flutter inappwebview render html file downloaded from - flutter

Question

I'm trying to create an application using
flutter_inappwebview: ^6.0.0-beta.14
base on the the following steps:
download html zipfile from internet.
extract on local storage (at path getting from getApplicationDocumentsDirectory())
use flutter_inappwebview to run localhost server and try to set the documentRoot to the path of getApplicationDocumentsDirectory()
but it show the blank screen and it seems like it cannot find the html file that was extracted. I've explored the directory and already see the html files and folder on that path.
But if I create an html file inside assets folder and run localhost server and access http://localhost:8080/index.html, it was success. But what I want is download html from internet
final dir = (await getApplicationDocumentsDirectory()).path;
final zippedFile = File('$dir/html.zip');// downloaded from internet
await zippedFile.writeAsBytes(zip.data);
final bytes = await zippedFile.readAsBytes();
final archive = ZipDecoder().decodeBytes(bytes);
for (final file in archive) {
final fileName = '$dir/${file.name}';
if (file.isFile && !fileName.contains("__MACOSX")) {
debugPrint(fileName);
final outFile = File(fileName);
await outFile.create(recursive: true);
await outFile.writeAsBytes(file.content);
}
}
and here is code to run localhost server
final dir = (await getApplicationDocumentsDirectory()).path;
final localhostServer = InAppLocalhostServer(
port: 8080,
documentRoot: $dir
);
if (!localhostServer.isRunning()) {
await localhostServer.start();
debugPrint('LOCALHOSTSERVER STARTED');
}