todo-app/lib/desktop/wrapper_server.dart

import 'dart:async';
import 'dart:convert';
import 'dart:io';

import 'package:crdt_sync/crdt_sync.dart';
import 'package:path/path.dart' as p;

import 'package:todo/desktop/static_content_type.dart';
import 'package:todo/desktop/wrapper_image_routes.dart';

export 'wrapper_paths.dart';

part 'wrapper_sync_routes.dart';

/// Route serving `todo`'s own seeded Firebase session (a `FirebaseCredentials`
/// JSON blob), alongside [kSyncAccountPath]'s email/password pair.
///
/// `todo`-local rather than added to `crdt_sync_dart`: no other app in the
/// fleet runs a desktop wrapper of its own, so a shared route would add
/// surface area five other apps never use. Gated by the same
/// [kSyncAccountEnvVar] as [kSyncAccountPath].
const kSyncCredentialsPath = '/sync-credentials';

/// Local HTTP server backing the desktop app.
///
/// The desktop app is a Flutter **web** build (Flutter's Linux embedder manages
/// only ~20fps at 4K — see `docs/desktop-performance-findings.md`), so it runs
/// in a browser and cannot touch the filesystem. This process is the other half
/// of the desktop app: it serves the build and owns the two files a browser
/// cannot write.
///
/// * `~/src/todo/BACKLOG.md` — the canonical backlog path the user's tooling and
///   the `todo` MCP server read.
/// * a copy of the note log — so a wiped Chrome profile is not a total-loss
///   event for notes that have not yet synced to GitHub.
///
/// Binds to loopback only. The endpoints read and overwrite files in the user's
/// home directory with no authentication, so exposing them on a routable
/// address would let anything on the network rewrite the backlog.
class WrapperServer {
  /// Creates a server serving [webRoot] and persisting under [backlogPath] and
  /// [logPath].
  WrapperServer({
    required this.webRoot,
    required this.backlogPath,
    required this.logPath,
    bool? serveSyncAccount,
    String? syncConfigDir,
    String? todoCredentialsPath,
    WrapperImageRoutes? images,
  }) : images =
           images ??
           defaultWrapperImageRoutes(Platform.environment['HOME'] ?? ''),
       serveSyncAccount =
           serveSyncAccount ??
           (Platform.environment[kSyncAccountEnvVar] ?? '').isNotEmpty,
       syncConfigDir =
           syncConfigDir ??
           p.join(Platform.environment['HOME'] ?? '', '.config', 'crdt-sync'),
       todoCredentialsPath =
           todoCredentialsPath ??
           p.join(
             Platform.environment['HOME'] ?? '',
             '.config',
             'todo',
             'firebase_auth.json',
           );

  /// The `/images/*` routes (attached images; see [WrapperImageRoutes]).
  final WrapperImageRoutes images;

  /// Whether the sync-account route answers; off unless explicitly enabled.
  final bool serveSyncAccount;

  /// Directory holding `firebase.json` and `password`.
  final String syncConfigDir;

  /// Whether [kSyncCredentialsPath] has served a valid credential yet.
  ///
  /// Flips to true after the first 200 and 404s every request after that,
  /// so a normal launch can self-provision with no env var to remember (see
  /// [_syncCredentials]) while the exposure window for a database-write
  /// credential stays "until the app finishes booting" rather than "for as
  /// long as the wrapper process runs". Independent of [serveSyncAccount]:
  /// that gate protects the legacy shared `/sync-account` route other apps'
  /// wrappers also serve, which stays opt-in.
  bool _todoCredentialsServed = false;

  /// `todo`'s own seeded Firebase session, written by
  /// `crdt-sync/tool/seed_session.py --app todo` in the same
  /// `{id_token, refresh_token, expires_at}` shape every other app's
  /// credential cache uses. The account's password grant is retired
  /// fleet-wide (see `link_google.py`/`seed_session.py`), so unlike
  /// [syncConfigDir]'s `password` file this is the only thing that actually
  /// authenticates.
  final String todoCredentialsPath;

  /// Directory holding the built Flutter web assets.
  final String webRoot;

  /// Absolute path of the Markdown backlog export.
  final String backlogPath;

  /// Absolute path of the on-disk note-log copy.
  final String logPath;

  HttpServer? _server;

  /// Port the server is listening on, once [start] has completed.
  int get port => _server!.port;

  /// Binds to loopback on [requestedPort] and begins serving.
  ///
  /// Pass 0 to let the OS choose a port (tests do this); the desktop launcher
  /// passes the fixed port, because the browser keys `localStorage` (the GitHub
  /// token) and IndexedDB (the notes) by origin — a changing port would
  /// silently hide both.
  Future<void> start(int requestedPort) async {
    _server = await HttpServer.bind(
      InternetAddress.loopbackIPv4,
      requestedPort,
    );
    unawaited(_serve(_server!));
  }

  /// Stops serving and releases the port.
  Future<void> stop() async => await _server?.close(force: true);

  Future<void> _serve(HttpServer server) async {
    await for (final request in server) {
      // Attachment routes can run for minutes (a multi-gigabyte upload, a
      // video being watched, a reconcile fetching a large file) and are safe
      // side by side, so they must not hold up the page's own requests.
      // Everything else stays one at a time: the backup files are
      // overwritten whole and must not interleave.
      if (request.uri.path.startsWith(WrapperImageRoutes.prefix)) {
        unawaited(_respond(request));
      } else {
        await _respond(request);
      }
    }
  }

  Future<void> _respond(HttpRequest request) async {
    try {
      if (_isCrossSiteWrite(request)) {
        // Read the body anyway: answering mid-upload looks like a dropped
        // connection, not a refusal.
        await request.drain<void>();
        request.response.statusCode = HttpStatus.forbidden;
      } else {
        await _handle(request);
      }
    } on Exception {
      request.response.statusCode = HttpStatus.internalServerError;
    }
    await request.response.close();
  }

  /// A write sent by some other site's page. Any website open in the same
  /// browser can POST here without a preflight (a CORS "simple request"),
  /// which would let it overwrite the backups or push unbounded files into
  /// the attachment store and on to dufs. The app's own page always sends its
  /// own origin; local tools (curl, tests) send none.
  bool _isCrossSiteWrite(HttpRequest request) {
    if (request.method == 'GET' || request.method == 'HEAD') return false;
    final origin = request.headers.value('origin');
    return origin != null &&
        origin != 'http://localhost:$port' &&
        origin != 'http://127.0.0.1:$port';
  }

  Future<void> _handle(HttpRequest request) async {
    final path = request.uri.path;
    if (path == '/backup/backlog') {
      return await _file(request, backlogPath);
    }
    if (path == '/backup/log') {
      return await _file(request, logPath);
    }
    if (path == kSyncAccountPath) {
      return await _syncAccount(request);
    }
    if (path == kSyncCredentialsPath) {
      return await _syncCredentials(request);
    }
    if (await images.handle(request)) return;
    return await _static(request, path);
  }

  /// GET returns the file's contents (404 when absent); POST overwrites it.
  Future<void> _file(HttpRequest request, String filePath) async {
    final file = File(filePath);
    if (request.method == 'POST') {
      await file.parent.create(recursive: true);
      await file.writeAsString(await utf8.decodeStream(request));
      request.response.statusCode = HttpStatus.noContent;
      return;
    }
    if (request.method != 'GET') {
      request.response.statusCode = HttpStatus.methodNotAllowed;
      return;
    }
    if (!file.existsSync()) {
      request.response.statusCode = HttpStatus.notFound;
      return;
    }
    request.response.headers.contentType = ContentType.text;
    request.response.write(await file.readAsString());
  }

  Future<void> _static(HttpRequest request, String path) async {
    final relative = path == '/' ? 'index.html' : path.substring(1);
    // Reject traversal before touching the filesystem: the served root sits
    // next to the user's files, so `../` must not escape it.
    final resolved = p.normalize(p.join(webRoot, relative));
    // coverage:ignore-start
    // Defence in depth, and currently unreachable: Dart's HttpServer decodes
    // and normalises the path before a handler runs, so even `%2e%2e` arrives
    // already collapsed (verified in wrapper_server_test). Kept so the
    // guarantee does not depend on that implementation detail holding.
    if (!p.isWithin(webRoot, resolved) && resolved != p.normalize(webRoot)) {
      request.response.statusCode = HttpStatus.forbidden;
      return;
    }
    // coverage:ignore-end
    final file = File(resolved);
    if (!file.existsSync()) {
      request.response.statusCode = HttpStatus.notFound;
      return;
    }
    request.response.headers.contentType = contentTypeFor(resolved);
    await request.response.addStream(file.openRead());
  }

  /// Content type for [filePath]; see [staticContentTypeFor].
  static ContentType contentTypeFor(String filePath) =>
      staticContentTypeFor(filePath);
}