feat(code/test): Dynamic validator set

code/examples/channel/src/app.rs

@@ -33,7 +33,7 @@ pub async fn run(state: &mut State, channels: &mut Channels<TestContext>) -> eyr
                 sleep(Duration::from_millis(200)).await;
 
                 if reply
-                    .send((start_height, state.get_validator_set().clone()))
+                    .send((start_height, state.get_validator_set(start_height).clone()))
                     .is_err()
                 {
                     error!("Failed to send ConsensusReady reply");
@@ -171,8 +171,11 @@ pub async fn run(state: &mut State, channels: &mut Channels<TestContext>) -> eyr
             //
             // In our case, our validator set stays constant between heights so we can
             // send back the validator set found in our genesis state.
-            AppMsg::GetValidatorSet { height: _, reply } => {
-                if reply.send(Some(state.get_validator_set().clone())).is_err() {
+            AppMsg::GetValidatorSet { height, reply } => {
+                if reply
+                    .send(Some(state.get_validator_set(height).clone()))
+                    .is_err()
+                {
                     error!("Failed to send GetValidatorSet reply");
                 }
             }
@@ -201,7 +204,7 @@ pub async fn run(state: &mut State, channels: &mut Channels<TestContext>) -> eyr
                         if reply
                             .send(ConsensusMsg::StartHeight(
                                 state.current_height,
-                                state.get_validator_set().clone(),
+                                state.get_validator_set(state.current_height).clone(),
                             ))
                             .is_err()
                         {
@@ -214,7 +217,7 @@ pub async fn run(state: &mut State, channels: &mut Channels<TestContext>) -> eyr
                         if reply
                             .send(ConsensusMsg::RestartHeight(
                                 state.current_height,
-                                state.get_validator_set().clone(),
+                                state.get_validator_set(state.current_height).clone(),
                             ))
                             .is_err()
                         {

code/examples/channel/src/state.rs

@@ -401,9 +401,27 @@ impl State {
         parts
     }
 
-    /// Returns the set of validators.
-    pub fn get_validator_set(&self) -> &ValidatorSet {
-        &self.genesis.validator_set
+    /// Returns the validator set for the given height.
+    /// The validator set is rotated based on the height, selecting floor((n+1)/2)
+    /// validators from the genesis validator set.
+    pub fn get_validator_set(&self, height: Height) -> ValidatorSet {
+        let num_validators = self.genesis.validator_set.len();
+        let selection_size = (num_validators + 1) / 2;
+
+        if num_validators <= selection_size {
+            return self.genesis.validator_set.clone();
+        }
+
+        ValidatorSet::new(
+            self.genesis
+                .validator_set
+                .iter()
+                .cycle()
+                .skip(height.as_u64() as usize % num_validators)
+                .take(selection_size)
+                .cloned()
+                .collect::<Vec<_>>(),
+        )
     }
 
     /// Verifies the signature of the proposal.
@@ -436,8 +454,8 @@ impl State {
         };
 
         // Retrieve the the proposer
-        let proposer = self
-            .get_validator_set()
+        let validator_set = self.get_validator_set(self.current_height);
+        let proposer = validator_set
             .get_by_address(&parts.proposer)
             .ok_or(SignatureVerificationError::ProposerNotFound)?;
 

docs/tutorials/channels.md

@@ -513,7 +513,7 @@ fn factor_value(value: Value) -> Vec<u64> {
 
 ```
 
-Then, let's introduce _getter_ methods that are quite self-explanatory:
+Then, let's introduce _getter_ methods that are quite self-explanatory. For the validator set, we select a  rotating subset (floor((n+1)/2)) of the validators from the genesis validator set based on the height. This is done to showcase the ability to change the validator set over time (or height, in this case).
 
 ```rust
 impl State {
@@ -549,9 +549,27 @@ impl State {
         )))
     }
 
-    // Returns the set of validators.
-    pub fn get_validator_set(&self) -> &ValidatorSet {
-        &self.genesis.validator_set
+    /// Returns the validator set for the given height.
+    /// The validator set is rotated based on the height,selecting floor((n+1)/2)
+    /// validators from the genesis validator set.
+    pub fn get_validator_set(&self, height: Height) -> ValidatorSet {
+        let num_validators = self.genesis.validator_set.len();
+        let selection_size = (num_validators + 1) / 2;
+
+        if num_validators <= selection_size {
+            return self.genesis.validator_set.clone();
+        }
+
+        ValidatorSet::new(
+            self.genesis
+                .validator_set
+                .iter()
+                .cycle()
+                .skip(height.as_u64() as usize % num_validators)
+                .take(selection_size)
+                .cloned()
+                .collect::<Vec<_>>(),
+        )
     }
 
     // ...
@@ -785,8 +803,8 @@ impl State {
         };
 
         // Retrieve the the proposer
-        let proposer = self
-            .get_validator_set()
+        let validator_set = self.get_validator_set(self.current_height);
+        let proposer = validator_set
             .get_by_address(&parts.proposer)
             .ok_or(SignatureVerificationError::ProposerNotFound)?;
 
@@ -1097,7 +1115,7 @@ which is either 1 or the next height after the last decided value in the store (
                 sleep(Duration::from_millis(200)).await;
 
                 if reply
-                    .send((start_height, state.get_validator_set().clone()))
+                    .send((start_height, state.get_validator_set(start_height).clone()))
                     .is_err()
                 {
                     error!("Failed to send ConsensusReady reply");
@@ -1310,8 +1328,8 @@ In our case, our validator set stays constant between heights so we can
 send back the validator set found in our genesis state.
 
 ```rust
-            AppMsg::GetValidatorSet { height: _, reply } => {
-                if reply.send(state.get_validator_set().clone()).is_err() {
+            AppMsg::GetValidatorSet { height, reply } => {
+                if reply.send(state.get_validator_set(height).clone()).is_err() {
                     error!("Failed to send GetValidatorSet reply");
                 }
             }
@@ -1391,7 +1409,7 @@ If `commit` fails we can re-run consensus for the same height.
                 if reply
                     .send(ConsensusMsg::StartHeight(
                         state.current_height,
-                        state.get_validator_set().clone(),
+                        state.get_validator_set(state.current_height).clone(),
                     ))
                     .is_err()
                 {
@@ -1404,7 +1422,7 @@ If `commit` fails we can re-run consensus for the same height.
                 if reply
                     .send(ConsensusMsg::RestartHeight(
                         state.current_height,
-                        state.get_validator_set().clone(),
+                        state.get_validator_set(state.current_height).clone(),
                     ))
                     .is_err()
                 {