Room::toJson(): save the last local user's read receipt

Read receipts are entangled with counting unread messages, and saving
them also helps in not sending receipts for too old events. Other users'
read receipts are still treated as truly ephemeral.

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/room.cpp b/lib/room.cpp
index e7d4e137..1c84ece0 100644
--- a/lib/room.cpp
+++ b/lib/room.cpp
@@ -3003,6 +3003,32 @@ QJsonObject Room::Private::toJson() const
                           { QStringLiteral("events"), accountDataEvents } });
     }
 
+    if (const auto& readReceiptEventId =
+            lastReadReceipts.value(q->localUser()).eventId;
+        !readReceiptEventId.isEmpty()) //
+    {
+        // Okay, that's a mouthful; but basically, it's simply placing an m.read
+        // event in the 'ephemeral' section of the cached sync payload.
+        // See also receiptevent.* and m.read example in the spec.
+        // Only the local user's read receipt is saved - others' are really
+        // considered ephemeral but this one is useful in understanding where
+        // the user is in the timeline before any history is loaded.
+        result.insert(
+            QStringLiteral("ephemeral"),
+            QJsonObject {
+                { QStringLiteral("events"),
+                  QJsonArray { QJsonObject {
+                      { TypeKey, ReceiptEvent::matrixTypeId() },
+                      { ContentKey,
+                        QJsonObject {
+                            { readReceiptEventId,
+                              QJsonObject {
+                                  { QStringLiteral("m.read"),
+                                    QJsonObject {
+                                        { connection->userId(),
+                                          QJsonObject {} } } } } } } } } } } });
+    }
+
     QJsonObject unreadNotifObj { { SyncRoomData::UnreadCountKey,
                                    unreadMessages } };