sdk: Push deserialization of UTD events down to BackupDownloadTask

This means the higher-level classes can be agnostic about the encryption
algorithm; we don't actually care about that until BackupDownloadTask.

Author: richvdh

crates/matrix-sdk/src/encryption/backups/mod.rs

@@ -37,7 +37,7 @@ use ruma::{
         error::ErrorKind,
     },
     events::{
-        room::encrypted::{EncryptedEventScheme, OriginalSyncRoomEncryptedEvent},
+        room::encrypted::OriginalSyncRoomEncryptedEvent,
         secret::{request::SecretName, send::ToDeviceSecretSendEvent},
     },
     serde::Raw,
@@ -891,21 +891,19 @@ impl Backups {
         room: Room,
         client: Client,
     ) {
-        if let Ok(event) = event.deserialize() {
-            if let EncryptedEventScheme::MegolmV1AesSha2(c) = &event.content.scheme {
-                client
-                    .encryption()
-                    .backups()
-                    .maybe_download_room_key(room.room_id().to_owned(), c.session_id.to_owned());
-            }
-        }
+        client.encryption().backups().maybe_download_room_key(room.room_id().to_owned(), event);
     }
 
-    pub(crate) fn maybe_download_room_key(&self, room_id: OwnedRoomId, session_id: String) {
+    /// Send a notification to the task responsible for key backup downloads
+    /// that it should attempt to download the keys for the given event.
+    pub(crate) fn maybe_download_room_key(
+        &self,
+        room_id: OwnedRoomId,
+        event: Raw<OriginalSyncRoomEncryptedEvent>,
+    ) {
         let tasks = self.client.inner.e2ee.tasks.lock().unwrap();
-
         if let Some(task) = tasks.download_room_keys.as_ref() {
-            task.trigger_download((room_id, session_id))
+            task.trigger_download_for_utd_event(room_id, event);
         }
     }
 

crates/matrix-sdk/src/encryption/tasks.rs

@@ -16,7 +16,11 @@ use std::{collections::BTreeMap, time::Duration};
 
 use futures_util::future::join_all;
 use matrix_sdk_common::failures_cache::FailuresCache;
-use ruma::OwnedRoomId;
+use ruma::{
+    events::room::encrypted::{EncryptedEventScheme, OriginalSyncRoomEncryptedEvent},
+    serde::Raw,
+    OwnedRoomId,
+};
 use tokio::sync::mpsc::{self, UnboundedReceiver};
 use tracing::{trace, warn};
 
@@ -124,8 +128,21 @@ impl BackupDownloadTask {
         Self { sender, join_handle }
     }
 
-    pub(crate) fn trigger_download(&self, room_key_info: RoomKeyInfo) {
-        let _ = self.sender.send(room_key_info);
+    /// Trigger a backup download for the keys for the given event.
+    ///
+    /// Does nothing unless the event is encrypted using `m.megolm.v1.aes-sha2`.
+    /// Otherwise, tells the listener task to set off a task to do a backup
+    /// download, unless there is one already running.
+    pub(crate) fn trigger_download_for_utd_event(
+        &self,
+        room_id: OwnedRoomId,
+        event: Raw<OriginalSyncRoomEncryptedEvent>,
+    ) {
+        if let Ok(deserialized_event) = event.deserialize() {
+            if let EncryptedEventScheme::MegolmV1AesSha2(c) = deserialized_event.content.scheme {
+                let _ = self.sender.send((room_id, c.session_id));
+            }
+        }
     }
 
     pub(crate) async fn download(

crates/matrix-sdk/src/room/mod.rs

@@ -1120,22 +1120,17 @@ impl Room {
         &self,
         event: &Raw<OriginalSyncRoomEncryptedEvent>,
     ) -> Result<TimelineEvent> {
-        use ruma::events::room::encrypted::EncryptedEventScheme;
-
         let machine = self.client.olm_machine().await;
         let machine = machine.as_ref().ok_or(Error::NoOlmMachine)?;
 
         let mut event =
             match machine.decrypt_room_event(event.cast_ref(), self.inner.room_id()).await {
                 Ok(event) => event,
                 Err(e) => {
-                    let event = event.deserialize()?;
-                    if let EncryptedEventScheme::MegolmV1AesSha2(c) = event.content.scheme {
-                        self.client
-                            .encryption()
-                            .backups()
-                            .maybe_download_room_key(self.room_id().to_owned(), c.session_id);
-                    }
+                    self.client
+                        .encryption()
+                        .backups()
+                        .maybe_download_room_key(self.room_id().to_owned(), event.clone());
 
                     return Err(e.into());
                 }