An app that plays audio becomes a music player at the point where the
screen can lock, a call can interrupt, and the headphones can come out.
None of that existed: the foreground service was typed for media but
had no MediaSession, no transport notification and no audio focus, so
oto would happily keep writing to a stream nobody could hear.
The apparent blocker is that Wails' androidBridge* helpers are
unexported, so Go cannot call arbitrary Java. It does not need to.
StartForegroundService(json) *is* exported, and build/android/ is our
tree, so widening the JSON WailsBridge already accepts is a local edit;
coming back, WailsBridge.emitEvent lands on the application event bus,
which Go subscribes to with app.Event.On. One document out, one command
event back, and no new JNI. No new Gradle dependency either: minSdk is
21, which is exactly when android.media.session.MediaSession and
Notification.MediaStyle arrived, so androidx.media buys two
Build.VERSION branches' worth of nothing.
Four things in it are load-bearing.
**A duck is not a volume change.** Player.SetDuck holds the attenuation
as an offset and re-applies the user's level through setVolumeLocked,
so it cannot accumulate across repeated ducks and getUserVolume -- which
feeds the event, the persisted state and every relative change -- still
reports what the user chose. Writing through to the volume would let
one notification tone permanently turn the music down.
**The duck path is pre-Oreo only.** From API 26 the framework ducks the
app itself and sends no CAN_DUCK focus change; asking to be told
instead (setWillPauseWhenDucked) would mean pausing for every
notification tone, and doing both would attenuate twice.
**An unchanged payload is not an event**, the rule emitStatus already
states one package over: every push crosses JNI and re-delivers an
Intent, and the player pushes state on several paths that can agree.
**After the first start, an update is startService.** From Android 12 a
background app may not *start* a foreground service but may keep
feeding one it already has, which is every track change with the screen
off. Relatedly, every path through onStartCommand calls startForeground
-- one that returns without it is killed.
The contract with Java lives in androidpayload.go *without* the android
build tag, and is tested. Everything left in android.go is untested by
construction: make lint and make test are three tag sets on
linux/amd64, so the only thing that compiles it is the cross-compiler
in make android, and the only thing that can run it is a phone.
None of the behaviour above has been observed on a device. The APK
builds and both halves compile; that is the whole of what is verified.
logan
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