crypto: add received room key bundles to store changes list

After we receive a to-device message holding room key bundle info, add the data
to the store's Changes structure

crates/matrix-sdk-crypto/src/machine/mod.rs

@@ -939,6 +939,26 @@ impl OlmMachine {
         }
     }
 
+    #[instrument()]
+    async fn receive_room_key_bundle(
+        &self,
+        sender_key: Curve25519PublicKey,
+        event: &DecryptedRoomKeyBundleEvent,
+        changes: &mut Changes,
+    ) -> OlmResult<()> {
+        let Some(sender_device_keys) = &event.sender_device_keys else {
+            warn!("Received a room key bundle with no sender device keys: ignoring");
+            return Ok(());
+        };
+
+        changes.received_room_key_bundles.push(StoredRoomKeyBundleData {
+            sender_user: event.sender.clone(),
+            sender_data: SenderData::device_info(sender_device_keys.clone()),
+            bundle_data: event.content.clone(),
+        });
+        Ok(())
+    }
+
     fn add_withheld_info(&self, changes: &mut Changes, event: &RoomKeyWithheldEvent) {
         debug!(?event.content, "Processing `m.room_key.withheld` event");
 
@@ -1186,6 +1206,7 @@ impl OlmMachine {
             }
             AnyDecryptedOlmEvent::RoomKeyBundle(e) => {
                 debug!("Received a room key bundle event {:?}", e);
+                self.receive_room_key_bundle(decrypted.result.sender_key, e, changes).await?;
             }
             AnyDecryptedOlmEvent::Custom(_) => {
                 warn!("Received an unexpected encrypted to-device event");

crates/matrix-sdk-crypto/src/store/mod.rs

@@ -70,7 +70,7 @@ use crate::{
     identities::{user::UserIdentity, Device, DeviceData, UserDevices, UserIdentityData},
     olm::{
         Account, ExportedRoomKey, InboundGroupSession, OlmMessageHash, OutboundGroupSession,
-        PrivateCrossSigningIdentity, Session, StaticAccountData,
+        PrivateCrossSigningIdentity, SenderData, Session, StaticAccountData,
     },
     types::{
         events::room_key_withheld::RoomKeyWithheldEvent, BackupSecrets, CrossSigningSecrets,
@@ -101,7 +101,8 @@ pub use memorystore::MemoryStore;
 pub use traits::{CryptoStore, DynCryptoStore, IntoCryptoStore};
 
 use crate::types::{
-    events::room_key_withheld::RoomKeyWithheldContent, room_history::RoomKeyBundle,
+    events::{room_key_bundle::RoomKeyBundleContent, room_key_withheld::RoomKeyWithheldContent},
+    room_history::RoomKeyBundle,
 };
 pub use crate::{
     dehydrated_devices::DehydrationError,
@@ -541,6 +542,26 @@ pub struct Changes {
     pub room_settings: HashMap<OwnedRoomId, RoomSettings>,
     pub secrets: Vec<GossippedSecret>,
     pub next_batch_token: Option<String>,
+
+    /// Historical room key history bundles that we have received and should
+    /// store.
+    pub received_room_key_bundles: Vec<StoredRoomKeyBundleData>,
+}
+
+/// Information about an [MSC4268] room key bundle.
+///
+/// [MSC4268]: https://github.com/matrix-org/matrix-spec-proposals/pull/4268
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct StoredRoomKeyBundleData {
+    /// The user that sent us this data.
+    pub sender_user: OwnedUserId,
+
+    /// Information about the sender of this data and how much we trust that
+    /// information.
+    pub sender_data: SenderData,
+
+    /// The room key bundle data itself.
+    pub bundle_data: RoomKeyBundleContent,
 }
 
 /// A user for which we are tracking the list of devices.
@@ -573,6 +594,7 @@ impl Changes {
             && self.room_settings.is_empty()
             && self.secrets.is_empty()
             && self.next_batch_token.is_none()
+            && self.received_room_key_bundles.is_empty()
     }
 }