Implement cachedAssetStore

srv/src/post/asset.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"sync"
 )
 
 var (
@@ -84,3 +85,69 @@ func (s *assetStore) Delete(id string) error {
 	_, err := s.db.Exec(`DELETE FROM assets WHERE id = ?`, id)
 	return err
 }
+
+////////////////////////////////////////////////////////////////////////////////
+
+type cachedAssetStore struct {
+	inner AssetStore
+	m     sync.Map
+}
+
+// NewCachedAssetStore wraps an AssetStore in an in-memory cache.
+func NewCachedAssetStore(assetStore AssetStore) AssetStore {
+	return &cachedAssetStore{
+		inner: assetStore,
+	}
+}
+
+func (s *cachedAssetStore) Set(id string, from io.Reader) error {
+
+	buf := new(bytes.Buffer)
+	from = io.TeeReader(from, buf)
+
+	if err := s.inner.Set(id, from); err != nil {
+		return err
+	}
+
+	s.m.Store(id, buf.Bytes())
+	return nil
+}
+
+func (s *cachedAssetStore) Get(id string, into io.Writer) error {
+
+	if bodyI, ok := s.m.Load(id); ok {
+
+		if err, ok := bodyI.(error); ok {
+			return err
+		}
+
+		if _, err := io.Copy(into, bytes.NewReader(bodyI.([]byte))); err != nil {
+			return fmt.Errorf("writing body to io.Writer: %w", err)
+		}
+
+		return nil
+	}
+
+	buf := new(bytes.Buffer)
+	into = io.MultiWriter(into, buf)
+
+	if err := s.inner.Get(id, into); errors.Is(err, ErrAssetNotFound) {
+		s.m.Store(id, err)
+		return err
+	} else if err != nil {
+		return err
+	}
+
+	s.m.Store(id, buf.Bytes())
+	return nil
+}
+
+func (s *cachedAssetStore) Delete(id string) error {
+
+	if err := s.inner.Delete(id); err != nil {
+		return err
+	}
+
+	s.m.Delete(id)
+	return nil
+}

srv/src/post/asset_test.go

@@ -12,14 +12,14 @@ type assetTestHarness struct {
 	store AssetStore
 }
 
-func newAssetTestHarness(t *testing.T) assetTestHarness {
+func newAssetTestHarness(t *testing.T) *assetTestHarness {
 
 	db := NewInMemSQLDB()
 	t.Cleanup(func() { db.Close() })
 
 	store := NewAssetStore(db)
 
-	return assetTestHarness{
+	return &assetTestHarness{
 		store: store,
 	}
 }
@@ -40,28 +40,41 @@ func (h *assetTestHarness) assertNotFound(t *testing.T, id string) {
 
 func TestAssetStore(t *testing.T) {
 
-	h := newAssetTestHarness(t)
+	testAssetStore := func(t *testing.T, h *assetTestHarness) {
+		t.Helper()
 
-	h.assertNotFound(t, "foo")
-	h.assertNotFound(t, "bar")
+		h.assertNotFound(t, "foo")
+		h.assertNotFound(t, "bar")
 
-	err := h.store.Set("foo", bytes.NewBufferString("FOO"))
-	assert.NoError(t, err)
+		err := h.store.Set("foo", bytes.NewBufferString("FOO"))
+		assert.NoError(t, err)
 
-	h.assertGet(t, "FOO", "foo")
-	h.assertNotFound(t, "bar")
+		h.assertGet(t, "FOO", "foo")
+		h.assertNotFound(t, "bar")
 
-	err = h.store.Set("foo", bytes.NewBufferString("FOOFOO"))
-	assert.NoError(t, err)
+		err = h.store.Set("foo", bytes.NewBufferString("FOOFOO"))
+		assert.NoError(t, err)
+
+		h.assertGet(t, "FOOFOO", "foo")
+		h.assertNotFound(t, "bar")
 
-	h.assertGet(t, "FOOFOO", "foo")
-	h.assertNotFound(t, "bar")
+		assert.NoError(t, h.store.Delete("foo"))
+		h.assertNotFound(t, "foo")
+		h.assertNotFound(t, "bar")
+
+		assert.NoError(t, h.store.Delete("bar"))
+		h.assertNotFound(t, "foo")
+		h.assertNotFound(t, "bar")
+	}
 
-	assert.NoError(t, h.store.Delete("foo"))
-	h.assertNotFound(t, "foo")
-	h.assertNotFound(t, "bar")
+	t.Run("sql", func(t *testing.T) {
+		h := newAssetTestHarness(t)
+		testAssetStore(t, h)
+	})
 
-	assert.NoError(t, h.store.Delete("bar"))
-	h.assertNotFound(t, "foo")
-	h.assertNotFound(t, "bar")
+	t.Run("mem", func(t *testing.T) {
+		h := newAssetTestHarness(t)
+		h.store = NewCachedAssetStore(h.store)
+		testAssetStore(t, h)
+	})
 }