Script to validate dart packages pubspec yaml that can it be converted to json or not

pubspecvalidate.dart

import 'dart:convert';
import 'package:yaml/yaml.dart';
import 'dart:io';
import 'package:tar/tar.dart';
import 'package:http/http.dart' as http;

void main(List<String> args) async {
  final httpClient = http.Client();
  var packageUrl = '';
  var pubspecContent;
  var validJson = false;
  try {
    pubspecContent =
        await _readPubspecFile(_downloadFile(httpClient, packageUrl));
  } catch (e) {
    //Log the error
    print(e);
  }
  try {
    validJson = _validateYaml(pubspecContent, 'packageName');
  } on InvalidYamlException catch (e) {
    //log the error.
    print(e);
  } catch (e) {
    //Log the error
    print(e);
  }
//TODO Wrtie to file
}

bool _validateYaml(String pubspecContent, String packageName) {
  try {
    final map = loadYaml(pubspecContent) as Map;
    json.decode(json.encode(map)) as Map<String, dynamic>;
    return true;
  } on JsonUnsupportedObjectError catch (e) {
    throw InvalidYamlException(
        errorMessage: e.toString(), packageName: packageName);
  } catch (e) {
    throw AssertionError('Unable to parse pubspec yaml');
  }
}

Stream<List<int>> _downloadFile(http.Client client, String url) async* {
  try {
    final request = await client.get(Uri.parse(url));
    yield request.bodyBytes;
  } catch (e) {
    print(e);
  }
}

Future<String> _readPubspecFile(Stream<List<int>> fileStream) async {
  final reader = TarReader(fileStream.transform(gzip.decoder));
  try {
    while (await reader.moveNext()) {
      var maxLength = 0;
      final entry = reader.current;
      if (entry.name != 'pubspec.yaml') continue;
      final builder = BytesBuilder();
      await for (final chunk in entry.contents) {
        builder.add(chunk);
      }
      var content = utf8.decode(builder.toBytes(), allowMalformed: true);
      if (maxLength > 0 && content.length > maxLength) {
        content = content.substring(0, maxLength) + '[...]\n\n';
      }
      return content;
    }
  } finally {
    await reader.cancel();
  }
  throw AssertionError('Unable to read the file');
}

class InvalidYamlException implements Exception {
  String errorMessage;
  String packageName;
  InvalidYamlException({this.packageName, this.errorMessage});
}