xP: embed web resources, tame browser caching

2025-07-09 21:53:19 +02:00
parent 80af5c22d6
commit 71e1a744c5
4 changed files with 73 additions and 17 deletions
--- a/xP/xP.go
+++ b/xP/xP.go
@@ -1,4 +1,4 @@
-// Copyright (c) 2022, Přemysl Eric Janouch <p@janouch.name>
+// Copyright (c) 2022 - 2025, Přemysl Eric Janouch <p@janouch.name>
 // SPDX-License-Identifier: 0BSD

 package main
@@ -6,12 +6,16 @@ package main
 import (
 	"bufio"
 	"context"
+	"crypto/sha1"
+	"embed"
 	"encoding/binary"
+	"encoding/hex"
 	"encoding/json"
 	"flag"
 	"fmt"
 	"html/template"
 	"io"
+	"io/fs"
 	"log"
 	"net"
 	"net/http"
@@ -23,7 +27,12 @@ import (
 )

 var (
-	debug = flag.Bool("debug", false, "enable debug output")
+	debug   = flag.Bool("debug", false, "enable debug output")
+	webRoot = flag.String("webroot", "", "override bundled web resources")
+
+	//go:embed public/*
+	webResources     embed.FS
+	webResourcesHash string

 	addressBind    string
 	addressConnect string
@@ -240,21 +249,20 @@ func handleWS(w http.ResponseWriter, r *http.Request) {

 // -----------------------------------------------------------------------------

-var staticHandler = http.FileServer(http.Dir("."))
-
 var page = template.Must(template.New("/").Parse(`<!DOCTYPE html>
 <html>
 <head>
 	<title>xP</title>
 	<meta charset="utf-8" />
 	<meta name="viewport" content="width=device-width, initial-scale=1">
+	<base href="{{ .Root }}/">
 	<link rel="stylesheet" href="xP.css" />
 </head>
 <body>
 	<script src="mithril.js">
 	</script>
 	<script>
-	let proxy = '{{ . }}'
+	let proxy = '{{ .Proxy }}'
 	</script>
 	<script type="module" src="xP.js">
 	</script>
@@ -262,20 +270,49 @@ var page = template.Must(template.New("/").Parse(`<!DOCTYPE html>
 </html>`))

 func handleDefault(w http.ResponseWriter, r *http.Request) {
-	if r.URL.Path != "/" {
-		staticHandler.ServeHTTP(w, r)
-		return
-	}
-
 	wsURI := addressWS
 	if wsURI == "" {
 		wsURI = fmt.Sprintf("ws://%s/ws", r.Host)
 	}
-	if err := page.Execute(w, wsURI); err != nil {
+
+	args := struct {
+		Root  string
+		Proxy string
+	}{
+		Root:  webResourcesHash,
+		Proxy: wsURI,
+	}
+	if err := page.Execute(w, &args); err != nil {
 		log.Println("Template execution failed: " + err.Error())
 	}
 }

+func hashFS(root fs.FS) []byte {
+	hasher := sha1.New()
+	callback := func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// Note that this can be fooled.
+		fmt.Fprintln(hasher, path)
+
+		if !d.IsDir() {
+			file, err := root.Open(path)
+			if err != nil {
+				return err
+			}
+			defer file.Close()
+			io.Copy(hasher, file)
+		}
+		return nil
+	}
+	if err := fs.WalkDir(root, ".", callback); err != nil {
+		log.Fatalln(err)
+	}
+	return hasher.Sum(nil)
+}
+
 func main() {
 	flag.Usage = func() {
 		fmt.Fprintf(flag.CommandLine.Output(),
@@ -294,6 +331,21 @@ func main() {
 		addressWS = flag.Arg(2)
 	}

+	subResources, err := fs.Sub(webResources, "public")
+	if err != nil {
+		log.Fatalln(err)
+	}
+	if *webRoot != "" {
+		subResources = os.DirFS(*webRoot)
+	}
+
+	// The simplest way of ensuring that web browsers don't use
+	// stale cached copies of our files.
+	webResourcesHash = hex.EncodeToString(hashFS(subResources))
+	http.Handle("/"+webResourcesHash+"/",
+		http.StripPrefix("/"+webResourcesHash+"/",
+			http.FileServerFS(subResources)))
+
 	http.Handle("/ws", http.HandlerFunc(handleWS))
 	http.Handle("/", http.HandlerFunc(handleDefault))