Add simple cache value

cache/value.go

@@ -0,0 +1,57 @@
+package cache
+
+import (
+	"sync"
+	"time"
+)
+
+// Value is a simple auto refresh cache hold.
+type Value struct {
+	locker sync.Mutex
+	value  interface{}
+	next   time.Time
+	TTL    time.Duration
+	Load   func() (interface{}, error)
+}
+
+// Get return cached value, it will return expired value if dirty is true and loading failed.
+func (v *Value) Get(dirty ...bool) (value interface{}, err error) {
+	if v.value != nil && time.Now().Before(v.next) {
+		return v.value, nil
+	}
+
+	v.locker.Lock()
+	defer v.locker.Unlock()
+
+	if v.value != nil && time.Now().Before(v.next) {
+		return v.value, nil
+	}
+
+	value, err = v.Load()
+	if err == nil {
+		ttl := v.TTL
+		if ttl == 0 {
+			ttl = time.Hour
+		}
+		v.value, v.next = value, time.Now().Add(ttl)
+	} else {
+		if v.value != nil && (len(dirty) > 0 && dirty[0]) {
+			return v.value, nil
+		}
+	}
+	return
+}
+
+// MustGet return cached value, it panics if error occurs.
+func (v *Value) MustGet(dirty ...bool) (value interface{}) {
+	value, err := v.Get(dirty...)
+	if err != nil {
+		panic(err)
+	}
+	return value
+}
+
+// Reset clears internal cache value.
+func (v *Value) Reset() {
+	v.value = nil
+}

cache/value_test.go

@@ -0,0 +1,41 @@
+package cache_test
+
+import (
+	"testing"
+	"time"
+
+	"errors"
+
+	"github.com/cuigh/auxo/cache"
+	"github.com/cuigh/auxo/test/assert"
+)
+
+func TestValue(t *testing.T) {
+	i := 0
+	v := cache.Value{
+		TTL: 100 * time.Millisecond,
+		Load: func() (interface{}, error) {
+			if i == 0 {
+				i++
+				return &struct{}{}, nil
+			}
+			return nil, errors.New("mock error")
+		},
+	}
+
+	value, err := v.Get()
+	assert.NoError(t, err)
+	assert.NotNil(t, value)
+
+	time.Sleep(101 * time.Millisecond)
+
+	value, err = v.Get()
+	assert.Error(t, err)
+	assert.Nil(t, value)
+
+	value, err = v.Get(true)
+	assert.NoError(t, err)
+	assert.NotNil(t, value)
+
+	v.Reset()
+}