BFT-463: Change LeaderSelectionMode::Sticky to allow multiple keys

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

@@ -28,7 +28,7 @@ message LeaderSelectionMode {
   }
   message RoundRobin{}
   message Sticky{
-    optional PublicKey key = 1; // required
+    repeated PublicKey keys = 1; // required
   }
   message Weighted{}
 }

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

@@ -459,8 +459,13 @@ impl ProtoFmt for LeaderSelectionMode {
                 Ok(LeaderSelectionMode::RoundRobin)
             }
             proto::leader_selection_mode::Mode::Sticky(inner) => {
-                let key = required(&inner.key).context("key")?;
-                Ok(LeaderSelectionMode::Sticky(PublicKey::read(key)?))
+                let _ = required(&inner.keys.first()).context("key")?;
+                let pks = inner
+                    .keys
+                    .iter()
+                    .map(PublicKey::read)
+                    .collect::<Result<Vec<_>, _>>()?;
+                Ok(LeaderSelectionMode::Sticky(pks))
             }
             proto::leader_selection_mode::Mode::Weighted(_) => Ok(LeaderSelectionMode::Weighted),
         }
@@ -472,10 +477,10 @@ impl ProtoFmt for LeaderSelectionMode {
                     proto::leader_selection_mode::RoundRobin {},
                 )),
             },
-            LeaderSelectionMode::Sticky(pk) => proto::LeaderSelectionMode {
+            LeaderSelectionMode::Sticky(pks) => proto::LeaderSelectionMode {
                 mode: Some(proto::leader_selection_mode::Mode::Sticky(
                     proto::leader_selection_mode::Sticky {
-                        key: Some(pk.build()),
+                        keys: pks.iter().map(|pk| pk.build()).collect(),
                     },
                 )),
             },

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

@@ -59,8 +59,8 @@ pub enum LeaderSelectionMode {
     /// Select in a round-robin fashion, based on validators' index within the set.
     RoundRobin,
 
-    /// Select based on a sticky assignment to a specific validator.
-    Sticky(validator::PublicKey),
+    /// Select based on a sticky assignment to a non-empty list of specific validators.
+    Sticky(Vec<validator::PublicKey>),
 
     /// Select pseudo-randomly, based on validators' weights.
     Weighted,
@@ -174,8 +174,9 @@ impl Committee {
                 }
                 unreachable!()
             }
-            LeaderSelectionMode::Sticky(pk) => {
-                let index = self.index(pk).unwrap();
+            LeaderSelectionMode::Sticky(pks) => {
+                let index = view_number.0 as usize % pks.len();
+                let index = self.index(&pks[index]).unwrap();
                 self.get(index).unwrap().key.clone()
             }
         }
@@ -309,9 +310,13 @@ impl fmt::Debug for Genesis {
 impl Genesis {
     /// Verifies correctness.
     pub fn verify(&self) -> anyhow::Result<()> {
-        if let LeaderSelectionMode::Sticky(pk) = &self.leader_selection {
-            if self.validators.index(pk).is_none() {
-                anyhow::bail!("leader_selection sticky mode public key is not in committee");
+        if let LeaderSelectionMode::Sticky(pks) = &self.leader_selection {
+            for pk in pks {
+                if self.validators.index(pk).is_none() {
+                    anyhow::bail!(
+                        "leader_selection sticky mode public key is not in committee: {pk:?}"
+                    );
+                }
             }
         }
 

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

@@ -92,14 +92,21 @@ fn test_sticky() {
     let ctx = ctx::test_root(&ctx::RealClock);
     let rng = &mut ctx.rng();
     let committee = validator_committee();
-    let want = committee
-        .get(rng.gen_range(0..committee.len()))
-        .unwrap()
-        .key
-        .clone();
+    let mut want = Vec::new();
+    for _ in 0..3 {
+        want.push(
+            committee
+                .get(rng.gen_range(0..committee.len()))
+                .unwrap()
+                .key
+                .clone(),
+        );
+    }
     let sticky = LeaderSelectionMode::Sticky(want.clone());
     for _ in 0..100 {
-        assert_eq!(want, committee.view_leader(rng.gen(), &sticky));
+        let vn: ViewNumber = rng.gen();
+        let pk = &want[vn.0 as usize % want.len()];
+        assert_eq!(*pk, committee.view_leader(vn, &sticky));
     }
 }
 
@@ -203,7 +210,7 @@ mod version1 {
     fn genesis_verify_leader_pubkey_not_in_committee() {
         let mut rng = StdRng::seed_from_u64(29483920);
         let mut genesis = rng.gen::<GenesisRaw>();
-        genesis.leader_selection = LeaderSelectionMode::Sticky(rng.gen());
+        genesis.leader_selection = LeaderSelectionMode::Sticky(vec![rng.gen()]);
         let genesis = genesis.with_hash();
         assert!(genesis.verify().is_err())
     }

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

@@ -269,7 +269,10 @@ impl Distribution<LeaderSelectionMode> for Standard {
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> LeaderSelectionMode {
         match rng.gen_range(0..=2) {
             0 => LeaderSelectionMode::RoundRobin,
-            1 => LeaderSelectionMode::Sticky(rng.gen()),
+            1 => LeaderSelectionMode::Sticky({
+                let n = rng.gen_range(1..=3);
+                rng.sample_iter(Standard).take(n).collect()
+            }),
             _ => LeaderSelectionMode::Weighted,
         }
     }

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

@@ -104,7 +104,7 @@ fn test_genesis_verify() {
     assert!(Genesis::read(&genesis.build()).is_ok());
 
     let mut genesis = (*genesis).clone();
-    genesis.leader_selection = LeaderSelectionMode::Sticky(rng.gen());
+    genesis.leader_selection = LeaderSelectionMode::Sticky(vec![rng.gen()]);
     let genesis = genesis.with_hash();
     assert!(genesis.verify().is_err());
     assert!(Genesis::read(&genesis.build()).is_err())

node/tools/src/tests.rs

@@ -11,10 +11,14 @@ impl Distribution<AppConfig> for EncodeDist {
     fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> AppConfig {
         let mut genesis: validator::GenesisRaw = rng.gen();
         // In order for the genesis to be valid, the sticky leader needs to be in the validator committee.
-        if let LeaderSelectionMode::Sticky(_) = genesis.leader_selection {
-            let i = rng.gen_range(0..genesis.validators.len());
-            genesis.leader_selection =
-                LeaderSelectionMode::Sticky(genesis.validators.get(i).unwrap().key.clone());
+        if let LeaderSelectionMode::Sticky(pks) = genesis.leader_selection {
+            let n = pks.len();
+            let i = rng.gen_range(0..genesis.committee.len());
+            let mut pks = Vec::new();
+            for _ in 0..n {
+                pks.push(genesis.validators.get(i).unwrap().key.clone());
+            }
+            genesis.leader_selection = LeaderSelectionMode::Sticky(pks);
         }
         AppConfig {
             server_addr: self.sample(rng),