desktop-mode / includes / portal.php

portal.php in OpenStation: Desktop Windows, Dock & Virtual Desktops for WP Admin 1.1.13, at includes/portal.php

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1	<?php
2	/**
3	* OpenStation — `/openstation` Portal Entry Point.
4	*
5	* Registers `/openstation` as a shareable URL that behaves like the
6	* front door of the desktop UI:
7	* 1. Logged-out users are bounced through `wp-login.php` with a
8	* redirect back to `/openstation/`.
9	* 2. Logged-in users with basic admin-read capability have the
10	* `desktop_mode_mode` user-meta toggle auto-enabled on first visit,
11	* then are forwarded to the shell screen
12	* (`admin.php?page=openstation`, see `includes/shell-screen.php`).
13	* An explicit `?target=` travels along as the page the shell opens
14	* first; without one the screen resolves the entry itself — the
15	* last-focused window of the saved session, else the default
16	* window, else the Dashboard.
17	*
18	* The URL is served virtually (no rewrite rules, no `.htaccess`
19	* surgery) by intercepting `parse_request` before WordPress routes the
20	* URL to 404. This keeps the plugin drop-in.
21	*
22	* @package OpenStation
23	*/
24
25	defined( 'ABSPATH' ) \|\| exit;
26
27	/** The URL path that triggers the portal handler. */
28	const OPENSTATION_PORTAL_PATH = 'openstation';
29
30	/**
31	* The pre-rebrand portal path, still accepted.
32	*
33	* The portal was reachable at `/desktop-mode/` before the rename, and
34	* that address is the kind of thing people bookmark or pin. It is not
35	* canonical: {@see openstation_portal_url()} always emits the current
36	* path, and a visit here forwards into wp-admin exactly as the canonical
37	* path does, so the address bar self-corrects on the next hop.
38	*
39	* The VALUE keeps its pre-rebrand spelling on purpose: it is a
40	* persisted or externally-visible identifier, so renaming it would
41	* orphan data already written by live installs (or break a live
42	* URL). The mismatch between this constant's name and its value is
43	* deliberate — it is NOT a half-finished rename.
44	*/
45	const OPENSTATION_PORTAL_PATH_LEGACY = 'desktop-mode';
46
47	/**
48	* Query var the admin shell reads to know it was entered via the portal.
49	*
50	* The VALUE keeps its pre-rebrand spelling on purpose: it is a
51	* persisted or externally-visible identifier, so renaming it would
52	* orphan data already written by live installs (or break a live
53	* URL). The mismatch between this constant's name and its value is
54	* deliberate — it is NOT a half-finished rename.
55	*/
56	const OPENSTATION_PORTAL_FLAG = 'desktop_mode_portal';
57
58	/**
59	* Query var set on portal redirects whose landing page came from an
60	* explicit `?target=…` URL the user (or a redirect chain originating
61	* from a click) provided — as opposed to the portal picking the
62	* session's focused window or the default-window fallback.
63	*
64	* The shell uses this to distinguish "user expressed navigation intent
65	* toward this URL" (open it) from "portal had to forward somewhere"
66	* (don't disturb the restored session).
67	*
68	* The VALUE keeps its pre-rebrand spelling on purpose: it is a
69	* persisted or externally-visible identifier, so renaming it would
70	* orphan data already written by live installs (or break a live
71	* URL). The mismatch between this constant's name and its value is
72	* deliberate — it is NOT a half-finished rename.
73	*/
74	const OPENSTATION_PORTAL_INTENT_FLAG = 'desktop_mode_portal_intent';
75
76	/**
77	* Query var set by the window-title-bar "Detach" action. Tells the
78	* admin_init redirect to skip portal forwarding for this request so the
79	* user can view the page as classic wp-admin in a new tab even when
80	* OpenStation is globally enabled for their account.
81	*
82	* The VALUE keeps its pre-rebrand spelling on purpose: it is a
83	* persisted or externally-visible identifier, so renaming it would
84	* orphan data already written by live installs (or break a live
85	* URL). The mismatch between this constant's name and its value is
86	* deliberate — it is NOT a half-finished rename.
87	*/
88	const OPENSTATION_CLASSIC_FLAG = 'desktop_mode_classic';
89
90	/**
91	* Returns the canonical portal URL, e.g. `https://example.com/openstation/`.
92	*
93	* @return string
94	*/
95	function openstation_portal_url() {
96	return home_url( '/' . OPENSTATION_PORTAL_PATH . '/' );
97	}
98
99	/**
100	* Intercepts requests to `/openstation` and forwards them into the admin.
101	*
102	* Hooks on `parse_request` — early enough to pre-empt 404 handling but
103	* late enough that `is_user_logged_in()` is reliable.
104	*
105	* @param WP $wp Current WordPress environment instance.
106	*/
107	function openstation_handle_portal_request( $wp ) {
108	unset( $wp );
109
110	if ( ! openstation_is_portal_request() ) {
111	return;
112	}
113
114	// Logged-out: bounce through login, returning to the portal URL.
115	if ( ! is_user_logged_in() ) {
116	wp_safe_redirect( wp_login_url( openstation_portal_url() ) );
117	exit;
118	}
119
120	// Require basic admin-read capability so subscribers of sites that
121	// blocked `read` from admin don't land in a broken window.
122	if ( ! current_user_can( 'read' ) ) {
123	wp_die(
124	esc_html__( 'Sorry, you are not allowed to access the WordPress desktop.', 'desktop-mode' ),
125	'',
126	array( 'response' => 403 )
127	);
128	}
129
130	$user_id = get_current_user_id();
131
132	/**
133	* Filters whether visiting the `/openstation` portal should auto-enable
134	* OpenStation for the current user.
135	*
136	* Default: true — the portal is an explicit opt-in action, so flipping
137	* the user meta mirrors the intent of visiting the URL.
138	*
139	* @param bool $auto_enable Whether to auto-enable OpenStation.
140	* @param int $user_id The current user's ID.
141	*/
142	$auto_enable = apply_filters( 'openstation_portal_auto_enable', true, $user_id );
143
144	// CSRF guard: only flip user-meta when the request is a same-origin
145	// top-level navigation. The portal is a GET URL by design (users
146	// follow shared `/openstation/` links), so we can't require a nonce
147	// — but we can require that the navigation originated from the
148	// same site (or a typed/bookmarked URL with no Referer/Sec-Fetch-
149	// Site). Off-origin hits still redirect into admin so shared
150	// links keep working; they just don't silently mutate user-meta.
151	if ( $auto_enable && openstation_portal_is_same_origin_navigation() && '1' !== get_user_meta( $user_id, 'desktop_mode_mode', true ) ) {
152	update_user_meta( $user_id, 'desktop_mode_mode', '1' );
153	// Same stamps + action as the AJAX toggle; the portal is the
154	// second of the two paths that turn a user on.
155	openstation_record_user_enabled( $user_id );
156	}
157
158	// Pick the page the shell opens first. An explicit `target` query
159	// arg — a same-origin wp-admin URL — is how
160	// `openstation_redirect_plain_admin_to_portal` preserves the user's
161	// navigation intent when they follow a link to a specific admin
162	// page (e.g. profile.php). Without one the shell screen resolves
163	// the entry itself: the last-focused window from the saved
164	// session, else the default window, else the Dashboard — see
165	// `openstation_shell_boot_target()`. The bare screen URL is the
166	// canonical address, and a reload of it re-resolves against the
167	// live session rather than against the window that was focused
168	// when the redirect happened.
169	$target = '';
170	$has_intent = false;
171	if ( ! empty( $_GET['target'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
172	// `esc_url_raw`, NOT `sanitize_text_field`: the latter strips
173	// every `%XX` percent-encoded sequence from its input as an XSS
174	// safeguard, which mangles request URIs that legitimately carry
175	// encoded slashes (e.g. `plugin=dir%2Ffile.php`). The downstream
176	// `openstation_sanitize_portal_target` validates the URL
177	// rigorously (scheme rejection, traversal rejection, and a
178	// hardcoded allowlist of canonical wp-admin filenames — see
179	// `openstation_admin_target_allowlist()`) so we don't lose
180	// any real safety by skipping `sanitize_text_field` here.
181	$target = openstation_sanitize_portal_target( esc_url_raw( wp_unslash( $_GET['target'] ) ) ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
182	if ( '' !== $target ) {
183	$has_intent = true;
184	}
185	}
186	// `intent=1` rides along with an explicit target so the shell treats
187	// the resulting `currentPage` as user intent and opens it on top of
188	// the restored session. Without it, a bare `/openstation/` visit and
189	// a portal-redirected admin-bar click would be indistinguishable
190	// downstream.
191	wp_safe_redirect( openstation_shell_url( $target, $has_intent ) );
192	exit;
193	}
194	add_action( 'parse_request', 'openstation_handle_portal_request' );
195
196	/**
197	* Decides whether the current request to the portal can mutate
198	* user-meta safely (same-origin) or should only redirect (cross-
199	* origin, possibly CSRF).
200	*
201	* Logic mirrors the `Sec-Fetch-Site` heuristic browsers use:
202	*
203	* - `Sec-Fetch-Site: same-origin \| same-site \| none` → trusted
204	* (the request originated from this site, or from a typed URL
205	* / bookmark with no referrer info).
206	* - `Sec-Fetch-Site: cross-site` → untrusted (a third-party page
207	* pointed the user at the portal — could be an `<img>` tag).
208	* - Header missing (older browsers): fall back to `Referer` —
209	* same host or empty referrer is trusted, anything else isn't.
210	*
211	* @return bool
212	*/
213	function openstation_portal_is_same_origin_navigation() {
214	if ( ! empty( $_SERVER['HTTP_SEC_FETCH_SITE'] ) ) {
215	$site = strtolower( sanitize_text_field( wp_unslash( $_SERVER['HTTP_SEC_FETCH_SITE'] ) ) );
216	return in_array( $site, array( 'same-origin', 'same-site', 'none' ), true );
217	}
218
219	if ( empty( $_SERVER['HTTP_REFERER'] ) ) {
220	return true;
221	}
222
223	$referer_host = wp_parse_url( esc_url_raw( wp_unslash( $_SERVER['HTTP_REFERER'] ) ), PHP_URL_HOST );
224	$home_host = wp_parse_url( home_url(), PHP_URL_HOST );
225
226	if ( ! is_string( $referer_host ) \|\| '' === $referer_host ) {
227	return true;
228	}
229
230	return is_string( $home_host ) && strtolower( $referer_host ) === strtolower( $home_host );
231	}
232
233	/**
234	* Detects whether the current request is for the portal URL.
235	*
236	* Strips any query string and trailing slash and compares against
237	* `/openstation` relative to the site's home path. The pre-rebrand
238	* `/desktop-mode` path is accepted too, so bookmarks made before the
239	* rename still land in the shell.
240	*
241	* @return bool
242	*/
243	function openstation_is_portal_request() {
244	if ( empty( $_SERVER['REQUEST_URI'] ) ) {
245	return false;
246	}
247
248	// `esc_url_raw` instead of `sanitize_text_field` so percent-encoded
249	// chars in the URI (notably `%2F` from query-arg slashes) survive
250	// long enough for `wp_parse_url` to split path / query correctly.
251	$uri = esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) );
252	$path = wp_parse_url( $uri, PHP_URL_PATH );
253	if ( ! is_string( $path ) ) {
254	return false;
255	}
256
257	$home_path = wp_parse_url( home_url( '/' ), PHP_URL_PATH );
258	$home_path = is_string( $home_path ) ? rtrim( $home_path, '/' ) : '';
259
260	$path = '/' . ltrim( rtrim( $path, '/' ), '/' );
261
262	return in_array(
263	$path,
264	array(
265	$home_path . '/' . OPENSTATION_PORTAL_PATH,
266	$home_path . '/' . OPENSTATION_PORTAL_PATH_LEGACY,
267	),
268	true
269	);
270	}
271
272	/**
273	* Sends plain `/wp-admin/...` requests into the desktop.
274	*
275	* The shell is served by its own screen (`includes/shell-screen.php`),
276	* so a plain admin page is never where the desktop renders: a user who
277	* typed or bookmarked `/wp-admin/edit.php` is forwarded to the shell
278	* screen with that URL as the page it opens first. Three routes out of
279	* here, cheapest first:
280	*
281	* 1. Straight to the shell screen when the portal would only hand
282	* this URL back — an allowlisted wp-admin file that is also the
283	* page being served, carrying no query arg the portal would strip
284	* ({@see openstation_portal_forward_is_redundant()}). One
285	* redirect; the portal hop would have cost a WordPress bootstrap
286	* to learn what is already known. `openstation_skip_redundant_portal_forward`
287	* (return false) forces the hop back on for a plugin that hooks
288	* the portal handler for side effects.
289	* 2. Through `/openstation/?target=…` otherwise — a network-admin
290	* URL, a path outside the wp-admin allowlist — so the portal can
291	* fall back to the saved session's focused window, which is a real
292	* change of destination the shell can't make from here.
293	* 3. The frozen-flag alias. A URL carrying `desktop_mode_portal=1`
294	* is the desktop's pre-screen address: the portal used to forward
295	* to a real admin page tagged with it, and bookmarks, the PWA start
296	* URL and plugin-built links still say so. It goes to the shell
297	* screen with that URL as the target, and `intent=1` when the
298	* intent flag was present. The flags stay frozen (see AGENTS.md);
299	* only what they resolve to moved.
300	*
301	* Narrowly scoped to bail on every automated or sub-request entry point
302	* — AJAX, REST, cron, admin-post.php, non-GET methods, and sub-resource
303	* fetches (an `<img>`, a script or an XHR whose URL is an admin page,
304	* see {@see openstation_is_subresource_request()}) — so the hook can't
305	* corrupt a form submission, break an API call or hand an image tag an
306	* HTML document. The shell screen itself, chromeless loads, solo boots
307	* and classic-flagged requests pass through.
308	*
309	* Disable via the `openstation_admin_redirect_to_portal` filter (return
310	* false); plain admin pages then render as classic admin and the
311	* desktop lives at `/openstation/` only. The alias route runs before
312	* the filter: a URL that names the desktop is not a plain admin page.
313	*/
314	function openstation_redirect_plain_admin_to_portal() {
315	if ( ! openstation_is_enabled() ) {
316	return;
317	}
318	// The screen the redirects land on. First in the chain: every other
319	// branch below ends in a redirect here, and the screen is a plain
320	// admin GET like any other.
321	if ( openstation_is_shell_screen_request() ) {
322	return;
323	}
324	if ( openstation_is_chromeless_request() ) {
325	return;
326	}
327	// A solo boot renders one window in place, wherever it landed.
328	if ( function_exists( 'openstation_is_solo_request' ) && openstation_is_solo_request() ) {
329	return;
330	}
331	// The user admin (`wp-admin/user/`, multisite's dashboard for users
332	// with no site role) renders classic. It has no shell screen of its
333	// own, and its URLs never survive the target allowlist — before
334	// this pass-through the redirect claimed the request anyway and
335	// silently forwarded the user to the site desktop's default entry.
336	if ( is_multisite() && is_user_admin() ) {
337	return;
338	}
339	if ( wp_doing_ajax() \|\| wp_doing_cron() ) {
340	return;
341	}
342	if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {
343	return;
344	}
345	if ( ! empty( $_SERVER['REQUEST_METHOD'] ) && 'GET' !== strtoupper( sanitize_text_field( wp_unslash( $_SERVER['REQUEST_METHOD'] ) ) ) ) {
346	return;
347	}
348	// The browser says what it is fetching for. An <img>, a script or
349	// an XHR aimed at an admin URL (Jetpack's admin-bar sparkline is
350	// admin.php?page=stats&noheader&proxy&chart=…) is not a user
351	// landing on a plain admin page, and forwarding it into the desktop
352	// only swaps the bytes it asked for with the shell's HTML.
353	if ( openstation_is_subresource_request() ) {
354	return;
355	}
356
357	// The "Detach to new tab" button tags its URL with this flag so the
358	// user can view one admin page classically without disabling desktop
359	// mode account-wide. Navigations inside that tab keep it (see the
360	// Referer check below).
361	if ( ! empty( $_GET[ OPENSTATION_CLASSIC_FLAG ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
362	return;
363	}
364
365	// admin-post.php and admin-ajax.php handle form submissions and JSON
366	// endpoints; redirecting them would break the call.
367	global $pagenow;
368	if ( in_array( $pagenow, array( 'admin-post.php', 'admin-ajax.php' ), true ) ) {
369	return;
370	}
371
372	// `esc_url_raw` instead of `sanitize_text_field`: the latter strips
373	// every `%XX` percent-encoded sequence, which corrupts URIs whose
374	// query string legitimately carries an encoded slash — e.g. WP's
375	// own `plugins.php?action=activate&plugin=dir%2Ffile.php` activate
376	// link. The shell screen validates the target on read.
377	$target = isset( $_SERVER['REQUEST_URI'] ) ? esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '';
378	$target = is_string( $target ) ? $target : '';
379
380	// Route 3: the frozen-flag alias. The sanitiser strips both flags
381	// from the target; an unresolvable one leaves the screen to pick
382	// the entry, exactly as the portal did for an invalid `target`.
383	if ( ! empty( $_GET[ OPENSTATION_PORTAL_FLAG ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
384	$clean = openstation_sanitize_portal_target( $target );
385	$intent = '' !== $clean && ! empty( $_GET[ OPENSTATION_PORTAL_INTENT_FLAG ] ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
386	wp_safe_redirect( openstation_shell_url( $clean, $intent ) );
387	exit;
388	}
389
390	/**
391	* Filters whether plain admin URLs should redirect into the desktop
392	* when OpenStation is active.
393	*
394	* @param bool $redirect Whether to redirect. Default true.
395	* @param int $user_id The current user's ID.
396	*/
397	$redirect = apply_filters( 'openstation_admin_redirect_to_portal', true, get_current_user_id() );
398	if ( ! $redirect ) {
399	return;
400	}
401
402	// A navigation out of a classic tab that lost the flag stays classic,
403	// with the flag back in the URL for the next navigation's Referer.
404	if ( '' !== $target && openstation_is_classic_referer() ) {
405	wp_safe_redirect( add_query_arg( OPENSTATION_CLASSIC_FLAG, '1', $target ) );
406	exit;
407	}
408
409	// Route 1: straight to the shell screen.
410	if ( openstation_portal_forward_is_redundant( $target ) ) {
411	/**
412	* Filters whether to skip the portal hop for a URL the portal
413	* would only hand straight back.
414	*
415	* Default: true — the request goes straight to the shell screen
416	* with this URL as its target. Return false to route through
417	* `/openstation/` anyway, e.g. for a plugin that hooks
418	* `openstation_handle_portal_request` for its own side effects
419	* and needs it to run on every admin entry.
420	*
421	* @param bool $skip Whether to skip the portal hop.
422	* @param string $request_uri The current request URI.
423	*/
424	if ( apply_filters( 'openstation_skip_redundant_portal_forward', true, $target ) ) {
425	wp_safe_redirect( openstation_shell_url( openstation_sanitize_portal_target( $target ), true ) );
426	exit;
427	}
428	}
429
430	// Route 2: through the portal, target preserved. Without it,
431	// navigating to a specific admin page (profile.php, plugins.php, any
432	// deep link) loses the user's intent — the portal would forward them
433	// to whichever window was last focused instead of the page they asked
434	// for. The portal handler reads `target`, validates it's same-origin
435	// wp-admin, and passes it on to the shell screen.
436	$portal_url = openstation_portal_url();
437	if ( '' !== $target ) {
438	$portal_url = add_query_arg( 'target', rawurlencode( $target ), $portal_url );
439	}
440
441	wp_safe_redirect( $portal_url );
442	exit;
443	}
444	add_action( 'admin_init', 'openstation_redirect_plain_admin_to_portal' );
445
446	/**
447	* Whether forwarding this request through `/openstation/` would only
448	* hand the URL already being served back as the shell's target.
449	*
450	* Answers locally, and without the HTTP round trip, the same question
451	* {@see openstation_handle_portal_request()} answers after another
452	* WordPress bootstrap. True means the hop is pure overhead and the
453	* caller can send the user straight to the shell screen with this URL
454	* as its target.
455	*
456	* Deliberately conservative: every "don't know" answers false, so the
457	* forward survives wherever the portal might genuinely choose a
458	* different destination.
459	*
460	* 1. The path must resolve through the same wp-admin allowlist the
461	* portal validates `?target=` against. Anything that list rejects
462	* — a `network/` or `user/` sub-path on multisite, a filename that
463	* isn't canonical wp-admin — makes the portal fall back to the
464	* session's focused window, which is a real change of destination.
465	* 2. The resolved filename must be the file this request is actually
466	* serving. If `$pagenow` disagrees with the URL path then a
467	* rewrite is in play and we can't claim to know what renders here.
468	* 3. The query must survive intact. The portal drops
469	* `openstation_chromeless`, both portal flags and `target` from
470	* the URL it rebuilds, so a request carrying any of them comes
471	* back as a different URL.
472	*
473	* @param string $request_uri The current request URI, unslashed.
474	* @return bool True when the portal would resolve this URL to itself.
475	*/
476	function openstation_portal_forward_is_redundant( $request_uri ) {
477	global $pagenow;
478
479	if ( ! is_string( $request_uri ) \|\| '' === $request_uri ) {
480	return false;
481	}
482
483	$path = wp_parse_url( $request_uri, PHP_URL_PATH );
484	if ( ! is_string( $path ) \|\| '' === $path ) {
485	return false;
486	}
487
488	$admin_path = wp_parse_url( admin_url(), PHP_URL_PATH );
489	$admin_path = is_string( $admin_path ) ? $admin_path : '/wp-admin/';
490	if ( 0 !== strpos( $path, $admin_path ) ) {
491	return false;
492	}
493
494	$file = ltrim( (string) substr( $path, strlen( $admin_path ) ), '/' );
495	if ( '' === $file ) {
496	$file = 'index.php';
497	}
498
499	// 1. The portal's allowlist has to accept it.
500	if ( is_wp_error( openstation_resolve_admin_target( $file ) ) ) {
501	return false;
502	}
503
504	// 2. …and it has to be the page we are actually serving.
505	if ( ! is_string( $pagenow ) \|\| strtolower( $file ) !== strtolower( $pagenow ) ) {
506	return false;
507	}
508
509	// 3. …carrying a query the portal would hand back unchanged.
510	$rewritten = array(
511	'openstation_chromeless',
512	OPENSTATION_PORTAL_FLAG,
513	OPENSTATION_PORTAL_INTENT_FLAG,
514	'target',
515	);
516	foreach ( $rewritten as $key ) {
517	if ( isset( $_GET[ $key ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
518	return false;
519	}
520	}
521
522	return true;
523	}
524
525	/**
526	* Resolves the admin URL the portal should forward to for a given user.
527	*
528	* Looks up the user's session and returns the URL of the window flagged
529	* as `focused`. If the session is empty, has no focused window, or the
530	* focused window's URL isn't same-origin admin, falls back to the
531	* dashboard.
532	*
533	* The portal navigates the TOP window, not an iframe, so any chromeless
534	* `openstation_chromeless=1` flag baked into the stored URL is stripped — a leftover
535	* flag would land the user in a standalone chromeless page (no admin
536	* bar, no toggle, no way out) instead of the shell.
537	*
538	* @param int $user_id The user whose session to consult.
539	* @return string The admin URL to redirect to.
540	*/
541	function openstation_portal_entry_url( $user_id ) {
542	$session = openstation_get_session( $user_id );
543
544	// User's configured default-window preference. When disabled, we
545	// still have to forward SOMEWHERE (the portal is an HTTP redirect),
546	// so we land on the Dashboard URL — but the shell detects the
547	// `enabled=false` state via the config and skips the auto-open,
548	// leaving the user with an empty desktop as they chose.
549	$default_window = openstation_get_default_window( $user_id );
550	$fallback = $default_window['url'];
551
552	// Native marker (e.g. "native:os-settings") is not a
553	// redirectable URL. The portal MUST forward somewhere — the
554	// redirect happens at HTTP level — so we land on the admin home
555	// and let the shell pick up `defaultWindow.url` from the config
556	// after init and call nativeWindows.openById( <slug> ).
557	if ( is_string( $fallback ) && 0 === strpos( $fallback, 'native:' ) ) {
558	$fallback = admin_url();
559	}
560
561	if ( empty( $session['focused'] ) \|\| empty( $session['windows'] ) ) {
562	return $fallback;
563	}
564
565	foreach ( $session['windows'] as $win ) {
566	if ( ! isset( $win['id'], $win['url'] ) ) {
567	continue;
568	}
569	if ( $win['id'] !== $session['focused'] ) {
570	continue;
571	}
572	if ( ! openstation_url_is_same_admin( $win['url'] ) ) {
573	return $fallback;
574	}
575	// The shell must never open itself. A saved window pointing at
576	// the shell screen cannot be produced by the shell, but a
577	// hand-edited session could say so; treat it as nothing focused.
578	if ( openstation_url_is_shell_screen( $win['url'] ) ) {
579	return $fallback;
580	}
581	return remove_query_arg( array( 'openstation_chromeless', OPENSTATION_PORTAL_FLAG ), $win['url'] );
582	}
583
584	return $fallback;
585	}
586
587	/**
588	* Validates and normalizes a `target` query arg on the portal URL.
589	*
590	* Accepts a raw request-URI-shaped string (path + optional query, e.g.
591	* `/wp-admin/profile.php?foo=bar`) and returns a fully-qualified admin
592	* URL if — and only if — it resolves to a same-origin `wp-admin/` path.
593	* Everything else returns an empty string so the caller falls back to
594	* the saved-session entry URL.
595	*
596	* Strips `openstation_chromeless` and the portal flag from the query so the target
597	* doesn't chain us into a chromeless standalone load or an infinite
598	* redirect loop.
599	*
600	* @param string $raw Raw value from `$_GET['target']` (already unslashed).
601	* @return string A safe absolute admin URL, or '' if the input is invalid.
602	*/
603	function openstation_sanitize_portal_target( $raw ) {
604	if ( ! is_string( $raw ) \|\| '' === $raw ) {
605	return '';
606	}
607
608	// Reject URIs with a scheme or protocol-relative prefix — we only
609	// accept relative paths so there's no way to redirect off-site.
610	if ( preg_match( '#^([a-z][a-z0-9+.-]*:\|//)#i', $raw ) ) {
611	return '';
612	}
613
614	// Must be an absolute path starting with /.
615	if ( '/' !== $raw[0] ) {
616	return '';
617	}
618
619	$path = wp_parse_url( $raw, PHP_URL_PATH );
620	$query = wp_parse_url( $raw, PHP_URL_QUERY );
621	if ( ! is_string( $path ) \|\| '' === $path ) {
622	return '';
623	}
624
625	$admin_path = wp_parse_url( admin_url(), PHP_URL_PATH );
626	$admin_path = is_string( $admin_path ) ? $admin_path : '/wp-admin/';
627	if ( 0 !== strpos( $path, $admin_path ) ) {
628	return '';
629	}
630
631	$file = substr( $path, strlen( $admin_path ) );
632	$file = ltrim( (string) $file, '/' );
633
634	// The network admin's own screens live one directory down and are
635	// resolved against their own list. Without this a network URL came
636	// back empty and the user was quietly forwarded to the site
637	// dashboard, which is a different admin.
638	$network = 0 === strpos( $file, 'network/' );
639	if ( $network ) {
640	$file = substr( $file, strlen( 'network/' ) );
641	}
642
643	if ( '' === $file ) {
644	$file = 'index.php';
645	}
646
647	// Resolve against the hardcoded allowlist of canonical wp-admin
648	// filenames (see `openstation_admin_target_allowlist()`). A
649	// regex alone would accept a plausible-looking filename that
650	// isn't a real core admin page (e.g. `custom_admin_page.php`)
651	// and effectively become an open redirect to a 404 page served
652	// under the admin path; the explicit allowlist closes that.
653	$target = openstation_resolve_admin_target( $file, $network );
654	if ( is_wp_error( $target ) ) {
655	return '';
656	}
657
658	if ( is_string( $query ) && '' !== $query ) {
659	parse_str( $query, $args );
660	unset( $args['openstation_chromeless'], $args[ OPENSTATION_PORTAL_FLAG ], $args[ OPENSTATION_PORTAL_INTENT_FLAG ], $args['target'] );
661	if ( ! empty( $args ) ) {
662	$target = add_query_arg( $args, $target );
663	}
664	}
665
666	// The shell screen is where a target is opened, never a target: the
667	// shell would open itself in a window, and a redirect chain built
668	// from it would loop. Fall back to the entry resolver instead.
669	if ( openstation_url_is_shell_screen( $target ) ) {
670	return '';
671	}
672
673	// `admin.php` is a bootstrap, not a page. Without a `page` arg core
674	// falls through the last `else` in `wp-admin/admin.php`, never
675	// requires `admin-header.php`, and answers 200 with an empty body —
676	// so the URL becomes a window showing nothing. The allowlist above
677	// matches filenames and cannot see the query, which is why the
678	// check belongs here, beside the shell-screen one: both are URLs
679	// that resolve but must not become a target. Returning '' hands the
680	// caller back to the entry resolver (session's focused window, else
681	// the default window, else the Dashboard).
682	if ( openstation_url_is_page_less_admin_php( $target ) ) {
683	return '';
684	}
685
686	return $target;
687	}
688