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. fox_utils (drag & drop, clipboard files and images; native Linux/Windows plugin) is the owner's shared package, a git dependency pinned to a tag of git.senkochan.moe/Foxyz/fox_utils: bump it by tagging there and changing ref in the desktop pubspec.

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
powershell -File tool/package_windows.ps1 [-SkipBuild]  # dist/*.zip (on Windows)
cd packages/server && dart compile exe --define=APP_VERSION=<x.y.z> bin/server.dart -o watch-together-server

APP_VERSION defaults to 0.0.0-dev; the packagers stamp it from the desktop pubspec into both the app and the server. 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. SYNC_RELAY_PRELOAD=0 turns Up next's preload player off; SYNC_RELAY_TRACE_SWITCH=1 prints the timings of each media change (SwitchTrace).

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), queue_switch_e2e (times Up next switches against a delayed, rate-capped fake Jellyfin and link host: an episode, a direct link, a link passed on and a server-fetched one; WT_SWITCH_PRELOAD=0 for the cold path, WT_SWITCH_DELAY_MS / WT_SWITCH_RATE_KBS for the link). 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 media_kit's Video in flutter test: the runner hangs (kill the flutter_tester by PID). AppShell(videoBuilder:) takes a stand-in, so shell tests run the real player layout without it; otherwise test pure logic (StateDiff, coordinator without widgets).
• A SyncServer started inside a test: relic reports an error writing a response (a relay response cut short when its relay is dropped at a swap or stop) to the zone the server started in, which fails the test; outside tests it is only logged. Start it in runZonedGuarded and fail on anything else (queue_switch_e2e).
• 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 (per-platform assets URLs are predictable; url stays the Linux tarball for builds <= 0.2.1), commits Release vX.Y.Z, makes an annotated tag.
2. Review, then git push --follow-tags.
3. .gitea/workflows/release.yml runs one job per platform: Linux builds with tool/package_linux.sh, Windows (runner yuuka-windows, host mode, PowerShell only) with tool/package_windows.ps1. Each then runs dart tool/release_publish.dart vX.Y.Z <archive>, which creates the release if the other job hasn't yet and uploads (or replaces) its asset. By hand: package, then the same dart tool/release_publish.dart line.

Test builds (Linux, no tag, no CI): tool/dev_release.sh [--no-publish] (token: RELEASE_TOKEN or ~/.config/watch-together-release-token, a Gitea access token with repository read/write) builds the working tree here as the next patch's -dev.N (N one past the published one) and replaces the assets of the dev prerelease with the tarball and its manifest.json. Dev builds update from it (Updater). A stable install moves onto it once with the command the script prints (run with the app open: it finds the install from the running process and copies the new files over it).

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. Hot restart kills the server isolate (flutter_tools kills every non-UI isolate first), so a [server] server crashed: the server stopped unexpectedly line just before it is expected. 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:).
• Hot restart with any media_kit Player alive (session, thumbnails, sfx) used to SIGSEGV on mpv's core thread: each mpv handle's wakeup callback is a NativeCallable of the old isolate, freed by the restart, and media_kit then sends the leftover handles quit, which fires it. fox_utils' Linux plugin (from 0.1.8, debug builds only) clears those callbacks on the engine's on-pre-engine-restart signal, reading the handles from media_kit's debug-only NativeReferenceHolder buffer (address in $TMPDIR/com.alexmercerind.media_kit.NativeReferenceHolder.<pid>). Old players are leaked, not destroyed, until the process exits. Re-check this after a media_kit upgrade.
• 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.
• toggleFullscreenOnDoublePress: false on the session controls is load-bearing: media_kit's double-click pushes its own fullscreen route with a second Video. A GestureDetector below media_kit's overlay never sees the click (its MouseRegion takes the hit) and one around it would delay every button click (double-tap holds the arena), so the double-click is a raw pointer observer (DoubleClickListener).
• The window is frameless: the party strip is the only drag area and holds the window buttons.
• Signal-backed singletons (Profile, SessionState) live across tests; never cache a Future in them (each test runs in its own zone, and a Future from an earlier test never completes in the next).
• Chat arrives twice from the server (see PROTOCOL.md); the client drops the textless feed copy.
• Tab traversal is disabled in the session player on purpose; Tab toggles chat & activity.
• After editing constants (ports, thresholds), grep to confirm the value landed.