Improve Backend Error page

Mostly handle things properly when the front-end is missing

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/web/views/auth_view.ex

@@ -23,7 +23,12 @@ defmodule Mobilizon.Web.AuthView do
       Tag.tag(:meta, name: "auth-user-actor-id", content: user_actor_id)
     ]
 
-    tags = Instance.build_tags() ++ info_tags
-    inject_tags(tags, get_locale(conn))
+    with tags <- Instance.build_tags() ++ info_tags,
+         {:ok, html} <- inject_tags(tags, get_locale(conn)) do
+      html
+    else
+      {:error, error} ->
+        return_error(conn, error)
+    end
   end
 end

lib/web/views/error_view.ex

@@ -7,8 +7,13 @@ defmodule Mobilizon.Web.ErrorView do
   import Mobilizon.Web.Views.Utils
 
   def render("404.html", %{conn: conn}) do
-    tags = Instance.build_tags()
-    inject_tags(tags, get_locale(conn))
+    with tags <- Instance.build_tags(),
+         {:ok, html} <- inject_tags(tags, get_locale(conn)) do
+      html
+    else
+      {:error, error} ->
+        return_error(conn, error)
+    end
   end
 
   def render("404.json", _assigns) do
@@ -38,12 +43,18 @@ defmodule Mobilizon.Web.ErrorView do
     }
   end
 
-  def render("500.html", _assigns) do
+  def render("500.html", assigns) do
     Mobilizon.Config.instance_config()
     |> Keyword.get(:default_language, "en")
     |> Gettext.put_locale()
 
-    render("500_page.html", %{})
+    assigns =
+      assigns
+      |> Map.update(:details, [], & &1)
+      |> Map.put(:instance, Mobilizon.Config.instance_name())
+      |> Map.put(:contact, Mobilizon.Config.contact())
+
+    render("500_page.html", assigns)
   end
 
   # In case no render clause matches or no

lib/web/views/page_view.ex

@@ -63,16 +63,26 @@ defmodule Mobilizon.Web.PageView do
 
   def render(page, %{object: object, conn: conn} = _assigns)
       when page in ["actor.html", "event.html", "comment.html", "post.html"] do
-    locale = get_locale(conn)
-    tags = object |> Metadata.build_tags(locale)
-    inject_tags(tags, locale)
+    with locale <- get_locale(conn),
+         tags <- object |> Metadata.build_tags(locale),
+         {:ok, html} <- inject_tags(tags, locale) do
+      html
+    else
+      {:error, error} ->
+        return_error(conn, error)
+    end
   end
 
   # Discussions are private, no need to embed metadata
   def render("discussion.html", params), do: render("index.html", params)
 
   def render("index.html", %{conn: conn}) do
-    tags = Instance.build_tags()
-    inject_tags(tags, get_locale(conn))
+    with tags <- Instance.build_tags(),
+         {:ok, html} <- inject_tags(tags, get_locale(conn)) do
+      html
+    else
+      {:error, error} ->
+        return_error(conn, error)
+    end
   end
 end

lib/web/views/utils.ex

@@ -4,18 +4,38 @@ defmodule Mobilizon.Web.Views.Utils do
   """
 
   alias Mobilizon.Service.Metadata.Utils, as: MetadataUtils
+  import Mobilizon.Web.Gettext, only: [dgettext: 2]
+  import Plug.Conn, only: [put_status: 2, halt: 1]
+
+  @index_file_path Path.join(Application.app_dir(:mobilizon, "priv/static"), "index.html")
 
   # sobelow_skip ["Traversal.FileModule"]
-  @spec inject_tags(Enum.t(), String.t()) :: {:safe, String.t()}
+  @spec inject_tags(Enum.t(), String.t()) :: {:ok, {:safe, String.t()}}
   def inject_tags(tags, locale \\ "en") do
-    with {:ok, index_content} <- File.read(index_file_path()) do
-      do_replacements(index_content, MetadataUtils.stringify_tags(tags), locale)
+    with {:exists, true} <- {:exists, File.exists?(@index_file_path)},
+         {:ok, index_content} <- File.read(@index_file_path),
+         safe <- do_replacements(index_content, MetadataUtils.stringify_tags(tags), locale) do
+      {:ok, {:safe, safe}}
+    else
+      {:exists, false} -> {:error, :index_not_found}
     end
   end
 
-  @spec index_file_path :: String.t()
-  defp index_file_path do
-    Path.join(Application.app_dir(:mobilizon, "priv/static"), "index.html")
+  @spec return_error(Plug.Conn.t(), atom()) :: Plug.Conn.t()
+  def return_error(conn, error) do
+    conn
+    |> put_status(500)
+    |> Phoenix.Controller.put_view(Mobilizon.Web.ErrorView)
+    |> Phoenix.Controller.render("500.html", %{details: details(error)})
+    |> halt()
+  end
+
+  defp details(:index_not_found) do
+    [dgettext("errors", "Index file not found. You need to recompile the front-end.")]
+  end
+
+  defp details(_) do
+    []
   end
 
   @spec replace_meta(String.t(), String.t()) :: String.t()
@@ -25,12 +45,11 @@ defmodule Mobilizon.Web.Views.Utils do
     |> String.replace("<meta name=\"server-injected-data\" />", tags)
   end
 
-  @spec do_replacements(String.t(), String.t(), String.t()) :: {:safe, String.t()}
+  @spec do_replacements(String.t(), String.t(), String.t()) :: String.t()
   defp do_replacements(index_content, tags, locale) do
     index_content
     |> replace_meta(tags)
     |> String.replace("<html lang=\"en\">", "<html lang=\"#{locale}\">")
-    |> (&{:safe, &1}).()
   end
 
   @spec get_locale(Conn.t()) :: String.t()