core_crypto/mls/session/
epoch_observer.rs

1use std::sync::Arc;
2
3use async_trait::async_trait;
4
5use super::{Error, Result, Session};
6use crate::ConversationId;
7
8/// An `EpochObserver` is notified whenever a conversation's epoch changes.
9#[cfg_attr(target_os = "unknown", async_trait(?Send))]
10#[cfg_attr(not(target_os = "unknown"), async_trait)]
11pub trait EpochObserver: Send + Sync {
12    /// This function will be called every time a conversation's epoch changes.
13    ///
14    /// The `epoch` parameter is the new epoch.
15    ///
16    /// <div class="warning">
17    /// This function must not block! Foreign implementors of this inteface can
18    /// spawn a task indirecting the notification, or (unblocking) send the notification
19    /// on some kind of channel, or anything else, as long as the operation completes
20    /// quickly.
21    /// </div>
22    async fn epoch_changed(&self, conversation_id: ConversationId, epoch: u64);
23}
24
25impl<D> Session<D> {
26    /// Add an epoch observer to this session.
27    /// (see [EpochObserver]).
28    ///
29    /// This function should be called 0 or 1 times in a session's lifetime. If called
30    /// when an epoch observer already exists, this will return an error.
31    pub async fn register_epoch_observer(&self, epoch_observer: Arc<dyn EpochObserver>) -> Result<()> {
32        let mut observer_guard = self.epoch_observer.write().await;
33        if observer_guard.is_some() {
34            return Err(Error::EpochObserverAlreadyExists);
35        }
36        observer_guard.replace(epoch_observer);
37        Ok(())
38    }
39
40    /// Notify the observer that the epoch has changed, if one is present.
41    pub(crate) async fn notify_epoch_changed(&self, conversation_id: ConversationId, epoch: u64) {
42        if let Some(observer) = self.epoch_observer.read().await.as_ref() {
43            observer.epoch_changed(conversation_id, epoch).await;
44        }
45    }
46}
47
48#[cfg(test)]
49mod tests {
50    use rstest::rstest;
51    use rstest_reuse::apply;
52
53    use crate::test_utils::{TestContext, TestEpochObserver, all_cred_cipher};
54
55    #[apply(all_cred_cipher)]
56    pub async fn observe_local_epoch_change(case: TestContext) {
57        let [session_context] = case.sessions().await;
58        Box::pin(async move {
59            let test_conv = case.create_conversation([&session_context]).await;
60
61            let observer = TestEpochObserver::new();
62            session_context
63                .session()
64                .await
65                .register_epoch_observer(observer.clone())
66                .await
67                .unwrap();
68
69            // trigger an epoch
70            let id = test_conv.advance_epoch().await.id;
71            session_context.transaction.finish().await.unwrap();
72
73            // ensure we have observed the epoch change
74            let observed_epochs = observer.observed_epochs().await;
75            assert_eq!(
76                observed_epochs.len(),
77                1,
78                "we triggered exactly one epoch change and so should observe one epoch change"
79            );
80            assert_eq!(
81                observed_epochs[0].0, id,
82                "conversation id of observed epoch change must match"
83            );
84        })
85        .await
86    }
87
88    #[apply(all_cred_cipher)]
89    pub async fn observe_remote_epoch_change(case: TestContext) {
90        let [alice, bob] = case.sessions().await;
91        Box::pin(async move {
92            let test_conv = case.create_conversation([&alice, &bob]).await;
93
94            //  bob has the observer
95            let observer = TestEpochObserver::new();
96            bob.session()
97                .await
98                .register_epoch_observer(observer.clone())
99                .await
100                .unwrap();
101
102            // alice triggers an epoch
103            let id = test_conv.advance_epoch().await.id;
104            bob.transaction.finish().await.unwrap();
105
106            // ensure we have observed the epoch change
107            let observed_epochs = observer.observed_epochs().await;
108            assert_eq!(
109                observed_epochs.len(),
110                1,
111                "we triggered exactly one epoch change and so should observe one epoch change"
112            );
113            assert_eq!(
114                observed_epochs[0].0, id,
115                "conversation id of observed epoch change must match"
116            );
117        })
118        .await
119    }
120}
core_crypto/mls/session/epoch_observer.rs

core_crypto/mls/session/
epoch_observer.rs
