Feature: add custom DNS support (#56)

common/cache/cache.go

@@ -0,0 +1,91 @@
+package cache
+
+import (
+	"runtime"
+	"sync"
+	"time"
+)
+
+// Cache store element with a expired time
+type Cache struct {
+	*cache
+}
+
+type cache struct {
+	mapping sync.Map
+	janitor *janitor
+}
+
+type element struct {
+	Expired time.Time
+	Payload interface{}
+}
+
+// Put element in Cache with its ttl
+func (c *cache) Put(key interface{}, payload interface{}, ttl time.Duration) {
+	c.mapping.Store(key, &element{
+		Payload: payload,
+		Expired: time.Now().Add(ttl),
+	})
+}
+
+// Get element in Cache, and drop when it expired
+func (c *cache) Get(key interface{}) interface{} {
+	item, exist := c.mapping.Load(key)
+	if !exist {
+		return nil
+	}
+	elm := item.(*element)
+	// expired
+	if time.Since(elm.Expired) > 0 {
+		c.mapping.Delete(key)
+		return nil
+	}
+	return elm.Payload
+}
+
+func (c *cache) cleanup() {
+	c.mapping.Range(func(k, v interface{}) bool {
+		key := k.(string)
+		elm := v.(*element)
+		if time.Since(elm.Expired) > 0 {
+			c.mapping.Delete(key)
+		}
+		return true
+	})
+}
+
+type janitor struct {
+	interval time.Duration
+	stop     chan struct{}
+}
+
+func (j *janitor) process(c *cache) {
+	ticker := time.NewTicker(j.interval)
+	for {
+		select {
+		case <-ticker.C:
+			c.cleanup()
+		case <-j.stop:
+			ticker.Stop()
+			return
+		}
+	}
+}
+
+func stopJanitor(c *Cache) {
+	c.janitor.stop <- struct{}{}
+}
+
+// New return *Cache
+func New(interval time.Duration) *Cache {
+	j := &janitor{
+		interval: interval,
+		stop:     make(chan struct{}),
+	}
+	c := &cache{janitor: j}
+	go j.process(c)
+	C := &Cache{c}
+	runtime.SetFinalizer(C, stopJanitor)
+	return C
+}