feat: defined PubLicense to get packages' licenses

analysis_options.yaml

@@ -2,3 +2,4 @@ include: package:very_good_analysis/analysis_options.5.1.0.yaml
 analyzer:
   exclude:
     - "**/version.dart"
+    - "bricks/**/__brick__"

lib/src/pub_license/pub_license.dart

@@ -0,0 +1,137 @@
+/// Enables checking a package's license from pub.dev.
+///
+/// This library is intented to be used by Very Good CLI to help extracting
+/// license information. The existance of this library is likely to be
+/// ephemeral. It may be obsolete once [pub.dev](https://pub.dev/) exposes
+/// stable license information in their official API; you may track the
+/// progress [here](https://github.com/dart-lang/pub-dev/issues/4717).
+library pub_license;
+
+import 'package:html/dom.dart' as html_dom;
+import 'package:html/parser.dart' as html_parser;
+import 'package:http/http.dart' as http;
+import 'package:meta/meta.dart';
+
+/// The pub.dev [Uri] used to retrieve the license of a package.
+Uri _pubPackageLicenseUri(String packageName) =>
+    Uri.parse('https://pub.dev/packages/$packageName/license');
+
+/// {@template pub_license_exception}
+/// An exception thrown by [PubLicense].
+/// {@endtemplate}
+class PubLicenseException implements Exception {
+  /// {@macro pub_license_exception}
+  const PubLicenseException(String message)
+      : message = '[pub_license] $message';
+
+  /// The exception message.
+  final String message;
+}
+
+/// The function signature for parsing HTML documents.
+@visibleForTesting
+typedef HtmlDocumentParse = html_dom.Document Function(
+  dynamic input, {
+  String? encoding,
+  bool generateSpans,
+  String? sourceUrl,
+});
+
+/// {@template pub_license}
+/// Enables checking pub.dev's hosted packages license.
+/// {@endtemplate}
+class PubLicense {
+  /// {@macro pub_license}
+  PubLicense({
+    @visibleForTesting http.Client? client,
+    @visibleForTesting HtmlDocumentParse? parse,
+  })  : _client = client ?? http.Client(),
+        _parse = parse ?? html_parser.parse;
+
+  final http.Client _client;
+
+  final html_dom.Document Function(
+    dynamic input, {
+    String? encoding,
+    bool generateSpans,
+    String? sourceUrl,
+  }) _parse;
+
+  /// Retrieves the license of a package.
+  ///
+  /// Some packages may have multiple licenses, hence a [Set] is returned.
+  ///
+  /// It may throw a [PubLicenseException] if:
+  /// * The response from pub.dev is not successful.
+  /// * The response body cannot be parsed.
+  Future<Set<String>> getLicense(String packageName) async {
+    final response = await _client.get(_pubPackageLicenseUri(packageName));
+
+    if (response.statusCode != 200) {
+      throw PubLicenseException(
+        '''Failed to retrieve the license of the package, received status code: ${response.statusCode}''',
+      );
+    }
+
+    late final html_dom.Document document;
+    try {
+      document = _parse(response.body);
+    } on html_parser.ParseError catch (e) {
+      throw PubLicenseException(
+        'Failed to parse the response body, received error: $e',
+      );
+    } catch (e) {
+      throw PubLicenseException(
+        '''An unknown error occurred when trying to parse the response body, received error: $e''',
+      );
+    }
+
+    return _scrapeLicense(document);
+  }
+}
+
+/// Scrapes the license from the pub.dev's package license page.
+///
+/// The expected HTML structure is:
+/// ```html
+/// <aside class="detail-info-box">
+///   <h3> ... </h3>
+///   <p> ... </p>
+///   <h3 class="title">License</h3>
+///   <p>
+///   <img/>
+///   MIT (<a href="/packages/very_good_cli/license">LICENSE</a>)
+///   </p>
+/// </aside>
+/// ```
+///
+/// It may throw a [PubLicenseException] if:
+/// * The detail info box is not found.
+/// * The license header is not found.
+Set<String> _scrapeLicense(html_dom.Document document) {
+  final detailInfoBox = document.querySelector('.detail-info-box');
+  if (detailInfoBox == null) {
+    throw const PubLicenseException(
+      '''Failed to scrape license because `.detail-info-box` was not found.''',
+    );
+  }
+
+  String? rawLicenseText;
+  for (var i = 0; i < detailInfoBox.children.length; i++) {
+    final child = detailInfoBox.children[i];
+
+    final headerText = child.text.trim().toLowerCase();
+    if (headerText == 'license') {
+      rawLicenseText = detailInfoBox.children[i + 1].text.trim();
+      break;
+    }
+  }
+  if (rawLicenseText == null) {
+    throw const PubLicenseException(
+      '''Failed to scrape license because the license header was not found.''',
+    );
+  }
+
+  final licenseText = rawLicenseText.split('(').first.trim();
+  return licenseText.split(',').map((e) => e.trim()).toSet();
+}

pubspec.yaml

@@ -15,6 +15,8 @@ dependencies:
   cli_completion: ^0.4.0
   collection: ^1.17.1
   glob: ^2.0.2
+  html: ^0.15.4 # This dependency is temporary and should be removed once pub_license is obsolete.
+  http: ^1.1.0 # This dependency is temporary and should be removed once pub_license is obsolete.
   lcov_parser: ^0.1.2
   mason: 0.1.0-dev.51
   mason_logger: ^0.2.2

test/src/pub_license/fixtures/generate_pub_license_fixtures.dart

@@ -0,0 +1,74 @@
+/// A small script used to generate the fixture for the pub_license test.
+///
+/// Fixtures are simply a temporary snapshot of an HTML response from pub.dev.
+/// The generated fixtures allow testing pub_license scraping logic without
+/// making a request to pub.dev every time the test is run.
+///
+/// To run this script, use the following command:
+/// ```bash
+/// dart test/src/pub_license/fixtures/generate_pub_license_fixtures.dart
+/// ```
+///
+/// Or simply use the "Run" CodeLens from VSCode's Dart extension if running
+/// from VSCode.
+library generate_pub_license_fixtures;
+
+// ignore_for_file: avoid_print
+
+import 'dart:io';
+
+import 'package:http/http.dart' as http;
+import 'package:path/path.dart' as path;
+
+/// [Uri] used to test the case where a package has a single license.
+final _singleLicenseUri = Uri.parse(
+  'https://pub.dev/packages/very_good_cli/license',
+);
+
+/// [Uri] used to test the case where a package has multiple licenses.
+final _multipleLicenseUri = Uri.parse(
+  'https://pub.dev/packages/just_audio/license',
+);
+
+/// [Uri] used to test the case where a package has no license.
+final _noLicenseUri = Uri.parse(
+  'https://pub.dev/packages/music_control_notification/license',
+);
+
+Future<void> main() async {
+  final fixtureUris = <String, Uri>{
+    'singleLicense': _singleLicenseUri,
+    'multipleLicense': _multipleLicenseUri,
+    'noLicense': _noLicenseUri,
+  };
+
+  final httpClient = http.Client();
+
+  for (final entry in fixtureUris.entries) {
+    final name = entry.key;
+    final uri = entry.value;
+
+    final response = await httpClient.get(uri);
+
+    if (response.statusCode != 200) {
+      print(
+        '''Failed to generate a fixture for $name, received status code: ${response.statusCode}''',
+      );
+      continue;
+    }
+
+    final fixturePath = path.joinAll([
+      Directory.current.path,
+      'test',
+      'src',
+      'pub_license',
+      'fixtures',
+      '$name.html',
+    ]);
+    File(fixturePath)
+      ..createSync(recursive: true)
+      ..writeAsStringSync(response.body);
+
+    print('Fixture generated at $fixturePath');
+  }
+}