w3vm: fix race in rpcFetcher (#157)

* `dirty` was unprotected

Co-authored-by: lmittmann <[email protected]>

w3vm/fetcher.go

@@ -9,6 +9,7 @@ import (
  "os"
  "path/filepath"
  "sync"
+ "sync/atomic"
  "testing"
 
  "github.com/ethereum/go-ethereum/common"
@@ -49,7 +50,7 @@ type rpcFetcher struct {
  mux3 sync.RWMutex
  headerHashes map[uint64]func() (common.Hash, error)
 
- dirty bool // indicates whether new state has been fetched
+ dirty uint32 // indicates whether new state has been fetched (0=false, 1=true)
 }
 
 // NewRPCFetcher returns a new [Fetcher] that fetches account state from the given
@@ -79,7 +80,7 @@ func (f *rpcFetcher) Account(addr common.Address) (a *types.StateAccount, e erro
  if ok {
  return acc()
  }
- f.dirty = true
+ atomic.StoreUint32(&f.dirty, 1)
 
  var (
  accNew = &types.StateAccount{Balance: new(uint256.Int)}
@@ -140,7 +141,7 @@ func (f *rpcFetcher) StorageAt(addr common.Address, slot common.Hash) (common.Ha
  if ok {
  return storage()
  }
- f.dirty = true
+ atomic.StoreUint32(&f.dirty, 1)
 
  var (
  storageVal common.Hash
@@ -165,7 +166,7 @@ func (f *rpcFetcher) HeaderHash(blockNumber uint64) (common.Hash, error) {
  if ok {
  return hash()
  }
- f.dirty = true
+ atomic.StoreUint32(&f.dirty, 1)
 
  var (
  header header
@@ -288,7 +289,7 @@ func (f *rpcFetcher) loadTestdataState(tb testing.TB, chainID uint64) error {
 }
 
 func (f *rpcFetcher) storeTestdataState(tb testing.TB, chainID uint64) error {
- if !f.dirty {
+ if atomic.LoadUint32(&f.dirty) == 0 {
  return nil // the state has not been modified
  }