feat: Add a stream to listen to room keys being inserted to the store

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

@@ -31,6 +31,7 @@ use futures_util::{
     stream::{self, StreamExt},
 };
 use matrix_sdk_base::crypto::{
+    store::RoomKeyInfo,
     types::requests::{
         OutgoingRequest, OutgoingVerificationRequest, RoomMessageRequest, ToDeviceRequest,
     },
@@ -55,6 +56,7 @@ use ruma::{
 };
 use serde::Deserialize;
 use tokio::sync::{Mutex, RwLockReadGuard};
+use tokio_stream::wrappers::errors::BroadcastStreamRecvError;
 use tracing::{debug, error, instrument, trace, warn};
 use url::Url;
 use vodozemac::Curve25519PublicKey;
@@ -1432,6 +1434,45 @@ impl Encryption {
         Ok(ret)
     }
 
+    /// Receive notifications of room keys being received as a [`Stream`].
+    ///
+    /// Each time a room key is updated in any way, an update will be sent to
+    /// the stream. Updates that happen at the same time are batched into a
+    /// [`Vec`].
+    ///
+    /// If the reader of the stream lags too far behind, a warning will be
+    /// logged and items will be dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// # use matrix_sdk::Client;
+    /// # use url::Url;
+    /// # async {
+    /// # let homeserver = Url::parse("http://example.com")?;
+    /// # let client = Client::new(homeserver).await?;
+    /// use futures_util::StreamExt;
+    ///
+    /// let Some(mut room_keys_stream) =
+    ///     client.encryption().room_keys_received_stream().await
+    /// else {
+    ///     return Ok(());
+    /// };
+    ///
+    /// while let Some(update) = room_keys_stream.next().await {
+    ///     println!("Received room keys {update:?}");
+    /// }
+    /// # anyhow::Ok(()) };
+    /// ```
+    pub async fn room_keys_received_stream(
+        &self,
+    ) -> Option<impl Stream<Item = Result<Vec<RoomKeyInfo>, BroadcastStreamRecvError>>> {
+        let olm = self.client.olm_machine().await;
+        let olm = olm.as_ref()?;
+
+        Some(olm.store().room_keys_received_stream())
+    }
+
     /// Get the secret storage manager of the client.
     pub fn secret_storage(&self) -> SecretStorage {
         SecretStorage { client: self.client.to_owned() }