fix(transaction): improve legacy gasPrice to EIP-1559 dynamic fee (#5225)

Author: gacevicljubisa

pkg/transaction/wrapped/fee.go

@@ -20,20 +20,44 @@ var (
 	ErrEIP1559NotSupported = errors.New("network does not appear to support EIP-1559 (no baseFee)")
 )
 
-// SuggestedFeeAndTip calculates the recommended gasFeeCap and gasTipCap for a transaction.
+// SuggestedFeeAndTip calculates the recommended gasFeeCap (maxFeePerGas) and gasTipCap (maxPriorityFeePerGas) for a transaction.
+// If gasPrice is provided (legacy mode):
+//   - On EIP-1559 networks: gasFeeCap = gasPrice; gasTipCap = max(gasPrice - baseFee, minimumTip) to respect the total cap while enforcing a tip floor where possible.
+//   - On pre-EIP-1559 networks: returns (gasPrice, gasPrice) for legacy transaction compatibility.
+//
+// If gasPrice is nil: Uses suggested tip with optional boost, enforces minimum, and sets gasFeeCap = 2 * baseFee + gasTipCap.
 func (b *wrappedBackend) SuggestedFeeAndTip(ctx context.Context, gasPrice *big.Int, boostPercent int) (*big.Int, *big.Int, error) {
 	if gasPrice != nil {
-		// 1. gasFeeCap: The absolute maximum price per gas does not exceed the user's specified price.
-		// 2. gasTipCap: The entire amount (gasPrice - baseFee) can be used as a priority fee.
-		return new(big.Int).Set(gasPrice), new(big.Int).Set(gasPrice), nil
+		latestBlockHeader, err := b.backend.HeaderByNumber(ctx, nil)
+		if err != nil {
+			return nil, nil, fmt.Errorf("failed to get latest block header: %w", err)
+		}
+		if latestBlockHeader == nil || latestBlockHeader.BaseFee == nil {
+			return new(big.Int).Set(gasPrice), new(big.Int).Set(gasPrice), nil
+		}
+
+		baseFee := latestBlockHeader.BaseFee
+		if gasPrice.Cmp(baseFee) < 0 {
+			return nil, nil, fmt.Errorf("specified gas price %s is below current base fee %s", gasPrice, baseFee)
+		}
+
+		// nominal tip = gasPrice - baseFee
+		gasTipCap := new(big.Int).Sub(gasPrice, baseFee)
+		gasFeeCap := new(big.Int).Set(gasPrice)
+
+		return gasFeeCap, gasTipCap, nil
 	}
 
 	gasTipCap, err := b.backend.SuggestGasTipCap(ctx)
 	if err != nil {
 		return nil, nil, fmt.Errorf("failed to suggest gas tip cap: %w", err)
 	}
+	gasTipCap = new(big.Int).Set(gasTipCap)
 
 	if boostPercent != 0 {
+		if boostPercent < 0 {
+			return nil, nil, fmt.Errorf("negative boostPercent (%d) not allowed", boostPercent)
+		}
 		// multiplier: 100 + boostPercent (e.g., 110 for 10% boost)
 		multiplier := new(big.Int).Add(big.NewInt(int64(percentageDivisor)), big.NewInt(int64(boostPercent)))
 		// gasTipCap = gasTipCap * (100 + boostPercent) / 100
@@ -53,7 +77,7 @@ func (b *wrappedBackend) SuggestedFeeAndTip(ctx context.Context, gasPrice *big.I
 		return nil, nil, ErrEIP1559NotSupported
 	}
 
-	// EIP-1559: gasFeeCap = (2 * baseFee) + gasTipCap
+	// gasFeeCap = (2 * baseFee) + gasTipCap
 	gasFeeCap := new(big.Int).Mul(latestBlockHeader.BaseFee, big.NewInt(int64(baseFeeMultiplier)))
 	gasFeeCap.Add(gasFeeCap, gasTipCap)
 

pkg/transaction/wrapped/fee_test.go

@@ -43,6 +43,13 @@ func TestSuggestedFeeAndTip(t *testing.T) {
 			wantGasFeeCap: big.NewInt(1000),
 			wantGasTipCap: big.NewInt(1000),
 		},
+		{
+			name:          "with gas price and base fee",
+			gasPrice:      big.NewInt(1000),
+			mockHeader:    &types.Header{BaseFee: baseFee},
+			wantGasFeeCap: big.NewInt(1000),
+			wantGasTipCap: big.NewInt(900),
+		},
 		{
 			name:              "suggest tip error",
 			mockSuggestGasErr: errors.New("suggest tip error"),