add custom marshaller for GetChainConfigResponse api

internal/ethapi/api.go

@@ -138,18 +138,8 @@ func (s *EthereumAPI) Syncing() (interface{}, error) {
 	return false, nil
 }
 
-type GetChainConfigResponse struct {
-	*params.ChainConfig
-	params.UpgradeConfig `json:"upgrades"`
-}
-
-func (s *BlockChainAPI) GetChainConfig(ctx context.Context) GetChainConfigResponse {
-	config := s.b.ChainConfig()
-	resp := GetChainConfigResponse{
-		ChainConfig:   config,
-		UpgradeConfig: config.UpgradeConfig,
-	}
-	return resp
+func (s *BlockChainAPI) GetChainConfig(ctx context.Context) *params.ChainConfigWithUpgradesMarshalled {
+	return s.b.ChainConfig().ToWithUpgradesMarshalled()
 }
 
 // TxPoolAPI offers and API for the transaction pool. It only operates on data that is non confidential.

params/config.go

@@ -40,6 +40,8 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 )
 
+const maxJSONLen = 64 * 1024 * 1024 // 64MB
+
 var (
 	errNonGenesisForkByHeight = errors.New("subnet-evm only supports forking by height at the genesis block")
 
@@ -211,6 +213,53 @@ func (c ChainConfig) MarshalJSON() ([]byte, error) {
 	return json.Marshal(raw)
 }
 
+type ChainConfigWithUpgradesMarshalled struct {
+	*ChainConfig
+	UpgradeConfig UpgradeConfig `json:"upgrades,omitempty"`
+}
+
+// MarshalJSON implements json.Marshaler. This is a workaround for the fact that
+// the embedded ChainConfig struct has a MarshalJSON method, which prevents
+// the default JSON marshalling from working for UpgradeConfig.
+// TODO: consider removing this method by allowing external tag for the embedded
+// ChainConfig struct.
+func (s *ChainConfigWithUpgradesMarshalled) MarshalJSON() ([]byte, error) {
+	// embed the ChainConfig struct into the response
+	chainConfigJSON, err := json.Marshal(s.ChainConfig)
+	if err != nil {
+		return nil, err
+	}
+	if len(chainConfigJSON) > maxJSONLen {
+		return nil, errors.New("value too large")
+	}
+
+	type upgrades struct {
+		UpgradeConfig UpgradeConfig `json:"upgrades"`
+	}
+
+	upgradeJSON, err := json.Marshal(upgrades{s.UpgradeConfig})
+	if err != nil {
+		return nil, err
+	}
+	if len(upgradeJSON) > maxJSONLen {
+		return nil, errors.New("value too large")
+	}
+
+	// merge the two JSON objects
+	mergedJSON := make([]byte, 0, len(chainConfigJSON)+len(upgradeJSON)+1)
+	mergedJSON = append(mergedJSON, chainConfigJSON[:len(chainConfigJSON)-1]...)
+	mergedJSON = append(mergedJSON, ',')
+	mergedJSON = append(mergedJSON, upgradeJSON[1:]...)
+	return mergedJSON, nil
+}
+
+func (c *ChainConfig) ToWithUpgradesMarshalled() *ChainConfigWithUpgradesMarshalled {
+	return &ChainConfigWithUpgradesMarshalled{
+		ChainConfig:   c,
+		UpgradeConfig: c.UpgradeConfig,
+	}
+}
+
 // UpgradeConfig includes the following configs that may be specified in upgradeBytes:
 // - Timestamps that enable avalanche network upgrades,
 // - Enabling or disabling precompiles as network upgrades.

params/config_test.go

@@ -34,6 +34,7 @@ import (
 
 	"github.com/ava-labs/subnet-evm/precompile/contracts/nativeminter"
 	"github.com/ava-labs/subnet-evm/precompile/contracts/rewardmanager"
+	"github.com/ava-labs/subnet-evm/precompile/contracts/txallowlist"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/stretchr/testify/require"
 )
@@ -227,3 +228,20 @@ func TestActivePrecompiles(t *testing.T) {
 	rules1 := config.AvalancheRules(common.Big0, common.Big1)
 	require.False(t, rules1.IsPrecompileEnabled(nativeminter.Module.Address))
 }
+
+func TestChainConfigMarshalWithUpgrades(t *testing.T) {
+	config := ChainConfigWithUpgradesMarshalled{
+		ChainConfig: TestChainConfig,
+		UpgradeConfig: UpgradeConfig{
+			PrecompileUpgrades: []PrecompileUpgrade{
+				{
+					Config: txallowlist.NewConfig(big.NewInt(100), nil, nil),
+				},
+			},
+		},
+	}
+	result, err := json.Marshal(&config)
+	require.NoError(t, err)
+	expectedJSON := `{"chainId":1,"feeConfig":{"gasLimit":8000000,"targetBlockRate":2,"minBaseFee":25000000000,"targetGas":15000000,"baseFeeChangeDenominator":36,"minBlockGasCost":0,"maxBlockGasCost":1000000,"blockGasCostStep":200000},"homesteadBlock":0,"eip150Block":0,"eip150Hash":"0x0000000000000000000000000000000000000000000000000000000000000000","eip155Block":0,"eip158Block":0,"byzantiumBlock":0,"constantinopleBlock":0,"petersburgBlock":0,"istanbulBlock":0,"muirGlacierBlock":0,"subnetEVMTimestamp":0,"upgrades":{"precompileUpgrades":[{"txAllowListConfig":{"blockTimestamp":100}}]}}`
+	require.JSONEq(t, expectedJSON, string(result))
+}