Allow use of finalized tag in rpc requests

This PR allows the use of the "finalized" tag to retrieve blocks or
headers via the RPC. Using the "finalized" tag is equivalent to using
the "latest" tag because all blocks are final in celo.

This is to supprt integration with chainlink since their system depends
on retrieving finalized blocks.

e2e_test/e2e_test.go

@@ -881,3 +881,37 @@ func TestSettingGingerbreadOnGenesisBlock(t *testing.T) {
 	require.Greater(t, block.BaseFee().Uint64(), uint64(0))
 	require.Greater(t, block.GasLimit(), uint64(0))
 }
+
+// This test checks that retreiveing the "finalized" block results in the same response as retrieving the "latest" block.
+func TestGetFinalizedBlock(t *testing.T) {
+	ac := test.AccountConfig(2, 2)
+	gingerbreadBlock := common.Big0
+	gc, ec, err := test.BuildConfig(ac, gingerbreadBlock)
+	require.NoError(t, err)
+	network, shutdown, err := test.NewNetwork(ac, gc, ec)
+	require.NoError(t, err)
+	defer shutdown()
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
+	defer cancel()
+
+	// Wait for at least one block to be built.
+	err = network.AwaitBlock(ctx, 1)
+	require.NoError(t, err)
+
+	// Stop one of the two validators, so no more blocks can be created.
+	err = network[1].Close()
+	require.NoError(t, err)
+
+	c := network[0].WsClient.GetRPCClient()
+	h := types.Header{}
+	err = c.CallContext(ctx, &h, "eth_getHeaderByNumber", "latest")
+	require.NoError(t, err)
+	require.GreaterOrEqual(t, h.Number.Uint64(), uint64(1))
+
+	h2 := types.Header{}
+	err = c.CallContext(ctx, &h2, "eth_getHeaderByNumber", "finalized")
+	require.NoError(t, err)
+
+	// Check latest and finalzed block are the same
+	require.Equal(t, h.Hash(), h2.Hash())
+}

rpc/types.go

@@ -84,8 +84,10 @@ type RPCTransaction struct {
 	EthCompatible       bool            `json:"ethCompatible"`
 }
 
-// UnmarshalJSON parses the given JSON fragment into a BlockNumber. It supports:
-// - "latest", "earliest" or "pending" as string arguments
+// UnmarshalJSON parses the given JSON fragment into a BlockNumber. It
+// supports: - "finalized", latest", "earliest" or "pending" as string
+// arguments where finalized is equivalent to latest since all blocks are final
+// in celo.
 // - the block number
 // Returned errors:
 // - an invalid block number error when the given argument isn't a known strings
@@ -106,6 +108,9 @@ func (bn *BlockNumber) UnmarshalJSON(data []byte) error {
 	case "pending":
 		*bn = PendingBlockNumber
 		return nil
+	case "finalized":
+		*bn = LatestBlockNumber
+		return nil
 	}
 
 	blckNum, err := hexutil.DecodeUint64(input)

rpc/types_test.go

@@ -45,9 +45,10 @@ func TestBlockNumberJSONUnmarshal(t *testing.T) {
 		11: {`"pending"`, false, PendingBlockNumber},
 		12: {`"latest"`, false, LatestBlockNumber},
 		13: {`"earliest"`, false, EarliestBlockNumber},
-		14: {`someString`, true, BlockNumber(0)},
-		15: {`""`, true, BlockNumber(0)},
-		16: {``, true, BlockNumber(0)},
+		14: {`"finalized"`, false, LatestBlockNumber},
+		15: {`someString`, true, BlockNumber(0)},
+		16: {`""`, true, BlockNumber(0)},
+		17: {``, true, BlockNumber(0)},
 	}
 
 	for i, test := range tests {
@@ -87,18 +88,20 @@ func TestBlockNumberOrHash_UnmarshalJSON(t *testing.T) {
 		11: {`"pending"`, false, BlockNumberOrHashWithNumber(PendingBlockNumber)},
 		12: {`"latest"`, false, BlockNumberOrHashWithNumber(LatestBlockNumber)},
 		13: {`"earliest"`, false, BlockNumberOrHashWithNumber(EarliestBlockNumber)},
-		14: {`someString`, true, BlockNumberOrHash{}},
-		15: {`""`, true, BlockNumberOrHash{}},
-		16: {``, true, BlockNumberOrHash{}},
-		17: {`"0x0000000000000000000000000000000000000000000000000000000000000000"`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), false)},
-		18: {`{"blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000"}`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), false)},
-		19: {`{"blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000","requireCanonical":false}`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), false)},
-		20: {`{"blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000","requireCanonical":true}`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), true)},
-		21: {`{"blockNumber":"0x1"}`, false, BlockNumberOrHashWithNumber(1)},
-		22: {`{"blockNumber":"pending"}`, false, BlockNumberOrHashWithNumber(PendingBlockNumber)},
-		23: {`{"blockNumber":"latest"}`, false, BlockNumberOrHashWithNumber(LatestBlockNumber)},
-		24: {`{"blockNumber":"earliest"}`, false, BlockNumberOrHashWithNumber(EarliestBlockNumber)},
-		25: {`{"blockNumber":"0x1", "blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000"}`, true, BlockNumberOrHash{}},
+		14: {`"finalized"`, false, BlockNumberOrHashWithNumber(EarliestBlockNumber)},
+		15: {`someString`, true, BlockNumberOrHash{}},
+		16: {`""`, true, BlockNumberOrHash{}},
+		17: {``, true, BlockNumberOrHash{}},
+		18: {`"0x0000000000000000000000000000000000000000000000000000000000000000"`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), false)},
+		19: {`{"blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000"}`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), false)},
+		20: {`{"blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000","requireCanonical":false}`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), false)},
+		21: {`{"blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000","requireCanonical":true}`, false, BlockNumberOrHashWithHash(common.HexToHash("0x0000000000000000000000000000000000000000000000000000000000000000"), true)},
+		22: {`{"blockNumber":"0x1"}`, false, BlockNumberOrHashWithNumber(1)},
+		23: {`{"blockNumber":"pending"}`, false, BlockNumberOrHashWithNumber(PendingBlockNumber)},
+		24: {`{"blockNumber":"latest"}`, false, BlockNumberOrHashWithNumber(LatestBlockNumber)},
+		25: {`{"blockNumber":"earliest"}`, false, BlockNumberOrHashWithNumber(EarliestBlockNumber)},
+		26: {`{"blockNumber":"finalized"}`, false, BlockNumberOrHashWithNumber(LatestBlockNumber)},
+		27: {`{"blockNumber":"0x1", "blockHash":"0x0000000000000000000000000000000000000000000000000000000000000000"}`, true, BlockNumberOrHash{}},
 	}
 
 	for i, test := range tests {