Adding light_client gossip topics (#3693)

## Issue Addressed
Implementing the light_client_gossip topics but I'm not there yet.

Which issue # does this PR address?
Partially #3651

## Proposed Changes
Add light client gossip topics.
Please list or describe the changes introduced by this PR.
I'm going to Implement light_client_finality_update and light_client_optimistic_update gossip topics. Currently I've attempted the former and I'm seeking feedback.

## Additional Info
I've only implemented the light_client_finality_update topic because I wanted to make sure I was on the correct path. Also checking that the gossiped LightClientFinalityUpdate is the same as the locally constructed one is not implemented because caching the updates will make this much easier. Could someone give me some feedback on this please? 

Please provide any additional information. For example, future considerations
or information useful for reviewers.

Co-authored-by: GeemoCandama <104614073+GeemoCandama@users.noreply.github.com>

consensus/types/src/lib.rs

@@ -51,6 +51,7 @@ pub mod graffiti;
 pub mod historical_batch;
 pub mod indexed_attestation;
 pub mod light_client_bootstrap;
+pub mod light_client_finality_update;
 pub mod light_client_optimistic_update;
 pub mod light_client_update;
 pub mod pending_attestation;
@@ -136,6 +137,8 @@ pub use crate::free_attestation::FreeAttestation;
 pub use crate::graffiti::{Graffiti, GRAFFITI_BYTES_LEN};
 pub use crate::historical_batch::HistoricalBatch;
 pub use crate::indexed_attestation::IndexedAttestation;
+pub use crate::light_client_finality_update::LightClientFinalityUpdate;
+pub use crate::light_client_optimistic_update::LightClientOptimisticUpdate;
 pub use crate::participation_flags::ParticipationFlags;
 pub use crate::participation_list::ParticipationList;
 pub use crate::payload::{BlindedPayload, BlockType, ExecPayload, FullPayload};

consensus/types/src/light_client_finality_update.rs

@@ -1,10 +1,10 @@
-use super::{BeaconBlockHeader, EthSpec, FixedVector, Hash256, Slot, SyncAggregate, SyncCommittee};
-use crate::{light_client_update::*, test_utils::TestRandom, BeaconBlock, BeaconState, ChainSpec};
-use safe_arith::ArithError;
+use super::{
+    BeaconBlockHeader, EthSpec, FixedVector, Hash256, SignedBeaconBlock, SignedBlindedBeaconBlock,
+    Slot, SyncAggregate,
+};
+use crate::{light_client_update::*, test_utils::TestRandom, BeaconState, ChainSpec};
 use serde_derive::{Deserialize, Serialize};
 use ssz_derive::{Decode, Encode};
-use ssz_types::typenum::{U5, U6};
-use std::sync::Arc;
 use test_random_derive::TestRandom;
 use tree_hash::TreeHash;
 
@@ -28,43 +28,38 @@ pub struct LightClientFinalityUpdate<T: EthSpec> {
 
 impl<T: EthSpec> LightClientFinalityUpdate<T> {
     pub fn new(
-        chain_spec: ChainSpec,
-        beacon_state: BeaconState<T>,
-        block: BeaconBlock<T>,
+        chain_spec: &ChainSpec,
+        beacon_state: &BeaconState<T>,
+        block: &SignedBeaconBlock<T>,
         attested_state: &mut BeaconState<T>,
-        finalized_block: BeaconBlock<T>,
+        finalized_block: &SignedBlindedBeaconBlock<T>,
     ) -> Result<Self, Error> {
         let altair_fork_epoch = chain_spec
             .altair_fork_epoch
             .ok_or(Error::AltairForkNotActive)?;
-        if attested_state.slot().epoch(T::slots_per_epoch()) < altair_fork_epoch {
+        if beacon_state.slot().epoch(T::slots_per_epoch()) < altair_fork_epoch {
             return Err(Error::AltairForkNotActive);
         }
 
-        let sync_aggregate = block.body().sync_aggregate()?;
+        let sync_aggregate = block.message().body().sync_aggregate()?;
         if sync_aggregate.num_set_bits() < chain_spec.min_sync_committee_participants as usize {
             return Err(Error::NotEnoughSyncCommitteeParticipants);
         }
 
         // Compute and validate attested header.
         let mut attested_header = attested_state.latest_block_header().clone();
-        attested_header.state_root = attested_state.tree_hash_root();
+        attested_header.state_root = attested_state.update_tree_hash_cache()?;
         // Build finalized header from finalized block
-        let finalized_header = BeaconBlockHeader {
-            slot: finalized_block.slot(),
-            proposer_index: finalized_block.proposer_index(),
-            parent_root: finalized_block.parent_root(),
-            state_root: finalized_block.state_root(),
-            body_root: finalized_block.body_root(),
-        };
+        let finalized_header = finalized_block.message().block_header();
+
         if finalized_header.tree_hash_root() != beacon_state.finalized_checkpoint().root {
             return Err(Error::InvalidFinalizedBlock);
         }
 
         let finality_branch = attested_state.compute_merkle_proof(FINALIZED_ROOT_INDEX)?;
         Ok(Self {
-            attested_header: attested_header,
-            finalized_header: finalized_header,
+            attested_header,
+            finalized_header,
             finality_branch: FixedVector::new(finality_branch)?,
             sync_aggregate: sync_aggregate.clone(),
             signature_slot: block.slot(),

consensus/types/src/light_client_optimistic_update.rs

@@ -1,6 +1,6 @@
 use super::{BeaconBlockHeader, EthSpec, Slot, SyncAggregate};
 use crate::{
-    light_client_update::Error, test_utils::TestRandom, BeaconBlock, BeaconState, ChainSpec,
+    light_client_update::Error, test_utils::TestRandom, BeaconState, ChainSpec, SignedBeaconBlock,
 };
 use serde_derive::{Deserialize, Serialize};
 use ssz_derive::{Decode, Encode};
@@ -23,9 +23,9 @@ pub struct LightClientOptimisticUpdate<T: EthSpec> {
 
 impl<T: EthSpec> LightClientOptimisticUpdate<T> {
     pub fn new(
-        chain_spec: ChainSpec,
-        block: BeaconBlock<T>,
-        attested_state: BeaconState<T>,
+        chain_spec: &ChainSpec,
+        block: &SignedBeaconBlock<T>,
+        attested_state: &BeaconState<T>,
     ) -> Result<Self, Error> {
         let altair_fork_epoch = chain_spec
             .altair_fork_epoch
@@ -34,7 +34,7 @@ impl<T: EthSpec> LightClientOptimisticUpdate<T> {
             return Err(Error::AltairForkNotActive);
         }
 
-        let sync_aggregate = block.body().sync_aggregate()?;
+        let sync_aggregate = block.message().body().sync_aggregate()?;
         if sync_aggregate.num_set_bits() < chain_spec.min_sync_committee_participants as usize {
             return Err(Error::NotEnoughSyncCommitteeParticipants);
         }