Allow next slot, and broadcast based on proposer index

beacon-chain/rpc/prysm/v1alpha1/validator/proposer_epbs.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/epbs"
+	"github.com/prysmaticlabs/prysm/v5/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/v5/consensus-types/blocks"
 	"github.com/prysmaticlabs/prysm/v5/consensus-types/interfaces"
 	enginev1 "github.com/prysmaticlabs/prysm/v5/proto/engine/v1"
@@ -34,12 +35,26 @@ func (vs *Server) SubmitSignedExecutionPayloadEnvelope(ctx context.Context, env
 
 // SubmitSignedExecutionPayloadHeader submits a signed execution payload header to the beacon node.
 func (vs *Server) SubmitSignedExecutionPayloadHeader(ctx context.Context, h *enginev1.SignedExecutionPayloadHeader) (*emptypb.Empty, error) {
-	if vs.TimeFetcher.CurrentSlot() != h.Message.Slot {
-		return nil, status.Errorf(codes.InvalidArgument, "current slot mismatch: expected %d, got %d", vs.TimeFetcher.CurrentSlot(), h.Message.Slot)
+	if vs.TimeFetcher.CurrentSlot() != h.Message.Slot && vs.TimeFetcher.CurrentSlot() != h.Message.Slot-1 {
+		return nil, status.Errorf(codes.InvalidArgument, "invalid slot: current slot %d, got %d", vs.TimeFetcher.CurrentSlot(), h.Message.Slot)
 	}
 
 	vs.signedExecutionPayloadHeader = h
 
+	headState, err := vs.HeadFetcher.HeadStateReadOnly(ctx)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "failed to retrieve head state: %v", err)
+	}
+	proposerIndex, err := helpers.BeaconProposerIndexAtSlot(ctx, headState, h.Message.Slot)
+	if err != nil {
+		return nil, status.Errorf(codes.Internal, "failed to retrieve proposer index: %v", err)
+	}
+	if proposerIndex != h.Message.BuilderIndex {
+		if err := vs.P2P.Broadcast(ctx, h); err != nil {
+			return nil, status.Errorf(codes.Internal, "failed to broadcast signed execution payload header: %v", err)
+		}
+	}
+
 	return nil, nil
 }
 

beacon-chain/rpc/prysm/v1alpha1/validator/proposer_epbs_test.go

@@ -49,6 +49,7 @@ func TestServer_SubmitSignedExecutionPayloadEnvelope(t *testing.T) {
 }
 
 func TestServer_SubmitSignedExecutionPayloadHeader(t *testing.T) {
+	st, _ := util.DeterministicGenesisStateEpbs(t, 1)
 	h := &enginev1.SignedExecutionPayloadHeader{
 		Message: &enginev1.ExecutionPayloadHeaderEPBS{
 			Slot: 1,
@@ -57,18 +58,21 @@ func TestServer_SubmitSignedExecutionPayloadHeader(t *testing.T) {
 	slot := primitives.Slot(1)
 	server := &Server{
 		TimeFetcher: &mockChain.ChainService{Slot: &slot},
+		HeadFetcher: &mockChain.ChainService{State: st},
+		P2P:         p2ptest.NewTestP2P(t),
 	}
 
 	t.Run("Happy case", func(t *testing.T) {
+		h.Message.BuilderIndex = 1
 		_, err := server.SubmitSignedExecutionPayloadHeader(context.Background(), h)
 		require.NoError(t, err)
 		require.DeepEqual(t, server.signedExecutionPayloadHeader, h)
 	})
 
 	t.Run("Incorrect slot", func(t *testing.T) {
-		h.Message.Slot = 2
+		h.Message.Slot = 3
 		_, err := server.SubmitSignedExecutionPayloadHeader(context.Background(), h)
-		require.ErrorContains(t, "current slot mismatch: expected 1, got 2", err)
+		require.ErrorContains(t, "invalid slot: current slot 1, got 3", err)
 	})
 }