Implement GetGenesis in the beacon API (#8380)

* span

* initial implementation

* test wip

* set nanos to zero

* more testing

* gzl

beacon-chain/rpc/beaconv1/BUILD.bazel

@@ -51,6 +51,7 @@ go_test(
         "blocks_test.go",
         "config_test.go",
         "server_test.go",
+        "state_test.go",
     ],
     embed = [":go_default_library"],
     deps = [

beacon-chain/rpc/beaconv1/state.go

@@ -1,16 +1,41 @@
 package beaconv1
 
 import (
+	"bytes"
 	"context"
 	"errors"
 
 	ptypes "github.com/gogo/protobuf/types"
 	ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1"
+	"github.com/prysmaticlabs/prysm/shared/params"
+	"go.opencensus.io/trace"
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
 )
 
 // GetGenesis retrieves details of the chain's genesis which can be used to identify chain.
 func (bs *Server) GetGenesis(ctx context.Context, _ *ptypes.Empty) (*ethpb.GenesisResponse, error) {
-	return nil, errors.New("unimplemented")
+	ctx, span := trace.StartSpan(ctx, "beaconv1.GetGenesis")
+	defer span.End()
+
+	genesisTime := bs.GenesisTimeFetcher.GenesisTime()
+	if genesisTime.IsZero() {
+		return nil, status.Errorf(codes.NotFound, "Chain genesis info is not yet known")
+	}
+	validatorRoot := bs.ChainInfoFetcher.GenesisValidatorRoot()
+	if bytes.Equal(validatorRoot[:], params.BeaconConfig().ZeroHash[:]) {
+		return nil, status.Errorf(codes.NotFound, "Chain genesis info is not yet known")
+	}
+	forkVersion := params.BeaconConfig().GenesisForkVersion
+
+	return &ethpb.GenesisResponse{
+		GenesisTime: &ptypes.Timestamp{
+			Seconds: genesisTime.Unix(),
+			Nanos:   0,
+		},
+		GenesisValidatorsRoot: validatorRoot[:],
+		GenesisForkVersion:    forkVersion,
+	}, nil
 }
 
 // GetStateRoot calculates HashTreeRoot for state with given 'stateId'. If stateId is root, same value will be returned.

beacon-chain/rpc/beaconv1/state_test.go

@@ -0,0 +1,65 @@
+package beaconv1
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	ptypes "github.com/gogo/protobuf/types"
+	chainMock "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing"
+	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
+	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+)
+
+func TestGetGenesis(t *testing.T) {
+	params.SetupTestConfigCleanup(t)
+	config := params.BeaconConfig()
+	config.GenesisForkVersion = []byte("genesis")
+	params.OverrideBeaconConfig(config)
+	genesis := time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC)
+	validatorsRoot := [32]byte{1, 2, 3, 4, 5, 6}
+
+	t.Run("OK", func(t *testing.T) {
+		chainService := &chainMock.ChainService{
+			Genesis:        genesis,
+			ValidatorsRoot: validatorsRoot,
+		}
+		s := Server{
+			GenesisTimeFetcher: chainService,
+			ChainInfoFetcher:   chainService,
+		}
+		resp, err := s.GetGenesis(context.Background(), &ptypes.Empty{})
+		require.NoError(t, err)
+		assert.Equal(t, genesis.Unix(), resp.GenesisTime.Seconds)
+		assert.Equal(t, int32(0), resp.GenesisTime.Nanos)
+		assert.DeepEqual(t, validatorsRoot[:], resp.GenesisValidatorsRoot)
+		assert.DeepEqual(t, []byte("genesis"), resp.GenesisForkVersion)
+	})
+
+	t.Run("No genesis time", func(t *testing.T) {
+		chainService := &chainMock.ChainService{
+			Genesis:        time.Time{},
+			ValidatorsRoot: validatorsRoot,
+		}
+		s := Server{
+			GenesisTimeFetcher: chainService,
+			ChainInfoFetcher:   chainService,
+		}
+		_, err := s.GetGenesis(context.Background(), &ptypes.Empty{})
+		assert.ErrorContains(t, "Chain genesis info is not yet known", err)
+	})
+
+	t.Run("No genesis validator root", func(t *testing.T) {
+		chainService := &chainMock.ChainService{
+			Genesis:        genesis,
+			ValidatorsRoot: [32]byte{},
+		}
+		s := Server{
+			GenesisTimeFetcher: chainService,
+			ChainInfoFetcher:   chainService,
+		}
+		_, err := s.GetGenesis(context.Background(), &ptypes.Empty{})
+		assert.ErrorContains(t, "Chain genesis info is not yet known", err)
+	})
+}