1 files changed, 66 insertions, 0 deletions
diff --git a/cmd/sklad/session.go b/cmd/sklad/session.go
new file mode 100644
index 0000000..02fe0b0
--- /dev/null
+++ b/cmd/sklad/session.go
@@ -0,0 +1,66 @@
+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)))
+	}
+}