packages/mesh/lib/streams/std/transform-stream.js
function TransformStreamCloseReadableInternal(transformStream) {
  assert(transformStream._errored === false);
  assert(transformStream._readableClosed === false);

  try {
    ReadableStreamDefaultControllerClose(transformStream._readableController);
  } catch (e) {
    assert(false);
  }

  transformStream._readableClosed = true;
}
function TransformStreamCloseReadableInternal(transformStream) {
  assert(transformStream._errored === false);
  assert(transformStream._readableClosed === false);

  try {
    ReadableStreamDefaultControllerClose(transformStream._readableController);
  } catch (e) {
    assert(false);
  }

  transformStream._readableClosed = true;
}
Abstract operations.