Eliminate Broadcast Channel bfcache eviction method #18
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… cache is disabled in DevTools
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Summary of Changes
Hello @westonruter, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request streamlines the bfcache invalidation strategy by completely removing the Broadcast Channel-based eviction method. This change addresses identified issues where the Broadcast Channel method was only partially effective and could lead to unexpected behavior with the HTTP cache, making the pageshow event-based invalidation the sole and more robust mechanism for ensuring user privacy after logout.
Highlights
- Removed Broadcast Channel Invalidation: The entire Broadcast Channel mechanism for evicting pages from the bfcache has been eliminated. This includes the removal of its emitter and listener JavaScript modules, associated PHP constants, functions, and script enqueues.
- Consolidated Invalidation Logic: The
pageshowevent-based bfcache invalidation, which relies on a session token cookie, is now the singular and primary method for protecting user privacy after logout, as it proved more robust. - Documentation Update: The
README.mdhas been updated to accurately reflect that only one safeguard (the cookie-based method) is in place for bfcache invalidation, removing outdated references to the Broadcast Channel method. - Code Cleanup and Refactoring: PHP constants for script module IDs have been moved from a dedicated interface file (
includes/interface-script-module-ids.php, which was removed) intoincludes/script-loader.php, simplifying the project structure and centralizing constant definitions.
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Code Review
This pull request refactors the bfcache invalidation mechanism by removing the BroadcastChannel approach, which was found to be unreliable. It now solely relies on a cookie-based session token and a pageshow event handler. The changes are logical and well-explained in the PR description. My review has identified two critical issues that need to be addressed: a fatal PHP error due to a missing file reference update, and a JavaScript runtime error caused by an inconsistent module ID in a renamed file. I've also included a suggestion to improve the clarity of the README.md.
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
westonruter
changed the title
It turns out that using Broadcast Channel to evict pages from bfcache is only partially successful. I had been testing with DevTools open in Chrome and Firefox, where “Disable Cache” is checked. In my testing, as soon as a message is broadcast, attempting to go back to a page which was in bfcache would send me to the login screen. However, this was because the page was evicted from bfcache and the browser's HTTP cache was disabled. If, however, I tried testing with DevTools closed and the HTTP cache is not disabled, then the broadcast channel invalidation method was causing a problem: it was indeed evicting the page from bfcache, but the page without
no-storeremained in HTTP cache. Thepageshowevent would report to me the bfcache blocking reason as beingbroadcastchannel-message. This meant that a page was restored from HTTP cache in the same way as a page is restored when re-opening a closed tab. So using Broadcast Channel was worse because thepageshowevent'spersistedproperty wasfalse, and thus it was not able to forcibly evict itself.