Return error if RPC returns empty header

- Enables graceful failure if RPC returns empty data with no error

pkg/fakes/mock_rpc_client.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"math/big"
 
-	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/ethereum/go-ethereum/p2p"
 	. "github.com/onsi/gomega"
@@ -19,6 +18,7 @@ type MockRpcClient struct {
 	passedContext    context.Context
 	passedMethod     string
 	passedResult     interface{}
+	returnPOAHeader  core.POAHeader
 	supportedModules map[string]string
 }
 
@@ -45,8 +45,7 @@ func (client *MockRpcClient) CallContext(ctx context.Context, result interface{}
 			*p = types.Header{Number: big.NewInt(123)}
 		}
 		if p, ok := result.(*core.POAHeader); ok {
-			n := hexutil.Big(*big.NewInt(123))
-			*p = core.POAHeader{Number: &n}
+			*p = client.returnPOAHeader
 		}
 		if client.callContextErr != nil {
 			return client.callContextErr
@@ -91,6 +90,10 @@ func (client *MockRpcClient) SetCallContextErr(err error) {
 	client.callContextErr = err
 }
 
+func (client *MockRpcClient) SetReturnPOAHeader(header core.POAHeader) {
+	client.returnPOAHeader = header
+}
+
 func (client *MockRpcClient) AssertCallContextCalledWith(ctx context.Context, result interface{}, method string) {
 	Expect(client.passedContext).To(Equal(ctx))
 	Expect(client.passedResult).To(BeAssignableToTypeOf(result))

pkg/geth/blockchain.go

@@ -9,10 +9,13 @@ import (
 
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/pkg/errors"
 	"github.com/vulcanize/vulcanizedb/pkg/core"
 	vulcCommon "github.com/vulcanize/vulcanizedb/pkg/geth/converters/common"
 )
 
+var ErrEmptyHeader = errors.New("empty header returned over RPC")
+
 type BlockChain struct {
 	blockConverter  vulcCommon.BlockConverter
 	ethClient       core.EthClient
@@ -62,6 +65,9 @@ func (blockChain *BlockChain) getPOAHeader(blockNumber int64) (header core.Heade
 	if err != nil {
 		return header, err
 	}
+	if POAHeader.Number == nil {
+		return header, ErrEmptyHeader
+	}
 	return blockChain.headerConverter.Convert(&types.Header{
 		ParentHash:  POAHeader.ParentHash,
 		UncleHash:   POAHeader.UncleHash,

pkg/geth/blockchain_test.go

@@ -10,6 +10,7 @@ import (
 	. "github.com/onsi/ginkgo"
 	. "github.com/onsi/gomega"
 
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	vulcCore "github.com/vulcanize/vulcanizedb/pkg/core"
 	"github.com/vulcanize/vulcanizedb/pkg/fakes"
 	"github.com/vulcanize/vulcanizedb/pkg/geth"
@@ -75,6 +76,8 @@ var _ = Describe("Geth blockchain", func() {
 		Describe("POA/Kovan", func() {
 			It("fetches header from rpcClient", func() {
 				node.NetworkID = vulcCore.KOVAN_NETWORK_ID
+				blockNumber := hexutil.Big(*big.NewInt(123))
+				mockRpcClient.SetReturnPOAHeader(vulcCore.POAHeader{Number: &blockNumber})
 				blockChain = geth.NewBlockChain(mockClient, mockRpcClient, node, cold_db.NewColdDbTransactionConverter())
 
 				_, err := blockChain.GetHeaderByNumber(100)
@@ -93,6 +96,16 @@ var _ = Describe("Geth blockchain", func() {
 				Expect(err).To(HaveOccurred())
 				Expect(err).To(MatchError(fakes.FakeError))
 			})
+
+			It("returns error if returned header is empty", func() {
+				node.NetworkID = vulcCore.KOVAN_NETWORK_ID
+				blockChain = geth.NewBlockChain(mockClient, mockRpcClient, node, cold_db.NewColdDbTransactionConverter())
+
+				_, err := blockChain.GetHeaderByNumber(100)
+
+				Expect(err).To(HaveOccurred())
+				Expect(err).To(MatchError(geth.ErrEmptyHeader))
+			})
 		})
 	})