clientv3: add database integrity check in snapshot status

Add database integrity check in snapshot status. If database is
corrupted, return with error message.

clientv3/snapshot/v3_snapshot.go

@@ -25,6 +25,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"strings"
 	"time"
 
 	"go.etcd.io/etcd/clientv3"
@@ -166,6 +167,18 @@ func (s *v3Manager) Status(dbPath string) (ds Status, err error) {
 	h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
 
 	if err = db.View(func(tx *bolt.Tx) error {
+		// check database integrity first
+		var (
+			count          int
+			db_err_strings []string
+		)
+		for db_err := range tx.Check() {
+			db_err_strings = append(db_err_strings, db_err.Error())
+			count++
+		}
+		if count > 0 {
+			return fmt.Errorf("database corrupted! %d errors found.\n"+strings.Join(db_err_strings, "\n"), count)
+		}
 		ds.TotalSize = tx.Size()
 		c := tx.Cursor()
 		for next, _ := c.First(); next != nil; next, _ = c.Next() {