Add cache for the Swift AppFS (#4178)

When loading html, js, css, and images for a webapp or a konnector, the
stack makes a call to the AppFS server. With many users and a Swift
cluster, we can improve latency by using a cache.

go.mod

@@ -24,6 +24,7 @@ require (
 	github.com/gorilla/websocket v1.5.0
 	github.com/h2non/filetype v1.1.3
 	github.com/hashicorp/go-multierror v1.1.1
+	github.com/hashicorp/golang-lru/v2 v2.0.7
 	github.com/howeyc/gopass v0.0.0-20210920133722-c8aef6fb66ef
 	github.com/justincampbell/bigduration v0.0.0-20160531141349-e45bf03c0666
 	github.com/labstack/echo/v4 v4.11.2

go.sum

@@ -214,6 +214,8 @@ github.com/hashicorp/go-multierror v1.1.1 h1:H5DkEtf6CXdFp0N0Em5UCwQpXMWke8IA0+l
 github.com/hashicorp/go-multierror v1.1.1/go.mod h1:iw975J/qwKPdAO1clOe2L8331t/9/fmwbPZ6JB6eMoM=
 github.com/hashicorp/golang-lru v0.5.0/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
 github.com/hashicorp/golang-lru v0.5.1/go.mod h1:/m3WP610KZHVQ1SGc6re/UDhFvYD7pJ4Ao+sR/qLZy8=
+github.com/hashicorp/golang-lru/v2 v2.0.7 h1:a+bsQ5rvGLjzHuww6tVxozPZFVghXaHOwFs4luLUK2k=
+github.com/hashicorp/golang-lru/v2 v2.0.7/go.mod h1:QeFd9opnmA6QUJc5vARoKUSoFhyfM2/ZepoAG6RGpeM=
 github.com/hashicorp/hcl v0.0.0-20170914154624-68e816d1c783/go.mod h1:oZtUIOe8dh44I2q6ScRibXws4Ajl+d+nod3AaR9vL5w=
 github.com/hashicorp/hcl v1.0.0 h1:0Anlzjpi4vEasTeNFn2mLJgTSwt0+6sfsiTG8qcWGx4=
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=

pkg/appfs/server.go

@@ -16,11 +16,13 @@ import (
 	"path"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/andybalholm/brotli"
 	"github.com/cozy/cozy-stack/pkg/consts"
 	web_utils "github.com/cozy/cozy-stack/pkg/utils"
+	lru "github.com/hashicorp/golang-lru/v2"
 	"github.com/labstack/echo/v4"
 	"github.com/ncw/swift/v2"
 	"github.com/spf13/afero"
@@ -99,19 +101,52 @@ func (g gzipReadCloser) Close() error {
 	return nil
 }
 
+type cacheEntry struct {
+	content []byte
+	headers swift.Headers
+}
+
+var cache *lru.Cache[string, cacheEntry]
+var initCacheOnce sync.Once
+
 // NewSwiftFileServer returns provides the apps.FileServer implementation
 // using the swift backend as file server.
 func NewSwiftFileServer(conn *swift.Connection, appsType consts.AppType) FileServer {
+	initCacheOnce.Do(func() {
+		c, err := lru.New[string, cacheEntry](128)
+		if err != nil {
+			panic(err)
+		}
+		cache = c
+	})
 	return &swiftServer{
 		c:         conn,
 		container: containerName(appsType),
 		ctx:       context.Background(),
 	}
 }
 
+func (s *swiftServer) openWithCache(objName string) (io.ReadCloser, swift.Headers, error) {
+	entry, ok := cache.Get(objName)
+	if !ok {
+		f, h, err := s.c.ObjectOpen(s.ctx, s.container, objName, false, nil)
+		if err != nil {
+			return f, h, err
+		}
+		entry.headers = h
+		entry.content, err = io.ReadAll(f)
+		if err != nil {
+			return nil, h, err
+		}
+		cache.Add(objName, entry)
+	}
+	f := io.NopCloser(bytes.NewReader(entry.content))
+	return f, entry.headers, nil
+}
+
 func (s *swiftServer) Open(slug, version, shasum, file string) (io.ReadCloser, error) {
 	objName := s.makeObjectName(slug, version, shasum, file)
-	f, h, err := s.c.ObjectOpen(s.ctx, s.container, objName, false, nil)
+	f, h, err := s.openWithCache(objName)
 	if err != nil {
 		return nil, wrapSwiftErr(err)
 	}
@@ -127,7 +162,7 @@ func (s *swiftServer) Open(slug, version, shasum, file string) (io.ReadCloser, e
 
 func (s *swiftServer) ServeFileContent(w http.ResponseWriter, req *http.Request, slug, version, shasum, file string) error {
 	objName := s.makeObjectName(slug, version, shasum, file)
-	f, h, err := s.c.ObjectOpen(s.ctx, s.container, objName, false, nil)
+	f, h, err := s.openWithCache(objName)
 	if err != nil {
 		return wrapSwiftErr(err)
 	}