.pid, cell_id)
+
+      send(
+        session.pid,
+        {:runtime_evaluation_output_to_clients, cell_id, {:stdout, "line 1\n"}}
+      )
+
+      assert_receive {:operation,
+                      {:add_cell_evaluation_output, _, ^cell_id, {:stdout, "line 1\n"}}}
+
+      {:ok, view, _} = live(conn, ~p"/sessions/#{session.id}")
+      refute render(view) =~ "line 1"
+    end
   end
 
   describe "smart cells" do