[bugfix] Always serialize orderedItems as array (#1673)

internal/ap/serialize.go

@@ -0,0 +1,64 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package ap
+
+import (
+	"errors"
+
+	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/activity/streams/vocab"
+)
+
+// SerializeOrderedCollection is a custom serializer for an ActivityStreamsOrderedCollection.
+// Unlike the standard streams.Serialize function, this serializer normalizes the orderedItems
+// value to always be an array/slice, regardless of how many items are contained therein.
+//
+// TODO: Remove this function if we can fix the underlying issue in Go-Fed.
+//
+// See:
+//   - https://github.com/go-fed/activity/issues/139
+//   - https://github.com/mastodon/mastodon/issues/24225
+func SerializeOrderedCollection(orderedCollection vocab.ActivityStreamsOrderedCollection) (map[string]interface{}, error) {
+	data, err := streams.Serialize(orderedCollection)
+	if err != nil {
+		return nil, err
+	}
+
+	return data, normalizeOrderedCollectionData(data)
+}
+
+func normalizeOrderedCollectionData(rawOrderedCollection map[string]interface{}) error {
+	orderedItems, ok := rawOrderedCollection["orderedItems"]
+	if !ok {
+		return errors.New("no orderedItems set on OrderedCollection")
+	}
+
+	if _, ok := orderedItems.([]interface{}); ok {
+		// Already slice.
+		return nil
+	}
+
+	orderedItemsString, ok := orderedItems.(string)
+	if !ok {
+		return errors.New("orderedItems was neither slice nor string")
+	}
+
+	rawOrderedCollection["orderedItems"] = []string{orderedItemsString}
+
+	return nil
+}