Allow restricting public timeline by instance

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -927,16 +927,8 @@ defp restrict_muted_reblogs(query, %{muting_user: %User{} = user} = opts) do
 
   defp restrict_muted_reblogs(query, _), do: query
 
-  defp restrict_instance(query, %{instance: instance}) do
+  defp restrict_instance(query, %{instance: instance}) when is_binary(instance) do
-    users =
+    from(activity in query, where: ilike(activity.actor, ^"%://#{instance}/%"))
-      from(
-        u in User,
-        select: u.ap_id,
-        where: fragment("? LIKE ?", u.nickname, ^"%@#{instance}")
-      )
-      |> Repo.all()
-
-    from(activity in query, where: activity.actor in ^users)
   end
 
   defp restrict_instance(query, _), do: query

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

@@ -59,6 +59,7 @@ def public_operation do
       security: [%{"oAuth" => ["read:statuses"]}],
       parameters: [
         local_param(),
+        instance_param(),
         only_media_param(),
         with_muted_param(),
         exclude_visibilities_param(),
@@ -158,6 +159,15 @@ defp local_param do
     )
   end
 
+  defp instance_param do
+    Operation.parameter(
+      :instance,
+      :query,
+      %Schema{type: :string},
+      "Show only statuses from the given domain"
+    )
+  end
+
   defp with_muted_param do
     Operation.parameter(:with_muted, :query, BooleanLike, "Includeactivities by muted users")
   end

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

@@ -110,6 +110,7 @@ def public(%{assigns: %{user: user}} = conn, params) do
         |> Map.put(:blocking_user, user)
         |> Map.put(:muting_user, user)
         |> Map.put(:reply_filtering_user, user)
+        |> Map.put(:instance, params[:instance])
         |> ActivityPub.fetch_public_activities()
 
       conn

test/web/mastodon_api/controllers/timeline_controller_test.exs

@@ -140,6 +140,18 @@ test "doesn't return replies if follow is posting with users from blocked domain
       activities = json_response_and_validate_schema(res_conn, 200)
       [%{"id" => ^activity_id}] = activities
     end
+
+    test "can be filtered by instance", %{conn: conn} do
+      user = insert(:user, ap_id: "https://lain.com/users/lain")
+      insert(:note_activity, local: false)
+      insert(:note_activity, local: false)
+
+      {:ok, _} = CommonAPI.post(user, %{status: "test"})
+
+      conn = get(conn, "/api/v1/timelines/public?instance=lain.com")
+
+      assert length(json_response_and_validate_schema(conn, :ok)) == 1
+    end
   end
 
   defp local_and_remote_activities do