Add Kino.tmp_dir/0 (#344)

lib/kino.ex

@@ -516,4 +516,16 @@ defmodule Kino do
   def interrupt!(variant, message) when variant in [:normal, :error] and is_binary(message) do
     raise Kino.InterruptError, variant: variant, message: message
   end
+
+  @doc """
+  Returns a temporary directory that gets removed when the runtime
+  terminates.
+  """
+  @spec tmp_dir() :: String.t() | nil
+  def tmp_dir() do
+    case Kino.Bridge.get_tmp_dir() do
+      {:ok, path} -> path
+      {:error, _} -> nil
+    end
+  end
 end

lib/kino/bridge.ex

@@ -202,6 +202,14 @@ defmodule Kino.Bridge do
     with {:ok, reply} <- io_request(:livebook_get_app_info), do: reply
   end
 
+  @doc """
+  Returns a temporary directory tied to the current runtime.
+  """
+  @spec get_tmp_dir() :: {:ok, String.t()} | {:error, request_error() | :not_available}
+  def get_tmp_dir() do
+    with {:ok, reply} <- io_request(:livebook_get_tmp_dir), do: reply
+  end
+
   @doc """
   Checks if the caller is running within Livebook context (group leader).
   """