op-service/txmgr: Return previous tx if no updates

Return the same transaction if we don't update any fields. We do this
because Ethereum signatures are not deterministic and therefore the
transaction hash will change wwhen we re-sign the tx. We don't want
to do that because we want to see ErrAlreadyKnown instead of
ErrReplacementUnderpriced.

op-service/txmgr/txmgr.go

@@ -122,6 +122,11 @@ func (m *SimpleTxManager) IncreaseGasPrice(ctx context.Context, tx *types.Transa
 		gasTipCap = tip
 	}
 
+	// Return the same transaction if we don't update any fields.
+	// We do this because ethereum signatures are not deterministic and therefore the transaction hash will change
+	// when we re-sign the tx. We don't want to do that because we want to see ErrAlreadyKnown instead of ErrReplacementUnderpriced
+	var reusedTip, reusedFeeCap bool
+
 	// new = old * (100 + priceBump) / 100
 	// Enforce a min priceBump on the tip. Do this before the feeCap is calculated
 	thresholdTip := new(big.Int).Mul(priceBumpPercent, tx.GasTipCap())
@@ -129,6 +134,7 @@ func (m *SimpleTxManager) IncreaseGasPrice(ctx context.Context, tx *types.Transa
 	if tx.GasTipCapIntCmp(gasTipCap) >= 0 {
 		m.l.Debug("Reusing the previous tip", "previous", tx.GasTipCap(), "suggested", gasTipCap)
 		gasTipCap = tx.GasTipCap()
+		reusedTip = true
 	} else if thresholdTip.Cmp(gasTipCap) > 0 {
 		m.l.Debug("Overriding the tip to enforce a price bump", "previous", tx.GasTipCap(), "suggested", gasTipCap, "new", thresholdTip)
 		gasTipCap = thresholdTip
@@ -150,11 +156,16 @@ func (m *SimpleTxManager) IncreaseGasPrice(ctx context.Context, tx *types.Transa
 	if tx.GasFeeCapIntCmp(gasFeeCap) >= 0 {
 		m.l.Debug("Reusing the previous fee cap", "previous", tx.GasFeeCap(), "suggested", gasFeeCap)
 		gasFeeCap = tx.GasFeeCap()
+		reusedFeeCap = true
 	} else if thresholdFeeCap.Cmp(gasFeeCap) > 0 {
 		m.l.Debug("Overriding the fee cap to enforce a price bump", "previous", tx.GasFeeCap(), "suggested", gasFeeCap, "new", thresholdFeeCap)
 		gasFeeCap = thresholdFeeCap
 	}
 
+	if reusedTip && reusedFeeCap {
+		return tx, nil
+	}
+
 	rawTx := &types.DynamicFeeTx{
 		ChainID:    tx.ChainId(),
 		Nonce:      tx.Nonce(),

op-service/txmgr/txmgr_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"math/big"
+	"math/rand"
 	"sync"
 	"testing"
 	"time"
@@ -11,9 +12,12 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/ethereum-optimism/optimism/op-node/testlog"
+	"github.com/ethereum-optimism/optimism/op-node/testutils"
+	opcrypto "github.com/ethereum-optimism/optimism/op-service/crypto"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/log"
 )
 
@@ -727,3 +731,42 @@ func TestIncreaseGasPriceUseLargeIncrease(t *testing.T) {
 	require.True(t, newTx.GasFeeCap().Cmp(feeCap) == 0, "new tx fee cap must be equal L1")
 	require.True(t, newTx.GasTipCap().Cmp(borkedBackend.gasTip) == 0, "new tx tip must be equal L1")
 }
+
+// TestIncreaseGasPriceReusesTransaction asserts that if the L1 basefee & tip remain the
+// same, the transaction is returned with the same signature values. The means that the error
+// when submitting the transaction to the network is ErrAlreadyKnown instead of ErrReplacementUnderpriced
+func TestIncreaseGasPriceReusesTransaction(t *testing.T) {
+	t.Parallel()
+
+	borkedBackend := failingBackend{
+		gasTip:  big.NewInt(10),
+		baseFee: big.NewInt(45),
+	}
+	pk := testutils.InsecureRandomKey(rand.New(rand.NewSource(123)))
+	signer := opcrypto.PrivateKeySignerFn(pk, big.NewInt(10))
+
+	mgr := &SimpleTxManager{
+		Config: Config{
+			ResubmissionTimeout:       time.Second,
+			ReceiptQueryInterval:      50 * time.Millisecond,
+			NumConfirmations:          1,
+			SafeAbortNonceTooLowCount: 3,
+			Signer: func(ctx context.Context, from common.Address, tx *types.Transaction) (*types.Transaction, error) {
+				return signer(from, tx)
+			},
+			From: crypto.PubkeyToAddress(pk.PublicKey),
+		},
+		name:    "TEST",
+		backend: &borkedBackend,
+		l:       testlog.Logger(t, log.LvlCrit),
+	}
+	tx := types.NewTx(&types.DynamicFeeTx{
+		GasTipCap: big.NewInt(10),
+		GasFeeCap: big.NewInt(100),
+	})
+
+	ctx := context.Background()
+	newTx, err := mgr.IncreaseGasPrice(ctx, tx)
+	require.NoError(t, err)
+	require.Equal(t, tx.Hash(), newTx.Hash())
+}