[consensus] Restore marshal ancestor stream symmetry

consensus/src/lib.rs

@@ -237,7 +237,7 @@ stability_scope!(ALPHA {
 });
 stability_scope!(ALPHA, cfg(not(target_arch = "wasm32")) {
     use commonware_cryptography::certificate::Scheme;
-    use futures::Stream;
+    use crate::marshal::ancestry::Ancestry;
     use commonware_runtime::{Clock, Metrics, Spawner};
     use rand::Rng;
 
@@ -272,7 +272,7 @@ stability_scope!(ALPHA, cfg(not(target_arch = "wasm32")) {
         fn propose(
             &mut self,
             context: (E, Self::Context),
-            ancestry: impl Stream<Item = Self::Block> + Send,
+            ancestry: impl Ancestry<Self::Block>,
         ) -> impl Future<Output = Option<Self::Block>> + Send;
 
         /// Verify a block produced by the application's proposer, relative to its ancestry.
@@ -287,7 +287,7 @@ stability_scope!(ALPHA, cfg(not(target_arch = "wasm32")) {
         fn verify(
             &mut self,
             context: (E, Self::Context),
-            ancestry: impl Stream<Item = Self::Block> + Send,
+            ancestry: impl Ancestry<Self::Block>,
         ) -> impl Future<Output = bool> + Send;
     }
 });

consensus/src/marshal/ancestry.rs

@@ -13,45 +13,37 @@ use std::{
     task::{Context, Poll},
 };
 
-/// An interface for providing blocks.
+/// A stream of blocks used by application propose and verify calls.
+pub trait Ancestry<B: Block>: Stream<Item = B> + Send + Unpin + 'static {}
+
+impl<T, B> Ancestry<B> for T
+where
+    T: Stream<Item = B> + Send + Unpin + 'static,
+    B: Block,
+{
+}
+
+/// An interface for providing parent blocks.
 pub trait BlockProvider: Clone + Send + 'static {
     /// The block type the provider walks.
     type Block: Block;
 
-    /// Subscribe to a block by its digest without requesting it from the network.
+    /// Subscribe to the parent of a known block.
     ///
-    /// If the block is found available locally, the block will be returned immediately.
+    /// If the parent is found available locally, the parent will be returned immediately.
     ///
-    /// If the block is not available locally, the subscription will be registered and the caller
-    /// will be notified when the block is available. If the block is not finalized, it's possible
+    /// If the parent is not available locally, the subscription will be registered and the caller
+    /// will be notified when the parent is available. If the parent is not finalized, it's possible
     /// that it may never become available.
     ///
     /// Returns `None` when the subscription is canceled or the provider can no longer deliver
-    /// the block.
+    /// the parent.
     ///
-    /// This is intentionally narrower than [`Self::subscribe_parent`]. A digest is enough to
-    /// identify a block in local storage, but it may not be enough to form the network request
-    /// used by a marshal variant. Variants whose consensus commitment contains extra context
-    /// should keep that logic in [`Self::subscribe_parent`], where the known child block is
-    /// still available.
-    fn subscribe(
-        self,
-        digest: <Self::Block as Digestible>::Digest,
-    ) -> impl Future<Output = Option<Self::Block>> + Send;
-
-    /// Subscribe to the parent of a known block.
-    ///
-    /// This is a separate hook from [`Self::subscribe`] because the child block can carry
-    /// variant-specific context needed to retrieve its parent. The default implementation
-    /// follows the digest link and waits locally, but providers may override this to derive a
-    /// full parent commitment and issue a fetching subscription.
+    /// The child block can carry variant-specific context needed to retrieve its parent.
     fn subscribe_parent(
         self,
         block: Self::Block,
-    ) -> impl Future<Output = Option<Self::Block>> + Send {
-        let digest = block.parent();
-        self.subscribe(digest)
-    }
+    ) -> impl Future<Output = Option<Self::Block>> + Send;
 }
 
 /// Yields the ancestors of a block while prefetching parents, _not_ including the genesis block.
@@ -114,9 +106,9 @@ where
         // If a result has been buffered, return it and queue the parent fetch if needed.
         if let Some(block) = this.buffered.pop() {
             let height = block.height();
-            let should_subscribe_parent = height > END_BOUND;
+            let should_walk_parent = height > END_BOUND;
             let end_of_buffered = this.buffered.is_empty();
-            if should_subscribe_parent && end_of_buffered {
+            if should_walk_parent && end_of_buffered {
                 let future = this.marshal.clone().subscribe_parent(block.clone()).boxed();
                 *this.pending.as_mut() = Some(future).into();
 
@@ -131,7 +123,7 @@ where
                     }
                     Poll::Ready(None) | Poll::Pending => {}
                 }
-            } else if !should_subscribe_parent {
+            } else if !should_walk_parent {
                 // No more parents to fetch; Finish the stream.
                 *this.pending.as_mut() = None.into();
             }
@@ -147,8 +139,8 @@ where
             }
             Poll::Ready(Some(Some(block))) => {
                 let height = block.height();
-                let should_subscribe_parent = height > END_BOUND;
-                if should_subscribe_parent {
+                let should_walk_parent = height > END_BOUND;
+                if should_walk_parent {
                     let future = this.marshal.clone().subscribe_parent(block.clone()).boxed();
                     *this.pending.as_mut() = Some(future).into();
 
@@ -187,8 +179,9 @@ mod test {
     impl BlockProvider for MockProvider {
         type Block = Block<Sha256Digest, ()>;
 
-        async fn subscribe(self, digest: Sha256Digest) -> Option<Self::Block> {
-            self.0.into_iter().find(|b| b.digest() == digest)
+        async fn subscribe_parent(self, block: Self::Block) -> Option<Self::Block> {
+            let parent = block.parent;
+            self.0.into_iter().find(|b| b.digest() == parent)
         }
     }
 

consensus/src/marshal/coding/mod.rs

@@ -65,6 +65,7 @@ pub use marshaled::{Marshaled, MarshaledConfig};
 mod tests {
     use crate::{
         marshal::{
+            ancestry::BlockProvider,
             coding::{
                 marshaled::genesis_coding_commitment,
                 shards,
@@ -103,7 +104,7 @@ mod tests {
     use commonware_parallel::Sequential;
     use commonware_resolver::{Delivery, Fetch, Resolver};
     use commonware_runtime::{
-        buffer::paged::CacheRef, deterministic, Clock, Metrics, Runner, Supervisor as _,
+        buffer::paged::CacheRef, deterministic, Clock, Metrics, Runner, Spawner, Supervisor as _,
     };
     use commonware_storage::archive::immutable;
     use commonware_utils::{
@@ -115,16 +116,27 @@ mod tests {
     type TestCodedBlock = CodedBlock<CodingB, ReedSolomon<Sha256>, Sha256>;
     type CodingSendRecord = (Round, TestCodedBlock, Recipients<K>);
 
+    #[test]
+    fn mailbox_provides_application_blocks() {
+        fn assert_provider<P: BlockProvider<Block = CodingB>>() {}
+        assert_provider::<core::Mailbox<S, TestCodingVariant>>();
+    }
+
     /// A coding buffer that records subscriptions and never resolves them.
     #[derive(Clone, Default)]
     struct RecordingCodingBuffer {
-        subscriptions: Arc<Mutex<Vec<oneshot::Sender<TestCodedBlock>>>>,
+        digest_subscriptions: Arc<Mutex<Vec<oneshot::Sender<TestCodedBlock>>>>,
+        commitment_subscriptions: Arc<Mutex<Vec<oneshot::Sender<TestCodedBlock>>>>,
         sends: Arc<Mutex<Vec<CodingSendRecord>>>,
     }
 
     impl RecordingCodingBuffer {
         fn subscription_count(&self) -> usize {
-            self.subscriptions.lock().len()
+            self.digest_subscriptions.lock().len() + self.commitment_subscriptions.lock().len()
+        }
+
+        fn commitment_subscription_count(&self) -> usize {
+            self.commitment_subscriptions.lock().len()
         }
     }
 
@@ -141,7 +153,7 @@ mod tests {
 
         fn subscribe_by_digest(&self, _digest: D) -> oneshot::Receiver<TestCodedBlock> {
             let (sender, receiver) = oneshot::channel();
-            self.subscriptions.lock().push(sender);
+            self.digest_subscriptions.lock().push(sender);
             receiver
         }
 
@@ -150,7 +162,7 @@ mod tests {
             _commitment: Commitment,
         ) -> oneshot::Receiver<TestCodedBlock> {
             let (sender, receiver) = oneshot::channel();
-            self.subscriptions.lock().push(sender);
+            self.commitment_subscriptions.lock().push(sender);
             receiver
         }
 
@@ -452,6 +464,46 @@ mod tests {
         (candidate_ctx, coded_candidate)
     }
 
+    #[test_traced("WARN")]
+    fn test_coding_block_provider_parent_fetches_by_commitment() {
+        let runner = deterministic::Runner::timed(Duration::from_secs(30));
+        runner.start(|mut context| async move {
+            let Fixture {
+                participants,
+                schemes,
+                ..
+            } = bls12381_threshold_vrf::fixture::<V, _>(&mut context, NAMESPACE, NUM_VALIDATORS);
+            let provider = ConstantProvider::new(schemes[0].clone());
+            let buffer = RecordingCodingBuffer::default();
+            let (marshal, _resolver, _actor_handle) = start_coding_actor_with_recording(
+                context.child("actor_stack"),
+                "coding-provider-parent-commitment",
+                provider,
+                buffer.clone(),
+            )
+            .await;
+
+            let (parent_ctx, parent) = missing_candidate(participants[0].clone());
+            let child_ctx = CodingCtx {
+                round: Round::new(Epoch::zero(), View::new(2)),
+                leader: participants[0].clone(),
+                parent: (parent_ctx.round.view(), parent.commitment()),
+            };
+            let child = make_coding_block(child_ctx, parent.digest(), Height::new(2), 200);
+            let subscription = context
+                .child("subscribe")
+                .spawn(move |_| BlockProvider::subscribe_parent(marshal, child));
+
+            context.sleep(Duration::from_millis(100)).await;
+            assert_eq!(
+                buffer.commitment_subscription_count(),
+                1,
+                "parent walkback should use the coding parent commitment"
+            );
+            drop(subscription);
+        });
+    }
+
     #[test_traced("WARN")]
     fn test_coding_verify_missing_candidate_waits_without_fetching() {
         let runner = deterministic::Runner::timed(Duration::from_secs(30));

consensus/src/marshal/coding/variant.rs

@@ -1,18 +1,19 @@
 use crate::{
     marshal::{
+        ancestry::BlockProvider,
         coding::{
             shards,
             types::{CodedBlock, CodedBlockCfg, StoredCodedBlock},
         },
-        core::{Buffer, Variant},
+        core::{Buffer, CommitmentFallback, Mailbox, Variant},
     },
     simplex::types::Context,
     types::{coding::Commitment, Round},
     CertifiableBlock,
 };
 use commonware_codec::Read;
 use commonware_coding::Scheme as CodingScheme;
-use commonware_cryptography::{Committable, Digestible, Hasher, PublicKey};
+use commonware_cryptography::{certificate::Scheme, Committable, Digestible, Hasher, PublicKey};
 use commonware_p2p::Recipients;
 use commonware_utils::channel::oneshot;
 
@@ -113,3 +114,28 @@ where
         self.proposed(round, block);
     }
 }
+
+impl<S, B, C, H, P> BlockProvider for Mailbox<S, Coding<B, C, H, P>>
+where
+    S: Scheme,
+    B: CertifiableBlock<Context = Context<Commitment, P>>,
+    C: CodingScheme,
+    H: Hasher,
+    P: PublicKey,
+{
+    type Block = B;
+
+    async fn subscribe_parent(self, block: Self::Block) -> Option<Self::Block> {
+        let parent_height = block.height().previous()?;
+        let commitment = block.context().parent.1;
+        self.subscribe_by_commitment(
+            commitment,
+            CommitmentFallback::FetchByCommitment {
+                height: parent_height,
+            },
+        )
+        .await
+        .ok()
+        .map(<Coding<B, C, H, P> as Variant>::into_inner)
+    }
+}

consensus/src/marshal/core/mailbox.rs

@@ -6,7 +6,7 @@ use crate::{
     },
     simplex::types::{Activity, Finalization, Notarization},
     types::{Height, Round},
-    Heightable, Reporter,
+    Reporter,
 };
 use commonware_actor::{
     mailbox::{Overflow, Policy, Sender},
@@ -15,7 +15,7 @@ use commonware_actor::{
 use commonware_cryptography::{certificate::Scheme, Digestible};
 use commonware_p2p::Recipients;
 use commonware_utils::{channel::oneshot, vec::NonEmptyVec};
-use futures::{Stream, StreamExt};
+use futures::Stream;
 use std::collections::{btree_map::Entry, BTreeMap, VecDeque};
 
 /// Messages sent to the marshal [Actor](super::Actor).
@@ -514,12 +514,6 @@ pub struct Mailbox<S: Scheme, V: Variant> {
     sender: Sender<Message<S, V>>,
 }
 
-/// Provider used by [`Mailbox::ancestor_stream`] to fetch missing certified parents.
-#[derive(Clone)]
-pub(crate) struct AncestryProvider<S: Scheme, V: Variant> {
-    mailbox: Mailbox<S, V>,
-}
-
 impl<S: Scheme, V: Variant> Mailbox<S, V> {
     /// Creates a new mailbox.
     pub(crate) const fn new(sender: Sender<Message<S, V>>) -> Self {
@@ -540,15 +534,10 @@ impl<S: Scheme, V: Variant> Mailbox<S, V> {
         initial: I,
     ) -> impl Stream<Item = V::ApplicationBlock> + Send + use<S, V, I>
     where
+        Self: BlockProvider<Block = V::ApplicationBlock>,
         I: IntoIterator<Item = V::Block>,
     {
-        AncestorStream::new(
-            AncestryProvider {
-                mailbox: self.clone(),
-            },
-            initial,
-        )
-        .map(V::into_inner)
+        AncestorStream::new(self.clone(), initial.into_iter().map(V::into_inner))
     }
 
     /// A request to retrieve the information about the highest finalized block.
@@ -690,7 +679,10 @@ impl<S: Scheme, V: Variant> Mailbox<S, V> {
     pub async fn ancestry(
         &self,
         (fallback, start_digest): (DigestFallback, <V::Block as Digestible>::Digest),
-    ) -> Option<impl Stream<Item = V::ApplicationBlock> + Send + use<S, V>> {
+    ) -> Option<impl Stream<Item = V::ApplicationBlock> + Send + use<S, V>>
+    where
+        Self: BlockProvider<Block = V::ApplicationBlock>,
+    {
         let receiver = self.subscribe_by_digest(start_digest, fallback);
         receiver
             .await
@@ -786,31 +778,6 @@ impl<S: Scheme, V: Variant> Mailbox<S, V> {
     }
 }
 
-impl<S: Scheme, V: Variant> BlockProvider for AncestryProvider<S, V> {
-    type Block = V::Block;
-
-    async fn subscribe(self, digest: <V::Block as Digestible>::Digest) -> Option<Self::Block> {
-        let subscription = self
-            .mailbox
-            .subscribe_by_digest(digest, DigestFallback::Wait);
-        subscription.await.ok()
-    }
-
-    async fn subscribe_parent(self, block: Self::Block) -> Option<Self::Block> {
-        // Ancestry walking does not carry the certified parent round. By this
-        // point the stream is walking accepted ancestry, so this height should
-        // be correct; it remains a local pruning bound rather than a peer
-        // response validity condition.
-        let parent_height = block.height().previous()?;
-        let commitment = V::parent_commitment(&block);
-        let fallback = CommitmentFallback::FetchByCommitment {
-            height: parent_height,
-        };
-        let subscription = self.mailbox.subscribe_by_commitment(commitment, fallback);
-        subscription.await.ok()
-    }
-}
-
 impl<S: Scheme, V: Variant> Reporter for Mailbox<S, V> {
     type Activity = Activity<S, V::Commitment>;