fix(news): answer within the browser's wait on a first read

A country's first World News API read, or Liveuamap's, could take up to
20 s while the browser waits 15, so the panel showed the browser's own
"signal timed out". A read with nothing to serve yet is now waited for
at most 12 s, as GDELT's already was: past that the section answers
unavailable while the read goes on, and the next refresh is served from
it. A client timeout reads "News feed unavailable".

server/providers/news/keyed.js

@@ -59,14 +59,13 @@ const DAY_MS = 24 * HOUR_MS;
 // published; one that fails GDELT_EXPORT_TRIES times (a try a round), or
 // cannot be read at all, is given up on, so one bad file never holds the
 // rest back. Only while GDELT itself answers is a file given up on. The first
-// answer waits at most GDELT_FIRST_MS for the first exports.
+// answer waits at most FIRST_ANSWER_MS for the first exports.
 const GDELT_FRESH_MS = 5 * 60_000;
 const GDELT_EXPORTS_PER_READ = 12;
 const GDELT_PARALLEL = 4;
 const GDELT_NEXT_MS = 2_000;
 const GDELT_GONE_MS = 90 * 60_000;
 const GDELT_EXPORT_TRIES = 3;
-const GDELT_FIRST_MS = 12_000;
 const MAX_GDELT_REPORTS = 5000;
 // Events kept of one story, to place it by.
 const MAX_STORY_EVENTS = 200;
@@ -80,6 +79,9 @@ const COUNTRY_FRESH_MS = 30 * 60_000;
 // A failed read is not tried again for a minute; what was read before is
 // served meanwhile, up to these ages (GDELT's: since an export last came in).
 const RETRY_MS = 60_000;
+// A read with nothing to serve yet is waited for at most this long, under the
+// browser's own 15 s: it goes on, and the next ask is served from it.
+const FIRST_ANSWER_MS = 12_000;
 const GDELT_STALE_MS = 2 * HOUR_MS;
 const LIVE_STALE_MS = HOUR_MS;
 const COUNTRY_STALE_MS = 6 * HOUR_MS;
@@ -276,6 +278,7 @@ export function createKeyedNews({
   now = () => Date.now(),
   log = (message) => console.warn(message),
   later = (run, ms) => setTimeout(run, ms).unref(),
+  firstAnswerMs = FIRST_ANSWER_MS,
 } = {}) {
   const keyOf = (id) => String(env()[NEWS_KEYS[id]] ?? '').trim();
   const inFlight = new Map();
@@ -373,7 +376,7 @@ export function createKeyedNews({
           .finally(() => inFlight.delete(flight)),
       );
     if (prior.value && at - prior.readAt < staleMs) return prior;
-    return inFlight.get(flight);
+    return firstAnswer(inFlight.get(flight), { ...prior, error: null });
   }
 
   /** An entry stored as the most recently used (the countries are capped). */
@@ -384,6 +387,22 @@ export function createKeyedNews({
   }
 
   /** An entry's reports while they may be served, else why there are none. */
+  /** `read`, waited for at most firstAnswerMs; then `fallback`, as it goes on. */
+  async function firstAnswer(read, fallback) {
+    let timer;
+    try {
+      return await Promise.race([
+        read,
+        new Promise((resolve) => {
+          timer = setTimeout(() => resolve(fallback), firstAnswerMs);
+          timer.unref?.();
+        }),
+      ]);
+    } finally {
+      clearTimeout(timer);
+    }
+  }
+
   function served(entry, staleMs, id) {
     if (entry.value && now() - entry.readAt < staleMs)
       return { reports: entry.value, readAt: entry.readAt };
@@ -602,19 +621,10 @@ export function createKeyedNews({
     // newest exports' events, not their titles.
     const current = () =>
       gdelt.readAt !== null && now() - gdelt.readAt < GDELT_STALE_MS;
-    if (!current() && inFlight.has('gdelt')) {
-      // At most GDELT_FIRST_MS: a slow GDELT must not outlast the browser's
-      // own timeout; what has come in by then is served.
-      let timer;
-      await Promise.race([
-        inFlight.get('gdelt'),
-        new Promise((resolve) => {
-          timer = setTimeout(resolve, GDELT_FIRST_MS);
-          timer.unref?.();
-        }),
-      ]);
-      clearTimeout(timer);
-    }
+    // A slow GDELT must not outlast the browser's own timeout: what has come
+    // in by then is served.
+    if (!current() && inFlight.has('gdelt'))
+      await firstAnswer(inFlight.get('gdelt'));
     if (!current()) return { failed: true };
     const dayAgo = new Date(now() - DAY_MS).toISOString();
     const reports = [...gdelt.reports.values()]

server/providers/news/keyed.test.mjs

@@ -1082,3 +1082,35 @@ test("a country's own news keeps World News API's category and no severity, what
   assert.equal(read('King visits Amman', 'politics').category, 'political');
   assert.equal(read('Parliament session opens', null).category, 'other');
 });
+
+test('a first read slower than the browser waits answers unavailable, and the next ask is served from it', async () => {
+  const fake = upstream();
+  let release;
+  const held = new Promise((resolve) => {
+    release = resolve;
+  });
+  const news = createKeyedNews({
+    env: () => ({ WORLDNEWSAPI_KEY: 'wna-key' }),
+    fetchImpl: async (url, init) => {
+      if (new URL(url).host === 'api.worldnewsapi.com') await held;
+      return fake.fetchImpl(url, init);
+    },
+    now: () => NOW,
+    log: () => {},
+    later: () => {},
+    firstAnswerMs: 20,
+  });
+  const local = () =>
+    news.answer('/feed', new URLSearchParams('hotspot=all&at=31.95,35.93'));
+  assert.deepEqual(await local(), UPSTREAM_ERROR);
+  // The read went on, and is not asked again.
+  release();
+  await new Promise((resolve) => setTimeout(resolve, 5));
+  const served = await local();
+  assert.equal(served.status, 200);
+  assert.deepEqual(
+    served.body.reports.map((r) => r.id),
+    ['wna-9001', 'wna-9002'],
+  );
+  assert.equal(count(fake.calls, 'api.worldnewsapi.com'), 1);
+});