test: do not hardcode V8 serialization header

The header changes when V8 is updated. Do not hardcode it to
avoid breaking V8 updates.

Signed-off-by: Joyee Cheung <joyeec9h3@gmail.com>

Author: joyeecheung

test/parallel/test-runner-v8-deserializer.mjs

@@ -39,37 +39,42 @@ const oversizedLengthStdout = String.fromCharCode(oversizedLengthHeader[0]) +
   Buffer.from(oversizedLengthHeader.subarray(1)).toString('utf-8');
 const unsignedOversizedLengthStdout = String.fromCharCode(unsignedOversizedLengthHeader[0]) +
   Buffer.from(unsignedOversizedLengthHeader.subarray(1)).toString('utf-8');
-// FF 0F followed by a small, plausible size (8) and 8 payload bytes. Unlike the
+function payloadSize(size) {
+  const buffer = Buffer.alloc(4);
+  buffer.writeUInt32BE(size);
+  return buffer;
+}
+// The v8 header followed by a small, plausible size (8) and 8 payload bytes. Unlike the
 // oversized headers above, this passes the size check, but its payload does not
 // begin with the inner v8 header a real frame carries, so it is treated as
 // stdout instead of reaching the deserializer.
 // Regression fixture for https://github.com/nodejs/node/issues/66164
-const plausibleSizeFalseHeader = Buffer.from([
-  0xff, 0x0f,             // V8 serializer header magic
-  0x00, 0x00, 0x00, 0x08, // Payload size of 8 bytes
-  0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, // "ABCDEFGH", not a real payload
+const plausibleSizeFalseHeader = Buffer.concat([
+  headerOnly,
+  payloadSize(8),
+  Buffer.from('ABCDEFGH'), // Not a real payload
 ]);
 const plausibleSizeFalseHeaderStdout = String.fromCharCode(plausibleSizeFalseHeader[0]) +
   Buffer.from(plausibleSizeFalseHeader.subarray(1)).toString('utf-8');
-// FF 0F, a valid size, then the inner v8 header a real frame repeats, followed
+// The v8 header, a valid size, then the inner v8 header a real frame repeats, followed
 // by a byte that is not a valid serialized value. This passes the inner header
 // check and reaches the deserializer, which throws. This is what a genuine
 // report-protocol regression looks like, so the parser must let the error
 // surface instead of hiding it as stdout.
-const headeredCorruptFrame = Buffer.from([
-  0xff, 0x0f,             // Outer v8 serializer header magic
-  0x00, 0x00, 0x00, 0x03, // Payload size of 3 bytes
-  0xff, 0x0f,             // Inner v8 header that a real frame repeats
-  0xee,                   // Not a valid serialized value
+const headeredCorruptFrame = Buffer.concat([
+  headerOnly,
+  payloadSize(headerLength + 1),
+  headerOnly,
+  Buffer.from([0xee]), // Not a valid serialized value
 ]);
-// FF 0F with a declared size of 1, then more header bytes. The payload is
+// The v8 header with a declared size of 1, then more header bytes. The payload is
 // shorter than the inner v8 header a real frame carries, so it can never be a
 // real frame. The length guard must reject it as stdout without reaching the
 // deserializer.
-const shortPayloadFalseHeader = Buffer.from([
-  0xff, 0x0f,             // Outer v8 serializer header magic
-  0x00, 0x00, 0x00, 0x01, // Payload size of 1 byte, too short for a header
-  0xff, 0x0f,             // Trailing bytes that also look like a header
+const shortPayloadFalseHeader = Buffer.concat([
+  headerOnly,
+  payloadSize(1),
+  headerOnly, // Trailing bytes that also look like a header
 ]);
 
 function collectStdout(reported) {