Implement metadata cache, metadata cache is used by top level donut right now. Rename trove as data cache

We should use it internally everywhere.

pkg/donut/cache/metadata/metadata.go

@@ -0,0 +1,112 @@
+/*
+ * Minimalist Object Storage, (C) 2015 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Package metadata implements in memory caching methods for metadata information
+package metadata
+
+import (
+	"sync"
+	"time"
+)
+
+var noExpiration = time.Duration(0)
+
+// Cache holds the required variables to compose an in memory cache system
+// which also provides expiring key mechanism and also maxSize
+type Cache struct {
+	// Mutex is used for handling the concurrent
+	// read/write requests for cache
+	sync.Mutex
+
+	// items hold the cached objects
+	items map[string]interface{}
+
+	// updatedAt holds the time that related item's updated at
+	updatedAt map[string]time.Time
+}
+
+// Stats current cache statistics
+type Stats struct {
+	Items int
+}
+
+// NewCache creates an inmemory cache
+//
+func NewCache() *Cache {
+	return &Cache{
+		items:     make(map[string]interface{}),
+		updatedAt: map[string]time.Time{},
+	}
+}
+
+// Stats get current cache statistics
+func (r *Cache) Stats() Stats {
+	return Stats{
+		Items: len(r.items),
+	}
+}
+
+// GetAll returs all the items
+func (r *Cache) GetAll() map[string]interface{} {
+	r.Lock()
+	defer r.Unlock()
+	// copy
+	items := r.items
+	return items
+}
+
+// Get returns a value of a given key if it exists
+func (r *Cache) Get(key string) interface{} {
+	r.Lock()
+	defer r.Unlock()
+	value, ok := r.items[key]
+	if !ok {
+		return nil
+	}
+	r.updatedAt[key] = time.Now()
+	return value
+}
+
+// Exists returns true if key exists
+func (r *Cache) Exists(key string) bool {
+	r.Lock()
+	defer r.Unlock()
+	_, ok := r.items[key]
+	return ok
+}
+
+// Set will persist a value to the cache
+func (r *Cache) Set(key string, value interface{}) bool {
+	r.Lock()
+	defer r.Unlock()
+	r.items[key] = value
+	r.updatedAt[key] = time.Now()
+	return true
+}
+
+// Delete deletes a given key if exists
+func (r *Cache) Delete(key string) {
+	r.Lock()
+	defer r.Unlock()
+	r.doDelete(key)
+}
+
+func (r *Cache) doDelete(key string) {
+	if _, ok := r.items[key]; ok {
+		delete(r.items, key)
+		delete(r.updatedAt, key)
+	}
+}

pkg/donut/cache/metadata/metadata_test.go

@@ -0,0 +1,46 @@
+/*
+ * Minimalist Object Storage, (C) 2015 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package metadata
+
+import (
+	"testing"
+
+	. "github.com/minio/check"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type MySuite struct{}
+
+var _ = Suite(&MySuite{})
+
+func (s *MySuite) TestCache(c *C) {
+	cache := NewCache()
+	data := []byte("Hello, world!")
+	ok := cache.Set("filename", data)
+
+	c.Assert(ok, Equals, true)
+	storedata := cache.Get("filename")
+
+	c.Assert(ok, Equals, true)
+	c.Assert(data, DeepEquals, storedata)
+
+	cache.Delete("filename")
+
+	ok = cache.Exists("filename")
+	c.Assert(ok, Equals, false)
+}