Always offer the teacher-layer selector via ?exe-teacher=1

CHANGELOG.md

@@ -23,6 +23,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Added
 
+- Viewer now makes the eXeLearning teacher-layer selector available by loading
+  the package index with `?exe-teacher=1`. eXeLearning exports hide teacher-only
+  content by default (see exelearning/exelearning#1972); since the Nextcloud
+  Viewer is a personal file viewer — the person opening the package is
+  effectively its author/teacher — the selector is always offered. It stays OFF
+  by default; the viewer reveals it, and the package's own JS persists the
+  choice and propagates the param across in-package navigation.
 - CI matrix (`.github/workflows/ci.yml`) covering NC 31/32/33 × PHP
   8.2/8.3/8.4 with rotated databases (sqlite/mysql/pgsql), plus an
   experimental PHP 8.5 cell. Each cell installs the app into a real

src/elpx/iframe-renderer.ts

@@ -25,6 +25,31 @@ const IFRAME_ALLOW = [
 	'clipboard-write',
 ].join('; ')
 
+/**
+ * URL parameter that eXeLearning packages read to expose the in-package
+ * "teacher layer" selector (see exelearning/exelearning#1972). Without it,
+ * exported packages hide teacher-only content and offer no way to reveal it.
+ *
+ * The Nextcloud Viewer is a personal file viewer — the person opening the
+ * package is effectively its author/teacher — so we always make the selector
+ * available. The selector itself stays OFF by default; the viewer activates
+ * it and the package's own JS persists the choice and propagates the param
+ * across in-package navigation links.
+ */
+const TEACHER_MODE_PARAM = 'exe-teacher=1'
+
+/**
+ * Appends {@link TEACHER_MODE_PARAM} to the top-level package index URL,
+ * preserving any existing query string and avoiding a double append.
+ * @param src Already-resolved index URL the iframe will load.
+ */
+function withTeacherMode(src: string): string {
+	if (src.includes(TEACHER_MODE_PARAM)) {
+		return src
+	}
+	return src + (src.includes('?') ? '&' : '?') + TEACHER_MODE_PARAM
+}
+
 export interface IframeOptions {
 	runtimeBase: string
 	sessionId: string
@@ -46,7 +71,13 @@ export function buildSandboxedIframe(src: string, title: string): HTMLIFrameElem
 	iframe.setAttribute('sandbox', SANDBOX_FLAGS.join(' '))
 	iframe.setAttribute('allow', IFRAME_ALLOW)
 	iframe.setAttribute('referrerpolicy', 'no-referrer')
-	iframe.src = src
+	// `src` is always the package *index* entry — both the Service Worker path
+	// ({@link createPackageIframe}) and the server-side asset fallback funnel
+	// the top-level page here, never a subresource. Adding the teacher-mode
+	// param only to this top-level document is enough: the package's own JS
+	// propagates it across in-package navigation, and the SW/AssetController
+	// match requests on the pathname only, so the extra query is harmless.
+	iframe.src = withTeacherMode(src)
 	iframe.addEventListener('load', () => {
 		try {
 			rewireExternalLinks(iframe)

tests/js/iframe-renderer.test.ts

@@ -0,0 +1,42 @@
+import { describe, expect, it } from 'vitest'
+import {
+	buildSandboxedIframe,
+	createPackageIframe,
+} from '../../src/elpx/iframe-renderer'
+import { RUNTIME_PREFIX } from '../../src/elpx/paths'
+
+describe('buildSandboxedIframe', () => {
+	it('appends the eXeLearning teacher-mode param to the index src', () => {
+		const iframe = buildSandboxedIframe('/apps/exelearning/asset/42/index.html', 'pkg')
+		expect(iframe.src).toContain('exe-teacher=1')
+		expect(iframe.src).toContain('/apps/exelearning/asset/42/index.html?exe-teacher=1')
+	})
+
+	it('uses & when the index src already carries a query string', () => {
+		const iframe = buildSandboxedIframe('/apps/exelearning/asset/42/index.html?foo=bar', 'pkg')
+		expect(iframe.src).toContain('?foo=bar&exe-teacher=1')
+	})
+
+	it('does not double-append when the param is already present', () => {
+		const iframe = buildSandboxedIframe('/apps/exelearning/asset/42/index.html?exe-teacher=1', 'pkg')
+		expect(iframe.src.match(/exe-teacher=1/g)).toHaveLength(1)
+	})
+
+	it('sets the sandbox flags and accessible title', () => {
+		const iframe = buildSandboxedIframe('/apps/exelearning/asset/42/index.html', 'My package')
+		expect(iframe.getAttribute('sandbox')).toContain('allow-scripts')
+		expect(iframe.title).toBe('My package')
+	})
+})
+
+describe('createPackageIframe', () => {
+	it('builds a runtime index src that exposes the teacher-mode selector', () => {
+		const iframe = createPackageIframe({
+			runtimeBase: RUNTIME_PREFIX,
+			sessionId: 'session-1',
+			indexEntry: 'index.html',
+			title: 'pkg',
+		})
+		expect(iframe.src).toContain(`${RUNTIME_PREFIX}/session-1/index.html?exe-teacher=1`)
+	})
+})