web: adopt Cache Components, Partial Prefetching and ensureStatic

web/src/instrumentation.ts

@@ -0,0 +1,88 @@
+import { osloDay } from "@/lib/date";
+import {
+  purgeOwnCache,
+  setInternalRevalidateSecret,
+} from "@/lib/internalRevalidate";
+import {
+  CMS_CACHE_TAG,
+  TODAY_CACHE_TAG,
+  secondsUntilOsloMidnight,
+} from "@/lib/revalidation";
+
+// How often the clock is checked. Timers alone can't be trusted to fire at
+// midnight: they stand still while a host or VM is paused
+const CHECK_INTERVAL_MS = 30_000;
+// Until the first purge has gone through; the server isn't listening yet
+// when register() runs
+const STARTUP_RETRY_MS = 1_000;
+
+function keepCacheCurrent() {
+  // the Oslo day the cache was last purged for; undefined until the startup
+  // purge has gone through
+  let purgedDay: string | undefined;
+  let repeatTodayPurge = false;
+  let failures = 0;
+
+  async function check() {
+    const day = osloDay();
+    let error: string | null = null;
+
+    if (purgedDay === undefined) {
+      // Pages prerendered by the build, or left on disk by an earlier run,
+      // may predate CMS edits and midnights this process never saw
+      error =
+        (await purgeOwnCache(CMS_CACHE_TAG)) ??
+        (await purgeOwnCache(TODAY_CACHE_TAG));
+      if (!error) purgedDay = day;
+    } else if (day !== purgedDay) {
+      error = await purgeOwnCache(TODAY_CACHE_TAG);
+      if (!error) {
+        purgedDay = day;
+        repeatTodayPurge = true;
+      }
+    } else if (repeatTodayPurge) {
+      // Next stamps a page when its render finishes, so a page that was
+      // being rendered across the purge looks newer than it and survives.
+      // A second purge one interval later catches those
+      error = await purgeOwnCache(TODAY_CACHE_TAG);
+      if (!error) repeatTodayPurge = false;
+    }
+
+    if (error) {
+      failures += 1;
+      // at startup, connection errors are expected for the first moments
+      if (failures === 1 ? purgedDay !== undefined : failures % 60 === 0) {
+        console.error(`Purging the page cache keeps failing: ${error}`);
+      }
+    } else {
+      failures = 0;
+    }
+    schedule();
+  }
+
+  function schedule() {
+    const delay =
+      purgedDay === undefined
+        ? STARTUP_RETRY_MS
+        : // one second past midnight, so the purge can't land on the old day
+          Math.min(CHECK_INTERVAL_MS, (secondsUntilOsloMidnight() + 1) * 1000);
+    setTimeout(check, delay).unref();
+  }
+
+  void check();
+}
+
+export function register() {
+  // only in the running production server: not during `next build`, in
+  // `next dev` (nothing is kept between requests there) or on the edge
+  if (
+    process.env.NEXT_RUNTIME !== "nodejs" ||
+    process.env.NODE_ENV !== "production" ||
+    process.env.NEXT_PHASE === "phase-production-build"
+  ) {
+    return;
+  }
+
+  setInternalRevalidateSecret(crypto.randomUUID());
+  keepCacheCurrent();
+}