eth: fix error casting regression during database open

eth/backend.go

@@ -65,7 +65,7 @@ const (
 var (
 	jsonlogger = logger.NewJsonLogger()
 
-	datadirInUseErrNos = []uint{11, 32, 35}
+	datadirInUseErrnos = map[uint]bool{11: true, 32: true, 35: true}
 	portInUseErrRE     = regexp.MustCompile("address already in use")
 
 	defaultBootNodes = []*discover.Node{
@@ -286,15 +286,7 @@ func New(config *Config) (*Ethereum, error) {
 	// Open the chain database and perform any upgrades needed
 	chainDb, err := newdb(filepath.Join(config.DataDir, "chaindata"))
 	if err != nil {
-		var ok bool
-		errno := uint(err.(syscall.Errno))
-		for _, no := range datadirInUseErrNos {
-			if errno == no {
-				ok = true
-				break
-			}
-		}
-		if ok {
+		if errno, ok := err.(syscall.Errno); ok && datadirInUseErrnos[uint(errno)] {
 			err = fmt.Errorf("%v (check if another instance of geth is already running with the same data directory '%s')", err, config.DataDir)
 		}
 		return nil, fmt.Errorf("blockchain db err: %v", err)
@@ -311,14 +303,7 @@ func New(config *Config) (*Ethereum, error) {
 
 	dappDb, err := newdb(filepath.Join(config.DataDir, "dapp"))
 	if err != nil {
-		var ok bool
-		for _, no := range datadirInUseErrNos {
-			if uint(err.(syscall.Errno)) == no {
-				ok = true
-				break
-			}
-		}
-		if ok {
+		if errno, ok := err.(syscall.Errno); ok && datadirInUseErrnos[uint(errno)] {
 			err = fmt.Errorf("%v (check if another instance of geth is already running with the same data directory '%s')", err, config.DataDir)
 		}
 		return nil, fmt.Errorf("dapp db err: %v", err)