Fix eth events query and sync inconsistent state

- kvdb
	- Fix path in Last when doing `setNew`
	- Only close if db != nil, and after closing, always set db to nil
		- This will avoid a panic in the case where the db is closed but
		  there's an error soon after, and a future call tries to close
		  again.  This is because pebble.Close() will panic if the db is
		  already closed.
	- Avoid calling pebble methods when a the Storage interface already
	  implements that method (like Close).
- statedb
	- In test, avoid calling KVDB method if the same method is available for
	  the StateDB (like MakeCheckpoint, CurrentBatch).
- eth
	- In *EventByBlock methods, take blockHash as input argument and use it
	  when querying the event logs.  Previously the blockHash was only taken
	  from the logs results *only if* there was any log.  This caused the
	  following issue: if there was no logs, it was not possible to know if
	  the result was from the expected block or an uncle block!  By querying
	  logs by blockHash we make sure that even if there are no logs, they
	  are from the right block.
	  	- Note that now the function can either be called with a
		  blockNum or blockHash, but not both at the same time.
- sync
	- If there's an error during call to Sync call resetState, which
	  internally resets the stateDB to avoid stale checkpoints (and a
	  corresponding invalid increase in the StateDB batchNum).
	- During a Sync, after very batch processed, make sure that the StateDB
	  currentBatch corresponds to the batchNum in the smart contract
	  log/event.

db/kvdb/kvdb.go

@@ -61,13 +61,13 @@ func (k *Last) setNew() error {
 	defer k.rw.Unlock()
 	if k.db != nil {
 		k.db.Close()
+		k.db = nil
 	}
 	lastPath := path.Join(k.path, PathLast)
-	err := os.RemoveAll(lastPath)
-	if err != nil {
+	if err := os.RemoveAll(lastPath); err != nil {
 		return tracerr.Wrap(err)
 	}
-	db, err := pebble.NewPebbleStorage(path.Join(k.path, lastPath), false)
+	db, err := pebble.NewPebbleStorage(lastPath, false)
 	if err != nil {
 		return tracerr.Wrap(err)
 	}
@@ -80,6 +80,7 @@ func (k *Last) set(kvdb *KVDB, batchNum common.BatchNum) error {
 	defer k.rw.Unlock()
 	if k.db != nil {
 		k.db.Close()
+		k.db = nil
 	}
 	lastPath := path.Join(k.path, PathLast)
 	if err := kvdb.MakeCheckpointFromTo(batchNum, lastPath); err != nil {
@@ -96,7 +97,10 @@ func (k *Last) set(kvdb *KVDB, batchNum common.BatchNum) error {
 func (k *Last) close() {
 	k.rw.Lock()
 	defer k.rw.Unlock()
-	k.db.Close()
+	if k.db != nil {
+		k.db.Close()
+		k.db = nil
+	}
 }
 
 // NewKVDB creates a new KVDB, allowing to use an in-memory or in-disk storage.
@@ -166,14 +170,12 @@ func (kvdb *KVDB) Reset(batchNum common.BatchNum) error {
 func (kvdb *KVDB) reset(batchNum common.BatchNum, closeCurrent bool) error {
 	currentPath := path.Join(kvdb.path, PathCurrent)
 
-	if closeCurrent {
-		if err := kvdb.db.Pebble().Close(); err != nil {
-			return tracerr.Wrap(err)
-		}
+	if closeCurrent && kvdb.db != nil {
+		kvdb.db.Close()
+		kvdb.db = nil
 	}
 	// remove 'current'
-	err := os.RemoveAll(currentPath)
-	if err != nil {
+	if err := os.RemoveAll(currentPath); err != nil {
 		return tracerr.Wrap(err)
 	}
 	// remove all checkpoints > batchNum
@@ -249,13 +251,13 @@ func (kvdb *KVDB) ResetFromSynchronizer(batchNum common.BatchNum, synchronizerKV
 	}
 
 	currentPath := path.Join(kvdb.path, PathCurrent)
-	if err := kvdb.db.Pebble().Close(); err != nil {
-		return tracerr.Wrap(err)
+	if kvdb.db != nil {
+		kvdb.db.Close()
+		kvdb.db = nil
 	}
 
 	// remove 'current'
-	err := os.RemoveAll(currentPath)
-	if err != nil {
+	if err := os.RemoveAll(currentPath); err != nil {
 		return tracerr.Wrap(err)
 	}
 	// remove all checkpoints
@@ -394,8 +396,7 @@ func (kvdb *KVDB) MakeCheckpoint() error {
 
 	// if checkpoint BatchNum already exist in disk, delete it
 	if _, err := os.Stat(checkpointPath); !os.IsNotExist(err) {
-		err := os.RemoveAll(checkpointPath)
-		if err != nil {
+		if err := os.RemoveAll(checkpointPath); err != nil {
 			return tracerr.Wrap(err)
 		}
 	} else if err != nil && !os.IsNotExist(err) {
@@ -501,8 +502,7 @@ func (kvdb *KVDB) MakeCheckpointFromTo(fromBatchNum common.BatchNum, dest string
 func pebbleMakeCheckpoint(source, dest string) error {
 	// Remove dest folder (if it exists) before doing the checkpoint
 	if _, err := os.Stat(dest); !os.IsNotExist(err) {
-		err := os.RemoveAll(dest)
-		if err != nil {
+		if err := os.RemoveAll(dest); err != nil {
 			return tracerr.Wrap(err)
 		}
 	} else if err != nil && !os.IsNotExist(err) {
@@ -513,12 +513,7 @@ func pebbleMakeCheckpoint(source, dest string) error {
 	if err != nil {
 		return tracerr.Wrap(err)
 	}
-	defer func() {
-		errClose := sto.Pebble().Close()
-		if errClose != nil {
-			log.Errorw("Pebble.Close", "err", errClose)
-		}
-	}()
+	defer sto.Close()
 
 	// execute Checkpoint
 	err = sto.Pebble().Checkpoint(dest)
@@ -531,6 +526,9 @@ func pebbleMakeCheckpoint(source, dest string) error {
 
 // Close the DB
 func (kvdb *KVDB) Close() {
-	kvdb.db.Close()
+	if kvdb.db != nil {
+		kvdb.db.Close()
+		kvdb.db = nil
+	}
 	kvdb.last.close()
 }