Add forbidden error

lib/kino/bridge.ex

@@ -79,15 +79,17 @@ defmodule Kino.Bridge do
   @doc """
   Requests the file path for notebook file with the given name.
   """
-  @spec get_file_entry_path(String.t()) :: {:ok, term()} | {:error, request_error() | String.t()}
+  @spec get_file_entry_path(String.t()) ::
+          {:ok, term()} | {:error, request_error() | :forbidden | String.t()}
   def get_file_entry_path(name) do
     with {:ok, reply} <- io_request({:livebook_get_file_entry_path, name}), do: reply
   end
 
   @doc """
   Requests the file spec for notebook file with the given name.
   """
-  @spec get_file_entry_spec(String.t()) :: {:ok, term()} | {:error, request_error() | String.t()}
+  @spec get_file_entry_spec(String.t()) ::
+          {:ok, term()} | {:error, request_error() | :forbidden | String.t()}
   def get_file_entry_spec(name) do
     with {:ok, reply} <- io_request({:livebook_get_file_entry_spec, name}), do: reply
   end

lib/kino/fs.ex

@@ -3,6 +3,19 @@ defmodule Kino.FS do
   Provides access to notebook files.
   """
 
+  defmodule ForbiddenError do
+    @moduledoc """
+    Exception raised when access to a notebook file is forbidden.
+    """
+
+    defexception [:name]
+
+    @impl true
+    def message(exception) do
+      "forbidden access to file #{inspect(exception.name)}"
+    end
+  end
+
   @doc """
   Accesses notebook file with the given name and returns a local path
   to ead its contents from.
@@ -24,6 +37,9 @@ defmodule Kino.FS do
       {:ok, path} ->
         path
 
+      {:error, :forbidden} ->
+        raise ForbiddenError, name: name
+
       {:error, message} when is_binary(message) ->
         raise message
 
@@ -57,6 +73,9 @@ defmodule Kino.FS do
       {:ok, spec} ->
         spec
 
+      {:error, :forbidden} ->
+        raise ForbiddenError, name: name
+
       {:error, message} when is_binary(message) ->
         raise message