Get all beacon committees at once (#14282)

* Get all beacon committees at once

* Update beacon-chain/core/helpers/beacon_committee.go

---------

Co-authored-by: Radosław Kapka <rkapka@wp.pl>

beacon-chain/core/helpers/beacon_committee.go

@@ -82,6 +82,47 @@ func AttestationCommittees(ctx context.Context, st state.ReadOnlyBeaconState, at
 	return committees, nil
 }
 
+// BeaconCommittees returns the list of all beacon committees for a given state at a given slot.
+func BeaconCommittees(ctx context.Context, state state.ReadOnlyBeaconState, slot primitives.Slot) ([][]primitives.ValidatorIndex, error) {
+	epoch := slots.ToEpoch(slot)
+	activeCount, err := ActiveValidatorCount(ctx, state, epoch)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not compute active validator count")
+	}
+	committeesPerSlot := SlotCommitteeCount(activeCount)
+	seed, err := Seed(state, epoch, params.BeaconConfig().DomainBeaconAttester)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not get seed")
+	}
+
+	committees := make([][]primitives.ValidatorIndex, committeesPerSlot)
+	var activeIndices []primitives.ValidatorIndex
+
+	for idx := primitives.CommitteeIndex(0); idx < primitives.CommitteeIndex(len(committees)); idx++ {
+		committee, err := committeeCache.Committee(ctx, slot, seed, idx)
+		if err != nil {
+			return nil, errors.Wrap(err, "could not interface with committee cache")
+		}
+		if committee != nil {
+			committees[idx] = committee
+			continue
+		}
+
+		if len(activeIndices) == 0 {
+			activeIndices, err = ActiveValidatorIndices(ctx, state, epoch)
+			if err != nil {
+				return nil, errors.Wrap(err, "could not get active indices")
+			}
+		}
+		committee, err = BeaconCommittee(ctx, activeIndices, seed, slot, idx)
+		if err != nil {
+			return nil, errors.Wrap(err, "could not compute beacon committee")
+		}
+		committees[idx] = committee
+	}
+	return committees, nil
+}
+
 // BeaconCommitteeFromState returns the crosslink committee of a given slot and committee index. This
 // is a spec implementation where state is used as an argument. In case of state retrieval
 // becomes expensive, consider using BeaconCommittee below.

beacon-chain/core/helpers/beacon_committee_test.go

@@ -18,6 +18,7 @@ import (
 	ethpb "github.com/prysmaticlabs/prysm/v5/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/v5/testing/assert"
 	"github.com/prysmaticlabs/prysm/v5/testing/require"
+	"github.com/prysmaticlabs/prysm/v5/testing/util"
 	"github.com/prysmaticlabs/prysm/v5/time/slots"
 )
 
@@ -749,3 +750,27 @@ func TestAttestationCommittees(t *testing.T) {
 		assert.Equal(t, params.BeaconConfig().TargetCommitteeSize, uint64(len(committees[1])))
 	})
 }
+
+func TestBeaconCommittees(t *testing.T) {
+	prevConfig := params.BeaconConfig().Copy()
+	defer params.OverrideBeaconConfig(prevConfig)
+	c := params.BeaconConfig().Copy()
+	c.MinGenesisActiveValidatorCount = 128
+	c.SlotsPerEpoch = 4
+	c.TargetCommitteeSize = 16
+	params.OverrideBeaconConfig(c)
+
+	state, _ := util.DeterministicGenesisState(t, 256)
+
+	activeCount, err := helpers.ActiveValidatorCount(context.Background(), state, 0)
+	require.NoError(t, err)
+	committeesPerSlot := helpers.SlotCommitteeCount(activeCount)
+	committees, err := helpers.BeaconCommittees(context.Background(), state, 0)
+	require.NoError(t, err)
+	require.Equal(t, committeesPerSlot, uint64(len(committees)))
+	for idx := primitives.CommitteeIndex(0); idx < primitives.CommitteeIndex(len(committees)); idx++ {
+		committee, err := helpers.BeaconCommitteeFromState(context.Background(), state, 0, idx)
+		require.NoError(t, err)
+		require.DeepEqual(t, committees[idx], committee)
+	}
+}