sync_replay_project/docs/DEVELOPMENT.md

Development

Layout and rules: ARCHITECTURE.md.

Build

Needs the Flutter SDK (beta channel, Dart 3.13+) and, for the Linux desktop build, the usual GTK toolchain (clang, cmake, ninja, pkg-config, libgtk-3-dev). mpv libraries come from media_kit_libs_video.

cd apps/desktop && flutter pub get && flutter run -d linux
cd apps/desktop && flutter build linux --release --dart-define=APP_VERSION=<x.y.z>
tool/package_linux.sh [--skip-build] [--noupload]    # dist/*.tar.gz
cd packages/server && dart compile exe bin/server.dart -o watch-together-server

APP_VERSION defaults to 0.0.0-dev; package_linux.sh stamps it from the desktop pubspec. Setting DISCORD_WEBHOOK_URL makes the packager post the tarball to Discord (never commit it). The packager always compiles the dedicated server (with the Flutter SDK's dart) into the tarball as watch-together-server, also with --skip-build.

Dev loop

Run a server without the app, then point apps at it:

dart run packages/server/bin/server.dart --port 8080 --secret x [--media FILE]

This is the same serve() the app runs when hosting and the same code as the dedicated binary. Prints READY port=... name=... and stops on SIGINT or SIGTERM. Then Join from one or more apps at 127.0.0.1:8080. Or just Host from the app. mpv env override: SYNC_RELAY_HWDEC (wins over the Settings choice). SYNC_RELAY_VO has no effect with embedded video: media_kit forces vo=libmpv.

Harnesses in tool/ (own pubspec.yaml, dart run tool/<name>.dart): range_logger (serve a file and log every Range request), shaper (bandwidth cap, latency, --kill-after for outage tests), fake_viewer and e2e_check (simulated viewers against a live server).

Tests

• cd packages/core && dart test, cd packages/server && dart test.
• cd apps/desktop && flutter test test/<file>.
• Real-mpv tests: sync_playback_e2e, coord_presence, video_reload_e2e, seek_drag_e2e, end_of_file_e2e, readahead_e2e, jellyfin_e2e (a local fake Jellyfin over HTTP; tests never talk to a real Jellyfin). The sync and end-of-file ones expect ~/Videos/chiyo.mp4; others generate media with ffmpeg into WT_TEST_TMP. Headless mpv (no video output attached) won't open video-only files, so test media needs an audio track. Tests always log media_kit "S/W rendering" because they have no display; that says nothing about the app. Run only tests related to what you changed.
• CI (.gitea/workflows/ci.yml): analyze + test for core and server, plus dart compile exe of the dedicated server (fails if Flutter creeps into packages/server). Desktop tests are not in CI.
• packages/server/test/serve_isolate_test.dart runs serve in a real isolate; apps/desktop/test/server_isolate_test.dart covers the app's host path (isolate server, raw WebSocket join, crash, rehost).
• Desktop tests that write files use WT_TEST_TMP (default: system temp).

Traps:

• Never pump the session screen or media_kit Video in flutter test: the runner hangs (kill the flutter_tester by PID). Test pure logic (StateDiff, coordinator without widgets) instead.
• Never depend on a server-side WebSocket onDone; assert presence with deadline polling.
• sub.asFuture() can resolve before onDone; poll with a deadline.
• Tests must not assume a threat model beyond the friends trust basis.

Releasing

User pushes tags; CI does the rest.

1. tool/release.sh [patch|minor|major] [--dry-run]: derives the next version from the latest tag, bumps the three pubspecs in lockstep, writes updates/manifest.json (asset URL is predictable), commits Release vX.Y.Z, makes an annotated tag.
2. Review, then git push --follow-tags.
3. .gitea/workflows/release.yml builds the Linux tarball and runs tool/release_publish.sh vX.Y.Z, which creates the release and uploads it. By hand: tool/package_linux.sh then tool/release_publish.sh vX.Y.Z.

Tokens come from the environment (RELEASE_TOKEN, or Actions-provided GITHUB_TOKEN/GITEA_TOKEN). The manifest has no sha256 by default; the updater skips the check when absent. Workflows live in .gitea/workflows (the forge reads .gitea before .github).

Debugging the hosted server

When hosting, the server runs on its own isolate (ServerIsolate, apps/desktop/lib/src/state/server_isolate.dart), in the same process. Breakpoints in packages/server work under flutter run: the debugger attaches to spawned isolates too (it shows as server). Its log lines are printed with a [server] prefix. Hot reload reloads the server isolate's code too, but its state (members, clock, sockets) survives until hosting restarts; changes to startup code (SyncServer.start, routes) need a new Host. Without the app: dart run packages/server/bin/server.dart.

Gotchas

• Relic gives Range as a typed RangeHeader; convert from unit + first range.
• A killed isolate (Isolate.kill) does not close its listening socket: the port stays bound in the process until exit. SyncServer binds with shared: true so a new hosted server in the same process can take it over; a normal stop closes it.
• Relic server-side onDone does not fire for dead peers. Presence is the isClosed sweep + onError forget + lastSeen timeouts.
• web_socket_channel 3.x: channel.ready errors are unhandled on refused connections; swallow them and report through the stream's onError. Streams are single-subscription: one listener per socket.
• media_kit has no public Player.setProperty; the code reaches mpv through a dynamic call on player.platform. Cache size goes through PlayerConfiguration(bufferSize:).
• mpv reconnect flags: comma form works, colon form is rejected. Re-verify through setProperty if touched.
• Overlays that are hidden but mounted keep focus (Space falls into a hidden button). Use ExcludeFocus on closed subtrees and unfocus on close; reuse the shared no-focus node for overlay buttons.
• modifyVolumeOnScroll: false on the session controls is load-bearing for window drag (volume is the speaker button only). A GestureDetector below media_kit's overlay loses the gesture arena; the drag layer is a raw pointer observer on top.
• New screens must bring their own drag area and window buttons (frameless window).
• Chat arrives twice from the server (see PROTOCOL.md); the client drops the textless feed copy.
• Tab traversal is disabled on the session screen on purpose; Tab toggles the side panel.
• After editing constants (ports, thresholds), grep to confirm the value landed.