Validation round number oracle (#3175)

## Motivation

For most uses of permissionless rounds (#3162), applications need to
have access to the round number, at least in multi-leader rounds.

## Proposal

Expose the round number in which the block is being validated to the
contract.

This is only `Some` in multi-leader rounds.

## Test Plan

An example application using this will be added in a separate PR.

## Release Plan

- Nothing to do / These changes follow the usual release cycle.

## Links

- Closes #3164.
- Closes #3162.
- [reviewer
checklist](https://github.com/linera-io/linera-protocol/blob/main/CONTRIBUTING.md#reviewer-checklist)

linera-base/src/data_types.rs

@@ -603,6 +603,14 @@ impl Round {
         matches!(self, Round::MultiLeader(_))
     }
 
+    /// Returns the round number if this is a multi-leader round, `None` otherwise.
+    pub fn multi_leader(&self) -> Option<u32> {
+        match self {
+            Round::MultiLeader(number) => Some(*number),
+            _ => None,
+        }
+    }
+
     /// Whether the round is the fast round.
     pub fn is_fast(&self) -> bool {
         matches!(self, Round::Fast)
@@ -763,6 +771,8 @@ pub enum OracleResponse {
     Blob(BlobId),
     /// An assertion oracle that passed.
     Assert,
+    /// The block's validation round.
+    Round(Option<u32>),
 }
 
 impl Display for OracleResponse {
@@ -774,6 +784,8 @@ impl Display for OracleResponse {
             OracleResponse::Post(bytes) => write!(f, "Post:{}", STANDARD_NO_PAD.encode(bytes))?,
             OracleResponse::Blob(blob_id) => write!(f, "Blob:{}", blob_id)?,
             OracleResponse::Assert => write!(f, "Assert")?,
+            OracleResponse::Round(Some(round)) => write!(f, "Round:{round}")?,
+            OracleResponse::Round(None) => write!(f, "Round:None")?,
         };
 
         Ok(())

linera-chain/src/chain.rs

@@ -666,6 +666,7 @@ where
         &mut self,
         block: &ProposedBlock,
         local_time: Timestamp,
+        round: Option<u32>,
         replaying_oracle_responses: Option<Vec<Vec<OracleResponse>>>,
     ) -> Result<BlockExecutionOutcome, ChainError> {
         #[cfg(with_metrics)]
@@ -785,6 +786,7 @@ where
                             posted_message,
                             incoming_bundle,
                             block,
+                            round,
                             txn_index,
                             local_time,
                             &mut txn_tracker,
@@ -803,6 +805,7 @@ where
                         chain_id,
                         height: block.height,
                         index: Some(txn_index),
+                        round,
                         authenticated_signer: block.authenticated_signer,
                         authenticated_caller_id: None,
                     };
@@ -935,6 +938,7 @@ where
         posted_message: &PostedMessage,
         incoming_bundle: &IncomingBundle,
         block: &ProposedBlock,
+        round: Option<u32>,
         txn_index: u32,
         local_time: Timestamp,
         txn_tracker: &mut TransactionTracker,
@@ -946,6 +950,7 @@ where
             chain_id: block.chain_id,
             is_bouncing: posted_message.is_bouncing(),
             height: block.height,
+            round,
             certificate_hash: incoming_bundle.bundle.certificate_hash,
             message_id,
             authenticated_signer: posted_message.authenticated_signer,

linera-chain/src/unit_tests/chain_tests.rs

@@ -160,7 +160,7 @@ async fn test_block_size_limit() {
             recipient: Recipient::root(0),
             amount: Amount::ONE,
         });
-    let result = chain.execute_block(&invalid_block, time, None).await;
+    let result = chain.execute_block(&invalid_block, time, None, None).await;
     assert_matches!(
         result,
         Err(ChainError::ExecutionError(
@@ -170,7 +170,10 @@ async fn test_block_size_limit() {
     );
 
     // The valid block is accepted...
-    let outcome = chain.execute_block(&valid_block, time, None).await.unwrap();
+    let outcome = chain
+        .execute_block(&valid_block, time, None, None)
+        .await
+        .unwrap();
     let block = Block::new(valid_block, outcome);
 
     // ...because its size is exactly at the allowed limit.
@@ -231,7 +234,7 @@ async fn test_application_permissions() -> anyhow::Result<()> {
     let invalid_block = make_first_block(chain_id)
         .with_incoming_bundle(bundle.clone())
         .with_simple_transfer(chain_id, Amount::ONE);
-    let result = chain.execute_block(&invalid_block, time, None).await;
+    let result = chain.execute_block(&invalid_block, time, None, None).await;
     assert_matches!(result, Err(ChainError::AuthorizedApplications(app_ids))
         if app_ids == vec![application_id]
     );
@@ -247,7 +250,7 @@ async fn test_application_permissions() -> anyhow::Result<()> {
         .with_incoming_bundle(bundle)
         .with_operation(app_operation.clone());
     let executed_block = chain
-        .execute_block(&valid_block, time, None)
+        .execute_block(&valid_block, time, None, None)
         .await?
         .with(valid_block);
     let value = Hashed::new(ConfirmedBlock::new(executed_block));
@@ -256,14 +259,14 @@ async fn test_application_permissions() -> anyhow::Result<()> {
     let invalid_block = make_child_block(&value.clone())
         .with_simple_transfer(chain_id, Amount::ONE)
         .with_operation(app_operation.clone());
-    let result = chain.execute_block(&invalid_block, time, None).await;
+    let result = chain.execute_block(&invalid_block, time, None, None).await;
     assert_matches!(result, Err(ChainError::AuthorizedApplications(app_ids))
         if app_ids == vec![application_id]
     );
 
     // Also, blocks without an application operation or incoming message are forbidden.
     let invalid_block = make_child_block(&value.clone());
-    let result = chain.execute_block(&invalid_block, time, None).await;
+    let result = chain.execute_block(&invalid_block, time, None, None).await;
     assert_matches!(result, Err(ChainError::MissingMandatoryApplications(app_ids))
         if app_ids == vec![application_id]
     );
@@ -272,7 +275,7 @@ async fn test_application_permissions() -> anyhow::Result<()> {
     application.expect_call(ExpectedCall::execute_operation(|_, _, _| Ok(vec![])));
     application.expect_call(ExpectedCall::default_finalize());
     let valid_block = make_child_block(&value).with_operation(app_operation);
-    chain.execute_block(&valid_block, time, None).await?;
+    chain.execute_block(&valid_block, time, None, None).await?;
 
     Ok(())
 }

linera-client/src/client_context.rs

@@ -972,11 +972,12 @@ where
     pub async fn stage_block_execution(
         &self,
         block: ProposedBlock,
+        round: Option<u32>,
     ) -> Result<ExecutedBlock, Error> {
         Ok(self
             .client
             .local_node()
-            .stage_block_execution(block)
+            .stage_block_execution(block, round)
             .await?
             .0)
     }

linera-core/src/chain_worker/actor.rs

@@ -85,6 +85,7 @@ where
     /// Execute a block but discard any changes to the chain state.
     StageBlockExecution {
         block: ProposedBlock,
+        round: Option<u32>,
         #[debug(skip)]
         callback: oneshot::Sender<Result<(ExecutedBlock, ChainInfoResponse), WorkerError>>,
     },
@@ -286,8 +287,12 @@ where
                 } => callback
                     .send(self.worker.describe_application(application_id).await)
                     .is_ok(),
-                ChainWorkerRequest::StageBlockExecution { block, callback } => callback
-                    .send(self.worker.stage_block_execution(block).await)
+                ChainWorkerRequest::StageBlockExecution {
+                    block,
+                    round,
+                    callback,
+                } => callback
+                    .send(self.worker.stage_block_execution(block, round).await)
                     .is_ok(),
                 ChainWorkerRequest::ProcessTimeout {
                     certificate,

linera-core/src/chain_worker/state/attempted_changes.rs

@@ -359,6 +359,7 @@ where
         let verified_outcome = Box::pin(self.state.chain.execute_block(
             &executed_block.block,
             local_time,
+            None,
             Some(executed_block.outcome.oracle_responses.clone()),
         ))
         .await?;

linera-core/src/chain_worker/state/mod.rs

@@ -179,10 +179,11 @@ where
     pub(super) async fn stage_block_execution(
         &mut self,
         block: ProposedBlock,
+        round: Option<u32>,
     ) -> Result<(ExecutedBlock, ChainInfoResponse), WorkerError> {
         ChainWorkerStateWithTemporaryChanges::new(self)
             .await
-            .stage_block_execution(block)
+            .stage_block_execution(block, round)
             .await
     }
 

linera-core/src/chain_worker/state/temporary_changes.rs

@@ -126,14 +126,15 @@ where
     /// Executes a block without persisting any changes to the state.
     pub(super) async fn stage_block_execution(
         &mut self,
-        proposal: ProposedBlock,
+        block: ProposedBlock,
+        round: Option<u32>,
     ) -> Result<(ExecutedBlock, ChainInfoResponse), WorkerError> {
         let local_time = self.0.storage.clock().current_time();
-        let signer = proposal.authenticated_signer;
+        let signer = block.authenticated_signer;
 
-        let executed_block = Box::pin(self.0.chain.execute_block(&proposal, local_time, None))
+        let executed_block = Box::pin(self.0.chain.execute_block(&block, local_time, round, None))
             .await?
-            .with(proposal);
+            .with(block);
 
         let mut response = ChainInfoResponse::new(&self.0.chain, None);
         if let Some(signer) = signer {
@@ -238,7 +239,12 @@ where
         let outcome = if let Some(outcome) = outcome {
             outcome.clone()
         } else {
-            Box::pin(self.0.chain.execute_block(block, local_time, None)).await?
+            Box::pin(
+                self.0
+                    .chain
+                    .execute_block(block, local_time, round.multi_leader(), None),
+            )
+            .await?
         };
 
         let executed_block = outcome.with(block.clone());

linera-core/src/client/mod.rs

@@ -1903,9 +1903,10 @@ where
     async fn stage_block_execution_and_discard_failing_messages(
         &self,
         mut block: ProposedBlock,
+        round: Option<u32>,
     ) -> Result<(ExecutedBlock, ChainInfoResponse), ChainClientError> {
         loop {
-            let result = self.stage_block_execution(block.clone()).await;
+            let result = self.stage_block_execution(block.clone(), round).await;
             if let Err(ChainClientError::LocalNodeError(LocalNodeError::WorkerError(
                 WorkerError::ChainError(chain_error),
             ))) = &result
@@ -1944,12 +1945,13 @@ where
     async fn stage_block_execution(
         &self,
         block: ProposedBlock,
+        round: Option<u32>,
     ) -> Result<(ExecutedBlock, ChainInfoResponse), ChainClientError> {
         loop {
             let result = self
                 .client
                 .local_node
-                .stage_block_execution(block.clone())
+                .stage_block_execution(block.clone(), round)
                 .await;
             if let Err(LocalNodeError::BlobsNotFound(blob_ids)) = &result {
                 self.receive_certificates_for_blobs(blob_ids.clone())
@@ -2122,8 +2124,18 @@ where
         };
         // Make sure every incoming message succeeds and otherwise remove them.
         // Also, compute the final certified hash while we're at it.
+
+        let info = self.chain_info().await?;
+        // Use the round number assuming there are oracle responses.
+        // Using the round number during execution counts as an oracle.
+        // Accessing the round number in single-leader rounds where we are not the leader
+        // is not currently supported.
+        let round = match Self::round_for_new_proposal(&info, &identity, &block, true)? {
+            Either::Left(round) => round.multi_leader(),
+            Either::Right(_) => None,
+        };
         let (executed_block, _) = self
-            .stage_block_execution_and_discard_failing_messages(block)
+            .stage_block_execution_and_discard_failing_messages(block, round)
             .await?;
         let blobs = self
             .read_local_blobs(executed_block.required_blob_ids())
@@ -2270,7 +2282,7 @@ where
             timestamp,
         };
         match self
-            .stage_block_execution_and_discard_failing_messages(block)
+            .stage_block_execution_and_discard_failing_messages(block, None)
             .await
         {
             Ok((_, response)) => Ok((
@@ -2424,6 +2436,7 @@ where
         {
             return self.finalize_locking_block(info).await;
         }
+        let identity = self.identity().await?;
 
         // Otherwise we have to re-propose the highest validated block, if there is one.
         let pending: Option<ProposedBlock> = self.state().pending_proposal().clone();
@@ -2432,18 +2445,28 @@ where
                 LockingBlock::Regular(certificate) => certificate.block().clone().into(),
                 LockingBlock::Fast(proposal) => {
                     let block = proposal.content.block.clone();
-                    self.stage_block_execution(block).await?.0
+                    self.stage_block_execution(block, None).await?.0
                 }
             }
         } else if let Some(block) = pending {
             // Otherwise we are free to propose our own pending block.
-            self.stage_block_execution(block).await?.0
+            // Use the round number assuming there are oracle responses.
+            // Using the round number during execution counts as an oracle.
+            let round = match Self::round_for_new_proposal(&info, &identity, &block, true)? {
+                Either::Left(round) => round.multi_leader(),
+                Either::Right(_) => None,
+            };
+            self.stage_block_execution(block, round).await?.0
         } else {
             return Ok(ClientOutcome::Committed(None)); // Nothing to do.
         };
 
-        let identity = self.identity().await?;
-        let round = match Self::round_for_new_proposal(&info, &identity, &executed_block)? {
+        let round = match Self::round_for_new_proposal(
+            &info,
+            &identity,
+            &executed_block.block,
+            executed_block.outcome.has_oracle_responses(),
+        )? {
             Either::Left(round) => round,
             Either::Right(timeout) => return Ok(ClientOutcome::WaitForTimeout(timeout)),
         };
@@ -2546,17 +2569,16 @@ where
     fn round_for_new_proposal(
         info: &ChainInfo,
         identity: &Owner,
-        executed_block: &ExecutedBlock,
+        block: &ProposedBlock,
+        has_oracle_responses: bool,
     ) -> Result<Either<Round, RoundTimeout>, ChainClientError> {
         let manager = &info.manager;
-        let block = &executed_block.block;
         // If there is a conflicting proposal in the current round, we can only propose if the
         // next round can be started without a timeout, i.e. if we are in a multi-leader round.
         // Similarly, we cannot propose a block that uses oracles in the fast round.
         let conflict = manager.requested_proposed.as_ref().is_some_and(|proposal| {
             proposal.content.round == manager.current_round && proposal.content.block != *block
-        }) || (manager.current_round.is_fast()
-            && executed_block.outcome.has_oracle_responses());
+        }) || (manager.current_round.is_fast() && has_oracle_responses);
         let round = if !conflict {
             manager.current_round
         } else if let Some(round) = manager

linera-core/src/local_node.rs

@@ -174,8 +174,9 @@ where
     pub async fn stage_block_execution(
         &self,
         block: ProposedBlock,
+        round: Option<u32>,
     ) -> Result<(ExecutedBlock, ChainInfoResponse), LocalNodeError> {
-        Ok(self.node.state.stage_block_execution(block).await?)
+        Ok(self.node.state.stage_block_execution(block, round).await?)
     }
 
     /// Reads blobs from storage.

linera-core/src/unit_tests/wasm_worker_tests.rs

@@ -273,6 +273,7 @@ where
         authenticated_signer: None,
         authenticated_caller_id: None,
         height: run_block.height,
+        round: Some(0),
         index: Some(0),
     };
     let mut controller = ResourceController::default();