From 3e759e28d7a032356450725bdb3273921ad41fb9 Mon Sep 17 00:00:00 2001
From: Philip Fan <fanwengang@hotmail.com>
Date: Tue, 12 Jul 2022 16:10:12 +0800
Subject: [PATCH] eth/tracers: add initial revertReasonTracer tracer (#25265)

Adds a native tracer that returns that in case of failure returns the error message or the revert reason of a transaction.

Co-authored-by: Martin Holst Swende <martin@swende.se>
---
 eth/tracers/native/revertreason.go | 108 +++++++++++++++++++++++++++++
 1 file changed, 108 insertions(+)
 create mode 100644 eth/tracers/native/revertreason.go

diff --git a/eth/tracers/native/revertreason.go b/eth/tracers/native/revertreason.go
new file mode 100644
index 000000000..b402396cb
--- /dev/null
+++ b/eth/tracers/native/revertreason.go
@@ -0,0 +1,108 @@
+// Copyright 2022 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
+
+import (
+	"bytes"
+	"encoding/json"
+	"math/big"
+	"sync/atomic"
+	"time"
+
+	"github.com/ethereum/go-ethereum/accounts/abi"
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/vm"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/eth/tracers"
+)
+
+func init() {
+	register("revertReasonTracer", newRevertReasonTracer)
+}
+
+var revertSelector = crypto.Keccak256([]byte("Error(string)"))[:4]
+
+// revertReasonTracer is a go implementation of the Tracer interface which
+// track the error message or revert reason return by the contract.
+type revertReasonTracer struct {
+	env          *vm.EVM
+	revertReason string // The revert reason return from the tx, if tx success, empty string return
+	interrupt    uint32 // Atomic flag to signal execution interruption
+	reason       error  // Textual reason for the interruption
+}
+
+// newRevertReasonTracer returns a new revert reason tracer.
+func newRevertReasonTracer(_ *tracers.Context) tracers.Tracer {
+	return &revertReasonTracer{}
+}
+
+// CaptureStart implements the EVMLogger interface to initialize the tracing operation.
+func (t *revertReasonTracer) CaptureStart(env *vm.EVM, _ common.Address, _ common.Address, _ bool, _ []byte, _ uint64, _ *big.Int) {
+	t.env = env
+}
+
+// CaptureEnd is called after the call finishes to finalize the tracing.
+func (t *revertReasonTracer) CaptureEnd(output []byte, _ uint64, _ time.Duration, err error) {
+	if err != nil {
+		if err == vm.ErrExecutionReverted && len(output) > 4 && bytes.Equal(output[:4], revertSelector) {
+			errMsg, _ := abi.UnpackRevert(output)
+			t.revertReason = err.Error() + ": " + errMsg
+		} else {
+			t.revertReason = err.Error()
+		}
+	}
+}
+
+// CaptureState implements the EVMLogger interface to trace a single step of VM execution.
+func (t *revertReasonTracer) CaptureState(_ uint64, _ vm.OpCode, _, _ uint64, _ *vm.ScopeContext, _ []byte, _ int, _ error) {
+}
+
+// CaptureFault implements the EVMLogger interface to trace an execution fault.
+func (t *revertReasonTracer) CaptureFault(_ uint64, _ vm.OpCode, _, _ uint64, _ *vm.ScopeContext, _ int, _ error) {
+}
+
+// CaptureEnter is called when EVM enters a new scope (via call, create or selfdestruct).
+func (t *revertReasonTracer) CaptureEnter(_ vm.OpCode, _ common.Address, _ common.Address, _ []byte, _ uint64, _ *big.Int) {
+	// Skip if tracing was interrupted
+	if atomic.LoadUint32(&t.interrupt) > 0 {
+		t.env.Cancel()
+		return
+	}
+}
+
+// CaptureExit is called when EVM exits a scope, even if the scope didn't
+// execute any code.
+func (t *revertReasonTracer) CaptureExit(_ []byte, _ uint64, _ error) {}
+
+func (t *revertReasonTracer) CaptureTxStart(_ uint64) {}
+
+func (t *revertReasonTracer) CaptureTxEnd(_ uint64) {}
+
+// GetResult returns an error message json object.
+func (t *revertReasonTracer) GetResult() (json.RawMessage, error) {
+	res, err := json.Marshal(t.revertReason)
+	if err != nil {
+		return nil, err
+	}
+	return res, t.reason
+}
+
+// Stop terminates execution of the tracer at the first opportune moment.
+func (t *revertReasonTracer) Stop(err error) {
+	t.reason = err
+	atomic.StoreUint32(&t.interrupt, 1)
+}