update trait

crates/hotshot/src/traits/election/randomized_committee.rs

@@ -41,6 +41,8 @@ pub struct RandomizedCommittee<T: NodeType> {
 }
 
 impl<TYPES: NodeType> Membership<TYPES> for RandomizedCommittee<TYPES> {
+    type Error = utils::anytrace::Error;
+
     /// Create a new election
     fn new(
         eligible_leaders: Vec<PeerConfig<<TYPES as NodeType>::SignatureKey>>,
@@ -139,7 +141,7 @@ impl<TYPES: NodeType> Membership<TYPES> for RandomizedCommittee<TYPES> {
     }
 
     /// Index the vector of public keys with the current view number
-    fn leader(
+    fn lookup_leader(
         &self,
         view_number: TYPES::View,
         _epoch: <TYPES as NodeType>::Epoch,

crates/hotshot/src/traits/election/static_committee.rs

@@ -39,6 +39,8 @@ pub struct StaticCommittee<T: NodeType> {
 }
 
 impl<TYPES: NodeType> Membership<TYPES> for StaticCommittee<TYPES> {
+    type Error = utils::anytrace::Error;
+
     /// Create a new election
     fn new(
         eligible_leaders: Vec<PeerConfig<<TYPES as NodeType>::SignatureKey>>,
@@ -137,7 +139,7 @@ impl<TYPES: NodeType> Membership<TYPES> for StaticCommittee<TYPES> {
     }
 
     /// Index the vector of public keys with the current view number
-    fn leader(
+    fn lookup_leader(
         &self,
         view_number: TYPES::View,
         _epoch: <TYPES as NodeType>::Epoch,

crates/hotshot/src/traits/election/static_committee_leader_two_views.rs

@@ -39,6 +39,8 @@ pub struct StaticCommitteeLeaderForTwoViews<T: NodeType> {
 }
 
 impl<TYPES: NodeType> Membership<TYPES> for StaticCommitteeLeaderForTwoViews<TYPES> {
+    type Error = utils::anytrace::Error;
+
     /// Create a new election
     fn new(
         eligible_leaders: Vec<PeerConfig<<TYPES as NodeType>::SignatureKey>>,
@@ -137,7 +139,7 @@ impl<TYPES: NodeType> Membership<TYPES> for StaticCommitteeLeaderForTwoViews<TYP
     }
 
     /// Index the vector of public keys with the current view number
-    fn leader(
+    fn lookup_leader(
         &self,
         view_number: TYPES::View,
         _epoch: <TYPES as NodeType>::Epoch,

crates/types/src/traits/election.rs

@@ -16,6 +16,9 @@ use crate::{traits::signature_key::SignatureKey, PeerConfig};
 pub trait Membership<TYPES: NodeType>:
     Clone + Debug + Eq + PartialEq + Send + Sync + Hash + 'static
 {
+    /// The error type returned by methods like `lookup_leader`.
+    type Error: std::fmt::Display;
+
     /// Create a committee
     fn new(
         // Note: eligible_leaders is currently a hack because the DA leader == the quorum leader
@@ -56,11 +59,30 @@ pub trait Membership<TYPES: NodeType>:
     /// See if a node has stake in the committee in a specific epoch
     fn has_stake(&self, pub_key: &TYPES::SignatureKey, epoch: TYPES::Epoch) -> bool;
 
+    /// The leader of the committee for view `view_number` in `epoch`.
+    ///
+    /// Note: this function uses a HotShot-internal error type.
+    /// You should implement `lookup_leader`, rather than implementing this function directly.
+    ///
+    /// # Errors
+    /// Returns an error if the leader cannot be calculated.
+    fn leader(&self, view: TYPES::View, epoch: TYPES::Epoch) -> Result<TYPES::SignatureKey> {
+        use utils::anytrace::*;
+
+        self.lookup_leader(view, epoch).wrap().context(info!(
+            "Failed to get leader for view {view} in epoch {epoch}"
+        ))
+    }
+
     /// The leader of the committee for view `view_number` in `epoch`.
     ///
     /// # Errors
     /// Returns an error if the leader cannot be calculated
-    fn leader(&self, view: TYPES::View, epoch: TYPES::Epoch) -> Result<TYPES::SignatureKey>;
+    fn lookup_leader(
+        &self,
+        view: TYPES::View,
+        epoch: TYPES::Epoch,
+    ) -> std::result::Result<TYPES::SignatureKey, Self::Error>;
 
     /// Get the network topic for the committee
     fn committee_topic(&self) -> Topic;