Uploading an avatar media exceeding max size returns a 413

Until now it was returning a 500 because the upload plug were going
through the changeset and ending in the JSON encoder, which raised
because struct has to @derive the encoder.

lib/pleroma/user.ex

@@ -611,7 +611,13 @@ defp put_change_if_present(changeset, map_field, value_function) do
          {:ok, new_value} <- value_function.(value) do
       put_change(changeset, map_field, new_value)
     else
-      _ -> changeset
+      {:error, :file_too_large} ->
+        Ecto.Changeset.validate_change(changeset, map_field, fn map_field, _value ->
+          [{map_field, "file is too large"}]
+        end)
+
+      _ ->
+        changeset
     end
   end
 

lib/pleroma/web/api_spec/operations/account_operation.ex

@@ -64,7 +64,8 @@ def update_credentials_operation do
       requestBody: request_body("Parameters", update_credentials_request(), required: true),
       responses: %{
         200 => Operation.response("Account", "application/json", Account),
-        403 => Operation.response("Error", "application/json", ApiError)
+        403 => Operation.response("Error", "application/json", ApiError),
+        413 => Operation.response("Error", "application/json", ApiError)
       }
     }
   end

lib/pleroma/web/mastodon_api/controllers/account_controller.ex

@@ -254,7 +254,11 @@ def update_credentials(%{assigns: %{user: user}, body_params: params} = conn, _p
         with_pleroma_settings: true
       )
     else
-      _e -> render_error(conn, :forbidden, "Invalid request")
+      {:error, %Ecto.Changeset{errors: [avatar: {"file is too large", _}]}} ->
+        render_error(conn, :request_entity_too_large, "File is too large")
+
+      _e ->
+        render_error(conn, :forbidden, "Invalid request")
     end
   end
 

test/pleroma/web/mastodon_api/update_credentials_test.exs

@@ -259,6 +259,34 @@ test "updates the user's avatar", %{user: user, conn: conn} do
       assert user.avatar == nil
     end
 
+    test "updates the user's avatar, upload_limit, returns a HTTP 413", %{conn: conn, user: user} do
+      upload_limit = Config.get([:instance, :upload_limit]) * 8 + 8
+
+      assert :ok ==
+               File.write(Path.absname("test/tmp/large_binary.data"), <<0::size(upload_limit)>>)
+
+      new_avatar_oversized = %Plug.Upload{
+        content_type: nil,
+        path: Path.absname("test/tmp/large_binary.data"),
+        filename: "large_binary.data"
+      }
+
+      assert user.avatar == %{}
+
+      res =
+        patch(conn, "/api/v1/accounts/update_credentials", %{"avatar" => new_avatar_oversized})
+
+      assert user_response = json_response_and_validate_schema(res, 413)
+      assert user_response["avatar"] != User.avatar_url(user)
+
+      user = User.get_by_id(user.id)
+      assert user.avatar == %{}
+
+      clear_config([:instance, :upload_limit], upload_limit)
+
+      assert :ok == File.rm(Path.absname("test/tmp/large_binary.data"))
+    end
+
     test "updates the user's banner", %{user: user, conn: conn} do
       new_header = %Plug.Upload{
         content_type: "image/jpeg",