Add specific Tornado transaction type - relayer_withdrawal_check_v4 - for backwards compatibility with old gas calculation algorithm

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@tornado/tornado-oracles",
-  "version": "0.1.1",
+  "version": "0.2.0",
   "description": "Gas oracle for Tornado-specific transactions",
   "main": "./lib/index.js",
   "types": "./lib/index.d.ts",

src/feeOracleV4.ts

@@ -23,6 +23,9 @@ export class TornadoFeeOracleV4 extends TornadoFeeOracle implements ITornadoFeeO
     // Need to bump relayer gas limit for transaction, because predefined gas limit to small to be 100% sure that transaction will be sent
     // This leads to fact that relayer often pays extra for gas from his own funds, however, this was designed by previous developers
     if (type === 'relayer_withdrawal') return bump(defaultWithdrawalGasLimit[this.chainId], bumpPercent || 20);
+    // For compatibility reasons, when wee check user-provided fee for V4 withdrawal transaction, we need dump gas limit
+    // for about 20 percent,so that the transaction will be sent, even if it results in some loss for the relayer
+    if (type === 'relayer_withdrawal_check_v4') return bump(defaultWithdrawalGasLimit[this.chainId], -20);
     if (!tx) return BigNumber.from(21_000);
 
     return this.provider.estimateGas(tx);

src/types.ts

@@ -9,7 +9,13 @@ export type LegacyGasPrices = {
   [gasPriceType in LegacyGasPriceKey]: number;
 };
 
-export type TxType = 'user_withdrawal' | 'relayer_withdrawal' | 'other';
+/* Tornado-specific transaction types:
+  - 'user_withdrawal' - Fee calculation on user side, when user withdraw funds itself or via relayer on site
+  - 'relayer_withdrawal' - Fee calculation on relayer side, when relayer sends withdrawal transaction
+  - 'relayer_withdrawal_check_v4' - Fee calculation on relayer side, when V4 relayer checks user-provided fee. For compatibility reasons
+  - 'other' - Any other non-specific transaction
+*/
+export type TxType = 'user_withdrawal' | 'relayer_withdrawal' | 'relayer_withdrawal_check_v4' | 'other';
 
 export interface TransactionData {
   to: string;
@@ -54,6 +60,7 @@ export type TornadoPoolInstance = {
   decimals: number;
 };
 
+// All non-native tokens from Tornado instances on ETH mainnet and TORN itself
 export type TokenSymbol = 'dai' | 'cdai' | 'usdc' | 'usdt' | 'wbtc' | 'torn';
 export type Token = {
   tokenAddress: string;