Compute recent lightclient updates (#4969)

* Compute recent lightclient updates

* Review PR

* Merge remote-tracking branch 'upstream/unstable' into lc-prod-recent-updates

* Review PR

* consistent naming

* add metrics

* revert dropping reprocessing queue

* Update light client optimistic update re-processing logic. (#7)

* Add light client server simulator tests. Co-authored by @dapplion.

* Merge branch 'unstable' into fork/dapplion/lc-prod-recent-updates

* Fix lint

* Enable light client server in simulator test.

* Fix test for light client optimistic updates and finality updates.

testing/simulator/src/checks.rs

@@ -1,5 +1,5 @@
 use crate::local_network::LocalNetwork;
-use node_test_rig::eth2::types::{BlockId, StateId};
+use node_test_rig::eth2::types::{BlockId, FinalityCheckpointsData, StateId};
 use std::time::Duration;
 use types::{Epoch, EthSpec, ExecPayload, ExecutionBlockHash, Hash256, Slot, Unsigned};
 
@@ -243,3 +243,93 @@ pub async fn verify_transition_block_finalized<E: EthSpec>(
         ))
     }
 }
+
+pub(crate) async fn verify_light_client_updates<E: EthSpec>(
+    network: LocalNetwork<E>,
+    start_slot: Slot,
+    end_slot: Slot,
+    slot_duration: Duration,
+) -> Result<(), String> {
+    slot_delay(start_slot, slot_duration).await;
+
+    // Tolerance of 2 slot allows for 1 single missed slot.
+    let light_client_update_slot_tolerance = Slot::new(2);
+    let remote_nodes = network.remote_nodes()?;
+    let client = remote_nodes.first().unwrap();
+    let mut have_seen_block = false;
+    let mut have_achieved_finality = false;
+
+    for slot in start_slot.as_u64()..=end_slot.as_u64() {
+        slot_delay(Slot::new(1), slot_duration).await;
+        let slot = Slot::new(slot);
+        let previous_slot = slot - 1;
+
+        let previous_slot_block = client
+            .get_beacon_blocks::<E>(BlockId::Slot(previous_slot))
+            .await
+            .map_err(|e| {
+                format!("Unable to get beacon block for previous slot {previous_slot:?}: {e:?}")
+            })?;
+        let previous_slot_has_block = previous_slot_block.is_some();
+
+        if !have_seen_block {
+            // Make sure we have seen the first block in Altair, to make sure we have sync aggregates available.
+            if previous_slot_has_block {
+                have_seen_block = true;
+            }
+            // Wait for another slot before we check the first update to avoid race condition.
+            continue;
+        }
+
+        // Make sure previous slot has a block, otherwise skip checking for the signature slot distance
+        if !previous_slot_has_block {
+            continue;
+        }
+
+        // Verify light client optimistic update. `signature_slot_distance` should be 1 in the ideal scenario.
+        let signature_slot = client
+            .get_beacon_light_client_optimistic_update::<E>()
+            .await
+            .map_err(|e| format!("Error while getting light client updates: {:?}", e))?
+            .ok_or(format!("Light client optimistic update not found {slot:?}"))?
+            .data
+            .signature_slot;
+        let signature_slot_distance = slot - signature_slot;
+        if signature_slot_distance > light_client_update_slot_tolerance {
+            return Err(format!("Existing optimistic update too old: signature slot {signature_slot}, current slot {slot:?}"));
+        }
+
+        // Verify light client finality update. `signature_slot_distance` should be 1 in the ideal scenario.
+        // NOTE: Currently finality updates are produced as long as the finalized block is known, even if the finalized header
+        // sync committee period does not match the signature slot committee period.
+        // TODO: This complies with the current spec, but we should check if this is a bug.
+        if !have_achieved_finality {
+            let FinalityCheckpointsData { finalized, .. } = client
+                .get_beacon_states_finality_checkpoints(StateId::Head)
+                .await
+                .map_err(|e| format!("Unable to get beacon state finality checkpoint: {e:?}"))?
+                .ok_or("Unable to get head state".to_string())?
+                .data;
+            if !finalized.root.is_zero() {
+                // Wait for another slot before we check the first finality update to avoid race condition.
+                have_achieved_finality = true;
+            }
+            continue;
+        }
+        let signature_slot = client
+            .get_beacon_light_client_finality_update::<E>()
+            .await
+            .map_err(|e| format!("Error while getting light client updates: {:?}", e))?
+            .ok_or(format!("Light client finality update not found {slot:?}"))?
+            .data
+            .signature_slot;
+        let signature_slot_distance = slot - signature_slot;
+        if signature_slot_distance > light_client_update_slot_tolerance {
+            return Err(format!(
+                "Existing finality update too old: signature slot {signature_slot}, current slot {slot:?}"
+            ));
+        }
+    }
+
+    Ok(())
+}

testing/simulator/src/eth1_sim.rs

@@ -220,6 +220,7 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
             fork,
             sync_aggregate,
             transition,
+            light_client_update,
         ) = futures::join!(
             // Check that the chain finalizes at the first given opportunity.
             checks::verify_first_finalization(network.clone(), slot_duration),
@@ -272,6 +273,13 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
                 Epoch::new(TERMINAL_BLOCK / MinimalEthSpec::slots_per_epoch()),
                 slot_duration,
                 post_merge_sim
+            ),
+            checks::verify_light_client_updates(
+                network.clone(),
+                // Sync aggregate available from slot 1 after Altair fork transition.
+                Epoch::new(ALTAIR_FORK_EPOCH).start_slot(MinimalEthSpec::slots_per_epoch()) + 1,
+                Epoch::new(END_EPOCH).start_slot(MinimalEthSpec::slots_per_epoch()),
+                slot_duration
             )
         );
 
@@ -282,6 +290,7 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
         fork?;
         sync_aggregate?;
         transition?;
+        light_client_update?;
 
         // The `final_future` either completes immediately or never completes, depending on the value
         // of `continue_after_checks`.
@@ -380,6 +389,9 @@ async fn create_local_network<E: EthSpec>(
     beacon_config.network.target_peers = node_count + proposer_nodes - 1;
 
     beacon_config.network.enr_address = (Some(Ipv4Addr::LOCALHOST), None);
+    beacon_config.network.enable_light_client_server = true;
+    beacon_config.chain.enable_light_client_server = true;
+    beacon_config.http_api.enable_light_client_server = true;
 
     if post_merge_sim {
         let el_config = execution_layer::Config {