[bugfix] Always serialize orderedItems as array in OrderedCollection

docs/federation/federating_with_gotosocial.md

@@ -236,13 +236,15 @@ Example of a featured collection of a user who has pinned multiple `Note`s:
 }
 ```
 
-Example of a user who has pinned one `Note` (`orderedItems` is just a URL string now!):
+Example of a user who has pinned one `Note`:
 
 ```json
 {
   "@context": "https://www.w3.org/ns/activitystreams",
   "id": "https://example.org/users/some_user/collections/featured",
-  "orderedItems": "https://example.org/users/some_user/statuses/01GS7VTYH0S77NNXTP6W4G9EAG",
+  "orderedItems": [
+    "https://example.org/users/some_user/statuses/01GS7VTYH0S77NNXTP6W4G9EAG"
+  ],
   "totalItems": 1,
   "type": "OrderedCollection"
 }

internal/ap/serialize.go

@@ -0,0 +1,64 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors [email protected]
+// 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
+}

internal/processing/fedi/collections.go

@@ -25,6 +25,7 @@ import (
 	"net/url"
 
 	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/gotosocial/internal/ap"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
 )
@@ -172,7 +173,7 @@ func (p *Processor) FeaturedCollectionGet(ctx context.Context, requestedUsername
 		return nil, gtserror.NewErrorInternalError(err)
 	}
 
-	data, err := streams.Serialize(collection)
+	data, err := ap.SerializeOrderedCollection(collection)
 	if err != nil {
 		return nil, gtserror.NewErrorInternalError(err)
 	}

internal/typeutils/internaltoas_test.go

@@ -26,6 +26,7 @@ import (
 
 	"github.com/stretchr/testify/suite"
 	"github.com/superseriousbusiness/activity/streams"
+	"github.com/superseriousbusiness/gotosocial/internal/ap"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
 	"github.com/superseriousbusiness/gotosocial/internal/gtsmodel"
 	"github.com/superseriousbusiness/gotosocial/testrig"
@@ -669,7 +670,7 @@ func (suite *InternalToASTestSuite) TestPinnedStatusesToASSomeItems() {
 		suite.FailNow(err.Error())
 	}
 
-	ser, err := streams.Serialize(collection)
+	ser, err := ap.SerializeOrderedCollection(collection)
 	suite.NoError(err)
 
 	bytes, err := json.MarshalIndent(ser, "", "  ")
@@ -701,7 +702,7 @@ func (suite *InternalToASTestSuite) TestPinnedStatusesToASNoItems() {
 		suite.FailNow(err.Error())
 	}
 
-	ser, err := streams.Serialize(collection)
+	ser, err := ap.SerializeOrderedCollection(collection)
 	suite.NoError(err)
 
 	bytes, err := json.MarshalIndent(ser, "", "  ")
@@ -730,7 +731,7 @@ func (suite *InternalToASTestSuite) TestPinnedStatusesToASOneItem() {
 		suite.FailNow(err.Error())
 	}
 
-	ser, err := streams.Serialize(collection)
+	ser, err := ap.SerializeOrderedCollection(collection)
 	suite.NoError(err)
 
 	bytes, err := json.MarshalIndent(ser, "", "  ")
@@ -739,7 +740,9 @@ func (suite *InternalToASTestSuite) TestPinnedStatusesToASOneItem() {
 	suite.Equal(`{
   "@context": "https://www.w3.org/ns/activitystreams",
   "id": "http://localhost:8080/users/1happyturtle/collections/featured",
-  "orderedItems": "http://localhost:8080/users/1happyturtle/statuses/01G20ZM733MGN8J344T4ZDDFY1",
+  "orderedItems": [
+    "http://localhost:8080/users/1happyturtle/statuses/01G20ZM733MGN8J344T4ZDDFY1"
+  ],
   "totalItems": 1,
   "type": "OrderedCollection"
 }`, string(bytes))