feat: content downloader with sha256 verify and atomic cache

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-06-12 13:05:56 +09:00
parent c7bdb9b9c9
commit bfa9c09b28
2 changed files with 229 additions and 0 deletions
@@ -0,0 +1,97 @@
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:crypto/crypto.dart';
+import 'package:http/http.dart' as http;
+
+import 'manifest.dart';
+
+/// Pulls the remote season manifest and downloads new/updated packs into
+/// [cacheDir] with SHA256 verification and atomic (temp + rename) writes.
+/// All failures are swallowed into a `false` return — remote content is an
+/// enhancement, never a crash source.
+class ContentDownloader {
+  ContentDownloader({
+    required this.baseUrl,
+    required this.cacheDir,
+    http.Client? client,
+  }) : _client = client ?? http.Client() {
+    _loadIndex();
+  }
+
+  final String baseUrl;
+  final Directory cacheDir;
+  final http.Client _client;
+  final Map<String, int> _index = {};
+
+  File get _indexFile => File('${cacheDir.path}/cache_index.json');
+
+  void _loadIndex() {
+    try {
+      if (_indexFile.existsSync()) {
+        final json =
+            jsonDecode(_indexFile.readAsStringSync()) as Map<String, dynamic>;
+        json.forEach((k, v) => _index[k] = v as int);
+      }
+    } catch (_) {
+      // Corrupt index: treat as empty; packs will re-download.
+      _index.clear();
+    }
+  }
+
+  Future<void> _saveIndex() async {
+    await cacheDir.create(recursive: true);
+    await _indexFile.writeAsString(jsonEncode(_index));
+  }
+
+  int? cachedVersion(String seasonId) => _index[seasonId];
+
+  /// Checks the manifest and downloads anything new. Returns true when at
+  /// least one pack was added or updated.
+  Future<bool> sync() async {
+    final RemoteManifest manifest;
+    try {
+      final res = await _client
+          .get(Uri.parse('$baseUrl/manifest.json'))
+          .timeout(const Duration(seconds: 10));
+      if (res.statusCode != 200) return false;
+      manifest = RemoteManifest.fromJson(
+          jsonDecode(res.body) as Map<String, dynamic>);
+    } catch (_) {
+      return false;
+    }
+
+    var changed = false;
+    for (final season in manifest.seasons) {
+      if (_index[season.seasonId] == season.version) continue;
+      if (await _downloadPack(season)) changed = true;
+    }
+    return changed;
+  }
+
+  Future<bool> _downloadPack(ManifestSeason season) async {
+    try {
+      final res = await _client
+          .get(Uri.parse('$baseUrl/${season.packUrl}'))
+          .timeout(const Duration(seconds: 30));
+      if (res.statusCode != 200) return false;
+
+      // Verify in memory before any file is touched, so a bad pack can
+      // never leave artifacts on disk.
+      final digest = sha256.convert(res.bodyBytes).toString();
+      if (digest != season.sha256) return false;
+
+      final dir = Directory('${cacheDir.path}/seasons/${season.seasonId}');
+      await dir.create(recursive: true);
+      final tmp = File('${dir.path}/pack.json.tmp');
+      await tmp.writeAsBytes(res.bodyBytes, flush: true);
+      await tmp.rename('${dir.path}/pack.json');
+
+      _index[season.seasonId] = season.version;
+      await _saveIndex();
+      return true;
+    } catch (_) {
+      return false;
+    }
+  }
+}