storage.go

package storage

import (

    "fmt"

    "os"

)

const DEFAULT_STORAGE_ENGINE = "bolt"  //默认存储引擎 为 bolt

//存储引擎map集合  

var supportedStorage = map[string]func(path string) (Storage, error){

    "kv":   openKVStorage,

    "bolt": openBoltStorage,

}

//存储引擎注册

func RegisterStorageEngine(name string, fn func(path string) (Storage, error)) {

    supportedStorage[name] = fn

}

//存储引擎接口

type Storage interface {

    Set(k, v []byte) error

    Get(k []byte) ([]byte, error)

    Delete(k []byte) error

    ForEach(fn func(k, v []byte) error) error

    Close() error

    WALName() string

}

//打开存储引擎  存储引擎 优先使用用户自定的引擎  ，默认引擎为bolt  。如果不存在 使用默认引擎

func OpenStorage(path string) (Storage, error) {

    wse := os.Getenv("WUKONG_STORAGE_ENGINE") //默认从环境变量中  加载存储引擎

    if wse == "" {

        wse = DEFAULT_STORAGE_ENGINE

    }

//从引擎map中获取 引擎对象

    if fn, has := supportedStorage[wse]; has {

        return fn(path)

    }

    return nil, fmt.Errorf("unsupported storage engine %v", wse)

}