feat: skip empty blocks

crates/engine/src/driver.rs

@@ -53,6 +53,8 @@ pub struct EngineDriver<EC, CS, P> {
     metrics: EngineDriverMetrics,
     /// The waker to notify when the engine driver should be polled.
     waker: AtomicWaker,
+    /// Whether to allow empty blocks.
+    allow_empty_blocks: bool,
 }
 
 impl<EC, CS, P> EngineDriver<EC, CS, P>
@@ -69,6 +71,7 @@ where
         fcs: ForkchoiceState,
         sync_at_start_up: bool,
         block_building_duration: Duration,
+        allow_empty_blocks: bool,
     ) -> Self {
         Self {
             client,
@@ -85,6 +88,7 @@ where
             engine_future: None,
             metrics: EngineDriverMetrics::default(),
             waker: AtomicWaker::new(),
+            allow_empty_blocks,
         }
     }
 
@@ -312,6 +316,12 @@ where
 
                 match result {
                     Ok(block) => {
+                        // Skip block if no transactions are present in block.
+                        if !self.allow_empty_blocks && block.body.transactions.is_empty() {
+                            tracing::trace!(target: "scroll::engine", "no transactions in block");
+                            return None;
+                        }
+
                         // Update the unsafe block info and return the block
                         let block_info = BlockInfo::new(block.number, block.hash_slow());
                         tracing::trace!(target: "scroll::engine", ?block_info, "updating unsafe block info from new payload");
@@ -531,8 +541,15 @@ mod tests {
             ForkchoiceState::from_block_info(BlockInfo { number: 0, hash: Default::default() });
         let duration = Duration::from_secs(2);
 
-        let mut driver =
-            EngineDriver::new(client, chain_spec, None::<ScrollRootProvider>, fcs, false, duration);
+        let mut driver = EngineDriver::new(
+            client,
+            chain_spec,
+            None::<ScrollRootProvider>,
+            fcs,
+            false,
+            duration,
+            true,
+        );
 
         // Initially, it should be false
         assert!(!driver.is_payload_building_in_progress());
@@ -559,6 +576,7 @@ mod tests {
             fcs,
             false,
             duration,
+            true,
         );
 
         // Initially, it should be false

crates/node/src/args.rs

@@ -79,6 +79,9 @@ pub struct ScrollRollupNodeConfig {
     /// The gas price oracle args
     #[command(flatten)]
     pub gas_price_oracle_args: GasPriceOracleArgs,
+    /// Enable empty blocks
+    #[arg(long)]
+    pub allow_empty_blocks: bool,
 }
 
 impl ScrollRollupNodeConfig {
@@ -261,6 +264,7 @@ impl ScrollRollupNodeConfig {
             fcs,
             self.engine_driver_args.sync_at_startup && !self.test && !chain_spec.is_dev_chain(),
             Duration::from_millis(self.sequencer_args.payload_building_duration),
+            self.allow_empty_blocks,
         );
 
         // Create the consensus.
@@ -711,6 +715,7 @@ mod tests {
                 algorithm: ConsensusAlgorithm::SystemContract,
                 authorized_signer: None,
             },
+            allow_empty_blocks: true,
         };
 
         let result = config.validate();
@@ -741,6 +746,7 @@ mod tests {
                 algorithm: ConsensusAlgorithm::SystemContract,
                 authorized_signer: None,
             },
+            allow_empty_blocks: true,
         };
 
         let result = config.validate();
@@ -766,6 +772,7 @@ mod tests {
             network_args: NetworkArgs::default(),
             gas_price_oracle_args: GasPriceOracleArgs::default(),
             consensus_args: ConsensusArgs::noop(),
+            allow_empty_blocks: true,
         };
 
         assert!(config.validate().is_ok());
@@ -789,6 +796,7 @@ mod tests {
             network_args: NetworkArgs::default(),
             gas_price_oracle_args: GasPriceOracleArgs::default(),
             consensus_args: ConsensusArgs::noop(),
+            allow_empty_blocks: true,
         };
 
         assert!(config.validate().is_ok());
@@ -808,6 +816,7 @@ mod tests {
             network_args: NetworkArgs::default(),
             gas_price_oracle_args: GasPriceOracleArgs::default(),
             consensus_args: ConsensusArgs::noop(),
+            allow_empty_blocks: true,
         };
 
         assert!(config.validate().is_ok());

crates/node/src/test_utils.rs

@@ -157,6 +157,7 @@ pub fn default_test_scroll_rollup_node_config() -> ScrollRollupNodeConfig {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     }
 }
 
@@ -193,5 +194,6 @@ pub fn default_sequencer_test_scroll_rollup_node_config() -> ScrollRollupNodeCon
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     }
 }

crates/node/tests/e2e.rs

@@ -73,6 +73,7 @@ async fn can_bridge_l1_messages() -> eyre::Result<()> {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
     let (mut nodes, _tasks, _wallet) = setup_engine(node_args, 1, chain_spec, false, false).await?;
     let node = nodes.pop().unwrap();
@@ -168,6 +169,7 @@ async fn can_sequence_and_gossip_blocks() {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     let (nodes, _tasks, wallet) =
@@ -266,6 +268,7 @@ async fn can_penalize_peer_for_invalid_block() {
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
         chain_orchestrator_args: ChainOrchestratorArgs::default(),
+        allow_empty_blocks: true,
     };
 
     let (nodes, _tasks, _) =

crates/node/tests/sync.rs

@@ -68,6 +68,7 @@ async fn test_should_consolidate_to_block_15k() -> eyre::Result<()> {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     let chain_spec = (*SCROLL_SEPOLIA).clone();
@@ -204,6 +205,7 @@ async fn test_should_consolidate_after_optimistic_sync() -> eyre::Result<()> {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     // Create the chain spec for scroll dev with Feynman activated and a test genesis.
@@ -451,6 +453,7 @@ async fn test_consolidation() -> eyre::Result<()> {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     // Create the chain spec for scroll dev with Feynman activated and a test genesis.
@@ -623,6 +626,7 @@ async fn test_chain_orchestrator_shallow_reorg_with_gap() -> eyre::Result<()> {
         signer_args: Default::default(),
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     // Create the chain spec for scroll dev with Feynman activated and a test genesis.

crates/sequencer/tests/e2e.rs

@@ -37,6 +37,61 @@ use tokio::{
     time::{Duration, Instant},
 };
 
+#[tokio::test]
+async fn skip_block_with_no_transactions() {
+    reth_tracing::init_test_tracing();
+
+    const BLOCK_BUILDING_DURATION: Duration = Duration::from_millis(0);
+
+    // setup a test node
+    let (mut nodes, _tasks, _wallet) = setup(1, false).await.unwrap();
+    let node = nodes.pop().unwrap();
+
+    // create a forkchoice state
+    let genesis_hash = node.inner.chain_spec().genesis_hash();
+    let fcs = ForkchoiceState::new(
+        BlockInfo { hash: genesis_hash, number: 0 },
+        Default::default(),
+        Default::default(),
+    );
+
+    // create the engine driver connected to the node
+    let auth_client = node.inner.engine_http_client();
+    let engine_client = ScrollAuthApiEngineClient::new(auth_client);
+    let mut engine_driver = EngineDriver::new(
+        Arc::new(engine_client),
+        (*SCROLL_DEV).clone(),
+        None::<ScrollRootProvider>,
+        fcs,
+        false,
+        BLOCK_BUILDING_DURATION,
+        false,
+    );
+
+    // create a test database
+    let database = Arc::new(setup_test_db().await);
+    let provider = Arc::new(DatabaseL1MessageProvider::new(database.clone(), 0));
+
+    // create a sequencer
+    let mut sequencer = Sequencer::new(
+        provider,
+        Default::default(),
+        SCROLL_GAS_LIMIT,
+        4,
+        1,
+        L1MessageInclusionMode::BlockDepth(0),
+    );
+
+    // send a new payload attributes request.
+    sequencer.build_payload_attributes();
+    let payload_attributes = sequencer.next().await.unwrap();
+    engine_driver.handle_build_new_payload(payload_attributes);
+
+    // assert that no new payload event is emitted
+    let res = tokio::time::timeout(Duration::from_secs(1), engine_driver.next()).await;
+    assert!(res.is_err(), "expected no new payload, but a block was built: {:?}", res.ok());
+}
+
 #[tokio::test]
 async fn can_build_blocks() {
     reth_tracing::init_test_tracing();
@@ -66,6 +121,7 @@ async fn can_build_blocks() {
         fcs,
         false,
         BLOCK_BUILDING_DURATION,
+        true,
     );
 
     // create a test database
@@ -192,6 +248,7 @@ async fn can_build_blocks_with_delayed_l1_messages() {
         fcs,
         false,
         BLOCK_BUILDING_DURATION,
+        true,
     );
 
     // create a test database
@@ -317,6 +374,7 @@ async fn can_build_blocks_with_finalized_l1_messages() {
         fcs,
         false,
         BLOCK_BUILDING_DURATION,
+        true,
     );
 
     // create a test database
@@ -460,6 +518,7 @@ async fn can_sequence_blocks_with_private_key_file() -> eyre::Result<()> {
         },
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     let (nodes, _tasks, wallet) =
@@ -551,6 +610,7 @@ async fn can_sequence_blocks_with_hex_key_file_without_prefix() -> eyre::Result<
         },
         gas_price_oracle_args: GasPriceOracleArgs::default(),
         consensus_args: ConsensusArgs::noop(),
+        allow_empty_blocks: true,
     };
 
     let (nodes, _tasks, wallet) =
@@ -658,6 +718,7 @@ async fn can_build_blocks_and_exit_at_gas_limit() {
         fcs,
         false,
         BLOCK_BUILDING_DURATION,
+        true,
     );
 
     // issue a new payload to the execution layer.
@@ -743,6 +804,7 @@ async fn can_build_blocks_and_exit_at_time_limit() {
         fcs,
         false,
         BLOCK_BUILDING_DURATION,
+        true,
     );
 
     // start timer.
@@ -809,6 +871,7 @@ async fn should_limit_l1_message_cumulative_gas() {
         fcs,
         false,
         BLOCK_BUILDING_DURATION,
+        true,
     );
 
     // create a test database