Snapshot Loop

1#!/usr/bin/env node
2// Periodic screenshot + DOM HTML + URL sampler. Invoked by start-capture.mjs;
3// not meant to be run directly.
4//
5// Each tick samples the traced CDP target through browse. Passing --cdp here
6// ensures this helper attaches to the traced target even when it runs outside
7// the user's main automation flow.
8
9import fs from 'node:fs';
10import path from 'node:path';
11import { spawnSync } from 'node:child_process';
12
13import { isoStampForFilename, sleepMs } from './lib.mjs';
14
15const [target, RD, intervalArg] = process.argv.slice(2);
16if (!target || !RD) {
17  console.error('usage: snapshot-loop.mjs <target> <run-dir> [interval-seconds]');
18  process.exit(2);
19}
20
21const intervalMs = (Number(intervalArg) || 2) * 1000;
22const indexPath = path.join(RD, 'index.jsonl');
23
24let stopping = false;
25process.on('SIGTERM', () => { stopping = true; });
26process.on('SIGINT',  () => { stopping = true; });
27
28function getJsonField(stdout, field) {
29  if (!stdout) return '';
30  try {
31    const parsed = JSON.parse(stdout);
32    return typeof parsed?.[field] === 'string' ? parsed[field] : '';
33  } catch {
34    return '';
35  }
36}
37
38while (!stopping) {
39  const ts   = isoStampForFilename();
40  const png  = path.join(RD, 'screenshots', `${ts}.png`);
41  const html = path.join(RD, 'dom',         `${ts}.html`);
42  const tmp  = `${html}.partial`;
43
44  // Best-effort screenshot. If browse fails we just don't get one this tick.
45  spawnSync('browse', ['screenshot', '--cdp', target, '--path', png], { stdio: 'ignore' });
46  if (fs.existsSync(png) && fs.statSync(png).size === 0) {
47    fs.unlinkSync(png);
48  }
49
50  // DOM dump via temp file → rename, so we never leave a 0-byte HTML behind.
51  try {
52    const r = spawnSync('browse', ['get', 'html', 'body', '--cdp', target], { encoding: 'utf8' });
53    const htmlBody = getJsonField(r.stdout, 'html');
54    if (htmlBody) {
55      fs.writeFileSync(tmp, htmlBody);
56      fs.renameSync(tmp, html);
57    }
58  } catch { /* best-effort */ }
59  // Cleanup any leftover .partial from a previous interrupted iteration.
60  if (fs.existsSync(tmp)) {
61    try { fs.unlinkSync(tmp); } catch {}
62  }
63
64  // URL from the traced target. Returns {"url": "..."}.
65  let urlValue = '';
66  const u = spawnSync('browse', ['get', 'url', '--cdp', target], { encoding: 'utf8' });
67  urlValue = getJsonField(u.stdout, 'url');
68
69  const screenshotRel = fs.existsSync(png)  ? `screenshots/${ts}.png` : '';
70  const domRel        = fs.existsSync(html) ? `dom/${ts}.html`        : '';
71  fs.appendFileSync(indexPath,
72    JSON.stringify({ ts, screenshot: screenshotRel, dom: domRel, url: urlValue }) + '\n');
73
74  await sleepMs(intervalMs);
75}