BFT-463: Add LeaderSelectionMode::Rota

node/libs/roles/src/proto/validator.proto

@@ -25,12 +25,16 @@ message LeaderSelectionMode {
     RoundRobin round_robin = 1;
     Sticky sticky = 2;
     Weighted weighted = 3;
+    Rota rota = 4;
   }
   message RoundRobin{}
   message Sticky{
     optional PublicKey key = 1; // required
   }
   message Weighted{}
+  message Rota {
+    repeated PublicKey keys = 1; // required
+  }
 }
 
 

node/libs/roles/src/validator/conv.rs

@@ -463,6 +463,15 @@ impl ProtoFmt for LeaderSelectionMode {
                 Ok(LeaderSelectionMode::Sticky(PublicKey::read(key)?))
             }
             proto::leader_selection_mode::Mode::Weighted(_) => Ok(LeaderSelectionMode::Weighted),
+            proto::leader_selection_mode::Mode::Rota(inner) => {
+                let _ = required(&inner.keys.first()).context("keys")?;
+                let pks = inner
+                    .keys
+                    .iter()
+                    .map(PublicKey::read)
+                    .collect::<Result<Vec<_>, _>>()?;
+                Ok(LeaderSelectionMode::Rota(pks))
+            }
         }
     }
     fn build(&self) -> Self::Proto {
@@ -484,6 +493,13 @@ impl ProtoFmt for LeaderSelectionMode {
                     proto::leader_selection_mode::Weighted {},
                 )),
             },
+            LeaderSelectionMode::Rota(pks) => proto::LeaderSelectionMode {
+                mode: Some(proto::leader_selection_mode::Mode::Rota(
+                    proto::leader_selection_mode::Rota {
+                        keys: pks.iter().map(|pk| pk.build()).collect(),
+                    },
+                )),
+            },
         }
     }
 }

node/libs/roles/src/validator/messages/consensus.rs

@@ -64,6 +64,9 @@ pub enum LeaderSelectionMode {
 
     /// Select pseudo-randomly, based on validators' weights.
     Weighted,
+
+    /// Select on a rotation of specific validator keys.
+    Rota(Vec<validator::PublicKey>),
 }
 
 /// Calculates the pseudo-random eligibility of a leader based on the input and total weight.
@@ -178,6 +181,11 @@ impl Committee {
                 let index = self.index(pk).unwrap();
                 self.get(index).unwrap().key.clone()
             }
+            LeaderSelectionMode::Rota(pks) => {
+                let index = view_number.0 as usize % pks.len();
+                let index = self.index(&pks[index]).unwrap();
+                self.get(index).unwrap().key.clone()
+            }
         }
     }
 
@@ -313,6 +321,14 @@ impl Genesis {
             if self.validators.index(pk).is_none() {
                 anyhow::bail!("leader_selection sticky mode public key is not in committee");
             }
+        } else if let LeaderSelectionMode::Rota(pks) = &self.leader_selection {
+            for pk in pks {
+                if self.validators.index(pk).is_none() {
+                    anyhow::bail!(
+                        "leader_selection rota mode public key is not in committee: {pk:?}"
+                    );
+                }
+            }
         }
 
         Ok(())

node/libs/roles/src/validator/messages/tests.rs

@@ -103,6 +103,29 @@ fn test_sticky() {
     }
 }
 
+#[test]
+fn test_rota() {
+    let ctx = ctx::test_root(&ctx::RealClock);
+    let rng = &mut ctx.rng();
+    let committee = validator_committee();
+    let mut want = Vec::new();
+    for _ in 0..3 {
+        want.push(
+            committee
+                .get(rng.gen_range(0..committee.len()))
+                .unwrap()
+                .key
+                .clone(),
+        );
+    }
+    let rota = LeaderSelectionMode::Rota(want.clone());
+    for _ in 0..100 {
+        let vn: ViewNumber = rng.gen();
+        let pk = &want[vn.0 as usize % want.len()];
+        assert_eq!(*pk, committee.view_leader(vn, &rota));
+    }
+}
+
 /// Hardcoded view numbers.
 fn views() -> impl Iterator<Item = ViewNumber> {
     [8394532, 2297897, 9089304, 7203483, 9982111]

node/libs/roles/src/validator/testonly.rs

@@ -267,9 +267,13 @@ impl Distribution<GenesisHash> for Standard {
 
 impl Distribution<LeaderSelectionMode> for Standard {
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> LeaderSelectionMode {
-        match rng.gen_range(0..=2) {
+        match rng.gen_range(0..=3) {
             0 => LeaderSelectionMode::RoundRobin,
             1 => LeaderSelectionMode::Sticky(rng.gen()),
+            3 => LeaderSelectionMode::Rota({
+                let n = rng.gen_range(1..=3);
+                rng.sample_iter(Standard).take(n).collect()
+            }),
             _ => LeaderSelectionMode::Weighted,
         }
     }

node/tools/src/tests.rs

@@ -15,6 +15,14 @@ impl Distribution<AppConfig> for EncodeDist {
             let i = rng.gen_range(0..genesis.validators.len());
             genesis.leader_selection =
                 LeaderSelectionMode::Sticky(genesis.validators.get(i).unwrap().key.clone());
+        } else if let LeaderSelectionMode::Rota(pks) = genesis.leader_selection {
+            let n = pks.len();
+            let i = rng.gen_range(0..genesis.validators.len());
+            let mut pks = Vec::new();
+            for _ in 0..n {
+                pks.push(genesis.validators.get(i).unwrap().key.clone());
+            }
+            genesis.leader_selection = LeaderSelectionMode::Rota(pks);
         }
         AppConfig {
             server_addr: self.sample(rng),