Subscribe to altair gossip topics 2 slots before fork (#2532)

## Issue Addressed

N/A

## Proposed Changes

Add a fork_digest to `ForkContext` only if it is set in the config.
Reject gossip messages on post fork topics before the fork happens.

Edit: Instead of rejecting gossip messages on post fork topics, we now subscribe to post fork topics 2 slots before the fork.

Co-authored-by: Age Manning <Age@AgeManning.com>

beacon_node/eth2_libp2p/src/behaviour/mod.rs

@@ -326,6 +326,15 @@ impl<TSpec: EthSpec> Behaviour<TSpec> {
         self.unsubscribe(gossip_topic)
     }
 
+    /// Subscribe to all currently subscribed topics with the new fork digest.
+    pub fn subscribe_new_fork_topics(&mut self, new_fork_digest: [u8; 4]) {
+        let subscriptions = self.network_globals.gossipsub_subscriptions.read().clone();
+        for mut topic in subscriptions.into_iter() {
+            topic.fork_digest = new_fork_digest;
+            self.subscribe(topic);
+        }
+    }
+
     /// Unsubscribe from all topics that doesn't have the given fork_digest
     pub fn unsubscribe_from_fork_topics_except(&mut self, except: [u8; 4]) {
         let subscriptions = self.network_globals.gossipsub_subscriptions.read().clone();

beacon_node/eth2_libp2p/src/rpc/codec/ssz_snappy.rs

@@ -615,7 +615,11 @@ mod tests {
     type Spec = types::MainnetEthSpec;
 
     fn fork_context() -> ForkContext {
-        ForkContext::new::<Spec>(types::Slot::new(0), Hash256::zero(), &Spec::default_spec())
+        let mut chain_spec = Spec::default_spec();
+        // Set fork_epoch to `Some` to ensure that the `ForkContext` object
+        // includes altair in the list of forks
+        chain_spec.altair_fork_epoch = Some(types::Epoch::new(42));
+        ForkContext::new::<Spec>(types::Slot::new(0), Hash256::zero(), &chain_spec)
     }
 
     fn base_block() -> SignedBeaconBlock<Spec> {

beacon_node/eth2_libp2p/tests/common/mod.rs

@@ -11,14 +11,18 @@ use std::sync::Arc;
 use std::sync::Weak;
 use std::time::Duration;
 use tokio::runtime::Runtime;
-use types::{ChainSpec, EnrForkId, ForkContext, Hash256, MinimalEthSpec};
+use types::{ChainSpec, EnrForkId, EthSpec, ForkContext, Hash256, MinimalEthSpec};
 
 type E = MinimalEthSpec;
 use tempfile::Builder as TempBuilder;
 
 /// Returns a dummy fork context
 fn fork_context() -> ForkContext {
-    ForkContext::new::<E>(types::Slot::new(0), Hash256::zero(), &ChainSpec::minimal())
+    let mut chain_spec = E::default_spec();
+    // Set fork_epoch to `Some` to ensure that the `ForkContext` object
+    // includes altair in the list of forks
+    chain_spec.altair_fork_epoch = Some(types::Epoch::new(42));
+    ForkContext::new::<E>(types::Slot::new(0), Hash256::zero(), &chain_spec)
 }
 
 pub struct Libp2pInstance(LibP2PService<E>, exit_future::Signal);

beacon_node/eth2_libp2p/tests/rpc_tests.rs

@@ -138,11 +138,16 @@ fn test_blocks_by_range_chunked_rpc() {
             step: 0,
         });
 
-        // BlocksByRange Response
         let spec = E::default_spec();
-        let empty_block = BeaconBlock::empty(&spec);
-        let empty_signed = SignedBeaconBlock::from_block(empty_block, Signature::empty());
-        let rpc_response = Response::BlocksByRange(Some(Box::new(empty_signed)));
+
+        // BlocksByRange Response
+        let full_block = BeaconBlock::Base(BeaconBlockBase::<E>::full(&spec));
+        let signed_full_block = SignedBeaconBlock::from_block(full_block, Signature::empty());
+        let rpc_response_base = Response::BlocksByRange(Some(Box::new(signed_full_block)));
+
+        let full_block = BeaconBlock::Altair(BeaconBlockAltair::<E>::full(&spec));
+        let signed_full_block = SignedBeaconBlock::from_block(full_block, Signature::empty());
+        let rpc_response_altair = Response::BlocksByRange(Some(Box::new(signed_full_block)));
 
         // keep count of the number of messages received
         let mut messages_received = 0;
@@ -167,7 +172,11 @@ fn test_blocks_by_range_chunked_rpc() {
                         warn!(log, "Sender received a response");
                         match response {
                             Response::BlocksByRange(Some(_)) => {
-                                assert_eq!(response, rpc_response.clone());
+                                if messages_received < 5 {
+                                    assert_eq!(response, rpc_response_base.clone());
+                                } else {
+                                    assert_eq!(response, rpc_response_altair.clone());
+                                }
                                 messages_received += 1;
                                 warn!(log, "Chunk received");
                             }
@@ -197,7 +206,14 @@ fn test_blocks_by_range_chunked_rpc() {
                         if request == rpc_request {
                             // send the response
                             warn!(log, "Receiver got request");
-                            for _ in 1..=messages_to_send {
+                            for i in 0..messages_to_send {
+                                // Send first half of responses as base blocks and
+                                // second half as altair blocks.
+                                let rpc_response = if i < 5 {
+                                    rpc_response_base.clone()
+                                } else {
+                                    rpc_response_altair.clone()
+                                };
                                 receiver.swarm.behaviour_mut().send_successful_response(
                                     peer_id,
                                     id,
@@ -481,7 +497,7 @@ fn test_blocks_by_root_chunked_rpc() {
     let log_level = Level::Debug;
     let enable_logging = false;
 
-    let messages_to_send = 3;
+    let messages_to_send = 10;
 
     let log = common::build_log(log_level, enable_logging);
     let spec = E::default_spec();
@@ -497,6 +513,13 @@ fn test_blocks_by_root_chunked_rpc() {
                 Hash256::from_low_u64_be(0),
                 Hash256::from_low_u64_be(0),
                 Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
+                Hash256::from_low_u64_be(0),
             ]),
         });
 

beacon_node/network/src/service.rs

@@ -25,14 +25,16 @@ use task_executor::ShutdownReason;
 use tokio::sync::mpsc;
 use tokio::time::Sleep;
 use types::{
-    EthSpec, ForkContext, ForkName, RelativeEpoch, SubnetId, SyncCommitteeSubscription,
-    SyncSubnetId, Unsigned, ValidatorSubscription,
+    ChainSpec, EthSpec, ForkContext, ForkName, RelativeEpoch, Slot, SubnetId,
+    SyncCommitteeSubscription, SyncSubnetId, Unsigned, ValidatorSubscription,
 };
 
 mod tests;
 
 /// The interval (in seconds) that various network metrics will update.
 const METRIC_UPDATE_INTERVAL: u64 = 1;
+/// Number of slots before the fork when we should subscribe to the new fork topics.
+const SUBSCRIBE_DELAY_SLOTS: u64 = 2;
 /// Delay after a fork where we unsubscribe from pre-fork topics.
 const UNSUBSCRIBE_DELAY_EPOCHS: u64 = 2;
 
@@ -129,6 +131,8 @@ pub struct NetworkService<T: BeaconChainTypes> {
     discovery_auto_update: bool,
     /// A delay that expires when a new fork takes place.
     next_fork_update: Pin<Box<OptionFuture<Sleep>>>,
+    /// A delay that expires when we need to subscribe to a new fork's topics.
+    next_fork_subscriptions: Pin<Box<OptionFuture<Sleep>>>,
     /// A delay that expires when we need to unsubscribe from old fork topics.
     next_unsubscribe: Pin<Box<OptionFuture<Sleep>>>,
     /// Subscribe to all the subnets once synced.
@@ -179,6 +183,7 @@ impl<T: BeaconChainTypes> NetworkService<T> {
 
         // keep track of when our fork_id needs to be updated
         let next_fork_update = Box::pin(next_fork_delay(&beacon_chain).into());
+        let next_fork_subscriptions = Box::pin(next_fork_subscriptions_delay(&beacon_chain).into());
         let next_unsubscribe = Box::pin(None.into());
 
         let current_slot = beacon_chain
@@ -192,6 +197,8 @@ impl<T: BeaconChainTypes> NetworkService<T> {
             &beacon_chain.spec,
         ));
 
+        debug!(network_log, "Current fork"; "fork_name" => ?fork_context.current_fork());
+
         // launch libp2p service
         let (network_globals, mut libp2p) = LibP2PService::new(
             executor.clone(),
@@ -254,6 +261,7 @@ impl<T: BeaconChainTypes> NetworkService<T> {
             upnp_mappings: (None, None),
             discovery_auto_update: config.discv5_config.enr_update,
             next_fork_update,
+            next_fork_subscriptions,
             next_unsubscribe,
             subscribe_all_subnets: config.subscribe_all_subnets,
             shutdown_after_sync: config.shutdown_after_sync,
@@ -274,12 +282,23 @@ impl<T: BeaconChainTypes> NetworkService<T> {
     /// digests since we should be subscribed to post fork topics before the fork.
     pub fn required_gossip_fork_digests(&self) -> Vec<[u8; 4]> {
         let fork_context = &self.fork_context;
+        let spec = &self.beacon_chain.spec;
         match fork_context.current_fork() {
             ForkName::Base => {
-                if fork_context.fork_exists(ForkName::Altair) {
-                    fork_context.all_fork_digests()
-                } else {
-                    vec![fork_context.genesis_context_bytes()]
+                // If we are SUBSCRIBE_DELAY_SLOTS before the fork slot, subscribe only to Base,
+                // else subscribe to Base and Altair.
+                let current_slot = self.beacon_chain.slot().unwrap_or(spec.genesis_slot);
+                match spec.next_fork_epoch::<T::EthSpec>(current_slot) {
+                    Some((_, fork_epoch)) => {
+                        if current_slot.saturating_add(Slot::new(SUBSCRIBE_DELAY_SLOTS))
+                            >= fork_epoch.start_slot(T::EthSpec::slots_per_epoch())
+                        {
+                            fork_context.all_fork_digests()
+                        } else {
+                            vec![fork_context.genesis_context_bytes()]
+                        }
+                    }
+                    None => vec![fork_context.genesis_context_bytes()],
                 }
             }
             ForkName::Altair => vec![fork_context
@@ -619,6 +638,7 @@ fn spawn_service<T: BeaconChainTypes>(
                             } => {
                                 // Update prometheus metrics.
                                 metrics::expose_receive_metrics(&message);
+
                                 match message {
                                     // attestation information gets processed in the attestation service
                                     PubsubMessage::Attestation(ref subnet_and_attestation) => {
@@ -671,7 +691,7 @@ fn spawn_service<T: BeaconChainTypes>(
                     if let Some(new_fork_name) = fork_context.from_context_bytes(new_enr_fork_id.fork_digest) {
                         info!(
                             service.log,
-                            "Updating enr fork version";
+                            "Transitioned to new fork";
                             "old_fork" => ?fork_context.current_fork(),
                             "new_fork" => ?new_fork_name,
                         );
@@ -701,6 +721,18 @@ fn spawn_service<T: BeaconChainTypes>(
                     info!(service.log, "Unsubscribed from old fork topics");
                     service.next_unsubscribe = Box::pin(None.into());
                 }
+                Some(_) = &mut service.next_fork_subscriptions => {
+                    if let Some((fork_name, _)) = service.beacon_chain.duration_to_next_fork() {
+                        let fork_version = service.beacon_chain.spec.fork_version_for_name(fork_name);
+                        let fork_digest = ChainSpec::compute_fork_digest(fork_version, service.beacon_chain.genesis_validators_root);
+                        info!(service.log, "Subscribing to new fork topics");
+                        service.libp2p.swarm.behaviour_mut().subscribe_new_fork_topics(fork_digest);
+                    }
+                    else {
+                        error!(service.log, "Fork subscription scheduled but no fork scheduled");
+                    }
+                    service.next_fork_subscriptions = Box::pin(next_fork_subscriptions_delay(&service.beacon_chain).into());
+                }
             }
             metrics::update_bandwidth_metrics(service.libp2p.bandwidth.clone());
         }
@@ -717,6 +749,22 @@ fn next_fork_delay<T: BeaconChainTypes>(
         .map(|(_, until_fork)| tokio::time::sleep(until_fork))
 }
 
+/// Returns a `Sleep` that triggers `SUBSCRIBE_DELAY_SLOTS` before the next fork.
+/// Returns `None` if there are no scheduled forks or we are already past `current_slot + SUBSCRIBE_DELAY_SLOTS > fork_slot`.
+fn next_fork_subscriptions_delay<T: BeaconChainTypes>(
+    beacon_chain: &BeaconChain<T>,
+) -> Option<tokio::time::Sleep> {
+    if let Some((_, duration_to_fork)) = beacon_chain.duration_to_next_fork() {
+        let duration_to_subscription = duration_to_fork.saturating_sub(Duration::from_secs(
+            beacon_chain.spec.seconds_per_slot * SUBSCRIBE_DELAY_SLOTS,
+        ));
+        if !duration_to_subscription.is_zero() {
+            return Some(tokio::time::sleep(duration_to_subscription));
+        }
+    }
+    None
+}
+
 impl<T: BeaconChainTypes> Drop for NetworkService<T> {
     fn drop(&mut self) {
         // network thread is terminating

consensus/types/src/chain_spec.rs

@@ -1,7 +1,8 @@
 use crate::*;
 use eth2_serde_utils::quoted_u64::MaybeQuoted;
 use int_to_bytes::int_to_bytes4;
-use serde_derive::{Deserialize, Serialize};
+use serde::{Deserializer, Serialize, Serializer};
+use serde_derive::Deserialize;
 use std::fs::File;
 use std::path::Path;
 use tree_hash::TreeHash;
@@ -467,7 +468,7 @@ impl ChainSpec {
             domain_sync_committee_selection_proof: 8,
             domain_contribution_and_proof: 9,
             altair_fork_version: [0x01, 0x00, 0x00, 0x00],
-            altair_fork_epoch: Some(Epoch::new(u64::MAX)),
+            altair_fork_epoch: None,
 
             /*
              * Network specific
@@ -506,7 +507,7 @@ impl ChainSpec {
             // Altair
             epochs_per_sync_committee_period: Epoch::new(8),
             altair_fork_version: [0x01, 0x00, 0x00, 0x01],
-            altair_fork_epoch: Some(Epoch::new(u64::MAX)),
+            altair_fork_epoch: None,
             // Other
             network_id: 2, // lighthouse testnet network id
             deposit_chain_id: 5,
@@ -544,7 +545,9 @@ pub struct Config {
 
     #[serde(with = "eth2_serde_utils::bytes_4_hex")]
     altair_fork_version: [u8; 4],
-    altair_fork_epoch: Option<MaybeQuoted<Epoch>>,
+    #[serde(serialize_with = "serialize_fork_epoch")]
+    #[serde(deserialize_with = "deserialize_fork_epoch")]
+    pub altair_fork_epoch: Option<MaybeQuoted<Epoch>>,
 
     #[serde(with = "eth2_serde_utils::quoted_u64")]
     seconds_per_slot: u64,
@@ -582,6 +585,35 @@ impl Default for Config {
     }
 }
 
+/// Util function to serialize a `None` fork epoch value
+/// as `Epoch::max_value()`.
+fn serialize_fork_epoch<S>(val: &Option<MaybeQuoted<Epoch>>, s: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    match val {
+        None => MaybeQuoted {
+            value: Epoch::max_value(),
+        }
+        .serialize(s),
+        Some(epoch) => epoch.serialize(s),
+    }
+}
+
+/// Util function to deserialize a u64::max() fork epoch as `None`.
+fn deserialize_fork_epoch<'de, D>(deserializer: D) -> Result<Option<MaybeQuoted<Epoch>>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let decoded: Option<MaybeQuoted<Epoch>> = serde::de::Deserialize::deserialize(deserializer)?;
+    if let Some(fork_epoch) = decoded {
+        if fork_epoch.value != Epoch::max_value() {
+            return Ok(Some(fork_epoch));
+        }
+    }
+    Ok(None)
+}
+
 impl Config {
     /// Maps `self` to an identifier for an `EthSpec` instance.
     ///
@@ -606,7 +638,7 @@ impl Config {
             altair_fork_version: spec.altair_fork_version,
             altair_fork_epoch: spec
                 .altair_fork_epoch
-                .map(|slot| MaybeQuoted { value: slot }),
+                .map(|epoch| MaybeQuoted { value: epoch }),
 
             seconds_per_slot: spec.seconds_per_slot,
             seconds_per_eth1_block: spec.seconds_per_eth1_block,

consensus/types/src/fork_context.rs

@@ -26,12 +26,13 @@ impl ForkContext {
             ChainSpec::compute_fork_digest(spec.genesis_fork_version, genesis_validators_root),
         )];
 
-        // Only add Altair to list of forks if it's enabled (i.e. spec.altair_fork_epoch != None)
+        // Only add Altair to list of forks if it's enabled
+        // Note: `altair_fork_epoch == None` implies altair hasn't been activated yet on the config.
         if spec.altair_fork_epoch.is_some() {
             fork_to_digest.push((
                 ForkName::Altair,
                 ChainSpec::compute_fork_digest(spec.altair_fork_version, genesis_validators_root),
-            ))
+            ));
         }
 
         let fork_to_digest: HashMap<ForkName, [u8; 4]> = fork_to_digest.into_iter().collect();