simple dart file upload server

main.dart

import 'dart:io';
import 'package:mime/mime.dart';

void main(List<String> arguments) async {
  const port = 8080;
  var lastId = (await _loadLastId()) ?? -1;
  final server = await HttpServer.bind(InternetAddress.anyIPv4, port);
  server.listen((request) async {
    void close(int statusCode) {
      request.response.statusCode = 404;
      request.response.close();
    }

    if (request.uri.path != '/screenshot' || request.method != 'POST') {
      close(404);
      return;
    }

    try {
      final boundary = request.headers.contentType!.parameters['boundary']!;
      final mimeTransformer = MimeMultipartTransformer(boundary);
      final parts = request.cast<List<int>>().transform(mimeTransformer);
      final part = await parts.first;
      final file = File('uploaded_files/${++lastId}.png');
      final write = file.openWrite();
      await part.pipe(write);
      await write.close();
      await _storeLastId(lastId);

      close(200);
    } catch (_) {
      close(500);
    }
  });
  print('screenshot server listening on $port.');
}

final _lastIdFile = File('uploaded_files/.last_id');
Future<int?> _loadLastId() async {
  final exists = await _lastIdFile.exists();
  if (!exists) return null;
  final contents = await _lastIdFile.readAsString();
  return int.tryParse(contents);
}

Future<void> _storeLastId(int id) async {
  _lastIdFile.writeAsString(id.toString());
}