chore: import upstream snapshot with attribution

cache/memory.go

@@ -0,0 +1,66 @@
+package cache
+
+import (
+	"context"
+	"sync"
+	"time"
+)
+
+type memCache struct {
+	opts Options
+
+	items map[string]Item
+	sync.RWMutex
+}
+
+func (c *memCache) Get(ctx context.Context, key string) (interface{}, time.Time, error) {
+	c.RLock()
+	defer c.RUnlock()
+
+	item, found := c.items[key]
+	if !found {
+		return nil, time.Time{}, ErrKeyNotFound
+	}
+	if item.Expired() {
+		return nil, time.Time{}, ErrItemExpired
+	}
+
+	return item.Value, time.Unix(0, item.Expiration), nil
+}
+
+func (c *memCache) Put(ctx context.Context, key string, val interface{}, d time.Duration) error {
+	var e int64
+	if d == DefaultExpiration {
+		d = c.opts.Expiration
+	}
+	if d > 0 {
+		e = time.Now().Add(d).UnixNano()
+	}
+
+	c.Lock()
+	defer c.Unlock()
+
+	c.items[key] = Item{
+		Value:      val,
+		Expiration: e,
+	}
+
+	return nil
+}
+
+func (c *memCache) Delete(ctx context.Context, key string) error {
+	c.Lock()
+	defer c.Unlock()
+
+	_, found := c.items[key]
+	if !found {
+		return ErrKeyNotFound
+	}
+
+	delete(c.items, key)
+	return nil
+}
+
+func (c *memCache) String() string {
+	return "memory"
+}