From fb687af5ad4b71d450eff429b42176e87102ba8d Mon Sep 17 00:00:00 2001
From: Gaston Ponti <pontigaston@gmail.com>
Date: Tue, 3 Dec 2024 18:55:04 -0300
Subject: [PATCH] Fix gas estimator for txs with feeCurrency + Value (#282)

* Fix gas estimator for txs with feeCurrency + Value

---------

Co-authored-by: Maximilian Langenfeld <15726643+ezdac@users.noreply.github.com>
---
 eth/gasestimator/gasestimator.go | 22 ++++++++++++++--------
 internal/ethapi/api.go           | 13 ++++++++-----
 2 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/eth/gasestimator/gasestimator.go b/eth/gasestimator/gasestimator.go
index f35a33eea9..2ebbbf1f1c 100644
--- a/eth/gasestimator/gasestimator.go
+++ b/eth/gasestimator/gasestimator.go
@@ -50,7 +50,7 @@ type Options struct {
 // Estimate returns the lowest possible gas limit that allows the transaction to
 // run successfully with the provided context options. It returns an error if the
 // transaction would always revert, or if there are unexpected failures.
-func Estimate(ctx context.Context, call *core.Message, opts *Options, gasCap uint64, exchangeRates common.ExchangeRates, balance *big.Int) (uint64, []byte, error) {
+func Estimate(ctx context.Context, call *core.Message, opts *Options, gasCap uint64, exchangeRates common.ExchangeRates, feeCurrencyBalance *big.Int) (uint64, []byte, error) {
 	// Binary search the gas limit, as it may need to be higher than the amount used
 	var (
 		lo uint64 // lowest-known gas limit where tx execution fails
@@ -72,7 +72,8 @@ func Estimate(ctx context.Context, call *core.Message, opts *Options, gasCap uin
 	}
 	// Recap the highest gas limit with account's available balance.
 	if feeCap.BitLen() != 0 {
-		available := balance
+		celoBalance := opts.State.GetBalance(call.From).ToBig()
+		available := celoBalance
 		if call.FeeCurrency != nil {
 			if !call.IsFeeCurrencyDenominated() {
 				// CIP-66, prices are given in native token.
@@ -83,12 +84,17 @@ func Estimate(ctx context.Context, call *core.Message, opts *Options, gasCap uin
 					return 0, nil, err
 				}
 			}
-		} else {
-			if call.Value != nil {
-				if call.Value.Cmp(available) >= 0 {
+			available = feeCurrencyBalance
+		}
+		if call.Value != nil {
+			if call.Value.Cmp(celoBalance) > 0 {
+				return 0, nil, core.ErrInsufficientFundsForTransfer
+			}
+			if call.FeeCurrency == nil {
+				available.Sub(available, call.Value)
+				if available.Cmp(big.NewInt(0)) <= 0 {
 					return 0, nil, core.ErrInsufficientFundsForTransfer
 				}
-				available.Sub(available, call.Value)
 			}
 		}
 
@@ -114,8 +120,8 @@ func Estimate(ctx context.Context, call *core.Message, opts *Options, gasCap uin
 			if transfer == nil {
 				transfer = new(big.Int)
 			}
-			log.Debug("Gas estimation capped by limited funds", "original", hi, "balance", balance,
-				"sent", transfer, "maxFeePerGas", feeCap, "fundable", allowance,
+			log.Debug("Gas estimation capped by limited funds", "original", hi, "celo balance", celoBalance,
+				"feeCurrency balance", feeCurrencyBalance, "sent", transfer, "maxFeePerGas", feeCap, "fundable", allowance,
 				"feeCurrency", call.FeeCurrency, "maxFeeInFeeCurrency", call.MaxFeeInFeeCurrency,
 			)
 			hi = allowance.Uint64()
diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index cec1f83a4d..ee686d83cf 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -1330,14 +1330,17 @@ func DoEstimateGas(ctx context.Context, b CeloBackend, args TransactionArgs, blo
 
 	call := args.ToMessage(header.BaseFee, exchangeRates)
 
-	// Celo specific: get balance
-	balance, err := b.GetFeeBalance(ctx, blockNrOrHash, call.From, args.FeeCurrency)
-	if err != nil {
-		return 0, err
+	// Celo specific: get balance of fee currency if fee currency is specified
+	feeCurrencyBalance := new(big.Int)
+	if args.FeeCurrency != nil {
+		feeCurrencyBalance, err = b.GetFeeBalance(ctx, blockNrOrHash, call.From, args.FeeCurrency)
+		if err != nil {
+			return 0, err
+		}
 	}
 
 	// Run the gas estimation and wrap any revertals into a custom return
-	estimate, revert, err := gasestimator.Estimate(ctx, call, opts, gasCap, exchangeRates, balance)
+	estimate, revert, err := gasestimator.Estimate(ctx, call, opts, gasCap, exchangeRates, feeCurrencyBalance)
 	if err != nil {
 		if len(revert) > 0 {
 			return 0, newRevertError(revert)