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Edge Cache (guest pages) — ekumanov/flarum-ext-edge-cache

Makes guest page views cookieless so Cloudflare can safely cache guest HTML — discussion pages, the index, and tag pages — at the edge, plus a client-side CSRF retry shim so auth flows survive landing on a cached page. It also preloads the discussion page's boot-critical JS chunks, emits Link: rel=preload headers for Cloudflare Early Hints, can purge Cloudflare on every content change so a long edge TTL never serves stale content, and pre-paints the server-rendered discussion content for guests so the first post is visible (and is the LCP) at first paint instead of after the SPA boots. Requires Flarum 2.0.

Installation

Components

1. EdgeCacheMiddleware (forum frontend, inserted before StartSession — StartSession attaches cookies on the response's way OUT, so only an outer middleware can strip them): credential-less GET/HEAD on an allowlisted path (/d/*, the index /, and /t/*) → strip ALL Set-Cookie + X-CSRF-Token, emit a Server-Timing: origin header and Cache-Control: public, s-maxage=<ttl>, max-age=0, must-revalidate. The edge TTL is 3600s when Cloudflare purge credentials are configured (see below) — purge-on-write keeps the long tail warm without stale content — and a conservative 300s otherwise. All other forum HTML → explicit Cache-Control: private, no-store.
2. JS retry shim: on a 400 whose JSON:API body carries code: csrf_token_mismatch, single-flight GET /api (refreshes session cookie + token via core's response-header update), then retry the original request once. This covers /api/* writes as well as login and register: although those POST to forum routes, Flarum 2.0's forum error handler content-negotiates, so an XHR (default catch-all Accept) receives the same JSON:API error the shim matches.
3. CSRF exemption for forum-widgets.guest-heartbeat, the guest presence beacon of ekumanov/flarum-ext-forum-widgets (spoofable anyway, and the highest-frequency 400 source on cached pages). A no-op when that extension isn't installed.
4. Discussion chunk preload: on /d/*, emits <link rel="preload" as="script"> for core's PostStream.js + PostStreamScrubber.js (hashes read from rev-manifest.json at runtime, so the preload URL always matches what the webpack runtime fetches — no double download). These chunks are otherwise fetched serially after boot; preloading lets them download in parallel with forum.js, collapsing that render-delay tail. Helps guests and logged-in members alike.
5. Cloudflare purge-on-write: when a discussion's content changes (post added/edited/deleted/hidden/restored, discussion renamed/deleted/hidden/ restored), queues a purge of every cached page the write invalidates: the discussion's canonical landing URL, its slugless /d/{id} variant (served directly, so it caches under its own key), the forum index, and the landing pages of its tags and their parents. Lets the edge TTL stay long without guests seeing stale pages. Best-effort and queued, so a Cloudflare hiccup never blocks the user's action; a no-op (with a log line) when no credentials are configured.
6. Early Hints Link headers: every 200 HTML response — cacheable or private — carries Link: <…>; rel=preload headers for forum.css, forum.js, the active locale bundle, and (on /d/*) the two PostStream chunks. With Early Hints enabled on Cloudflare (Speed → Optimization; available on the Free plan) these are replayed as a 103 Early Hints response while the origin is still rendering, so the browser downloads the render-critical assets during server think-time. That helps most exactly where the edge cache can't: logged-in members (always DYNAMIC) and cold-MISS guests. Browsers de-duplicate against the identical in-HTML references, so where 103 isn't supported the headers are inert.
7. Visible pre-paint (guests, /d/*): Flarum already server-renders the discussion title + posts into <noscript id="flarum-content"> — JS-enabled browsers never paint it. This swaps the content wrapper view so that same markup is emitted as a visible, styled block instead, and an inline MutationObserver removes it on the first childList mutation of #content — a microtask, i.e. in the same rendering frame in which Mithril's first render lands, so exactly one of (pre-paint | hydrated page) is ever painted. The first post's text becomes the LCP at ≈first paint; the hydrated repaint is equal-or-smaller so it cannot re-trigger LCP (removed elements remain LCP candidates in Chromium). In lab testing at a phone-calibrated CPU throttle this collapsed the LCP−FCP gap from ~3s to 0 (LCP −58%) with zero CLS across the swap. If JS never boots, the block simply stays — a strictly better no-JS story than core's <noscript>. Media discipline while the block is visible: images wrapped by ekumanov/flarum-ext-cls-fix keep their reserved aspect-ratio boxes (its CSS is unscoped on purpose), emoji are size-stable via CSS, s9e MediaEmbed iframes sit in responsive padding-box wrappers and are loading="lazy"; any other unsized <img> is hidden inside the pre-paint, which only shortens the block — the safe direction. Post images additionally get their src renamed in the pre-paint copy (the placeholder box stays) so nothing fetches during the critical window and the hydration timeline is byte-identical to a non-pre-painted load, and below-fold posts are render-skipped via content-visibility: auto so a 20-post page costs no more main-thread time than a short one. Members are never pre-painted (their hydrated page differs from the guest render).

The matching Cloudflare Cache Rule (v2)

Expression: host eq "example.com" AND (path eq "/" OR starts_with(path, "/d/") OR starts_with(path, "/t/")) AND method GET AND NOT (cookie contains "flarum_session" OR cookie contains "flarum_remember" OR cookie contains "locale") → Eligible for cache, Edge TTL: respect origin, Browser TTL: respect origin. Adjust the host and the paths to your install (e.g. path eq "/forum/" plus prefixes /forum/d/, /forum/t/ when Flarum is mounted under /forum). The locale clause keeps a language-switched guest render off the shared cache — it matches both the bare locale cookie and prefixed variants like flarum_locale, in lockstep with the origin (see Invariants).

Upgrading from the v1 rule (/d/ only): deploying the extension first is safe — Cloudflare doesn't cache HTML without a matching rule, so the wider origin allowlist is inert for the extra paths until the rule covers them. Extend the rule right after deploying, then confirm cf-cache-status: MISS → HIT on /. Enable Early Hints (Speed → Optimization) at the same time to activate the Link-header preloads.

Cloudflare credentials (for purge-on-write + the long TTL)

Add to config.php (kept server-side, never exposed to the frontend):

Create a scoped token in the Cloudflare dashboard (My Profile → API Tokens → Create Custom Token → permission Zone : Cache Purge, restricted to this zone) — do not use a Global API Key. Without these keys the extension keeps the conservative 300s edge TTL and the purge listener is a logged no-op, so it is safe to install before (or without) Cloudflare.

Known staleness

Purge-on-write fires on discussion content events only (post added/edited/deleted/hidden/restored, discussion renamed/deleted/hidden/ restored). Anything else embedded in a cached guest payload refreshes only within the edge TTL, not instantly — e.g. sticky/lock state, tag moves, poll votes, and like counts. Likewise, after a rename the old-slug URL keeps serving its cached page (then 301s) until it ages out under the TTL; after a re-tag, the OLD tag's landing page waits for the TTL (or the next write that touches that tag). Index/tag sort variants (?sort=…) cache under their own keys and are not purge-enumerable either. All of this is bounded by the edge TTL by design; the TTL is the freshness floor for everything the purge list doesn't enumerate.

Invariants — read before changing anything

• The middleware path allowlist and the CF rule scope move in lockstep, in the same deploy.
• API responses must keep their Set-Cookie forever (heartbeat session-dedupe and the shim's refresh GET depend on it). This middleware is forum-only.
• /reset, /confirm etc. are server-rendered Blade forms needing their session cookie — permanently denylisted.
• A guest-facing language switcher would poison the shared cache (CF ignores Vary). Origin-side this is now enforced — a request carrying a locale cookie is served private, no-store — but keep the CF rule in lockstep (it must also exclude the locale cookie, as above).
• CSRF 400s never reach flarum.log (KnownError) — monitor nginx access-log double-400s instead.
• The pre-paint's LCP lock depends on one geometry rule: the pre-paint stack above the first post must sit equal-or-HIGHER than the hydrated one (the CSS deliberately undershoots by ~10px), so the pre-paint copy of the LCP paragraph is always the equal-or-larger paint. If a theme change makes the pre-paint sit lower, nothing breaks visually — but LCP silently returns to hydration time. Re-verify after theme/hero changes (the class docblock in PrePaintDiscussion documents the tuning).
• The pre-paint view must keep the #flarum-loading, #flarum-loading-error and #flarum-content element ids — core's boot scripts getElementById them unconditionally.

Rollback order

Disable this extension → clear the Flarum cache and purge the Cloudflare cache immediately (cached HTML referencing a rebuilt forum.js without the shim would otherwise strand guests until TTL expiry). Deleting the CF rule is safe at any point, in any order.

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