core_crypto/mls/client/
epoch_observer.rs

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use std::sync::Arc;

use async_trait::async_trait;

use crate::{CoreCrypto, RecursiveError, mls::HasClientAndProvider as _, prelude::ConversationId};

use super::{Client, Error, Result};

/// An `EpochObserver` is notified whenever a conversation's epoch changes.
#[async_trait]
pub trait EpochObserver: Send + Sync {
    /// This function will be called every time a conversation's epoch changes.
    ///
    /// The `epoch` parameter is the new epoch.
    ///
    /// <div class="warning">
    /// This function must not block! Foreign implementors of this inteface can
    /// spawn a task indirecting the notification, or (unblocking) send the notification
    /// on some kind of channel, or anything else, as long as the operation completes
    /// quickly.
    /// </div>
    async fn epoch_changed(&self, conversation_id: ConversationId, epoch: u64);
}

impl Client {
    /// Add an epoch observer to this client.
    ///
    /// This function should be called 0 or 1 times in a client's lifetime. If called
    /// when an epoch observer already exists, this will return an error.
    pub(crate) async fn register_epoch_observer(&self, epoch_observer: Arc<dyn EpochObserver>) -> Result<()> {
        let mut guard = self.state.write().await;
        let inner = guard.as_mut().ok_or(Error::MlsNotInitialized)?;
        if inner.epoch_observer.is_some() {
            return Err(Error::EpochObserverAlreadyExists);
        }
        inner.epoch_observer = Some(epoch_observer);
        Ok(())
    }

    /// Notify the observer that the epoch has changed, if one is present.
    pub(crate) async fn notify_epoch_changed(&self, conversation_id: ConversationId, epoch: u64) {
        let guard = self.state.read().await;
        if let Some(inner) = guard.as_ref() {
            if let Some(observer) = inner.epoch_observer.as_ref() {
                observer.epoch_changed(conversation_id, epoch).await;
            }
        }
    }
}

impl CoreCrypto {
    /// Add an epoch observer to this client.
    ///
    /// This function should be called 0 or 1 times in a client's lifetime.
    /// If called when an epoch observer already exists, this will return an error.
    pub async fn register_epoch_observer(&self, epoch_observer: Arc<dyn EpochObserver>) -> Result<()> {
        let client = self.client().await.map_err(RecursiveError::mls("getting mls client"))?;
        client.register_epoch_observer(epoch_observer).await
    }
}

#[cfg(test)]
mod tests {
    use rstest::rstest;
    use rstest_reuse::apply;
    use wasm_bindgen_test::*;

    use crate::test_utils::{TestCase, TestEpochObserver, all_cred_cipher, conversation_id, run_test_with_client_ids};

    #[apply(all_cred_cipher)]
    #[wasm_bindgen_test]
    pub async fn observe_local_epoch_change(case: TestCase) {
        run_test_with_client_ids(case.clone(), ["alice"], move |[client]| {
            Box::pin(async move {
                let id = conversation_id();
                client
                    .context
                    .new_conversation(&id, case.credential_type, case.cfg.clone())
                    .await
                    .unwrap();

                let observer = TestEpochObserver::new();
                client
                    .client()
                    .await
                    .register_epoch_observer(observer.clone())
                    .await
                    .unwrap();

                // trigger an epoch
                client
                    .context
                    .conversation(&id)
                    .await
                    .unwrap()
                    .update_key_material()
                    .await
                    .unwrap();

                // ensure we have observed the epoch change
                let observed_epochs = observer.observed_epochs().await;
                assert_eq!(
                    observed_epochs.len(),
                    1,
                    "we triggered exactly one epoch change and so should observe one epoch change"
                );
                assert_eq!(
                    observed_epochs[0].0, id,
                    "conversation id of observed epoch change must match"
                );
            })
        })
        .await
    }

    #[apply(all_cred_cipher)]
    #[wasm_bindgen_test]
    pub async fn observe_remote_epoch_change(case: TestCase) {
        run_test_with_client_ids(case.clone(), ["alice", "bob"], move |[alice, bob]| {
            Box::pin(async move {
                let id = conversation_id();
                alice
                    .context
                    .new_conversation(&id, case.credential_type, case.cfg.clone())
                    .await
                    .unwrap();

                alice.invite_all(&case, &id, [&bob]).await.unwrap();

                //  bob has the observer
                let observer = TestEpochObserver::new();
                bob.client()
                    .await
                    .register_epoch_observer(observer.clone())
                    .await
                    .unwrap();

                // alice triggers an epoch
                alice
                    .context
                    .conversation(&id)
                    .await
                    .unwrap()
                    .update_key_material()
                    .await
                    .unwrap();

                // communicate that to bob
                let commit = alice.mls_transport.latest_commit().await;
                bob.context
                    .conversation(&id)
                    .await
                    .unwrap()
                    .decrypt_message(commit.to_bytes().unwrap())
                    .await
                    .unwrap();

                // ensure we have observed the epoch change
                let observed_epochs = observer.observed_epochs().await;
                assert_eq!(
                    observed_epochs.len(),
                    1,
                    "we triggered exactly one epoch change and so should observe one epoch change"
                );
                assert_eq!(
                    observed_epochs[0].0, id,
                    "conversation id of observed epoch change must match"
                );
            })
        })
        .await
    }
}