Add Getter for Genesis Block (#4271)

* test passing

* kafka

beacon-chain/db/iface/interface.go

@@ -8,6 +8,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	eth "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
 	"github.com/prysmaticlabs/prysm/beacon-chain/db/filters"
+	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
 	ethereum_beacon_p2p_v1 "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
 )
 
@@ -38,6 +39,7 @@ type Database interface {
 	SaveBlock(ctx context.Context, block *eth.BeaconBlock) error
 	SaveBlocks(ctx context.Context, blocks []*eth.BeaconBlock) error
 	SaveHeadBlockRoot(ctx context.Context, blockRoot [32]byte) error
+	GenesisBlock(ctx context.Context) (*ethpb.BeaconBlock, error)
 	SaveGenesisBlockRoot(ctx context.Context, blockRoot [32]byte) error
 	IsFinalizedBlock(ctx context.Context, blockRoot [32]byte) bool
 	// Validator related methods.

beacon-chain/db/kafka/passthrough.go

@@ -6,6 +6,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	eth "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
 	"github.com/prysmaticlabs/prysm/beacon-chain/db/filters"
+	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
 	ethereum_beacon_p2p_v1 "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
 )
 
@@ -199,6 +200,11 @@ func (e Exporter) SaveHeadBlockRoot(ctx context.Context, blockRoot [32]byte) err
 	return e.db.SaveHeadBlockRoot(ctx, blockRoot)
 }
 
+// GenesisBlock -- passthrough.
+func (e Exporter) GenesisBlock(ctx context.Context) (*ethpb.BeaconBlock, error) {
+	return e.db.GenesisBlock(ctx)
+}
+
 // SaveGenesisBlockRoot -- passthrough.
 func (e Exporter) SaveGenesisBlockRoot(ctx context.Context, blockRoot [32]byte) error {
 	return e.db.SaveGenesisBlockRoot(ctx, blockRoot)

beacon-chain/db/kv/blocks.go

@@ -318,6 +318,24 @@ func (k *Store) SaveHeadBlockRoot(ctx context.Context, blockRoot [32]byte) error
 	})
 }
 
+// GenesisBlock retrieves the genesis block of the beacon chain.
+func (k *Store) GenesisBlock(ctx context.Context) (*ethpb.BeaconBlock, error) {
+	ctx, span := trace.StartSpan(ctx, "BeaconDB.GenesisBlock")
+	defer span.End()
+	var block *ethpb.BeaconBlock
+	err := k.db.View(func(tx *bolt.Tx) error {
+		bkt := tx.Bucket(blocksBucket)
+		root := bkt.Get(genesisBlockRootKey)
+		enc := bkt.Get(root)
+		if enc == nil {
+			return nil
+		}
+		block = &ethpb.BeaconBlock{}
+		return decode(enc, block)
+	})
+	return block, err
+}
+
 // SaveGenesisBlockRoot to the db.
 func (k *Store) SaveGenesisBlockRoot(ctx context.Context, blockRoot [32]byte) error {
 	ctx, span := trace.StartSpan(ctx, "BeaconDB.SaveGenesisBlockRoot")

beacon-chain/db/kv/blocks_test.go

@@ -139,6 +139,33 @@ func TestStore_BlocksBatchDelete(t *testing.T) {
 	}
 }
 
+func TestStore_GenesisBlock(t *testing.T) {
+	db := setupDB(t)
+	defer teardownDB(t, db)
+	ctx := context.Background()
+	genesisBlock := &ethpb.BeaconBlock{
+		Slot:       0,
+		ParentRoot: []byte{1, 2, 3},
+	}
+	blockRoot, err := ssz.SigningRoot(genesisBlock)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := db.SaveGenesisBlockRoot(ctx, blockRoot); err != nil {
+		t.Fatal(err)
+	}
+	if err := db.SaveBlock(ctx, genesisBlock); err != nil {
+		t.Fatal(err)
+	}
+	retrievedBlock, err := db.GenesisBlock(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !proto.Equal(genesisBlock, retrievedBlock) {
+		t.Errorf("Wanted %v, received %v", genesisBlock, retrievedBlock)
+	}
+}
+
 func TestStore_BlocksCRUD_NoCache(t *testing.T) {
 	db := setupDB(t)
 	defer teardownDB(t, db)