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#6.3 Session storage We introduced session manager work principle in previous section, we defined a session storage interface. In this section, I'm going to show you an example of memory-based session storage engine that implements the interface. You can change this to others forms of session storage as well.

package memory

import (
    "container/list"
    "github.com/astaxie/session"
    "sync"
    "time"
)

var pder = &Provider{list: list.New()}

type SessionStore struct {
    sid          string                      // unique session id
    timeAccessed time.Time                   // last access time
    value        map[interface{}]interface{} // session value stored inside
}

func (st *SessionStore) Set(key, value interface{}) error {
    st.value[key] = value
    pder.SessionUpdate(st.sid)
    return nil
}

func (st *SessionStore) Get(key interface{}) interface{} {
    pder.SessionUpdate(st.sid)
    if v, ok := st.value[key]; ok {
        return v
    } else {
        return nil
    }
    return nil
}

func (st *SessionStore) Delete(key interface{}) error {
    delete(st.value, key)
    pder.SessionUpdate(st.sid)
    return nil
}

func (st *SessionStore) SessionID() string {
    return st.sid
}

type Provider struct {
    lock     sync.Mutex               // lock
    sessions map[string]*list.Element // save in memory
    list     *list.List               // gc
}

func (pder *Provider) SessionInit(sid string) (session.Session, error) {
    pder.lock.Lock()
    defer pder.lock.Unlock()
    v := make(map[interface{}]interface{}, 0)
    newsess := &SessionStore{sid: sid, timeAccessed: time.Now(), value: v}
    element := pder.list.PushBack(newsess)
    pder.sessions[sid] = element
    return newsess, nil
}

func (pder *Provider) SessionRead(sid string) (session.Session, error) {
    if element, ok := pder.sessions[sid]; ok {
        return element.Value.(*SessionStore), nil
    } else {
        sess, err := pder.SessionInit(sid)
        return sess, err
    }
    return nil, nil
}

func (pder *Provider) SessionDestroy(sid string) error {
    if element, ok := pder.sessions[sid]; ok {
        delete(pder.sessions, sid)
        pder.list.Remove(element)
        return nil
    }
    return nil
}

func (pder *Provider) SessionGC(maxlifetime int64) {
    pder.lock.Lock()
    defer pder.lock.Unlock()

    for {
        element := pder.list.Back()
        if element == nil {
            break
        }
        if (element.Value.(*SessionStore).timeAccessed.Unix() + maxlifetime) < time.Now().Unix() {
            pder.list.Remove(element)
            delete(pder.sessions, element.Value.(*SessionStore).sid)
        } else {
            break
        }
    }
}

func (pder *Provider) SessionUpdate(sid string) error {
    pder.lock.Lock()
    defer pder.lock.Unlock()
    if element, ok := pder.sessions[sid]; ok {
        element.Value.(*SessionStore).timeAccessed = time.Now()
        pder.list.MoveToFront(element)
        return nil
    }
    return nil
}

func init() {
    pder.sessions = make(map[string]*list.Element, 0)
    session.Register("memory", pder)
}

The above example implemented a memory-based session storage mechanism, then use init() function to register this storage engine to session manager. So how to register this engine?

import (
    "github.com/astaxie/session"
    _ "github.com/astaxie/session/providers/memory"
)

Use import mechanism to register this engine in init() function automatically to session manager, then we use following code to initialize a session manager:

var globalSessions *session.Manager

// initialize in init() function
func init() {
    globalSessions, _ = session.NewManager("memory", "gosessionid", 3600)
    go globalSessions.GC()
}

##Links