Cached JSON

1'use strict';
2
3// Parsed artifacts are immutable and reused only while their on-disk identity is unchanged.
4// Resolve symlinks and include ctime so atomic replacement and same-size edits invalidate.
5const fs = require('node:fs');
6const path = require('node:path');
7const cache = new Map();
8function freeze(value) {
9  if (value && typeof value === 'object') {
10    for (const child of Object.values(value)) freeze(child);
11    Object.freeze(value);
12  }
13  return value;
14}
15function readJson(file, fallback) {
16  const requested = path.resolve(file);
17  let resolved, stat;
18  try { resolved = fs.realpathSync(requested); stat = fs.statSync(resolved, { bigint: true }); }
19  catch (error) { cache.delete(requested); if (error.code === 'ENOENT') return fallback; throw error; }
20  const signature = [resolved, stat.dev, stat.ino, stat.size, stat.mtimeNs, stat.ctimeNs].join(':');
21  const previous = cache.get(requested);
22  if (previous?.signature === signature) return previous.value;
23  // Never retain a stale success after a malformed rewrite.
24  cache.delete(requested);
25  const value = freeze(JSON.parse(fs.readFileSync(resolved, 'utf8')));
26  if (cache.size >= 32) cache.delete(cache.keys().next().value);
27  cache.set(requested, { signature, value });
28  return value;
29}
30module.exports = { readJson };