Type assertions on session values.

server.go

package main

import (
    "encoding/gob"
    "net/http"
    "code.google.com/p/gorilla/sessions"
    "log"
   
)

var store = sessions.NewCookieStore([]byte("something-very-secret"))

type IUser interface{
    GetUsername() string
}

type User struct{
  Id int64
  Username string  
}

func (u *User) GetUsername() string{
    return u.Username
}

func FirstHandler(w http.ResponseWriter, r *http.Request) {
    // Get a session. We're ignoring the error resulted from decoding an
    // existing session: Get() always returns a session, even if empty.
    session, _ := store.Get(r, "session-name")
    // Set some session values.
    user := User{Id: 3, Username: "someguy"}
    session.Values["user"] = user
    session.Values["foo"] = "bar"
       
    session.Save(r, w)
}

func AnotherHandler(w http.ResponseWriter, r *http.Request) {
    session, err := store.Get(r, "session-name")
    if err != nil{
        log.Println(err)
    }
    su := session.Values["user"]
    user := su.(IUser)
    username := user.GetUsername()
    log.Printf("Username is %v",username)
}

// Hitting localhost:8080/part1 sets the session values
// Hitting localhost:8080/part2 panics:
// "interface conversion: main.User is not main.IUser: missing method GetUsername"
func main(){
    gob.Register(User{})
    http.HandleFunc("/part1",FirstHandler)
    http.HandleFunc("/part2",AnotherHandler)
	log.Fatal(http.ListenAndServe(":8080", nil))
}