From d67270f8992569c59223fc26141b5a2e575c74b9 Mon Sep 17 00:00:00 2001
From: dapplion <35266934+dapplion@users.noreply.github.com>
Date: Wed, 19 Jun 2024 12:59:27 +0200
Subject: [PATCH] committees are sorted

---
 .../beacon_chain/src/attestation_verification.rs |  9 +++++----
 .../src/common/get_attesting_indices.rs          | 16 ++++++++--------
 .../types/src/beacon_state/committee_cache.rs    |  2 ++
 3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/beacon_node/beacon_chain/src/attestation_verification.rs b/beacon_node/beacon_chain/src/attestation_verification.rs
index a5635a3392..51b5b11b09 100644
--- a/beacon_node/beacon_chain/src/attestation_verification.rs
+++ b/beacon_node/beacon_chain/src/attestation_verification.rs
@@ -597,6 +597,8 @@ impl<'a, T: BeaconChainTypes> IndexedAggregatedAttestation<'a, T> {
                 ))
             }
         };
+
+        // Committees must be sorted by ascending index order 0..committees_per_slot
         let get_indexed_attestation_with_committee =
             |(committees, _): (Vec<BeaconCommittee>, CommitteesPerSlot)| {
                 let (index, aggregator_index, selection_proof, data) = match signed_aggregate {
@@ -622,10 +624,7 @@ impl<'a, T: BeaconChainTypes> IndexedAggregatedAttestation<'a, T> {
                 let slot = data.slot;
 
                 let committee = committees
-                    .iter()
-                    .filter(|&committee| committee.index == index)
-                    .at_most_one()
-                    .map_err(|_| Error::NoCommitteeForSlotAndIndex { slot, index })?
+                    .get(index as usize)
                     .ok_or(Error::NoCommitteeForSlotAndIndex { slot, index })?;
 
                 if !SelectionProof::from(selection_proof)
@@ -1422,6 +1421,8 @@ pub fn obtain_indexed_attestation_and_committees_per_slot<T: BeaconChainTypes>(
 ///
 /// If the committees for an `attestation`'s slot isn't found in the `shuffling_cache`, we will read a state
 /// from disk and then update the `shuffling_cache`.
+///
+/// Committees are sorted by ascending index order 0..committees_per_slot
 fn map_attestation_committees<T, F, R>(
     chain: &BeaconChain<T>,
     attestation: AttestationRef<T::EthSpec>,
diff --git a/consensus/state_processing/src/common/get_attesting_indices.rs b/consensus/state_processing/src/common/get_attesting_indices.rs
index 9fb88407d3..0657100999 100644
--- a/consensus/state_processing/src/common/get_attesting_indices.rs
+++ b/consensus/state_processing/src/common/get_attesting_indices.rs
@@ -44,13 +44,16 @@ pub mod attesting_indices_base {
 }
 
 pub mod attesting_indices_electra {
-    use std::collections::{HashMap, HashSet};
+    use std::collections::HashSet;
 
     use crate::per_block_processing::errors::{AttestationInvalid as Invalid, BlockOperationError};
     use itertools::Itertools;
     use safe_arith::SafeArith;
     use types::*;
 
+    /// Compute an Electra IndexedAttestation given a list of committees.
+    ///
+    /// Committees must be sorted by ascending order 0..committees_per_slot
     pub fn get_indexed_attestation<E: EthSpec>(
         committees: &[BeaconCommittee],
         attestation: &AttestationElectra<E>,
@@ -103,6 +106,8 @@ pub mod attesting_indices_electra {
     }
 
     /// Returns validator indices which participated in the attestation, sorted by increasing index.
+    ///
+    /// Committees must be sorted by ascending order 0..committees_per_slot
     pub fn get_attesting_indices<E: EthSpec>(
         committees: &[BeaconCommittee],
         aggregation_bits: &BitList<E::MaxValidatorsPerSlot>,
@@ -114,16 +119,11 @@ pub mod attesting_indices_electra {
 
         let mut committee_offset = 0;
 
-        let committees_map: HashMap<u64, &BeaconCommittee> = committees
-            .iter()
-            .map(|committee| (committee.index, committee))
-            .collect();
-
         let committee_count_per_slot = committees.len() as u64;
         let mut participant_count = 0;
         for index in committee_indices {
-            let beacon_committee = committees_map
-                .get(&index)
+            let beacon_committee = committees
+                .get(index as usize)
                 .ok_or(Error::NoCommitteeFound(index))?;
 
             // This check is new to the spec's `process_attestation` in Electra.
diff --git a/consensus/types/src/beacon_state/committee_cache.rs b/consensus/types/src/beacon_state/committee_cache.rs
index 209659ea88..161f854157 100644
--- a/consensus/types/src/beacon_state/committee_cache.rs
+++ b/consensus/types/src/beacon_state/committee_cache.rs
@@ -183,6 +183,8 @@ impl CommitteeCache {
     }
 
     /// Get all the Beacon committees at a given `slot`.
+    ///
+    /// Committees are sorted by ascending index order 0..committees_per_slot
     pub fn get_beacon_committees_at_slot(&self, slot: Slot) -> Result<Vec<BeaconCommittee>, Error> {
         if self.initialized_epoch.is_none() {
             return Err(Error::CommitteeCacheUninitialized(None));