From 450136a0c0dbd675a87d6af54f7aba5c9d079c21 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Sat, 7 May 2022 18:22:57 -0600
Subject: Implement cachedAssetStore

---
 srv/src/post/asset.go | 67 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

(limited to 'srv/src/post/asset.go')

diff --git a/srv/src/post/asset.go b/srv/src/post/asset.go
index 3e6ae28..18af8f6 100644
--- a/srv/src/post/asset.go
+++ b/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
+}
-- 
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