node/test/parallel/test-snapshot-reproducible.js

'use strict';

require('../common');
const { spawnSyncAndAssert } = require('../common/child_process');
const tmpdir = require('../common/tmpdir');
const fs = require('fs');
const assert = require('assert');

// When the test fails this helper can be modified to write outputs
// differently and aid debugging.
function log(line) {
  console.log(line);
}

function generateSnapshot() {
  tmpdir.refresh();

  spawnSyncAndAssert(
    process.execPath,
    [
      '--random_seed=42',
      '--predictable',
      '--build-snapshot',
      'node:generate_default_snapshot',
    ],
    {
      env: { ...process.env, NODE_DEBUG_NATIVE: 'SNAPSHOT_SERDES' },
      cwd: tmpdir.path
    },
    {
      stderr(output) {
        const lines = output.split('\n');
        for (const line of lines) {
          if (line.startsWith('0x')) {
            log(line);
          }
        }
      },
    }
  );
  const blobPath = tmpdir.resolve('snapshot.blob');
  return fs.readFileSync(blobPath);
}

const buf1 = generateSnapshot();
const buf2 = generateSnapshot();

const diff = [];
let offset = 0;
const step = 16;
do {
  const length = Math.min(buf1.length - offset, step);
  const slice1 = buf1.slice(offset, offset + length).toString('hex');
  const slice2 = buf2.slice(offset, offset + length).toString('hex');
  if (slice1 !== slice2) {
    diff.push({ offset: '0x' + (offset).toString(16), slice1, slice2 });
  }
  offset += length;
} while (offset < buf1.length);

assert.strictEqual(offset, buf1.length);
if (offset < buf2.length) {
  const length = Math.min(buf2.length - offset, step);
  const slice2 = buf2.slice(offset, offset + length).toString('hex');
  diff.push({ offset, slice1: '', slice2 });
  offset += length;
} while (offset < buf2.length);

assert.deepStrictEqual(diff, []);
assert.strictEqual(buf1.length, buf2.length);