From eb83523ceadf84d862e406df3ee0b0d7d3a3736e Mon Sep 17 00:00:00 2001
From: Barak Amar <barak.amar@treeverse.io>
Date: Sat, 9 Dec 2023 09:52:56 +0200
Subject: [PATCH 1/2] UI etag embedded content

Scan embedded content on startup and serve etag header to FileServer.
FileServer will use the Etag and provide no content change if needed.

This will allow cache all static resources, which allow better
performance after the first load, in the web ui.
---
 pkg/api/etag_middleware.go | 77 ++++++++++++++++++++++++++++++++++++++
 pkg/api/ui_handler.go      |  5 +--
 2 files changed, 79 insertions(+), 3 deletions(-)
 create mode 100644 pkg/api/etag_middleware.go

diff --git a/pkg/api/etag_middleware.go b/pkg/api/etag_middleware.go
new file mode 100644
index 00000000000..ba5aa2954da
--- /dev/null
+++ b/pkg/api/etag_middleware.go
@@ -0,0 +1,77 @@
+package api
+
+import (
+	"crypto/md5"
+	"encoding/hex"
+	"io"
+	"io/fs"
+	"net/http"
+	"path"
+	"strings"
+)
+
+// EtagMiddleware returns a new Etag middleware handler.
+// It designs to work on embedded FS, where the content doesn't change.
+// It calculates the Etag for each file on startup and serves it on each request.
+func EtagMiddleware(root fs.FS, next http.Handler) http.Handler {
+	etags, err := scanFSEtags(root)
+	if err != nil {
+		panic(err)
+	}
+	return &etagHandler{
+		root:  root,
+		next:  next,
+		etags: etags,
+	}
+}
+
+type etagHandler struct {
+	root  fs.FS
+	next  http.Handler
+	etags map[string]string
+}
+
+func (e *etagHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	upath := r.URL.Path
+	if !strings.HasPrefix(upath, "/") {
+		upath = "/" + upath
+	}
+	upath = path.Clean(upath)
+	if strings.HasSuffix(upath, "/") {
+		upath += "index.html"
+	}
+	etag, ok := e.etags[upath]
+	if ok {
+		w.Header().Set("Etag", "\""+etag+"\"")
+	}
+	e.next.ServeHTTP(w, r)
+}
+
+func scanFSEtags(fSys fs.FS) (map[string]string, error) {
+	etags := make(map[string]string)
+	err := fs.WalkDir(fSys, ".", func(fpath string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			return nil
+		}
+
+		f, err := fSys.Open(fpath)
+		if err != nil {
+			return err
+		}
+		defer func() { _ = f.Close() }()
+
+		h := md5.New()
+		if _, err := io.Copy(h, f); err != nil {
+			return err
+		}
+		etags["/"+fpath] = hex.EncodeToString(h.Sum(nil))
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+	return etags, nil
+}
diff --git a/pkg/api/ui_handler.go b/pkg/api/ui_handler.go
index 899a7a18867..72d4f25781b 100644
--- a/pkg/api/ui_handler.go
+++ b/pkg/api/ui_handler.go
@@ -9,7 +9,6 @@ import (
 	"strings"
 
 	gomime "github.com/cubewise-code/go-mime"
-	"github.com/go-chi/chi/v5/middleware"
 	"github.com/treeverse/lakefs/pkg/api/params"
 	gwerrors "github.com/treeverse/lakefs/pkg/gateway/errors"
 	"github.com/treeverse/lakefs/pkg/gateway/operations"
@@ -34,7 +33,7 @@ func NewUIHandler(gatewayDomains []string, snippets []params.CodeSnippet) http.H
 		panic(err)
 	}
 	fileSystem := http.FS(injectedContent)
-	nocacheContent := middleware.NoCache(http.StripPrefix("/", http.FileServer(fileSystem)))
+	nocacheContent := EtagMiddleware(injectedContent, http.StripPrefix("/", http.FileServer(fileSystem)))
 	return NewHandlerWithDefault(fileSystem, nocacheContent, gatewayDomains)
 }
 
@@ -45,7 +44,7 @@ func NewS3GatewayEndpointErrorHandler(gatewayDomains []string) http.Handler {
 			return
 		}
 
-		// For other requests, return generic not found error
+		// For other requests, return generic "not found" error
 		w.WriteHeader(http.StatusNotFound)
 	})
 }

From 6b2f34148a4a1b1434b4654b57b058c89d663820 Mon Sep 17 00:00:00 2001
From: Barak Amar <barak.amar@treeverse.io>
Date: Sat, 9 Dec 2023 13:18:35 +0200
Subject: [PATCH 2/2] apply code review changes

---
 pkg/api/etag_middleware.go | 7 ++++---
 pkg/api/ui_handler.go      | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/pkg/api/etag_middleware.go b/pkg/api/etag_middleware.go
index ba5aa2954da..32d54895782 100644
--- a/pkg/api/etag_middleware.go
+++ b/pkg/api/etag_middleware.go
@@ -1,7 +1,7 @@
 package api
 
 import (
-	"crypto/md5"
+	"crypto/md5" //nolint:gosec
 	"encoding/hex"
 	"io"
 	"io/fs"
@@ -63,11 +63,12 @@ func scanFSEtags(fSys fs.FS) (map[string]string, error) {
 		}
 		defer func() { _ = f.Close() }()
 
-		h := md5.New()
+		h := md5.New() //nolint:gosec
 		if _, err := io.Copy(h, f); err != nil {
 			return err
 		}
-		etags["/"+fpath] = hex.EncodeToString(h.Sum(nil))
+		hashValue := hex.EncodeToString(h.Sum(nil))
+		etags["/"+fpath] = hashValue
 		return nil
 	})
 	if err != nil {
diff --git a/pkg/api/ui_handler.go b/pkg/api/ui_handler.go
index 72d4f25781b..8db6a18aafd 100644
--- a/pkg/api/ui_handler.go
+++ b/pkg/api/ui_handler.go
@@ -33,8 +33,8 @@ func NewUIHandler(gatewayDomains []string, snippets []params.CodeSnippet) http.H
 		panic(err)
 	}
 	fileSystem := http.FS(injectedContent)
-	nocacheContent := EtagMiddleware(injectedContent, http.StripPrefix("/", http.FileServer(fileSystem)))
-	return NewHandlerWithDefault(fileSystem, nocacheContent, gatewayDomains)
+	etagHandler := EtagMiddleware(injectedContent, http.StripPrefix("/", http.FileServer(fileSystem)))
+	return NewHandlerWithDefault(fileSystem, etagHandler, gatewayDomains)
 }
 
 func NewS3GatewayEndpointErrorHandler(gatewayDomains []string) http.Handler {