Function runTests

test/parallel/test-fastutf8stream-partial-write-utf8.js:32–322

(sync)

runTests(true);

function runTests(sync) {
  // Test 1: Partial write splitting a 3-byte UTF-8 character (CJK)
  // "abc中def" where "中" is 3 bytes (E4 B8 AD)
  // Simulate partial write of 4 bytes: "abc" (3 bytes) + first byte of "中"
  // The remaining buffer should be "中def" (not "def")
  {
    const dest = getTempFile();
    const fd = openSync(dest, 'w');

    let firstWrite = true;
    const writtenChunks = [];
    const fsOverride = {};

    if (sync) {
      fsOverride.writeSync = common.mustCall((...args) => {
        const data = args[1];
        writtenChunks.push(typeof data === 'string' ? data : data.toString());
        if (firstWrite) {
          firstWrite = false;
          // Simulate partial write: only 4 bytes written out of 9
          // This splits the 3-byte "中" character
          return 4;
        }
        return writeSync(...args);
      }, 2);
    } else {
      fsOverride.write = common.mustCall((...args) => {
        const data = args[1];
        writtenChunks.push(typeof data === 'string' ? data : data.toString());
        const callback = args[args.length - 1];
        if (firstWrite) {
          firstWrite = false;
          // Simulate partial write: only 4 bytes written out of 9
          process.nextTick(callback, null, 4);
          return;
        }
        return write(...args);
      }, 2);
    }

    const stream = new Utf8Stream({
      fd,
      sync,
      minLength: 0,
      fs: fsOverride,
    });

    stream.on('ready', common.mustCall(() => {
      stream.write('abc中def');
      stream.end();

      stream.on('finish', common.mustCall(() => {
        // Verify the second chunk contains the preserved CJK character
        assert.strictEqual(writtenChunks.length, 2);
        assert.strictEqual(writtenChunks[0], 'abc中def'); // First attempt
        assert.strictEqual(writtenChunks[1], '中def'); // Retry with preserved char
      }));
    }));