Sending large binary data with XMLHTTPRequest to PHP as stream

uploadBigFiles.php

<?php

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
  $filePath = __DIR__ . '/out.tmp';

  $input = fopen('php://input', 'r');
  $output = fopen($filePath, 'w+');

  stream_copy_to_stream($input, $output);

  fclose($input);
  fclose($output);
  exit(0);
}

?>

<form id="upload" action="" method="post">
  <label for="file">file:</label>
  <input name="file" type="file">

  <button type="submit">Upload</button>
</form>

<script>
  const form = document.forms.upload;
  const inputFile = form.elements.file;

  async function fileToBlob(file) {
    return new Blob([new Uint8Array(await file.arrayBuffer())], { type: file.type });
  }

  function sendToServer(url, data) {
    const req = new XMLHttpRequest();
    req.open("POST", url, true);
    req.send(data);
  }

  async function onSubmit(e) {
    e.preventDefault();

    const file = inputFile.files[0];
    sendToServer('/', await fileToBlob(file));
  }

  form.addEventListener('submit', onSubmit);
</script>