chore(code/blocksync): Include synced certificate in decision if one exists, otherwise derive (#598)

* Include synced certificate in decision if one exists, otherwise derive
from seen commits.

* Add `get_certificate` method on `Driver`

---------

Co-authored-by: Romain Ruetschi <[email protected]>

Author: ancazamfir

code/crates/consensus/src/handle/decide.rs

@@ -14,8 +14,8 @@ where
     let proposal_round = proposal.round();
     let value = proposal.value();
 
-    // Restore the commits. Note that they will be removed from `state`
-    let commits = state.restore_precommits(height, proposal_round, value);
+    // We only decide proposals for the current height
+    assert_eq!(height, state.driver.height());
 
     // Clean proposals and values
     state.remove_full_proposals(height);
@@ -46,7 +46,17 @@ where
         }
     }
 
-    let certificate = CommitCertificate::new(height, proposal_round, value.id(), commits);
+    // Look for an existing certificate
+    let certificate = state
+        .driver
+        .get_certificate(proposal_round, value.id())
+        .cloned()
+        .unwrap_or_else(|| {
+            // Restore the commits. Note that they will be removed from `state`
+            let commits = state.restore_precommits(height, proposal_round, value);
+            // TODO: should we verify we have 2/3rd commits?
+            CommitCertificate::new(height, proposal_round, value.id(), commits)
+        });
 
     perform!(co, Effect::Decide { certificate });
 

code/crates/driver/src/driver.rs

@@ -4,7 +4,7 @@ use core::fmt;
 
 use malachite_common::{
     CommitCertificate, Context, Proposal, Round, SignedProposal, SignedVote, Timeout, TimeoutStep,
-    Validator, ValidatorSet, Validity, Vote,
+    Validator, ValidatorSet, Validity, ValueId, Vote,
 };
 use malachite_round::input::Input as RoundInput;
 use malachite_round::output::Output as RoundOutput;
@@ -38,6 +38,9 @@ where
     /// The validator set at the current height
     validator_set: Ctx::ValidatorSet,
 
+    /// The proposer for the current round, None for round nil.
+    proposer: Option<Ctx::Address>,
+
     /// The proposals to decide on.
     pub(crate) proposal_keeper: ProposalKeeper<Ctx>,
 
@@ -50,9 +53,6 @@ where
     /// The state of the round state machine.
     pub(crate) round_state: RoundState<Ctx>,
 
-    /// The proposer for the current round, None for round nil.
-    proposer: Option<Ctx::Address>,
-
     /// The pending inputs to be processed next, if any.
     /// The first element of the tuple is the round at which that input has been emitted.
     pending_inputs: Vec<(Round, RoundInput<Ctx>)>,
@@ -176,6 +176,17 @@ where
         }
     }
 
+    /// Get a commit certificate for the given round and value id.
+    pub fn get_certificate(
+        &self,
+        round: Round,
+        value_id: ValueId<Ctx>,
+    ) -> Option<&CommitCertificate<Ctx>> {
+        self.certificates
+            .iter()
+            .find(|c| c.round == round && c.value_id == value_id)
+    }
+
     /// Process the given input, returning the outputs to be broadcast to the network.
     pub fn process(&mut self, msg: Input<Ctx>) -> Result<Vec<Output<Ctx>>, Error<Ctx>> {
         let round_output = match self.apply(msg)? {

code/crates/driver/src/mux.rs

@@ -119,11 +119,10 @@ where
 
         // We have a valid proposal. Check if there is already a certificate for it.
         // L49
-        if self
-            .certificates
-            .iter()
-            .any(|c| c.value_id == proposal.value().id() && proposal.round() == c.round)
-            && self.round_state.decision.is_none()
+        if self.round_state.decision.is_none()
+            && self
+                .get_certificate(proposal.round(), proposal.value().id())
+                .is_some()
         {
             return Some(RoundInput::ProposalAndPrecommitValue(proposal));
         }
@@ -189,15 +188,18 @@ where
         // Should only receive proposals for our height.
         assert_eq!(self.height(), certificate.height);
 
+        let certificate_round = certificate.round;
+        let certificate_value_id = certificate.value_id.clone();
+
         // Store the certificate
-        self.certificates.push(certificate.clone());
+        self.certificates.push(certificate);
 
         if let Some((signed_proposal, validity)) = self
             .proposal_keeper
-            .get_proposal_and_validity_for_round(certificate.round)
+            .get_proposal_and_validity_for_round(certificate_round)
         {
             let proposal = &signed_proposal.message;
-            if proposal.value().id() == certificate.value_id && validity.is_valid() {
+            if proposal.value().id() == certificate_value_id && validity.is_valid() {
                 return Some(RoundInput::ProposalAndPrecommitValue(proposal.clone()));
             }
         }