聊聊rocketmq-client-go的localFileOffsetStore

type OffsetStore interface {
    persist(mqs []*primitive.MessageQueue)
    remove(mq *primitive.MessageQueue)
    read(mq *primitive.MessageQueue, t readType) int64
    update(mq *primitive.MessageQueue, offset int64, increaseOnly bool)
}

type localFileOffsetStore struct {
    group       string
    path        string
    OffsetTable map[MessageQueueKey]int64
    // mutex for offset file
    mutex sync.Mutex
}

func NewLocalFileOffsetStore(clientID, group string) OffsetStore {
    store := &localFileOffsetStore{
        group:       group,
        path:        filepath.Join(_LocalOffsetStorePath, clientID, group, "offset.json"),
        OffsetTable: make(map[MessageQueueKey]int64),
    }
    store.load()
    return store
}

func (local *localFileOffsetStore) load() {
    local.mutex.Lock()
    defer local.mutex.Unlock()
    data, err := utils.FileReadAll(local.path)
    if os.IsNotExist(err) {
        return
    }
    if err != nil {
        rlog.Info("read from local store error, try to use bak file", map[string]interface{}{
            rlog.LogKeyUnderlayError: err,
        })
        data, err = utils.FileReadAll(filepath.Join(local.path, ".bak"))
    }
    if err != nil {
        rlog.Info("read from local store bak file error", map[string]interface{}{
            rlog.LogKeyUnderlayError: err,
        })
        return
    }
    datas := make(map[MessageQueueKey]int64)
​
    wrapper := OffsetSerializeWrapper{
        OffsetTable: datas,
    }
​
    err = jsoniter.Unmarshal(data, &wrapper)
    if err != nil {
        rlog.Warning("unmarshal local offset error", map[string]interface{}{
            "local_path":             local.path,
            rlog.LogKeyUnderlayError: err.Error(),
        })
        return
    }
​
    if datas != nil {
        local.OffsetTable = datas
    }
}

func (local *localFileOffsetStore) read(mq *primitive.MessageQueue, t readType) int64 {
    switch t {
    case _ReadFromMemory, _ReadMemoryThenStore:
        off := readFromMemory(local.OffsetTable, mq)
        if off >= 0 || (off == -1 && t == _ReadFromMemory) {
            return off
        }
        fallthrough
    case _ReadFromStore:
        local.load()
        return readFromMemory(local.OffsetTable, mq)
    default:
​
    }
    return -1
}

func (local *localFileOffsetStore) update(mq *primitive.MessageQueue, offset int64, increaseOnly bool) {
    local.mutex.Lock()
    defer local.mutex.Unlock()
    rlog.Debug("update offset", map[string]interface{}{
        rlog.LogKeyMessageQueue: mq,
        "new_offset":            offset,
    })
    key := MessageQueueKey(*mq)
    localOffset, exist := local.OffsetTable[key]
    if !exist {
        local.OffsetTable[key] = offset
        return
    }
    if increaseOnly {
        if localOffset < offset {
            local.OffsetTable[key] = offset
        }
    } else {
        local.OffsetTable[key] = offset
    }
}

func (local *localFileOffsetStore) persist(mqs []*primitive.MessageQueue) {
    if len(mqs) == 0 {
        return
    }
    local.mutex.Lock()
    defer local.mutex.Unlock()
​
    wrapper := OffsetSerializeWrapper{
        OffsetTable: local.OffsetTable,
    }
​
    data, _ := jsoniter.Marshal(wrapper)
    utils.CheckError(fmt.Sprintf("persist offset to %s", local.path), utils.WriteToFile(local.path, data))
}