Add read only public port on volume server

Add read only public port on volume server

go/operation/assign_file_id.go

@@ -3,6 +3,7 @@ package operation
 import (
 	"encoding/json"
 	"errors"
+	"fmt"
 	"net/url"
 	"strconv"
 
@@ -38,7 +39,7 @@ func Assign(server string, count int, replication string, collection string, ttl
 	var ret AssignResult
 	err = json.Unmarshal(jsonBlob, &ret)
 	if err != nil {
-		return nil, err
+		return nil, fmt.Errorf("JSON unmarshal error:%v, json:%s", err, string(jsonBlob))
 	}
 	if ret.Count <= 0 {
 		return nil, errors.New(ret.Error)