session.go

package webca

import (
	"crypto/rand"
	"encoding/hex"
	"net/http"
	"sync"
)

const (
	SESSIONID = "goSessionId"
)

// session type
type session map[string]interface{}

// sessions holds all sessions
var sessions map[string]session

// mutex lock for session access
var smutex sync.RWMutex

// requestSessionId retrieves the session cookie from the request or creates a new one
func requestSessionId(w http.ResponseWriter, r *http.Request) (string,error) {
	cookie,e:=r.Cookie(SESSIONID)
	if e!=nil && e!=http.ErrNoCookie {
		return "",e
	}
	if e==http.ErrNoCookie || cookie==nil {
		id,e:=genId()
		if e!=nil {
			return "",e
		}
		cookie=&http.Cookie{Name:SESSIONID,Value:id,Path:"/", MaxAge:0}
		http.SetCookie(w,cookie)
		r.AddCookie(cookie) // for future references of this request
	}	
	return cookie.Value,nil
}

// SessionFor gets a session bound to a Request by Session ID
func SessionFor(w http.ResponseWriter, r *http.Request) (session, error) {
	id,e := requestSessionId(w,r)
	if e!=nil {
		return nil, e
	}
	smutex.RLock()
	defer smutex.RUnlock()
	if sessions==nil {
		sessions=make(map[string]session)
	}
	s := sessions[id]
	if s==nil {
		s=make(session)
		s[SESSIONID]=id
		sessions[id]=s
	}
	return s.clone(), nil // this copy allows concurrent session access
}

// Id returns the session ID or ""
func (s session) Id() string {
	if s[SESSIONID]!=nil {
		return s[SESSIONID].(string)
	}
	return ""
}

// Save stores the session state 
func (s session) Save() {
	smutex.Lock()
	defer smutex.Unlock()
	sessions[s.Id()] = s.clone()
}

// clone makes a copy of a session and returns it
func (s session) clone() session {
	c := make(session,len(s))
	for k, v := range s {
		c[k] = v
	}
	return c
}

// genId generates a new session ID
func genId() (string, error) {
	uuid := make([]byte, 16)
	n, err := rand.Read(uuid)
	if n != len(uuid) || err != nil {
		return "", err
	}
	// TODO: verify the two lines implement RFC 4122 correctly
	uuid[8] = 0x80 // variant bits see page 5
	uuid[4] = 0x40 // version 4 Pseudo Random, see page 7
	return hex.EncodeToString(uuid), nil
}