protocol

type Error struct {
	Code    int
	Message string
	Tm      time.Time
}

type MessageConsumer struct {
	Num  uint64
	Size uint32 //等于Data和Crc的长度之和
	Data []byte
	Crc  uint32
}

type MessagePublisher struct {
	Num       uint64
	Size      uint32 //等于后续字段长度之和
	TopicSize uint16
	Topic     []byte
	Data      []byte
	Crc       uint32
}

type MessageQuery struct {
	Topic      string
	MessagePos uint64
	Limit      int
	Result     chan *MessageQueryResult //查询结果
}

type MessageQueryResult struct {
	Message *MessageConsumer
	Error   error
}

type MessageStorage struct {
	Num      uint64
	Size     uint32 //等于Data和crc的长度之和
	Data     []byte
	Crc      uint32
	TailSize uint32 //等于size, 放在每一条消息记录的末尾，方便对消息文件进行从尾部开始的回溯
}

type Storage interface {
	SaveMessage(msg *MessageStorage) error
	QueryMessage(query *MessageQuery)
}