test_runner: convert to uint during deserialization

lib/internal/test_runner/runner.js

@@ -466,12 +466,12 @@ class FileTest extends Test {
     while (bufferHead?.length >= kSerializedSizeHeader) {
       // We call `readUInt32BE` manually here, because this is faster than first converting
       // it to a buffer and using `readUInt32BE` on that.
-      const fullMessageSize = (
+      const fullMessageSize = ((
         bufferHead[kV8HeaderLength] << 24 |
         bufferHead[kV8HeaderLength + 1] << 16 |
         bufferHead[kV8HeaderLength + 2] << 8 |
         bufferHead[kV8HeaderLength + 3]
-      ) + kSerializedSizeHeader;
+      ) >>> 0) + kSerializedSizeHeader;
 
       if (this.#rawBufferSize < fullMessageSize) break;
 

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

@@ -30,12 +30,15 @@ defaultSerializer.writeHeader();
 const headerLength = defaultSerializer.releaseBuffer().length;
 const headerOnly = Buffer.from([0xff, 0x0f]);
 const oversizedLengthHeader = Buffer.from([0xff, 0x0f, 0x7f, 0xff, 0xff, 0xff]);
+const unsignedOversizedLengthHeader = Buffer.from([0xff, 0x0f, 0x80, 0x00, 0x00, 0x00]);
 const truncatedLengthHeader = Buffer.from([0xff, 0x0f, 0x00, 0x01, 0x00, 0x00]);
 // Expected stdout for oversizedLengthHeader: first byte is emitted via
 // String.fromCharCode (byte-by-byte fallback in #drainRawBuffer), remaining
 // bytes go through the nonSerialized UTF-8 decode path in #processRawBuffer.
 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');
 
 function collectStdout(reported) {
   return reported
@@ -112,6 +115,12 @@ describe('v8 deserializer', common.mustCall(() => {
     assert.strictEqual(collectStdout(reported), oversizedLengthStdout);
   });
 
+  it('should read an oversized length as an unsigned integer', async () => {
+    const reported = await collectReported([unsignedOversizedLengthHeader]);
+    assert(reported.every((event) => event.type === 'test:stdout'));
+    assert.strictEqual(collectStdout(reported), unsignedOversizedLengthStdout);
+  });
+
   it('should flush incomplete v8 frame as stdout and keep prior valid data', async () => {
     // A valid non-serialized message followed by bytes that look like
     // a v8 header with a truncated/oversized length.