op-chain-ops: migrated withdrawal gas limit tests

op-chain-ops/crossdomain/migrate.go

@@ -83,6 +83,20 @@ func MigrateWithdrawal(withdrawal *LegacyWithdrawal, l1CrossDomainMessenger *com
 		return nil, fmt.Errorf("cannot abi encode relayMessage: %w", err)
 	}
 
+	gasLimit := MigrateWithdrawalGasLimit(data)
+
+	w := NewWithdrawal(
+		versionedNonce,
+		&predeploys.L2CrossDomainMessengerAddr,
+		l1CrossDomainMessenger,
+		value,
+		new(big.Int).SetUint64(gasLimit),
+		data,
+	)
+	return w, nil
+}
+
+func MigrateWithdrawalGasLimit(data []byte) uint64 {
 	// Compute the cost of the calldata
 	dataCost := uint64(0)
 	for _, b := range data {
@@ -101,13 +115,5 @@ func MigrateWithdrawal(withdrawal *LegacyWithdrawal, l1CrossDomainMessenger *com
 		gasLimit = 25_000_000
 	}
 
-	w := NewWithdrawal(
-		versionedNonce,
-		&predeploys.L2CrossDomainMessengerAddr,
-		l1CrossDomainMessenger,
-		value,
-		new(big.Int).SetUint64(gasLimit),
-		data,
-	)
-	return w, nil
+	return gasLimit
 }

op-chain-ops/crossdomain/migrate_test.go

@@ -2,6 +2,7 @@ package crossdomain_test
 
 import (
 	"fmt"
+	"math/big"
 	"testing"
 
 	"github.com/ethereum-optimism/optimism/op-bindings/predeploys"
@@ -11,6 +12,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+var big25Million = big.NewInt(25_000_000)
+
 func TestMigrateWithdrawal(t *testing.T) {
 	withdrawals := make([]*crossdomain.LegacyWithdrawal, 0)
 
@@ -31,6 +34,57 @@ func TestMigrateWithdrawal(t *testing.T) {
 			require.Equal(t, legacy.XDomainNonce.Uint64(), withdrawal.Nonce.Uint64())
 			require.Equal(t, *withdrawal.Sender, predeploys.L2CrossDomainMessengerAddr)
 			require.Equal(t, *withdrawal.Target, l1CrossDomainMessenger)
+			// Always equal to or lower than the cap
+			require.True(t, withdrawal.GasLimit.Cmp(big25Million) <= 0)
 		})
 	}
 }
+
+// TestMigrateWithdrawalGasLimitMax computes the migrated withdrawal
+// gas limit with a very large amount of data. The max value for a migrated
+// withdrawal's gas limit is 25 million.
+func TestMigrateWithdrawalGasLimitMax(t *testing.T) {
+	size := 300_000_000 / 16
+	data := make([]byte, size)
+	for _, i := range data {
+		data[i] = 0xff
+	}
+
+	result := crossdomain.MigrateWithdrawalGasLimit(data)
+	require.Equal(t, result, big25Million.Uint64())
+}
+
+// TestMigrateWithdrawalGasLimit tests an assortment of zero and non zero
+// bytes when computing the migrated withdrawal's gas limit.
+func TestMigrateWithdrawalGasLimit(t *testing.T) {
+	tests := []struct {
+		input  []byte
+		output uint64
+	}{
+		{
+			input:  []byte{},
+			output: 200_000,
+		},
+		{
+			input:  []byte{0xff},
+			output: 200_000 + 16,
+		},
+		{
+			input:  []byte{0xff, 0x00},
+			output: 200_000 + 16 + 4,
+		},
+		{
+			input:  []byte{0x00},
+			output: 200_000 + 4,
+		},
+		{
+			input:  []byte{0x00, 0x00, 0x00},
+			output: 200_000 + 4 + 4 + 4,
+		},
+	}
+
+	for _, test := range tests {
+		result := crossdomain.MigrateWithdrawalGasLimit(test.input)
+		require.Equal(t, test.output, result)
+	}
+}