From f04f51cd0c2e484340c1dbee90873fbb5ef12791 Mon Sep 17 00:00:00 2001
From: Shane Bammel <sjb933@gmail.com>
Date: Tue, 15 Feb 2022 21:26:18 -0600
Subject: [PATCH] Simplify DoEstimateGas with RequiredGas field

By tracking the RequiredGas independently from refunds,
DoEstimateGas() can return an accurate gas estimate without the
complexity of the binary search.
---
 internal/ethapi/api.go | 71 ++++++++++++++----------------------------
 1 file changed, 23 insertions(+), 48 deletions(-)

diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index 65e34752b..c5df292b7 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -995,19 +995,14 @@ func (s *PublicBlockChainAPI) Call(ctx context.Context, args TransactionArgs, bl
 }
 
 func DoEstimateGas(ctx context.Context, b Backend, args TransactionArgs, blockNrOrHash rpc.BlockNumberOrHash, gasCap uint64) (hexutil.Uint64, error) {
-	// Binary search the gas requirement, as it may be higher than the amount used
-	var (
-		lo  uint64 = params.TxGas - 1
-		hi  uint64
-		cap uint64
-	)
+	var maxGas uint64
 	// Use zero address if sender unspecified.
 	if args.From == nil {
 		args.From = new(common.Address)
 	}
 	// Determine the highest gas limit can be used during the estimation.
 	if args.Gas != nil && uint64(*args.Gas) >= params.TxGas {
-		hi = uint64(*args.Gas)
+		maxGas = uint64(*args.Gas)
 	} else {
 		// Retrieve the block to act as the gas ceiling
 		block, err := b.BlockByNumberOrHash(ctx, blockNrOrHash)
@@ -1017,7 +1012,7 @@ func DoEstimateGas(ctx context.Context, b Backend, args TransactionArgs, blockNr
 		if block == nil {
 			return 0, errors.New("block not found")
 		}
-		hi = block.GasLimit()
+		maxGas = block.GasLimit()
 	}
 	// Normalize the max fee per gas the call is willing to spend.
 	var feeCap *big.Int
@@ -1047,23 +1042,21 @@ func DoEstimateGas(ctx context.Context, b Backend, args TransactionArgs, blockNr
 		allowance := new(big.Int).Div(available, feeCap)
 
 		// If the allowance is larger than maximum uint64, skip checking
-		if allowance.IsUint64() && hi > allowance.Uint64() {
+		if allowance.IsUint64() && maxGas > allowance.Uint64() {
 			transfer := args.Value
 			if transfer == nil {
 				transfer = new(hexutil.Big)
 			}
-			log.Warn("Gas estimation capped by limited funds", "original", hi, "balance", balance,
+			log.Warn("Gas estimation capped by limited funds", "original", maxGas, "balance", balance,
 				"sent", transfer.ToInt(), "maxFeePerGas", feeCap, "fundable", allowance)
-			hi = allowance.Uint64()
+			maxGas = allowance.Uint64()
 		}
 	}
 	// Recap the highest gas allowance with specified gascap.
-	if gasCap != 0 && hi > gasCap {
-		log.Warn("Caller gas above allowance, capping", "requested", hi, "cap", gasCap)
-		hi = gasCap
+	if gasCap != 0 && maxGas > gasCap {
+		log.Warn("Caller gas above allowance, capping", "requested", maxGas, "cap", gasCap)
+		maxGas = gasCap
 	}
-	cap = hi
-
 	// Create a helper to check if a gas allowance results in an executable transaction
 	executable := func(gas uint64) (bool, *core.ExecutionResult, error) {
 		args.Gas = (*hexutil.Uint64)(&gas)
@@ -1077,41 +1070,23 @@ func DoEstimateGas(ctx context.Context, b Backend, args TransactionArgs, blockNr
 		}
 		return result.Failed(), result, nil
 	}
-	// Execute the binary search and hone in on an executable gas limit
-	for lo+1 < hi {
-		mid := (hi + lo) / 2
-		failed, _, err := executable(mid)
 
-		// If the error is not nil(consensus error), it means the provided message
-		// call or transaction will never be accepted no matter how much gas it is
-		// assigned. Return the error directly, don't struggle any more.
-		if err != nil {
-			return 0, err
-		}
-		if failed {
-			lo = mid
-		} else {
-			hi = mid
-		}
-	}
 	// Reject the transaction as invalid if it still fails at the highest allowance
-	if hi == cap {
-		failed, result, err := executable(hi)
-		if err != nil {
-			return 0, err
-		}
-		if failed {
-			if result != nil && result.Err != vm.ErrOutOfGas {
-				if len(result.Revert()) > 0 {
-					return 0, newRevertError(result)
-				}
-				return 0, result.Err
-			}
-			// Otherwise, the specified gas cap is too low
-			return 0, fmt.Errorf("gas required exceeds allowance (%d)", cap)
-		}
+	failed, result, err := executable(maxGas)
+	if err != nil {
+		return 0, err
 	}
-	return hexutil.Uint64(hi), nil
+	if failed {
+		if result != nil && result.Err != vm.ErrOutOfGas {
+			if len(result.Revert()) > 0 {
+				return 0, newRevertError(result)
+			}
+			return 0, result.Err
+		}
+		// Otherwise, the specified gas cap is too low
+		return 0, fmt.Errorf("gas required exceeds allowance (%d)", maxGas)
+	}
+	return hexutil.Uint64(result.RequiredGas), nil
 }
 
 // EstimateGas returns an estimate of the amount of gas needed to execute the