Add fee currencies to gas price RPC API (#96)

* Add fee currencies to gas price RPC API

* Fix typo

Co-authored-by: Karl Bartel <[email protected]>

* Format JS e2e tests

---------

Co-authored-by: Karl Bartel <[email protected]>

e2e_test/js-tests/package.json

@@ -1,17 +1,17 @@
 {
-  "name": "js-tests",
-  "version": "1.0.0",
-  "description": "",
-  "main": "index.js",
-  "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
-  },
-  "author": "",
-  "license": "MIT",
-  "dependencies": {
-    "chai": "^5.0.0",
-    "ethers": "^6.10.0",
-    "mocha": "^10.2.0",
-    "viem": "^2.9.6"
-  }
+	"name": "js-tests",
+	"version": "1.0.0",
+	"description": "",
+	"main": "index.js",
+	"scripts": {
+		"test": "echo \"Error: no test specified\" && exit 1"
+	},
+	"author": "",
+	"license": "MIT",
+	"dependencies": {
+		"chai": "^5.0.0",
+		"ethers": "^6.10.0",
+		"mocha": "^10.2.0",
+		"viem": "^2.9.6"
+	}
 }

e2e_test/js-tests/test_viem_tx.mjs

@@ -142,6 +142,45 @@ describe("viem send tx", () => {
 		assert.equal(receipt.status, "success", "receipt status 'failure'");
 	}).timeout(10_000);
 
+	it("test gas price difference for fee currency", async () => {
+		const request = await walletClient.prepareTransactionRequest({
+			account,
+			to: "0x00000000000000000000000000000000DeaDBeef",
+			value: 2,
+			gas: 90000,
+			feeCurrency: process.env.FEE_CURRENCY,
+		});
+
+		const gasPriceNative = await publicClient.getGasPrice({});
+		var maxPriorityFeePerGasNative =
+			await publicClient.estimateMaxPriorityFeePerGas({});
+		const block = await publicClient.getBlock({});
+		assert.equal(
+			BigInt(block.baseFeePerGas) + maxPriorityFeePerGasNative,
+			gasPriceNative,
+		);
+
+		// viem's getGasPrice does not expose additional request parameters,
+		// but Celo's override 'chain.fees.estimateFeesPerGas' action does.
+		// this will call the eth_gasPrice and eth_maxPriorityFeePerGas methods
+		// with the additional feeCurrency parameter internally
+		var fees = await publicClient.estimateFeesPerGas({
+			type: "eip1559",
+			request: {
+				feeCurrency: process.env.FEE_CURRENCY,
+			},
+		});
+		// first check that the fee currency denominated gas price
+		// converts properly to the native gas price
+		assert.equal(fees.maxFeePerGas, gasPriceNative * 2n);
+		assert.equal(fees.maxPriorityFeePerGas, maxPriorityFeePerGasNative * 2n);
+
+		// check that the prepared transaction request uses the
+		// converted gas price internally
+		assert.equal(request.maxFeePerGas, fees.maxFeePerGas);
+		assert.equal(request.maxPriorityFeePerGas, fees.maxPriorityFeePerGas);
+	}).timeout(10_000);
+
 	it("send overlapping nonce tx in different currencies", async () => {
 		const priceBump = 1.1;
 		const rate = 2;

eth/backend.go

@@ -47,6 +47,7 @@ import (
 	"github.com/ethereum/go-ethereum/eth/tracers"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/event"
+	"github.com/ethereum/go-ethereum/internal/celoapi"
 	"github.com/ethereum/go-ethereum/internal/ethapi"
 	"github.com/ethereum/go-ethereum/internal/shutdowncheck"
 	"github.com/ethereum/go-ethereum/log"
@@ -395,6 +396,13 @@ func (s *Ethereum) APIs() []rpc.API {
 			Namespace: "net",
 			Service:   s.netRPCService,
 		},
+		// CELO specific API backend.
+		// For methods in the backend that are already defined (match by name)
+		// on the eth namespace, this will overwrite the original procedures.
+		{
+			Namespace: "eth",
+			Service:   celoapi.NewCeloAPI(s, s.APIBackend),
+		},
 	}...)
 }
 

internal/celoapi/backend.go

@@ -0,0 +1,97 @@
+package celoapi
+
+import (
+	"context"
+	"fmt"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/exchange"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/contracts"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/internal/ethapi"
+)
+
+type Ethereum interface {
+	BlockChain() *core.BlockChain
+}
+
+type CeloAPI struct {
+	ethAPI *ethapi.EthereumAPI
+	eth    Ethereum
+}
+
+func NewCeloAPI(e Ethereum, b ethapi.Backend) *CeloAPI {
+	return &CeloAPI{
+		ethAPI: ethapi.NewEthereumAPI(b),
+		eth:    e,
+	}
+}
+
+func (c *CeloAPI) convertedCurrencyValue(v *hexutil.Big, feeCurrency *common.Address) (*hexutil.Big, error) {
+	if feeCurrency != nil {
+		convertedTipCap, err := c.convertGoldToCurrency(v.ToInt(), feeCurrency)
+		if err != nil {
+			return nil, fmt.Errorf("convert to feeCurrency: %w", err)
+		}
+		v = (*hexutil.Big)(convertedTipCap)
+	}
+	return v, nil
+}
+
+func (c *CeloAPI) celoBackendCurrentState() (*contracts.CeloBackend, error) {
+	state, err := c.eth.BlockChain().State()
+	if err != nil {
+		return nil, fmt.Errorf("retrieve HEAD blockchain state': %w", err)
+	}
+
+	cb := &contracts.CeloBackend{
+		ChainConfig: c.eth.BlockChain().Config(),
+		State:       state,
+	}
+	return cb, nil
+}
+
+func (c *CeloAPI) convertGoldToCurrency(nativePrice *big.Int, feeCurrency *common.Address) (*big.Int, error) {
+	cb, err := c.celoBackendCurrentState()
+	if err != nil {
+		return nil, err
+	}
+	er, err := contracts.GetExchangeRates(cb)
+	if err != nil {
+		return nil, fmt.Errorf("retrieve exchange rates from current state: %w", err)
+	}
+	return exchange.ConvertCeloToCurrency(er, feeCurrency, nativePrice)
+}
+
+// GasPrice wraps the original JSON RPC `eth_gasPrice` and adds an additional
+// optional parameter `feeCurrency` for fee-currency conversion.
+// When `feeCurrency` is not given, then the original JSON RPC method is called without conversion.
+func (c *CeloAPI) GasPrice(ctx context.Context, feeCurrency *common.Address) (*hexutil.Big, error) {
+	tipcap, err := c.ethAPI.GasPrice(ctx)
+	if err != nil {
+		return nil, err
+	}
+	// Between the call to `ethapi.GasPrice` and the call to fetch and convert the rates,
+	// there is a chance of a state-change. This means that gas-price suggestion is calculated
+	// based on state of block x, while the currency conversion could be calculated based on block
+	// x+1.
+	// However, a similar race condition is present in the `ethapi.GasPrice` method itself.
+	return c.convertedCurrencyValue(tipcap, feeCurrency)
+}
+
+// MaxPriorityFeePerGas wraps the original JSON RPC `eth_maxPriorityFeePerGas` and adds an additional
+// optional parameter `feeCurrency` for fee-currency conversion.
+// When `feeCurrency` is not given, then the original JSON RPC method is called without conversion.
+func (c *CeloAPI) MaxPriorityFeePerGas(ctx context.Context, feeCurrency *common.Address) (*hexutil.Big, error) {
+	tipcap, err := c.ethAPI.MaxPriorityFeePerGas(ctx)
+	if err != nil {
+		return nil, err
+	}
+	// Between the call to `ethapi.MaxPriorityFeePerGas` and the call to fetch and convert the rates,
+	// there is a chance of a state-change. This means that gas-price suggestion is calculated
+	// based on state of block x, while the currency conversion could be calculated based on block
+	// x+1.
+	return c.convertedCurrencyValue(tipcap, feeCurrency)
+}