#6.3 session存储
上一节我们介绍了Session管理器的实现原理，定义了如何实现session存储的接口，这小节我们讲通过一个例子来实现内存的session存储，其他类似数据库或者文件的存储，用户可以根据相应的接口定义来实现，内存的实现请看下面的例子代码

	package memory
	
	import (
		"session/session"
		"time"
	)
	
	var d = &Provider{}
	
	type SessionStore struct {
		sid          string                      //session id唯一标示	  	
		timeAccessed time.Time                   //最后访问时间	  	
		value        map[interface{}]interface{} //session里面存储的值
	}
	
	func (this *SessionStore) Set(key, value interface{}) bool {
		this.value[key] = value
		d.SessionUpdate(this.sid)
		return true
	}
	
	func (this *SessionStore) Get(key interface{}) interface{} {
		d.SessionUpdate(this.sid)
		if v, ok := this.value[key]; ok {
			return v
		} else {
			return ""
		}
	}
	
	func (this *SessionStore) Del(key interface{}) bool {
		delete(this.value, key)
		d.SessionUpdate(this.sid)
		return true
	}
	
	type Provider struct {
		lock     sync.Mutex               //用来锁
		sessions map[string]*SessionStore //用来存储在内存
		list     *list.List               //用来做gc
	}
	
	func (this *Provider) SessionInit(sid string) (session.Session, error) {
		this.lock.Lock()
		defer this.lock.Unlock()
		v := make(map[interface{}]interface{}, 0)
		newsess := &SessionStore{"sid": sid, "timeAccessed": time.Now(), "value": v}
		this.sessions[sid] = newsess
		this.list.Push(newsess)
		return newsess
	}
	
	func (this *Provider) SessionRead(sid string) (session.Session, error) {
		if s, ok := this.sessions[sid]; ok {
			return s, nil
		} else {
			sess, err := this.SessionInit(sid)
			return sess, err
		}
	}
	
	func (this *Provider) SessionDestroy(sid string) bool {
		if s, ok := this.sessions[sid]; ok {
			delete(this.table, sid)
			this.list.Remove(s)
			return true
		} else {
			return false
		}
	}
	
	func (this *Provider) SessionGC(maxlifetime int64) {
		this.lock.Lock()
		defer this.lock.Unlock()
	
		for {
			element := this.list.Back()
			if element == nil {
				break
			}
			if (element.Value.(*SessionStore).timeAccessed.Unix() + maxlifetime) < time.Now().Unix() {
				this.list.Remove(element)
				delete(this.table, element.Value.(*SessionStore).sid)
			} else {
				break
			}
		}
	}
	
	func (this *Provider) SessionUpdate(sid string) bool {
		this.lock.Lock()
		defer this.lock.Unlock()
		if element, ok := this.sessions[sid]; ok {
			element.Value.(*SessionStore).value = s.value
			this.moveToFront(element)
			return true
		} else {
			return false
		}
	}
	
	func (this *Provider) moveToFront(element *list.Element) {
		this.lock.Lock()
		defer this.lock.Unlock()
		element.Value.(*SessionStore).timeAccessed = time.Now()
		this.list.MoveToFront(element)
	}
	
	func init() {
		session.Register("memory", d)
	}

上面这个代码实现了一个内存存储实现的session机制
## links
   * [目录](<preface.md>)
   * 上一节: [Go如何使用session](<6.2.md>)
   * 下一节: [预防session劫持](<6.4.md>)

## LastModified 
   * $Id$