From 0aa08303bc0730cb48b8c4b20c063512940db878 Mon Sep 17 00:00:00 2001
From: Leon Klingele <git@leonklingele.de>
Date: Mon, 14 Nov 2022 03:18:42 +0100
Subject: [PATCH 1/3] memory: cache timestamp

---
 memory/memory.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/memory/memory.go b/memory/memory.go
index b1bd2f4e..bb4f0b00 100644
--- a/memory/memory.go
+++ b/memory/memory.go
@@ -110,10 +110,11 @@ func (s *Storage) gc() {
 		case <-s.done:
 			return
 		case <-ticker.C:
+			ts := atomic.LoadUint32(&internal.Timestamp)
 			expired = expired[:0]
 			s.mux.RLock()
 			for id, v := range s.db {
-				if v.expiry != 0 && v.expiry < atomic.LoadUint32(&internal.Timestamp) {
+				if v.expiry != 0 && v.expiry < ts {
 					expired = append(expired, id)
 				}
 			}

From 318b2fc04c418618bedc0e61425a1dcb107bc666 Mon Sep 17 00:00:00 2001
From: Leon Klingele <git@leonklingele.de>
Date: Mon, 14 Nov 2022 03:19:31 +0100
Subject: [PATCH 2/3] memory: ensure to never delete non-expired items

This fixes a TOCTOU problem between a mutex rlock and a mutex lock.
---
 memory/memory.go | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/memory/memory.go b/memory/memory.go
index bb4f0b00..49b1a117 100644
--- a/memory/memory.go
+++ b/memory/memory.go
@@ -120,8 +120,13 @@ func (s *Storage) gc() {
 			}
 			s.mux.RUnlock()
 			s.mux.Lock()
+			// Double-checked locking.
+			// We might have replaced the item in the meantime.
 			for i := range expired {
-				delete(s.db, expired[i])
+				v := s.db[expired[i]]
+				if v.expiry != 0 && v.expiry <= ts {
+					delete(s.db, expired[i])
+				}
 			}
 			s.mux.Unlock()
 		}

From 117838fd0eb60b1dfb3e58670023b0562ab27919 Mon Sep 17 00:00:00 2001
From: Leon Klingele <git@leonklingele.de>
Date: Mon, 14 Nov 2022 03:20:20 +0100
Subject: [PATCH 3/3] memory: move costly operations outside of locked area

---
 memory/memory.go | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/memory/memory.go b/memory/memory.go
index 49b1a117..3acf1ec6 100644
--- a/memory/memory.go
+++ b/memory/memory.go
@@ -68,8 +68,9 @@ func (s *Storage) Set(key string, val []byte, exp time.Duration) error {
 		expire = uint32(exp.Seconds()) + atomic.LoadUint32(&internal.Timestamp)
 	}
 
+	e := entry{val, expire}
 	s.mux.Lock()
-	s.db[key] = entry{val, expire}
+	s.db[key] = e
 	s.mux.Unlock()
 	return nil
 }
@@ -88,8 +89,9 @@ func (s *Storage) Delete(key string) error {
 
 // Reset all keys
 func (s *Storage) Reset() error {
+	ndb := make(map[string]entry)
 	s.mux.Lock()
-	s.db = make(map[string]entry)
+	s.db = ndb
 	s.mux.Unlock()
 	return nil
 }