Change snapshot tests to compare decompressed bitstreams

The snapshots are compressed differently in Node.js 21. The compression has been stable for many versions but that is not a guarantee, see nodejs/node#50138 for background.

Change tests to compare the decompressed data instead.

lib/snapshot-manager.js

@@ -198,7 +198,7 @@ async function encodeSnapshots(snapshotData) {
 	], READABLE_PREFIX.byteLength + VERSION_HEADER.byteLength + SHA_256_HASH_LENGTH + compressed.byteLength);
 }
 
-function decodeSnapshots(buffer, snapPath) {
+export function extractCompressedSnapshot(buffer, snapPath) {
 	if (isLegacySnapshot(buffer)) {
 		throw new LegacyError(snapPath);
 	}
@@ -220,6 +220,12 @@ function decodeSnapshots(buffer, snapPath) {
 	const compressedOffset = sha256sumOffset + SHA_256_HASH_LENGTH;
 	const compressed = buffer.slice(compressedOffset);
 
+	return {version, compressed, sha256sumOffset, compressedOffset};
+}
+
+function decodeSnapshots(buffer, snapPath) {
+	const {compressed, sha256sumOffset, compressedOffset} = extractCompressedSnapshot(buffer, snapPath);
+
 	const sha256sum = crypto.createHash('sha256').update(compressed).digest();
 	const expectedSum = buffer.slice(sha256sumOffset, compressedOffset);
 	if (!sha256sum.equals(expectedSum)) {

test/snapshot-workflow/helpers/macros.js

@@ -1,9 +1,11 @@
 
 import {promises as fs} from 'node:fs';
 import path from 'node:path';
+import {gunzipSync} from 'node:zlib';
 
 import concordance from 'concordance';
 
+import {extractCompressedSnapshot} from '../../../lib/snapshot-manager.js';
 import {fixture} from '../../helpers/exec.js';
 import {withTemporaryFixture} from '../../helpers/with-temporary-fixture.js';
 
@@ -63,9 +65,12 @@ export async function beforeAndAfter(t, {
 }
 
 async function readSnapshots(cwd) {
+	const snapPath = path.join(cwd, 'test.js.snap');
 	const [snapshot, report] = await Promise.all([
-		fs.readFile(path.join(cwd, 'test.js.snap')),
+		fs.readFile(snapPath),
 		fs.readFile(path.join(cwd, 'test.js.md'), 'utf8'),
 	]);
-	return {snapshot, report};
+
+	const {version, compressed} = extractCompressedSnapshot(snapshot, snapPath);
+	return {snapshot: {version, decompressed: gunzipSync(compressed)}, report};
 }