问cos使用restful接口上传文件报ErrOffGoBack？

文件比较大，大概有3G左右，slice_size是3145728，开始时上传正常，但一段时间后就开始报ErrOffGoBack{u'message': u'ErrOffGoBack', u'code': -4024}with open(local_path,'rb') as local_file: local_file.seek(offset) while(offset<file_size): file_content=local_file.read(slice_size) retry_count=0 max_retry=3 while(retry_count<max_retry): http_data_body={} http_data_body'op'='upload_slice' http_data_body'filecontent'=file_content http_data_body'session'=session http_data_body'offset'=str(offset) data_ret=http_session.post(upload_url,headers=http_header,files=http_data_body).json() if data_retu'code' == 0: if data_retu'data'.has_key('access_url'): print data_ret else: break else: retry_count+=1 if retry_count==max_retry: print data_ret else: offset+=slice_size