chore(node-api): stub for state finality checkpoints

mod/node-api/handlers/beacon/historical.go

@@ -24,6 +24,7 @@ import (
 	beacontypes "github.com/berachain/beacon-kit/mod/node-api/handlers/beacon/types"
 	"github.com/berachain/beacon-kit/mod/node-api/handlers/types"
 	"github.com/berachain/beacon-kit/mod/node-api/handlers/utils"
+	"github.com/berachain/beacon-kit/mod/primitives/pkg/common"
 )
 
 func (h *Handler[_, ContextT, _, _, _]) GetStateRoot(c ContextT) (any, error) {
@@ -72,3 +73,43 @@ func (h *Handler[_, ContextT, _, _, _]) GetStateFork(c ContextT) (any, error) {
 		Data:                beacontypes.ForkData{Fork: fork},
 	}, nil
 }
+
+func (h *Handler[_, ContextT, _, _, _]) GetStateFinalityCheckpoints(
+	c ContextT,
+) (any, error) {
+	req, err := utils.BindAndValidate[beacontypes.GetStateForkRequest](
+		c, h.Logger(),
+	)
+	if err != nil {
+		return nil, err
+	}
+	slot, err := utils.SlotFromStateID(req.StateID, h.backend)
+	if err != nil {
+		return nil, err
+	}
+	fork, err := h.backend.StateForkAtSlot(slot)
+	if err != nil {
+		return nil, err
+	}
+
+	return beacontypes.ValidatorResponse{
+		ExecutionOptimistic: false, // stubbed
+		Finalized:           false, // stubbed
+		Data: beacontypes.FinalityCheckpointsData{
+			// In case finality is not achieved yet, return the
+			// epoch 0 and ZERO_HASH as root.
+			PreviousJustified: common.Checkpoint{
+				Epoch: fork.GetEpoch(),
+				Root:  [32]byte{},
+			},
+			CurrentJustified: common.Checkpoint{
+				Epoch: fork.GetEpoch(),
+				Root:  [32]byte{},
+			},
+			Finalized: common.Checkpoint{
+				Epoch: 0,
+				Root:  [32]byte{},
+			},
+		},
+	}, nil
+}

mod/node-api/handlers/beacon/routes.go

@@ -51,7 +51,7 @@ func (h *Handler[_, ContextT, _, _, _]) RegisterRoutes(
 		{
 			Method:  http.MethodGet,
 			Path:    "/eth/v1/beacon/states/:state_id/finality_checkpoints",
-			Handler: h.NotImplemented,
+			Handler: h.GetStateFinalityCheckpoints,
 		},
 		{
 			Method:  http.MethodGet,

mod/node-api/handlers/beacon/types/response.go

@@ -197,3 +197,9 @@ func (fr ForkData) MarshalJSON() ([]byte, error) {
 		Epoch:           strconv.FormatUint(fr.GetEpoch().Unwrap(), 10),
 	})
 }
+
+type FinalityCheckpointsData struct {
+	PreviousJustified common.Checkpoint `json:"previous_justified"`
+	CurrentJustified  common.Checkpoint `json:"current_justified"`
+	Finalized         common.Checkpoint `json:"finalized"`
+}

mod/primitives/pkg/common/consensus.go

@@ -21,6 +21,9 @@
 package common
 
 import (
+	encodinghex "encoding/hex"
+	"strconv"
+
 	"github.com/berachain/beacon-kit/mod/chain-spec/pkg/chain"
 	"github.com/berachain/beacon-kit/mod/primitives/pkg/bytes"
 	"github.com/berachain/beacon-kit/mod/primitives/pkg/encoding/hex"
@@ -118,3 +121,23 @@ func (r Root) MarshalJSON() ([]byte, error) {
 func (r *Root) UnmarshalJSON(input []byte) error {
 	return r.UnmarshalText(input[1 : len(input)-1])
 }
+
+// Checkpoint provides information about a checkpoint.
+type Checkpoint struct {
+	Epoch math.Epoch
+	Root  Root `ssz-size:"32"`
+}
+
+// checkpointJSON is an internal representation of the struct.
+type checkpointJSON struct {
+	Epoch string `json:"epoch"`
+	Root  string `json:"root"`
+}
+
+// MarshalJSON implements json.Marshaler.
+func (c Checkpoint) MarshalJSON() ([]byte, error) {
+	return json.Marshal(&checkpointJSON{
+		Epoch: strconv.FormatUint(uint64(c.Epoch), 10),
+		Root:  "0x" + encodinghex.EncodeToString(c.Root[:]),
+	})
+}