Promise.any 搶到錯誤回應？先驗證 HTTP 與 JSON 再選最快結果

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async function readCandidate(url) {
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  const response = await fetch(url, {
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    signal: AbortSignal.timeout(3_000),
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  });
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  if (!response.ok) throw new Error(`HTTP ${response.status}`);
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  const data = await response.json();
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  if (typeof data?.title !== 'string' || data.title.trim() === '') {
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    throw new TypeError('title must be a non-empty string');
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  }
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  return { url, data };
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}

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import assert from 'node:assert/strict';
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import http from 'node:http';
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import { once } from 'node:events';
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let release;
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const gate = new Promise(resolve => { release = resolve; });
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const server = http.createServer(async (req, res) => {
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  res.setHeader('Content-Type', 'application/json');
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  if (req.url === '/good') {
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    await gate;
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    res.end('{"title":"可用資料"}');
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  } else if (req.url === '/status') {
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    res.statusCode = 503;
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    res.end('{"error":"unavailable"}');
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  } else if (req.url === '/syntax') {
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    res.end('not json');
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  } else {
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    res.end('{"error":"wrong shape"}');
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  }
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});
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server.listen(0, '127.0.0.1');
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await once(server, 'listening');
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const base = `http://127.0.0.1:${server.address().port}`;
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try {
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  // HTTP 503 本身不會讓 fetch reject。
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  const raw = await fetch(base + '/status');
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  assert.equal(raw.ok, false);
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  assert.equal(raw.status, 503);
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  await raw.text();
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  const urls = ['/good', '/status', '/shape'].map(path => base + path);
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  const jobs = urls.map(readCandidate);
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  let settled = false;
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  const winner = Promise.any(jobs).finally(() => { settled = true; });
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  await Promise.allSettled(jobs.slice(1));
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  assert.equal(settled, false);
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  release();
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  assert.deepEqual(await winner, {
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    url: base + '/good', data: { title: '可用資料' },
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  });
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  await Promise.allSettled(jobs);
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  await assert.rejects(Promise.any([
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    readCandidate(base + '/status'),
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    readCandidate(base + '/syntax'),
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    readCandidate(base + '/shape'),
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  ]), error => {
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    assert.ok(error instanceof AggregateError);
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    assert.equal(error.errors.length, 3);
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    assert.equal(error.errors[0].message, 'HTTP 503');
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    assert.ok(error.errors[1] instanceof SyntaxError);
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    assert.ok(error.errors[2] instanceof TypeError);
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    return true;
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  });
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  await assert.rejects(Promise.any([]), error => {
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    assert.ok(error instanceof AggregateError);
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    assert.deepEqual(error.errors, []);
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    return true;
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  });
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  console.log('HTTP、解析、格式、全部失敗與空清單檢查通過');
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} finally {
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  release();
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  server.closeAllConnections();
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  await new Promise(resolve => server.close(resolve));
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}