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package main
import (
"context"
"encoding/hex"
"math/rand"
"net/http"
"net/url"
)
// session storage indexed by a random UUID
var sessions = map[string]*Session{}
type Session struct {
LoggedIn bool // may access the DB
}
type sessionContextKey struct{}
func sessionGenId() string {
u := make([]byte, 16)
if _, err := rand.Read(u); err != nil {
panic("cannot generate random bytes")
}
return hex.EncodeToString(u)
}
// TODO: We don't want to keep an unlimited amount of cookies in the storage.
// - The essential question is: how do we avoid DoS?
// - Which cookies are worth keeping?
// - Definitely logged-in users, only one person should know the password.
// - Evict by FIFO? LRU?
func sessionGet(w http.ResponseWriter, r *http.Request) (session *Session) {
if c, _ := r.Cookie("sessionid"); c != nil {
session, _ = sessions[c.Value]
}
if session == nil {
id := sessionGenId()
session = &Session{LoggedIn: false}
sessions[id] = session
http.SetCookie(w, &http.Cookie{Name: "sessionid", Value: id})
}
return
}
func sessionWrap(inner func(http.ResponseWriter, *http.Request)) func(
http.ResponseWriter, *http.Request) {
return func(w http.ResponseWriter, r *http.Request) {
// We might also try no-cache with an ETag for the whole database,
// though I don't expect any substantial improvements of anything.
w.Header().Set("Cache-Control", "no-store")
redirect := "/login"
if r.RequestURI != "/" && r.Method == http.MethodGet {
redirect += "?redirect=" + url.QueryEscape(r.RequestURI)
}
session := sessionGet(w, r)
if !session.LoggedIn {
http.Redirect(w, r, redirect, http.StatusSeeOther)
return
}
inner(w, r.WithContext(
context.WithValue(r.Context(), sessionContextKey{}, session)))
}
}
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