fix(ethrpc): report zero native balance and gas

The EVM facade reported a fake 1000-coin native balance and a 1 gwei
gas price so MetaMask's `balance >= value + gasLimit*gasPrice` pre-flight
check would pass. The fake balance is confusing — users with no native
coin see 1000.

There is no native gas token, so report 0. Since the facade only accepts
zero-value ERC-20 transfers, MetaMask's check collapses to `0 >= 0` as
long as gas is also 0, so transfers still go through.

Gas price and the cosmetic gas limit are fixed values, not deployment
knobs, so hardcode them in code and drop them from config:
- native balance: always 0 (token.Native.GetBalance)
- gas price: always 0 (eth_gasPrice, maxPriorityFeePerGas, baseFeePerGas,
  effectiveGasPrice)
- gas limit: service.DefaultGasLimit (21000), cosmetic only

The relayer's ethereum.gas_limit (real on-chain gas) is unaffected.

Author: sadiq1971

config.e2e-local.yaml

@@ -87,15 +87,11 @@ token:
       symbol: "USDCx"
       decimals: 6
       instrument_id: "USDCx"
-  native_balance_wei: "1000000000000000000000"
 
 # Ethereum JSON-RPC facade (MetaMask compatibility)
 eth_rpc:
   enabled: true
   chain_id: 31337
-  gas_price_wei: "1000000000"
-  gas_limit: 21000
-  native_balance_wei: "1000000000000000000000"
   request_timeout: "30s"
 
 jwks:

pkg/app/api/server.go

@@ -239,7 +239,7 @@ func initServices(
 	if cfg.EthRPC.Enabled {
 		m := ethrpcminer.New(
 			evmStore,
-			cfg.EthRPC.ChainID, cfg.EthRPC.GasLimit,
+			cfg.EthRPC.ChainID, ethrpc.DefaultGasLimit,
 			cfg.EthRPC.MinerMaxTxsPerBlock, cfg.EthRPC.MinerInterval,
 			ethrpcminer.NewMetrics(reg),
 			logger,

pkg/config/config_test.go

@@ -125,22 +125,9 @@ func TestLoadAPIServer_AppliesDefaults(t *testing.T) {
 		t.Fatalf("auth.expiry_leeway default mismatch: got %s", cfg.Canton.Ledger.Auth.ExpiryLeeway)
 	}
 
-	if cfg.Token.NativeBalanceWei != "1000000000000000000000" {
-		t.Fatalf("token.native_balance_wei default mismatch: got %q", cfg.Token.NativeBalanceWei)
-	}
-
 	if cfg.EthRPC.Enabled {
 		t.Fatal("eth_rpc.enabled default mismatch: expected false")
 	}
-	if cfg.EthRPC.GasPriceWei != "1000000000" {
-		t.Fatalf("eth_rpc.gas_price_wei default mismatch: got %q", cfg.EthRPC.GasPriceWei)
-	}
-	if cfg.EthRPC.GasLimit != 21000 {
-		t.Fatalf("eth_rpc.gas_limit default mismatch: got %d", cfg.EthRPC.GasLimit)
-	}
-	if cfg.EthRPC.NativeBalanceWei != "1000000000000000000000" {
-		t.Fatalf("eth_rpc.native_balance_wei default mismatch: got %q", cfg.EthRPC.NativeBalanceWei)
-	}
 	if cfg.EthRPC.RequestTimeout != 30*time.Second {
 		t.Fatalf("eth_rpc.request_timeout default mismatch: got %s", cfg.EthRPC.RequestTimeout)
 	}

pkg/config/defaults/config.api-server.docker.yaml

@@ -91,15 +91,11 @@ token:
       symbol: "USDCx"
       decimals: 6
       instrument_id: "USDCx"
-  native_balance_wei: "1000000000000000000000"
 
 # Ethereum JSON-RPC facade (MetaMask compatibility)
 eth_rpc:
   enabled: true
   chain_id: 31337  # Anvil local chain ID
-  gas_price_wei: "1000000000"
-  gas_limit: 21000
-  native_balance_wei: "1000000000000000000000"
   request_timeout: "30s"
 
 # JWKS endpoint for JWT validation (optional - if not using EVM signatures)

pkg/config/defaults/config.api-server.local-devnet.yaml

@@ -84,15 +84,11 @@ token:
       symbol: "USDCx"
       decimals: 6
       instrument_id: "USDCx"
-  native_balance_wei: "1000000000000000000000"
 
 # Ethereum JSON-RPC facade (MetaMask compatibility)
 eth_rpc:
   enabled: true
   chain_id: 1155111101  # Custom: Sepolia (11155111) + 01 suffix for Canton local
-  gas_price_wei: "1000000000"
-  gas_limit: 21000
-  native_balance_wei: "1000000000000000000000"
   request_timeout: "60s"
 
 jwks:

pkg/config/defaults/config.api-server.mainnet.yaml

@@ -67,14 +67,10 @@ token:
       symbol: "USDCx"
       decimals: 6
       instrument_id: "USDCx"
-  native_balance_wei: "1000000000000000000000"
 
 eth_rpc:
   enabled: true
   chain_id: 1337
-  gas_price_wei: "1000000000"
-  gas_limit: 21000
-  native_balance_wei: "1000000000000000000000"
   request_timeout: "60s"
 
 jwks:

pkg/ethrpc/config.go

@@ -10,9 +10,6 @@ import (
 type Config struct {
 	Enabled             bool          `yaml:"enabled" default:"false"`
 	ChainID             uint64        `yaml:"chain_id" validate:"required_if=Enabled true"`
-	GasPriceWei         string        `yaml:"gas_price_wei" default:"1000000000"`
-	GasLimit            uint64        `yaml:"gas_limit" default:"21000"`
-	NativeBalanceWei    string        `yaml:"native_balance_wei" default:"1000000000000000000000"`
 	RequestTimeout      time.Duration `yaml:"request_timeout"  default:"30s"`
 	MinerInterval       time.Duration `yaml:"miner_interval"   default:"2s"`
 	MinerMaxTxsPerBlock int           `yaml:"miner_max_txs_per_block" default:"500"`

pkg/ethrpc/service/service.go

@@ -83,13 +83,14 @@ type ethService struct {
 }
 
 const (
-	decimalStringBase         = 10
-	defaultGasPriceWeiInt64   = int64(1_000_000_000)
-	defaultGasPriceWeiUint64  = uint64(1_000_000_000)
 	functionSelectorSize      = 4
-	topicSizeBytes            = 32
 	confirmationBufferBlocks  = uint64(12)
 	syntheticBlockTimeSeconds = uint64(12)
+	// DefaultGasLimit is the cosmetic gas limit the facade reports (eth_estimateGas,
+	// block gasLimit, tx gas, synthetic block gasUsed). The facade executes
+	// transfers on Canton rather than an EVM, so gas is never metered — and the
+	// gas price is fixed at 0 — making this value purely informational for wallets.
+	DefaultGasLimit = 21_000
 )
 
 // NewService creates a new ethService.
@@ -140,21 +141,24 @@ func (s *ethService) BlockNumber(ctx context.Context) (hexutil.Uint64, error) {
 	return hexutil.Uint64(max(baseBlock, timeBasedBlocks)), nil
 }
 
-func (s *ethService) GasPrice(_ context.Context) (*hexutil.Big, error) {
-	gasPrice := new(big.Int)
-	if _, ok := gasPrice.SetString(s.cfg.GasPriceWei, decimalStringBase); !ok {
-		return nil, apperr.GeneralError(fmt.Errorf("invalid gas price wei: %q", s.cfg.GasPriceWei))
-	}
-
-	return (*hexutil.Big)(gasPrice), nil
+// GasPrice always reports 0, and so do maxPriorityFeePerGas, block
+// baseFeePerGas, and receipt effectiveGasPrice. The facade never charges gas,
+// and MetaMask's client-side pre-flight check is
+// `balance >= value + gasLimit*gasPrice`. Since eth_getBalance reports a zero
+// native balance and this facade only accepts zero-value ERC-20 transfers, the
+// check collapses to `0 >= 0` only while gas is 0 — any non-zero gas price would
+// make MetaMask reject transfers with "insufficient funds for gas". Gas is
+// therefore fixed at 0 in code rather than exposed as config.
+func (*ethService) GasPrice(_ context.Context) (*hexutil.Big, error) {
+	return (*hexutil.Big)(big.NewInt(0)), nil
 }
 
 func (*ethService) MaxPriorityFeePerGas(_ context.Context) (*hexutil.Big, error) {
-	return (*hexutil.Big)(big.NewInt(defaultGasPriceWeiInt64)), nil
+	return (*hexutil.Big)(big.NewInt(0)), nil
 }
 
-func (s *ethService) EstimateGas(_ context.Context, _ *ethrpc.CallArgs) (hexutil.Uint64, error) {
-	return hexutil.Uint64(s.cfg.GasLimit), nil
+func (*ethService) EstimateGas(_ context.Context, _ *ethrpc.CallArgs) (hexutil.Uint64, error) {
+	return hexutil.Uint64(DefaultGasLimit), nil
 }
 
 func (s *ethService) GetBalance(ctx context.Context, address common.Address) (*hexutil.Big, error) {
@@ -328,7 +332,7 @@ func (s *ethService) GetTransactionReceipt(ctx context.Context, hash common.Hash
 		Logs:              logs,
 		LogsBloom:         bloom,
 		Status:            hexutil.Uint64(row.Status),
-		EffectiveGasPrice: hexutil.Uint64(defaultGasPriceWeiUint64),
+		EffectiveGasPrice: hexutil.Uint64(0),
 		Type:              hexutil.Uint64(2),
 		// RevertReason is omitted when empty (omitempty), so successful
 		// receipts keep the standard JSON shape.
@@ -350,7 +354,7 @@ func (s *ethService) GetTransactionByHash(ctx context.Context, hash common.Hash)
 	blockHash := common.BytesToHash(row.BlockHash)
 	blockNum := hexutil.Uint64(row.BlockNumber)
 	txIndex := hexutil.Uint(row.TxIndex)
-	gasPrice := big.NewInt(defaultGasPriceWeiInt64)
+	gasPrice := big.NewInt(0)
 
 	return &ethrpc.RPCTransaction{
 		Hash:             hash,
@@ -362,7 +366,7 @@ func (s *ethService) GetTransactionByHash(ctx context.Context, hash common.Hash)
 		To:               &to,
 		Value:            (*hexutil.Big)(big.NewInt(0)),
 		GasPrice:         (*hexutil.Big)(gasPrice),
-		Gas:              hexutil.Uint64(s.cfg.GasLimit),
+		Gas:              hexutil.Uint64(DefaultGasLimit),
 		Input:            row.Input,
 		Type:             hexutil.Uint64(2),
 		ChainID:          (*hexutil.Big)(new(big.Int).Set(s.chainID)),
@@ -557,12 +561,12 @@ func (s *ethService) GetBlockByNumber(ctx context.Context, block ethrpc.BlockNum
 		TotalDifficulty:  (*hexutil.Big)(big.NewInt(0)),
 		ExtraData:        []byte{},
 		Size:             hexutil.Uint64(0),
-		GasLimit:         hexutil.Uint64(s.cfg.GasLimit),
+		GasLimit:         hexutil.Uint64(DefaultGasLimit),
 		GasUsed:          hexutil.Uint64(0),
 		Timestamp:        hexutil.Uint64(blockNum * syntheticBlockTimeSeconds),
 		Transactions:     []any{},
 		Uncles:           []common.Hash{},
-		BaseFeePerGas:    (*hexutil.Big)(big.NewInt(defaultGasPriceWeiInt64)),
+		BaseFeePerGas:    (*hexutil.Big)(big.NewInt(0)),
 	}, nil
 }
 

pkg/ethrpc/service/service_test.go

@@ -24,11 +24,8 @@ import (
 // defaultCfg returns a minimal EthRPCConfig suitable for unit tests.
 func defaultCfg() *ethrpc.Config {
 	return &ethrpc.Config{
-		ChainID:          31337,
-		GasPriceWei:      "1000000000",
-		GasLimit:         21000,
-		RequestTimeout:   30 * time.Second,
-		NativeBalanceWei: "1000000000000000000000",
+		ChainID:        31337,
+		RequestTimeout: 30 * time.Second,
 	}
 }
 
@@ -73,46 +70,44 @@ func TestService_BlockNumber(t *testing.T) {
 
 // ─── GasPrice ─────────────────────────────────────────────────────────────────
 
+// Gas is fixed at 0 in code (not configurable). See TestService_ZeroGas for the
+// MetaMask-compatibility rationale.
 func TestService_GasPrice(t *testing.T) {
-	t.Run("valid config returns configured price", func(t *testing.T) {
-		svc := newSvc(t, defaultCfg(), nil, nil)
-
-		got, err := svc.GasPrice(context.Background())
-		require.NoError(t, err)
-		assert.Equal(t, big.NewInt(1_000_000_000), got.ToInt())
-	})
-
-	t.Run("non-numeric wei string returns error", func(t *testing.T) {
-		cfg := defaultCfg()
-		cfg.GasPriceWei = "not-a-number"
-		svc := newSvc(t, cfg, nil, nil)
-
-		_, err := svc.GasPrice(context.Background())
-		require.Error(t, err)
-		assert.True(t, apperr.Is(err, apperr.CategoryGeneralError))
-	})
+	got, err := newSvc(t, defaultCfg(), nil, nil).GasPrice(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, big.NewInt(0), got.ToInt())
 }
 
 // ─── MaxPriorityFeePerGas ─────────────────────────────────────────────────────
 
 func TestService_MaxPriorityFeePerGas(t *testing.T) {
-	svc := newSvc(t, defaultCfg(), nil, nil)
+	got, err := newSvc(t, defaultCfg(), nil, nil).MaxPriorityFeePerGas(context.Background())
+	require.NoError(t, err)
+	assert.Equal(t, big.NewInt(0), got.ToInt())
+}
 
-	got, err := svc.MaxPriorityFeePerGas(context.Background())
+// ─── Zero gas (MetaMask compatibility) ────────────────────────────────────────
+
+// TestService_ZeroGas locks in the MetaMask-compatibility contract: gas is fixed
+// at 0 across every fee surface a wallet reads, so a zero native balance
+// satisfies MetaMask's `balance >= value + gas*price` pre-flight check for the
+// zero-value ERC-20 transfers this facade accepts. A non-zero gas price would
+// make MetaMask reject transfers with "insufficient funds for gas".
+func TestService_ZeroGas(t *testing.T) {
+	blockNum := hexutil.Uint64(42)
+	got, err := newSvc(t, defaultCfg(), nil, nil).
+		GetBlockByNumber(context.Background(), ethrpc.BlockNumberOrHash{BlockNumber: &blockNum}, false)
 	require.NoError(t, err)
-	assert.Equal(t, big.NewInt(1_000_000_000), got.ToInt())
+	require.NotNil(t, got)
+	assert.Equal(t, big.NewInt(0), got.BaseFeePerGas.ToInt())
 }
 
 // ─── EstimateGas ──────────────────────────────────────────────────────────────
 
 func TestService_EstimateGas(t *testing.T) {
-	cfg := defaultCfg()
-	cfg.GasLimit = 50_000
-	svc := newSvc(t, cfg, nil, nil)
-
-	got, err := svc.EstimateGas(context.Background(), nil)
+	got, err := newSvc(t, defaultCfg(), nil, nil).EstimateGas(context.Background(), nil)
 	require.NoError(t, err)
-	assert.Equal(t, hexutil.Uint64(50_000), got)
+	assert.Equal(t, hexutil.Uint64(service.DefaultGasLimit), got)
 }
 
 // ─── GetBalance ───────────────────────────────────────────────────────────────

pkg/token/config.go

@@ -18,15 +18,13 @@ type ERC20Token struct {
 
 // Config holds token metadata indexed by contract address.
 type Config struct {
-	SupportedTokens  map[common.Address]ERC20Token `yaml:"supported_tokens" validate:"required,min=1"`
-	NativeBalanceWei string                        `yaml:"native_balance_wei" default:"1000000000000000000000"`
+	SupportedTokens map[common.Address]ERC20Token `yaml:"supported_tokens" validate:"required,min=1"`
 }
 
 // NewConfig creates a token Config.
-func NewConfig(nativeBalanceWei string) *Config {
+func NewConfig() *Config {
 	return &Config{
-		NativeBalanceWei: nativeBalanceWei,
-		SupportedTokens:  make(map[common.Address]ERC20Token),
+		SupportedTokens: make(map[common.Address]ERC20Token),
 	}
 }