Profiles and space isolation

Isolation between spaces is not something JBrowser implements itself: it is Chromium's profile mechanism. ProfileManager (engine/profiles.py) gives every space its own QWebEngineProfile, created the first time a card in that space needs one.

Persistent and incognito profiles#

Two cards in different spaces can be signed in to the same site as different people, and a tracker cookie set in Home is invisible in Work. Closing an incognito space destroys its profile and everything in it.

Qt creates a named profile's default folders before the paths can be redirected; ProfileManager removes those empty stray folders again, so nothing is left in QtWebEngine\ under the user's AppData.

What every profile gets#

_create() configures each profile the same way:

• User agent: Qt's default with the QtWebEngine/x.y token removed, so sites see a normal Chrome user agent.
• Accept-Language: built by accept_language() from the Windows display languages, like Chrome does (for example en-AU,en;q=0.9). Qt sends none by default, and a browser without one looks automated.
• Two interceptors: the profile-wide ProfileInterceptor (headers, HTTPS upgrades, link cleaning, developer hosts) and, per page, the card's PageInterceptor (blocking). See the request pipeline.
• A cookie filter: PrivacyService.allow_cookie() decides about third-party cookies.
• Downloads go to the DownloadManager, tagged with the space and whether it is incognito.
• Notifications go through AppContext.present_notification() to the in-app and Windows notification.
• Page scripts (_install_base_scripts), see page scripts and script worlds, plus the user's own scripts and styles for that space.
• Web settings (_apply_settings): full screen allowed, smooth scrolling following Fluid animations, DNS prefetch and hyperlink auditing (<a ping>) off, pop-ups blocked unless the user allowed them, WebRTC limited to public interfaces (no local IP leaks), optional autoplay blocking and forced dark mode, and the back/forward cache on.

Changing a related setting re-applies it to every open profile: privacy switches reinstall the page scripts, other privacy.* keys and appearance.force_dark_web re-apply the web settings.

Lifetime#

• Created lazily by profile_for(space) when EngineRegistry creates the first TabController of the space.
• Released by release(space) when the space is deleted. Chromium keeps the files open until the profile object is gone, so a persistent space's folders are deleted at the next start (profiles.pending_wipe).
• Disposed by dispose_all() at shutdown, after every page (start-up and shutdown).

One network stack#

Chromium has a single network service per process, shared by all profiles. Two consequences:

• A space's proxy can't apply to that space alone. JBrowser applies the active space's proxy to everything and re-applies it on every space switch (networking).
• DNS-over-HTTPS is global.

Popups#

window.open() with window features (OAuth sign-ins, payment pages) asks the page for a WebDialog. TabController.create_window() then asks the UI (ctx.hooks.create_popup) for a small PopupWindow that shares the opener's profile, so the sign-in lands in the right space and window.opener keeps working. Other new windows (links with target=_blank, middle-clicks) become new cards next to the opener.