Web export: the page build key covers the runtime and scripts, so a new engine gets new immutable URLs

app/export/web.go

@@ -3,7 +3,9 @@ package export
 import (
 	"bytes"
 	"compress/gzip"
+	"crypto/sha256"
 	"embed"
+	"encoding/hex"
 	"encoding/json"
 	"html/template"
 	"io/fs"
@@ -141,6 +143,21 @@ func (j *job) webTitle() string {
 	return AppName(j.p)
 }
 
+// webBuild keys the page's ?v= URLs on the data, the runtime and both scripts, so a new engine gets new URLs under immutable caching.
+func (j *job) webBuild(scripts ...[]byte) (string, error) {
+	wasm, err := os.ReadFile(j.l.binary())
+	if err != nil {
+		return "", errs.Wrap(err, errs.VFSIO, "cannot read the web runtime")
+	}
+	h := sha256.New()
+	h.Write([]byte(j.rep.Hash))
+	h.Write(wasm)
+	for _, s := range scripts {
+		h.Write(s)
+	}
+	return hex.EncodeToString(h.Sum(nil))[:buildKeyLen], nil
+}
+
 func (j *job) packWeb() error {
 	src, err := wasmExecPath(j.goroot)
 	if err != nil {
@@ -176,9 +193,9 @@ func (j *job) packWeb() error {
 	if err := writeFile(filepath.Join(j.l.data, WebFiles), list, WebFiles); err != nil {
 		return err
 	}
-	build := j.rep.Hash
-	if len(build) > buildKeyLen {
-		build = build[:buildKeyLen]
+	build, err := j.webBuild(exec, loader)
+	if err != nil {
+		return err
 	}
 	var page bytes.Buffer
 	if err := webIndexTmpl.Execute(&page, webPage{Title: j.webTitle(), Build: build, Icon: j.icon != nil}); err != nil {

app/export/web_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 
@@ -60,9 +61,16 @@ func TestPackWeb(t *testing.T) {
 	if !strings.Contains(string(page), "&lt;Game &amp;") || strings.Contains(string(page), "<Game") {
 		t.Fatal("the title is not escaped")
 	}
-	if !strings.Contains(string(page), `data-build="abababababab"`) {
+	key := regexp.MustCompile(`data-build="([0-9a-f]{12})"`).FindStringSubmatch(string(page))
+	if key == nil {
 		t.Fatal("the build key is missing")
 	}
+	if err := os.WriteFile(j.l.binary(), append(wasm, '!'), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if again, err := j.webBuild(); err != nil || again == key[1] {
+		t.Fatalf("a new runtime kept the build key %s (%v)", again, err)
+	}
 	raw, err := os.ReadFile(filepath.Join(j.l.data, WebFiles))
 	if err != nil {
 		t.Fatal(err)