eth/tracers/native: fix flatCallTracer Stop() bug (#29623)

Co-authored-by: Sina Mahmoodi <itz.s1na@gmail.com>

eth/tracers/native/call_flat.go

@@ -23,6 +23,7 @@ import (
 	"math/big"
 	"slices"
 	"strings"
+	"sync/atomic"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
@@ -114,7 +115,7 @@ type flatCallTracer struct {
 	tracer            *callTracer
 	config            flatCallTracerConfig
 	ctx               *tracers.Context // Holds tracer context data
-	reason            error            // Textual reason for the interruption
+	interrupt         atomic.Bool      // Atomic flag to signal execution interruption
 	activePrecompiles []common.Address // Updated on tx start based on given rules
 }
 
@@ -154,6 +155,9 @@ func newFlatCallTracer(ctx *tracers.Context, cfg json.RawMessage) (*tracers.Trac
 
 // OnEnter is called when EVM enters a new scope (via call, create or selfdestruct).
 func (t *flatCallTracer) OnEnter(depth int, typ byte, from common.Address, to common.Address, input []byte, gas uint64, value *big.Int) {
+	if t.interrupt.Load() {
+		return
+	}
 	t.tracer.OnEnter(depth, typ, from, to, input, gas, value)
 
 	if depth == 0 {
@@ -169,6 +173,9 @@ func (t *flatCallTracer) OnEnter(depth int, typ byte, from common.Address, to co
 // OnExit is called when EVM exits a scope, even if the scope didn't
 // execute any code.
 func (t *flatCallTracer) OnExit(depth int, output []byte, gasUsed uint64, err error, reverted bool) {
+	if t.interrupt.Load() {
+		return
+	}
 	t.tracer.OnExit(depth, output, gasUsed, err, reverted)
 
 	if depth == 0 {
@@ -194,6 +201,9 @@ func (t *flatCallTracer) OnExit(depth int, output []byte, gasUsed uint64, err er
 }
 
 func (t *flatCallTracer) OnTxStart(env *tracing.VMContext, tx *types.Transaction, from common.Address) {
+	if t.interrupt.Load() {
+		return
+	}
 	t.tracer.OnTxStart(env, tx, from)
 	// Update list of precompiles based on current block
 	rules := env.ChainConfig.Rules(env.BlockNumber, env.Random != nil, env.Time)
@@ -201,6 +211,9 @@ func (t *flatCallTracer) OnTxStart(env *tracing.VMContext, tx *types.Transaction
 }
 
 func (t *flatCallTracer) OnTxEnd(receipt *types.Receipt, err error) {
+	if t.interrupt.Load() {
+		return
+	}
 	t.tracer.OnTxEnd(receipt, err)
 }
 
@@ -219,12 +232,13 @@ func (t *flatCallTracer) GetResult() (json.RawMessage, error) {
 	if err != nil {
 		return nil, err
 	}
-	return res, t.reason
+	return res, t.tracer.reason
 }
 
 // Stop terminates execution of the tracer at the first opportune moment.
 func (t *flatCallTracer) Stop(err error) {
 	t.tracer.Stop(err)
+	t.interrupt.Store(true)
 }
 
 // isPrecompiled returns whether the addr is a precompile.

eth/tracers/native/call_flat_test.go

@@ -0,0 +1,64 @@
+// Copyright 2024 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package native_test
+
+import (
+	"errors"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/tracing"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/eth/tracers"
+	"github.com/ethereum/go-ethereum/params"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCallFlatStop(t *testing.T) {
+	tracer, err := tracers.DefaultDirectory.New("flatCallTracer", &tracers.Context{}, nil)
+	require.NoError(t, err)
+
+	// this error should be returned by GetResult
+	stopError := errors.New("stop error")
+
+	// simulate a transaction
+	tx := types.NewTx(&types.LegacyTx{
+		Nonce:    0,
+		To:       &common.Address{},
+		Value:    big.NewInt(0),
+		Gas:      0,
+		GasPrice: big.NewInt(0),
+		Data:     nil,
+	})
+
+	tracer.OnTxStart(&tracing.VMContext{
+		ChainConfig: params.MainnetChainConfig,
+	}, tx, common.Address{})
+
+	tracer.OnEnter(0, byte(vm.CALL), common.Address{}, common.Address{}, nil, 0, big.NewInt(0))
+
+	// stop before the transaction is finished
+	tracer.Stop(stopError)
+
+	tracer.OnTxEnd(&types.Receipt{GasUsed: 0}, nil)
+
+	// check that the error is returned by GetResult
+	_, tracerError := tracer.GetResult()
+	require.Equal(t, stopError, tracerError)
+}