From f12346e39c606f3aa3fd5a754f4d00cc269a0ec6 Mon Sep 17 00:00:00 2001
From: James Elliott <james-d-elliott@users.noreply.github.com>
Date: Mon, 25 Jul 2022 20:43:50 +1000
Subject: [PATCH] fix(server): missing cache-control header (#3737)

This fixes a missing cache control header.

Fixes #3732.
---
 internal/server/asset.go | 95 ++++++++++++++++++++++++++++++++++------
 internal/server/const.go | 12 +++++
 2 files changed, 93 insertions(+), 14 deletions(-)

diff --git a/internal/server/asset.go b/internal/server/asset.go
index 4df0d4211..d834ccbed 100644
--- a/internal/server/asset.go
+++ b/internal/server/asset.go
@@ -1,15 +1,20 @@
 package server
 
 import (
+	"bytes"
+	"crypto/sha1" //nolint:gosec // Usage is for collision avoidance not security.
 	"embed"
 	"errors"
 	"fmt"
 	"io/fs"
+	"mime"
 	"net/http"
+	"path"
+	"path/filepath"
 
 	"github.com/valyala/fasthttp"
-	"github.com/valyala/fasthttp/fasthttpadaptor"
 
+	"github.com/authelia/authelia/v4/internal/handlers"
 	"github.com/authelia/authelia/v4/internal/middlewares"
 	"github.com/authelia/authelia/v4/internal/utils"
 )
@@ -21,9 +26,43 @@ var locales embed.FS
 var assets embed.FS
 
 func newPublicHTMLEmbeddedHandler() fasthttp.RequestHandler {
-	embeddedPath, _ := fs.Sub(assets, "public_html")
+	etags := map[string][]byte{}
 
-	return fasthttpadaptor.NewFastHTTPHandler(http.FileServer(http.FS(embeddedPath)))
+	getEmbedETags(assets, "public_html", etags)
+
+	return func(ctx *fasthttp.RequestCtx) {
+		p := path.Join("public_html", string(ctx.Path()))
+
+		if etag, ok := etags[p]; ok {
+			ctx.Response.Header.SetBytesKV(headerETag, etag)
+			ctx.Response.Header.SetBytesKV(headerCacheControl, headerValueCacheControlETaggedAssets)
+
+			if bytes.Equal(etag, ctx.Request.Header.PeekBytes(headerIfNoneMatch)) {
+				ctx.SetStatusCode(fasthttp.StatusNotModified)
+
+				return
+			}
+		}
+
+		var (
+			data []byte
+			err  error
+		)
+
+		if data, err = assets.ReadFile(p); err != nil {
+			hfsHandleErr(ctx, err)
+
+			return
+		}
+
+		contentType := mime.TypeByExtension(path.Ext(p))
+		if len(contentType) == 0 {
+			contentType = http.DetectContentType(data)
+		}
+
+		ctx.SetContentType(contentType)
+		ctx.SetBody(data)
+	}
 }
 
 func newLocalesEmbeddedHandler() (handler fasthttp.RequestHandler) {
@@ -72,18 +111,46 @@ func newLocalesEmbeddedHandler() (handler fasthttp.RequestHandler) {
 	}
 }
 
-func hfsHandleErr(ctx *fasthttp.RequestCtx, err error) {
-	switch {
-	case errors.Is(err, fs.ErrNotExist):
-		writeStatus(ctx, fasthttp.StatusNotFound)
-	case errors.Is(err, fs.ErrPermission):
-		writeStatus(ctx, fasthttp.StatusForbidden)
-	default:
-		writeStatus(ctx, fasthttp.StatusInternalServerError)
+func getEmbedETags(embedFS embed.FS, root string, etags map[string][]byte) {
+	var (
+		err     error
+		entries []fs.DirEntry
+	)
+
+	if entries, err = embedFS.ReadDir(root); err != nil {
+		return
+	}
+
+	for _, entry := range entries {
+		if entry.IsDir() {
+			getEmbedETags(embedFS, filepath.Join(root, entry.Name()), etags)
+
+			continue
+		}
+
+		p := filepath.Join(root, entry.Name())
+
+		var data []byte
+
+		if data, err = embedFS.ReadFile(p); err != nil {
+			continue
+		}
+
+		sum := sha1.New() //nolint:gosec // Usage is for collision avoidance not security.
+
+		sum.Write(data)
+
+		etags[p] = []byte(fmt.Sprintf("%x", sum.Sum(nil)))
 	}
 }
 
-func writeStatus(ctx *fasthttp.RequestCtx, status int) {
-	ctx.SetStatusCode(status)
-	ctx.SetBodyString(fmt.Sprintf("%d %s", status, fasthttp.StatusMessage(status)))
+func hfsHandleErr(ctx *fasthttp.RequestCtx, err error) {
+	switch {
+	case errors.Is(err, fs.ErrNotExist):
+		handlers.SetStatusCodeResponse(ctx, fasthttp.StatusNotFound)
+	case errors.Is(err, fs.ErrPermission):
+		handlers.SetStatusCodeResponse(ctx, fasthttp.StatusForbidden)
+	default:
+		handlers.SetStatusCodeResponse(ctx, fasthttp.StatusInternalServerError)
+	}
 }
diff --git a/internal/server/const.go b/internal/server/const.go
index ae815cd45..483a3ab0f 100644
--- a/internal/server/const.go
+++ b/internal/server/const.go
@@ -1,5 +1,9 @@
 package server
 
+import (
+	"github.com/valyala/fasthttp"
+)
+
 const (
 	embeddedAssets = "public_html/"
 	swaggerAssets  = embeddedAssets + "api/"
@@ -50,6 +54,14 @@ const (
 	schemeHTTPS = "https"
 )
 
+var (
+	headerETag         = []byte(fasthttp.HeaderETag)
+	headerIfNoneMatch  = []byte(fasthttp.HeaderIfNoneMatch)
+	headerCacheControl = []byte(fasthttp.HeaderCacheControl)
+
+	headerValueCacheControlETaggedAssets = []byte("public, max-age=0, must-revalidate")
+)
+
 const healthCheckEnv = `# Written by Authelia Process
 X_AUTHELIA_HEALTHCHECK=1
 X_AUTHELIA_HEALTHCHECK_SCHEME=%s