From 30dcb99ba3388405eadc6413f221dabea0595a95 Mon Sep 17 00:00:00 2001
From: Armon Dadgar <armon.dadgar@gmail.com>
Date: Tue, 14 Apr 2015 11:00:51 -0700
Subject: [PATCH] physical: Adding simple LRU write-through cache

---
 physical/cache.go      | 75 ++++++++++++++++++++++++++++++++++++++++++
 physical/cache_test.go | 48 +++++++++++++++++++++++++++
 2 files changed, 123 insertions(+)
 create mode 100644 physical/cache.go
 create mode 100644 physical/cache_test.go

diff --git a/physical/cache.go b/physical/cache.go
new file mode 100644
index 000000000..c13a52c98
--- /dev/null
+++ b/physical/cache.go
@@ -0,0 +1,75 @@
+package physical
+
+import "github.com/hashicorp/golang-lru"
+
+const (
+	// DefaultCacheSize is used if no cache size is specified
+	// for NewPhysicalCache
+	DefaultCacheSize = 32 * 1024
+)
+
+// PhysicalCache is used to wrap an underlying physical backend
+// and provide an LRU cache layer on top. Most of the reads done by
+// Vault are for policy objects so there is a large read reduction
+// by using a simple write-through cache.
+type PhysicalCache struct {
+	backend Backend
+	lru     *lru.Cache
+}
+
+// NewPhysicalCache returns a physical cache of the given size.
+// If no size is provided, the default size is used.
+func NewPhysicalCache(b Backend, size int) *PhysicalCache {
+	if size <= 0 {
+		size = DefaultCacheSize
+	}
+	cache, _ := lru.New(size)
+	c := &PhysicalCache{
+		backend: b,
+		lru:     cache,
+	}
+	return c
+}
+
+// Purge is used to clear the cache
+func (c *PhysicalCache) Purge() {
+	c.lru.Purge()
+}
+
+func (c *PhysicalCache) Put(entry *Entry) error {
+	err := c.backend.Put(entry)
+	c.lru.Add(entry.Key, entry)
+	return err
+}
+
+func (c *PhysicalCache) Get(key string) (*Entry, error) {
+	// Check the LRU first
+	if raw, ok := c.lru.Get(key); ok {
+		if raw == nil {
+			return nil, nil
+		} else {
+			return raw.(*Entry), nil
+		}
+	}
+
+	// Read from the underlying backend
+	ent, err := c.backend.Get(key)
+	if err != nil {
+		return nil, err
+	}
+
+	// Cache the result
+	c.lru.Add(key, ent)
+	return ent, err
+}
+
+func (c *PhysicalCache) Delete(key string) error {
+	err := c.backend.Delete(key)
+	c.lru.Remove(key)
+	return err
+}
+
+func (c *PhysicalCache) List(prefix string) ([]string, error) {
+	// Always pass-through as this would be difficult to cache.
+	return c.backend.List(prefix)
+}
diff --git a/physical/cache_test.go b/physical/cache_test.go
new file mode 100644
index 000000000..39d953cfe
--- /dev/null
+++ b/physical/cache_test.go
@@ -0,0 +1,48 @@
+package physical
+
+import "testing"
+
+func TestCache(t *testing.T) {
+	inm := NewInmem()
+	cache := NewPhysicalCache(inm, 0)
+	testBackend(t, cache)
+	testBackend_ListPrefix(t, cache)
+}
+
+func TestCache_Purge(t *testing.T) {
+	inm := NewInmem()
+	cache := NewPhysicalCache(inm, 0)
+
+	ent := &Entry{
+		Key:   "foo",
+		Value: []byte("bar"),
+	}
+	err := cache.Put(ent)
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	// Delete from under
+	inm.Delete("foo")
+
+	// Read should work
+	out, err := cache.Get("foo")
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if out == nil {
+		t.Fatalf("should have key")
+	}
+
+	// Clear the cache
+	cache.Purge()
+
+	// Read should fail
+	out, err = cache.Get("foo")
+	if err != nil {
+		t.Fatalf("err: %v", err)
+	}
+	if out != nil {
+		t.Fatalf("should not have key")
+	}
+}