Pass native amount to estimate gas if non-zero

There's an upstream geth bug where gas estimation fails unless a
non-zero Value provided as a call arg. This bug doesn't affect Optimism
right now, but it will in the future once we upgrade to Bedrock. We pass
the Value now in rosetta so we don't regress after the Bedrock upgrade.
Providing the Value call arg is a no-op right now.

fixes #10

Author: Inphi

services/construction_service.go

@@ -259,7 +259,7 @@ func (s *ConstructionAPIService) ConstructionMetadata(
 		to = checkTokenContractAddress
 
 		var err *types.Error
-		gasLimit, err = s.calculateGasLimit(ctx, checkFrom, checkTokenContractAddress, input.Data)
+		gasLimit, err = s.calculateGasLimit(ctx, checkFrom, checkTokenContractAddress, input.Data, nil)
 		if err != nil {
 			return nil, err
 		}
@@ -278,7 +278,7 @@ func (s *ConstructionAPIService) ConstructionMetadata(
 		to = checkContractAddress
 
 		var err *types.Error
-		gasLimit, err = s.calculateGasLimit(ctx, checkFrom, checkContractAddress, input.Data)
+		gasLimit, err = s.calculateGasLimit(ctx, checkFrom, checkContractAddress, input.Data, input.Value)
 		if err != nil {
 			return nil, err
 		}
@@ -602,13 +602,19 @@ func (s *ConstructionAPIService) calculateGasLimit(
 	from string,
 	to string,
 	data []byte,
+	value *big.Int,
 ) (uint64, *types.Error) {
 	fromAddress := common.HexToAddress(from)
 	toAddress := common.HexToAddress(to)
+	var v *big.Int
+	if value != nil && value.Cmp(big.NewInt(0)) != 0 {
+		v = value
+	}
 	gasLimit, err := s.client.EstimateGas(ctx, ethereum.CallMsg{
-		From: fromAddress,
-		To:   &toAddress,
-		Data: data,
+		From:  fromAddress,
+		To:    &toAddress,
+		Data:  data,
+		Value: v,
 	})
 
 	if err != nil {

services/construction_service_test.go

@@ -437,6 +437,49 @@ func TestMetadata(t *testing.T) {
 				},
 			},
 		},
+		"happy path: Generic contract call with value": {
+			options: map[string]interface{}{
+				"from":             metadataFrom,
+				"to":               metadataTo,
+				"value":            "0x5f5e100",
+				"nonce":            transferNonceHex2,
+				"contract_address": tokenContractAddress,
+				"data":             metadataGenericData,
+				"method_signature": "approve(address,uint256)",
+				"method_args":      []string{"0xD10a72Cf054650931365Cc44D912a4FD75257058", "1000"},
+			},
+			mocks: func(ctx context.Context, client *mocks.Client) {
+				to := common.HexToAddress(tokenContractAddress)
+				dataBytes, _ := hexutil.Decode(metadataGenericData)
+				client.On("EstimateGas", ctx, ethereum.CallMsg{
+					From:  common.HexToAddress(metadataFrom),
+					To:    &to,
+					Data:  dataBytes,
+					Value: big.NewInt(100000000),
+				}).Return(transferGasLimitERC20, nil)
+
+				client.On("SuggestGasPrice", ctx).
+					Return(big.NewInt(int64(transferGasPrice)), nil)
+			},
+			expectedResponse: &types.ConstructionMetadataResponse{
+				Metadata: map[string]interface{}{
+					"to":               tokenContractAddress,
+					"value":            "0x5f5e100",
+					"nonce":            transferNonceHex2,
+					"gas_price":        transferGasPriceHex,
+					"gas_limit":        transferGasLimitERC20Hex,
+					"data":             metadataGenericData,
+					"method_signature": "approve(address,uint256)",
+					"method_args":      []interface{}{"0xD10a72Cf054650931365Cc44D912a4FD75257058", "1000"},
+				},
+				SuggestedFee: []*types.Amount{
+					{
+						Value:    fmt.Sprintf("%d", transferGasPrice*transferGasLimitERC20),
+						Currency: optimism.Currency,
+					},
+				},
+			},
+		},
 		"error: missing source address": {
 			options: map[string]interface{}{
 				"to":    metadataTo,