desktop-mode / includes / portal.php

portal.php in OpenStation: Desktop Windows, Dock & Virtual Desktops for WP Admin 1.1.9, 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	}
154
155	// Pick the page the shell opens first. An explicit `target` query
156	// arg — a same-origin wp-admin URL — is how
157	// `openstation_redirect_plain_admin_to_portal` preserves the user's
158	// navigation intent when they follow a link to a specific admin
159	// page (e.g. profile.php). Without one the shell screen resolves
160	// the entry itself: the last-focused window from the saved
161	// session, else the default window, else the Dashboard — see
162	// `openstation_shell_boot_target()`. The bare screen URL is the
163	// canonical address, and a reload of it re-resolves against the
164	// live session rather than against the window that was focused
165	// when the redirect happened.
166	$target = '';
167	$has_intent = false;
168	if ( ! empty( $_GET['target'] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
169	// `esc_url_raw`, NOT `sanitize_text_field`: the latter strips
170	// every `%XX` percent-encoded sequence from its input as an XSS
171	// safeguard, which mangles request URIs that legitimately carry
172	// encoded slashes (e.g. `plugin=dir%2Ffile.php`). The downstream
173	// `openstation_sanitize_portal_target` validates the URL
174	// rigorously (scheme rejection, traversal rejection, and a
175	// hardcoded allowlist of canonical wp-admin filenames — see
176	// `openstation_admin_target_allowlist()`) so we don't lose
177	// any real safety by skipping `sanitize_text_field` here.
178	$target = openstation_sanitize_portal_target( esc_url_raw( wp_unslash( $_GET['target'] ) ) ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
179	if ( '' !== $target ) {
180	$has_intent = true;
181	}
182	}
183	// `intent=1` rides along with an explicit target so the shell treats
184	// the resulting `currentPage` as user intent and opens it on top of
185	// the restored session. Without it, a bare `/openstation/` visit and
186	// a portal-redirected admin-bar click would be indistinguishable
187	// downstream.
188	wp_safe_redirect( openstation_shell_url( $target, $has_intent ) );
189	exit;
190	}
191	add_action( 'parse_request', 'openstation_handle_portal_request' );
192
193	/**
194	* Decides whether the current request to the portal can mutate
195	* user-meta safely (same-origin) or should only redirect (cross-
196	* origin, possibly CSRF).
197	*
198	* Logic mirrors the `Sec-Fetch-Site` heuristic browsers use:
199	*
200	* - `Sec-Fetch-Site: same-origin \| same-site \| none` → trusted
201	* (the request originated from this site, or from a typed URL
202	* / bookmark with no referrer info).
203	* - `Sec-Fetch-Site: cross-site` → untrusted (a third-party page
204	* pointed the user at the portal — could be an `<img>` tag).
205	* - Header missing (older browsers): fall back to `Referer` —
206	* same host or empty referrer is trusted, anything else isn't.
207	*
208	* @return bool
209	*/
210	function openstation_portal_is_same_origin_navigation() {
211	if ( ! empty( $_SERVER['HTTP_SEC_FETCH_SITE'] ) ) {
212	$site = strtolower( sanitize_text_field( wp_unslash( $_SERVER['HTTP_SEC_FETCH_SITE'] ) ) );
213	return in_array( $site, array( 'same-origin', 'same-site', 'none' ), true );
214	}
215
216	if ( empty( $_SERVER['HTTP_REFERER'] ) ) {
217	return true;
218	}
219
220	$referer_host = wp_parse_url( esc_url_raw( wp_unslash( $_SERVER['HTTP_REFERER'] ) ), PHP_URL_HOST );
221	$home_host = wp_parse_url( home_url(), PHP_URL_HOST );
222
223	if ( ! is_string( $referer_host ) \|\| '' === $referer_host ) {
224	return true;
225	}
226
227	return is_string( $home_host ) && strtolower( $referer_host ) === strtolower( $home_host );
228	}
229
230	/**
231	* Detects whether the current request is for the portal URL.
232	*
233	* Strips any query string and trailing slash and compares against
234	* `/openstation` relative to the site's home path. The pre-rebrand
235	* `/desktop-mode` path is accepted too, so bookmarks made before the
236	* rename still land in the shell.
237	*
238	* @return bool
239	*/
240	function openstation_is_portal_request() {
241	if ( empty( $_SERVER['REQUEST_URI'] ) ) {
242	return false;
243	}
244
245	// `esc_url_raw` instead of `sanitize_text_field` so percent-encoded
246	// chars in the URI (notably `%2F` from query-arg slashes) survive
247	// long enough for `wp_parse_url` to split path / query correctly.
248	$uri = esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) );
249	$path = wp_parse_url( $uri, PHP_URL_PATH );
250	if ( ! is_string( $path ) ) {
251	return false;
252	}
253
254	$home_path = wp_parse_url( home_url( '/' ), PHP_URL_PATH );
255	$home_path = is_string( $home_path ) ? rtrim( $home_path, '/' ) : '';
256
257	$path = '/' . ltrim( rtrim( $path, '/' ), '/' );
258
259	return in_array(
260	$path,
261	array(
262	$home_path . '/' . OPENSTATION_PORTAL_PATH,
263	$home_path . '/' . OPENSTATION_PORTAL_PATH_LEGACY,
264	),
265	true
266	);
267	}
268
269	/**
270	* Sends plain `/wp-admin/...` requests into the desktop.
271	*
272	* The shell is served by its own screen (`includes/shell-screen.php`),
273	* so a plain admin page is never where the desktop renders: a user who
274	* typed or bookmarked `/wp-admin/edit.php` is forwarded to the shell
275	* screen with that URL as the page it opens first. Three routes out of
276	* here, cheapest first:
277	*
278	* 1. Straight to the shell screen when the portal would only hand
279	* this URL back — an allowlisted wp-admin file that is also the
280	* page being served, carrying no query arg the portal would strip
281	* ({@see openstation_portal_forward_is_redundant()}). One
282	* redirect; the portal hop would have cost a WordPress bootstrap
283	* to learn what is already known. `openstation_skip_redundant_portal_forward`
284	* (return false) forces the hop back on for a plugin that hooks
285	* the portal handler for side effects.
286	* 2. Through `/openstation/?target=…` otherwise — a network-admin
287	* URL, a path outside the wp-admin allowlist — so the portal can
288	* fall back to the saved session's focused window, which is a real
289	* change of destination the shell can't make from here.
290	* 3. The frozen-flag alias. A URL carrying `desktop_mode_portal=1`
291	* is the desktop's pre-screen address: the portal used to forward
292	* to a real admin page tagged with it, and bookmarks, the PWA start
293	* URL and plugin-built links still say so. It goes to the shell
294	* screen with that URL as the target, and `intent=1` when the
295	* intent flag was present. The flags stay frozen (see AGENTS.md);
296	* only what they resolve to moved.
297	*
298	* Narrowly scoped to bail on every automated or sub-request entry point
299	* — AJAX, REST, cron, admin-post.php, non-GET methods, and sub-resource
300	* fetches (an `<img>`, a script or an XHR whose URL is an admin page,
301	* see {@see openstation_is_subresource_request()}) — so the hook can't
302	* corrupt a form submission, break an API call or hand an image tag an
303	* HTML document. The shell screen itself, chromeless loads, solo boots
304	* and classic-flagged requests pass through.
305	*
306	* Disable via the `openstation_admin_redirect_to_portal` filter (return
307	* false); plain admin pages then render as classic admin and the
308	* desktop lives at `/openstation/` only. The alias route runs before
309	* the filter: a URL that names the desktop is not a plain admin page.
310	*/
311	function openstation_redirect_plain_admin_to_portal() {
312	if ( ! openstation_is_enabled() ) {
313	return;
314	}
315	// The screen the redirects land on. First in the chain: every other
316	// branch below ends in a redirect here, and the screen is a plain
317	// admin GET like any other.
318	if ( openstation_is_shell_screen_request() ) {
319	return;
320	}
321	if ( openstation_is_chromeless_request() ) {
322	return;
323	}
324	// A solo boot renders one window in place, wherever it landed.
325	if ( function_exists( 'openstation_is_solo_request' ) && openstation_is_solo_request() ) {
326	return;
327	}
328	// The user admin (`wp-admin/user/`, multisite's dashboard for users
329	// with no site role) renders classic. It has no shell screen of its
330	// own, and its URLs never survive the target allowlist — before
331	// this pass-through the redirect claimed the request anyway and
332	// silently forwarded the user to the site desktop's default entry.
333	if ( is_multisite() && is_user_admin() ) {
334	return;
335	}
336	if ( wp_doing_ajax() \|\| wp_doing_cron() ) {
337	return;
338	}
339	if ( defined( 'REST_REQUEST' ) && REST_REQUEST ) {
340	return;
341	}
342	if ( ! empty( $_SERVER['REQUEST_METHOD'] ) && 'GET' !== strtoupper( sanitize_text_field( wp_unslash( $_SERVER['REQUEST_METHOD'] ) ) ) ) {
343	return;
344	}
345	// The browser says what it is fetching for. An <img>, a script or
346	// an XHR aimed at an admin URL (Jetpack's admin-bar sparkline is
347	// admin.php?page=stats&noheader&proxy&chart=…) is not a user
348	// landing on a plain admin page, and forwarding it into the desktop
349	// only swaps the bytes it asked for with the shell's HTML.
350	if ( openstation_is_subresource_request() ) {
351	return;
352	}
353
354	// The "Detach to new tab" button tags its URL with this flag so the
355	// user can view one admin page classically without disabling desktop
356	// mode account-wide. Only affects the single request — subsequent
357	// navigations inside the tab lose the flag and follow normal rules.
358	if ( ! empty( $_GET[ OPENSTATION_CLASSIC_FLAG ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
359	return;
360	}
361
362	// admin-post.php and admin-ajax.php handle form submissions and JSON
363	// endpoints; redirecting them would break the call.
364	global $pagenow;
365	if ( in_array( $pagenow, array( 'admin-post.php', 'admin-ajax.php' ), true ) ) {
366	return;
367	}
368
369	// `esc_url_raw` instead of `sanitize_text_field`: the latter strips
370	// every `%XX` percent-encoded sequence, which corrupts URIs whose
371	// query string legitimately carries an encoded slash — e.g. WP's
372	// own `plugins.php?action=activate&plugin=dir%2Ffile.php` activate
373	// link. The shell screen validates the target on read.
374	$target = isset( $_SERVER['REQUEST_URI'] ) ? esc_url_raw( wp_unslash( $_SERVER['REQUEST_URI'] ) ) : '';
375	$target = is_string( $target ) ? $target : '';
376
377	// Route 3: the frozen-flag alias. The sanitiser strips both flags
378	// from the target; an unresolvable one leaves the screen to pick
379	// the entry, exactly as the portal did for an invalid `target`.
380	if ( ! empty( $_GET[ OPENSTATION_PORTAL_FLAG ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
381	$clean = openstation_sanitize_portal_target( $target );
382	$intent = '' !== $clean && ! empty( $_GET[ OPENSTATION_PORTAL_INTENT_FLAG ] ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
383	wp_safe_redirect( openstation_shell_url( $clean, $intent ) );
384	exit;
385	}
386
387	/**
388	* Filters whether plain admin URLs should redirect into the desktop
389	* when OpenStation is active.
390	*
391	* @param bool $redirect Whether to redirect. Default true.
392	* @param int $user_id The current user's ID.
393	*/
394	$redirect = apply_filters( 'openstation_admin_redirect_to_portal', true, get_current_user_id() );
395	if ( ! $redirect ) {
396	return;
397	}
398
399	// Route 1: straight to the shell screen.
400	if ( openstation_portal_forward_is_redundant( $target ) ) {
401	/**
402	* Filters whether to skip the portal hop for a URL the portal
403	* would only hand straight back.
404	*
405	* Default: true — the request goes straight to the shell screen
406	* with this URL as its target. Return false to route through
407	* `/openstation/` anyway, e.g. for a plugin that hooks
408	* `openstation_handle_portal_request` for its own side effects
409	* and needs it to run on every admin entry.
410	*
411	* @param bool $skip Whether to skip the portal hop.
412	* @param string $request_uri The current request URI.
413	*/
414	if ( apply_filters( 'openstation_skip_redundant_portal_forward', true, $target ) ) {
415	wp_safe_redirect( openstation_shell_url( openstation_sanitize_portal_target( $target ), true ) );
416	exit;
417	}
418	}
419
420	// Route 2: through the portal, target preserved. Without it,
421	// navigating to a specific admin page (profile.php, plugins.php, any
422	// deep link) loses the user's intent — the portal would forward them
423	// to whichever window was last focused instead of the page they asked
424	// for. The portal handler reads `target`, validates it's same-origin
425	// wp-admin, and passes it on to the shell screen.
426	$portal_url = openstation_portal_url();
427	if ( '' !== $target ) {
428	$portal_url = add_query_arg( 'target', rawurlencode( $target ), $portal_url );
429	}
430
431	wp_safe_redirect( $portal_url );
432	exit;
433	}
434	add_action( 'admin_init', 'openstation_redirect_plain_admin_to_portal' );
435
436	/**
437	* Whether forwarding this request through `/openstation/` would only
438	* hand the URL already being served back as the shell's target.
439	*
440	* Answers locally, and without the HTTP round trip, the same question
441	* {@see openstation_handle_portal_request()} answers after another
442	* WordPress bootstrap. True means the hop is pure overhead and the
443	* caller can send the user straight to the shell screen with this URL
444	* as its target.
445	*
446	* Deliberately conservative: every "don't know" answers false, so the
447	* forward survives wherever the portal might genuinely choose a
448	* different destination.
449	*
450	* 1. The path must resolve through the same wp-admin allowlist the
451	* portal validates `?target=` against. Anything that list rejects
452	* — a `network/` or `user/` sub-path on multisite, a filename that
453	* isn't canonical wp-admin — makes the portal fall back to the
454	* session's focused window, which is a real change of destination.
455	* 2. The resolved filename must be the file this request is actually
456	* serving. If `$pagenow` disagrees with the URL path then a
457	* rewrite is in play and we can't claim to know what renders here.
458	* 3. The query must survive intact. The portal drops
459	* `openstation_chromeless`, both portal flags and `target` from
460	* the URL it rebuilds, so a request carrying any of them comes
461	* back as a different URL.
462	*
463	* @param string $request_uri The current request URI, unslashed.
464	* @return bool True when the portal would resolve this URL to itself.
465	*/
466	function openstation_portal_forward_is_redundant( $request_uri ) {
467	global $pagenow;
468
469	if ( ! is_string( $request_uri ) \|\| '' === $request_uri ) {
470	return false;
471	}
472
473	$path = wp_parse_url( $request_uri, PHP_URL_PATH );
474	if ( ! is_string( $path ) \|\| '' === $path ) {
475	return false;
476	}
477
478	$admin_path = wp_parse_url( admin_url(), PHP_URL_PATH );
479	$admin_path = is_string( $admin_path ) ? $admin_path : '/wp-admin/';
480	if ( 0 !== strpos( $path, $admin_path ) ) {
481	return false;
482	}
483
484	$file = ltrim( (string) substr( $path, strlen( $admin_path ) ), '/' );
485	if ( '' === $file ) {
486	$file = 'index.php';
487	}
488
489	// 1. The portal's allowlist has to accept it.
490	if ( is_wp_error( openstation_resolve_admin_target( $file ) ) ) {
491	return false;
492	}
493
494	// 2. …and it has to be the page we are actually serving.
495	if ( ! is_string( $pagenow ) \|\| strtolower( $file ) !== strtolower( $pagenow ) ) {
496	return false;
497	}
498
499	// 3. …carrying a query the portal would hand back unchanged.
500	$rewritten = array(
501	'openstation_chromeless',
502	OPENSTATION_PORTAL_FLAG,
503	OPENSTATION_PORTAL_INTENT_FLAG,
504	'target',
505	);
506	foreach ( $rewritten as $key ) {
507	if ( isset( $_GET[ $key ] ) ) { // phpcs:ignore WordPress.Security.NonceVerification.Recommended
508	return false;
509	}
510	}
511
512	return true;
513	}
514
515	/**
516	* Resolves the admin URL the portal should forward to for a given user.
517	*
518	* Looks up the user's session and returns the URL of the window flagged
519	* as `focused`. If the session is empty, has no focused window, or the
520	* focused window's URL isn't same-origin admin, falls back to the
521	* dashboard.
522	*
523	* The portal navigates the TOP window, not an iframe, so any chromeless
524	* `openstation_chromeless=1` flag baked into the stored URL is stripped — a leftover
525	* flag would land the user in a standalone chromeless page (no admin
526	* bar, no toggle, no way out) instead of the shell.
527	*
528	* @param int $user_id The user whose session to consult.
529	* @return string The admin URL to redirect to.
530	*/
531	function openstation_portal_entry_url( $user_id ) {
532	$session = openstation_get_session( $user_id );
533
534	// User's configured default-window preference. When disabled, we
535	// still have to forward SOMEWHERE (the portal is an HTTP redirect),
536	// so we land on the Dashboard URL — but the shell detects the
537	// `enabled=false` state via the config and skips the auto-open,
538	// leaving the user with an empty desktop as they chose.
539	$default_window = openstation_get_default_window( $user_id );
540	$fallback = $default_window['url'];
541
542	// Native marker (e.g. "native:os-settings") is not a
543	// redirectable URL. The portal MUST forward somewhere — the
544	// redirect happens at HTTP level — so we land on the admin home
545	// and let the shell pick up `defaultWindow.url` from the config
546	// after init and call nativeWindows.openById( <slug> ).
547	if ( is_string( $fallback ) && 0 === strpos( $fallback, 'native:' ) ) {
548	$fallback = admin_url();
549	}
550
551	if ( empty( $session['focused'] ) \|\| empty( $session['windows'] ) ) {
552	return $fallback;
553	}
554
555	foreach ( $session['windows'] as $win ) {
556	if ( ! isset( $win['id'], $win['url'] ) ) {
557	continue;
558	}
559	if ( $win['id'] !== $session['focused'] ) {
560	continue;
561	}
562	if ( ! openstation_url_is_same_admin( $win['url'] ) ) {
563	return $fallback;
564	}
565	// The shell must never open itself. A saved window pointing at
566	// the shell screen cannot be produced by the shell, but a
567	// hand-edited session could say so; treat it as nothing focused.
568	if ( openstation_url_is_shell_screen( $win['url'] ) ) {
569	return $fallback;
570	}
571	return remove_query_arg( array( 'openstation_chromeless', OPENSTATION_PORTAL_FLAG ), $win['url'] );
572	}
573
574	return $fallback;
575	}
576
577	/**
578	* Validates and normalizes a `target` query arg on the portal URL.
579	*
580	* Accepts a raw request-URI-shaped string (path + optional query, e.g.
581	* `/wp-admin/profile.php?foo=bar`) and returns a fully-qualified admin
582	* URL if — and only if — it resolves to a same-origin `wp-admin/` path.
583	* Everything else returns an empty string so the caller falls back to
584	* the saved-session entry URL.
585	*
586	* Strips `openstation_chromeless` and the portal flag from the query so the target
587	* doesn't chain us into a chromeless standalone load or an infinite
588	* redirect loop.
589	*
590	* @param string $raw Raw value from `$_GET['target']` (already unslashed).
591	* @return string A safe absolute admin URL, or '' if the input is invalid.
592	*/
593	function openstation_sanitize_portal_target( $raw ) {
594	if ( ! is_string( $raw ) \|\| '' === $raw ) {
595	return '';
596	}
597
598	// Reject URIs with a scheme or protocol-relative prefix — we only
599	// accept relative paths so there's no way to redirect off-site.
600	if ( preg_match( '#^([a-z][a-z0-9+.-]*:\|//)#i', $raw ) ) {
601	return '';
602	}
603
604	// Must be an absolute path starting with /.
605	if ( '/' !== $raw[0] ) {
606	return '';
607	}
608
609	$path = wp_parse_url( $raw, PHP_URL_PATH );
610	$query = wp_parse_url( $raw, PHP_URL_QUERY );
611	if ( ! is_string( $path ) \|\| '' === $path ) {
612	return '';
613	}
614
615	$admin_path = wp_parse_url( admin_url(), PHP_URL_PATH );
616	$admin_path = is_string( $admin_path ) ? $admin_path : '/wp-admin/';
617	if ( 0 !== strpos( $path, $admin_path ) ) {
618	return '';
619	}
620
621	$file = substr( $path, strlen( $admin_path ) );
622	$file = ltrim( (string) $file, '/' );
623
624	// The network admin's own screens live one directory down and are
625	// resolved against their own list. Without this a network URL came
626	// back empty and the user was quietly forwarded to the site
627	// dashboard, which is a different admin.
628	$network = 0 === strpos( $file, 'network/' );
629	if ( $network ) {
630	$file = substr( $file, strlen( 'network/' ) );
631	}
632
633	if ( '' === $file ) {
634	$file = 'index.php';
635	}
636
637	// Resolve against the hardcoded allowlist of canonical wp-admin
638	// filenames (see `openstation_admin_target_allowlist()`). A
639	// regex alone would accept a plausible-looking filename that
640	// isn't a real core admin page (e.g. `custom_admin_page.php`)
641	// and effectively become an open redirect to a 404 page served
642	// under the admin path; the explicit allowlist closes that.
643	$target = openstation_resolve_admin_target( $file, $network );
644	if ( is_wp_error( $target ) ) {
645	return '';
646	}
647
648	if ( is_string( $query ) && '' !== $query ) {
649	parse_str( $query, $args );
650	unset( $args['openstation_chromeless'], $args[ OPENSTATION_PORTAL_FLAG ], $args[ OPENSTATION_PORTAL_INTENT_FLAG ], $args['target'] );
651	if ( ! empty( $args ) ) {
652	$target = add_query_arg( $args, $target );
653	}
654	}
655
656	// The shell screen is where a target is opened, never a target: the
657	// shell would open itself in a window, and a redirect chain built
658	// from it would loop. Fall back to the entry resolver instead.
659	if ( openstation_url_is_shell_screen( $target ) ) {
660	return '';
661	}
662
663	// `admin.php` is a bootstrap, not a page. Without a `page` arg core
664	// falls through the last `else` in `wp-admin/admin.php`, never
665	// requires `admin-header.php`, and answers 200 with an empty body —
666	// so the URL becomes a window showing nothing. The allowlist above
667	// matches filenames and cannot see the query, which is why the
668	// check belongs here, beside the shell-screen one: both are URLs
669	// that resolve but must not become a target. Returning '' hands the
670	// caller back to the entry resolver (session's focused window, else
671	// the default window, else the Dashboard).
672	if ( openstation_url_is_page_less_admin_php( $target ) ) {
673	return '';
674	}
675
676	return $target;
677	}
678