Let the media session live when playback is paused.

As per Android policy and internal logic, we stopped the playback
foreground service when playback was paused. This made our PlayService
elligible for garbage collection by the OS. This had the consequences of
not allowing someone to pause playback and resume it after some time.
Android would always kill the service after around one minute.

This commit, on supported Android version (7.0+) detaches the
notification when stopping the foreground service, leaving the
notification in place even when the service is killed, allowing the user
to resume playback whenever they please.

We also had to move the MediaSession out of the service, for it to
remain alive between service killing and resurrection.

app/src/main/AndroidManifest.xml

@@ -42,7 +42,7 @@
     <activity android:name="com.github.apognu.otter.activities.SettingsActivity" />
     <activity android:name="com.github.apognu.otter.activities.LicencesActivity" />
 
-    <service android:name="com.github.apognu.otter.playback.PlayerService" />
+    <service android:name="com.github.apognu.otter.playback.PlayerService" android:foregroundServiceType="mediaPlayback" />
 
     <service
       android:name=".playback.PinService"

app/src/main/java/com/github/apognu/otter/Otter.kt

@@ -1,6 +1,8 @@
 package com.github.apognu.otter
 
 import android.app.Application
+import android.support.v4.media.session.MediaSessionCompat
+import android.support.v4.media.session.PlaybackStateCompat
 import androidx.appcompat.app.AppCompatDelegate
 import com.github.apognu.otter.playback.QueueManager
 import com.github.apognu.otter.utils.*
@@ -60,6 +62,26 @@ class Otter : Application() {
     }
   }
 
+  private val playbackStateBuilder = PlaybackStateCompat.Builder().apply {
+    setActions(
+      PlaybackStateCompat.ACTION_PLAY_PAUSE or
+        PlaybackStateCompat.ACTION_PLAY or
+        PlaybackStateCompat.ACTION_PAUSE or
+        PlaybackStateCompat.ACTION_SKIP_TO_NEXT or
+        PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS or
+        PlaybackStateCompat.ACTION_SEEK_TO or
+        PlaybackStateCompat.ACTION_SKIP_TO_QUEUE_ITEM
+    )
+  }
+
+  val mediaSession: MediaSessionCompat by lazy {
+    MediaSessionCompat(this, applicationContext.packageName).apply {
+      setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS or MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS)
+      setPlaybackState(playbackStateBuilder.build())
+      isActive = true
+    }
+  }
+
   override fun onCreate() {
     super.onCreate()
 

app/src/main/java/com/github/apognu/otter/activities/MainActivity.kt

@@ -286,6 +286,12 @@ class MainActivity : AppCompatActivity() {
     lifecycleScope.launch(Main) {
       CommandBus.get().collect { command ->
         when (command) {
+          is Command.StartService -> {
+            startService(Intent(this@MainActivity, PlayerService::class.java).apply {
+              putExtra(PlayerService.INITIAL_COMMAND_KEY, command.command.toString())
+            })
+          }
+
           is Command.RefreshTrack -> refreshCurrentTrack(command.track)
         }
       }

app/src/main/java/com/github/apognu/otter/playback/MediaControlsManager.kt

@@ -6,8 +6,6 @@ import android.app.Service
 import android.content.BroadcastReceiver
 import android.content.Context
 import android.content.Intent
-import android.media.MediaMetadata
-import android.support.v4.media.MediaMetadataCompat
 import android.support.v4.media.session.MediaSessionCompat
 import androidx.core.app.NotificationCompat
 import androidx.core.app.NotificationManagerCompat
@@ -18,9 +16,7 @@ import com.github.apognu.otter.utils.*
 import com.squareup.picasso.Picasso
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers.Default
-import kotlinx.coroutines.Dispatchers.IO
 import kotlinx.coroutines.launch
-import kotlinx.coroutines.runBlocking
 
 class MediaControlsManager(val context: Service, private val scope: CoroutineScope, private val mediaSession: MediaSessionCompat) {
   companion object {
@@ -32,27 +28,6 @@ class MediaControlsManager(val context: Service, private val scope: CoroutineSco
 
   private var notification: Notification? = null
 
-  fun buildTrackMetadata(track: Track?): MediaMetadataCompat {
-    track?.let {
-      val coverUrl = maybeNormalizeUrl(track.album.cover.original)
-
-      return MediaMetadataCompat.Builder().apply {
-        putString(MediaMetadataCompat.METADATA_KEY_TITLE, track.title)
-        putString(MediaMetadataCompat.METADATA_KEY_ARTIST, track.artist.name)
-        putLong(MediaMetadata.METADATA_KEY_DURATION, (track.bestUpload()?.duration?.toLong() ?: 0L) * 1000)
-
-        try {
-          runBlocking(IO) {
-            this@apply.putBitmap(MediaMetadataCompat.METADATA_KEY_ALBUM_ART, Picasso.get().load(coverUrl).get())
-          }
-        } catch (e: Exception) {
-        }
-      }.build()
-    }
-
-    return MediaMetadataCompat.Builder().build()
-  }
-
   fun updateNotification(track: Track?, playing: Boolean) {
     if (notification == null && !playing) return
 
@@ -82,7 +57,10 @@ class MediaControlsManager(val context: Service, private val scope: CoroutineSco
           .setSmallIcon(R.drawable.ottershape)
           .run {
             coverUrl?.let {
-              try { setLargeIcon(Picasso.get().load(coverUrl).get()) } catch (_: Exception) {}
+              try {
+                setLargeIcon(Picasso.get().load(coverUrl).get())
+              } catch (_: Exception) {
+              }
 
               return@run this
             }
@@ -114,18 +92,14 @@ class MediaControlsManager(val context: Service, private val scope: CoroutineSco
           .build()
 
         notification?.let {
+          if (playing) {
+            context.startForeground(AppContext.NOTIFICATION_MEDIA_CONTROL, it)
+          } else {
             NotificationManagerCompat.from(context).notify(AppContext.NOTIFICATION_MEDIA_CONTROL, it)
           }
-
-        if (playing) tick()
         }
       }
     }
-
-  fun tick() {
-    notification?.let {
-      context.startForeground(AppContext.NOTIFICATION_MEDIA_CONTROL, it)
-    }
   }
 
   private fun action(icon: Int, title: String, id: Int): NotificationCompat.Action {
@@ -138,16 +112,16 @@ class MediaControlsManager(val context: Service, private val scope: CoroutineSco
 
 class MediaControlActionReceiver : BroadcastReceiver() {
   override fun onReceive(context: Context?, intent: Intent?) {
-    when (intent?.action) {
-      MediaControlsManager.NOTIFICATION_ACTION_PREVIOUS.toString() -> CommandBus.send(
-        Command.PreviousTrack
-      )
-      MediaControlsManager.NOTIFICATION_ACTION_TOGGLE.toString() -> CommandBus.send(
-        Command.ToggleState
-      )
-      MediaControlsManager.NOTIFICATION_ACTION_NEXT.toString() -> CommandBus.send(
-        Command.NextTrack
-      )
+    val command = when (intent?.action) {
+      MediaControlsManager.NOTIFICATION_ACTION_PREVIOUS.toString() -> Command.PreviousTrack
+      MediaControlsManager.NOTIFICATION_ACTION_TOGGLE.toString() -> Command.ToggleState
+      MediaControlsManager.NOTIFICATION_ACTION_NEXT.toString() -> Command.NextTrack
+      else -> null
+    }
+
+    command?.let {
+      CommandBus.send(command)
+      CommandBus.send(Command.StartService(command))
     }
   }
 }

app/src/main/java/com/github/apognu/otter/playback/PlayerService.kt

@@ -8,28 +8,32 @@ import android.content.IntentFilter
 import android.media.AudioAttributes
 import android.media.AudioFocusRequest
 import android.media.AudioManager
+import android.media.MediaMetadata
 import android.os.Build
 import android.os.Bundle
 import android.os.IBinder
 import android.os.ResultReceiver
-import android.support.v4.media.session.MediaSessionCompat
+import android.support.v4.media.MediaMetadataCompat
 import android.support.v4.media.session.PlaybackStateCompat
 import android.view.KeyEvent
+import com.github.apognu.otter.Otter
 import com.github.apognu.otter.R
 import com.github.apognu.otter.utils.*
 import com.google.android.exoplayer2.*
 import com.google.android.exoplayer2.ext.mediasession.MediaSessionConnector
 import com.google.android.exoplayer2.source.TrackGroupArray
 import com.google.android.exoplayer2.trackselection.TrackSelectionArray
-import kotlinx.coroutines.CoroutineScope
+import com.squareup.picasso.Picasso
+import kotlinx.coroutines.*
 import kotlinx.coroutines.Dispatchers.IO
 import kotlinx.coroutines.Dispatchers.Main
-import kotlinx.coroutines.Job
-import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.collect
-import kotlinx.coroutines.launch
 
 class PlayerService : Service() {
+  companion object {
+    const val INITIAL_COMMAND_KEY = "start_command"
+  }
+
   private var started = false
   private val scope: CoroutineScope = CoroutineScope(Job() + Main)
 
@@ -40,9 +44,10 @@ class PlayerService : Service() {
 
   private lateinit var queue: QueueManager
   private lateinit var mediaControlsManager: MediaControlsManager
-  private lateinit var mediaSession: MediaSessionCompat
   private lateinit var player: SimpleExoPlayer
 
+  private val mediaMetadataBuilder = MediaMetadataCompat.Builder()
+
   private lateinit var playerEventListener: PlayerEventListener
   private val headphonesUnpluggedReceiver = HeadphonesUnpluggedReceiver()
 
@@ -51,7 +56,17 @@ class PlayerService : Service() {
   private lateinit var radioPlayer: RadioPlayer
 
   override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
-    if (!started) watchEventBus()
+    if (!started) {
+      watchEventBus()
+
+      intent?.extras?.getString(INITIAL_COMMAND_KEY)?.let {
+        when (it) {
+          Command.ToggleState.toString() -> togglePlayback()
+          Command.NextTrack.toString() -> skipToNextTrack()
+          Command.PreviousTrack.toString() -> skipToPreviousTrack()
+        }
+      }
+    }
 
     started = true
 
@@ -82,18 +97,7 @@ class PlayerService : Service() {
       }
     }
 
-    mediaSession = MediaSessionCompat(this, applicationContext.packageName).apply {
-      isActive = true
-      setPlaybackState(PlaybackStateCompat.Builder()
-        .setActions(
-          PlaybackStateCompat.ACTION_PLAY_PAUSE or
-          PlaybackStateCompat.ACTION_SEEK_TO or
-          PlaybackStateCompat.ACTION_SKIP_TO_NEXT or
-          PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS
-        ).build())
-    }
-
-    mediaControlsManager = MediaControlsManager(this, scope, mediaSession)
+    mediaControlsManager = MediaControlsManager(this, scope, Otter.get().mediaSession)
 
     player = SimpleExoPlayer.Builder(this).build().apply {
       playWhenReady = false
@@ -102,40 +106,21 @@ class PlayerService : Service() {
         addListener(it)
       }
 
-      MediaSessionConnector(mediaSession).also {
+      MediaSessionConnector(Otter.get().mediaSession).also {
         it.setPlayer(this)
+        it.setQueueNavigator(OtterQueueNavigator())
         it.setMediaMetadataProvider {
-          mediaControlsManager.buildTrackMetadata(queue.current())
+          buildTrackMetadata(queue.current())
         }
 
-        it.setQueueNavigator(object : MediaSessionConnector.QueueNavigator {
-          override fun onSkipToQueueItem(player: Player, controlDispatcher: ControlDispatcher, id: Long) {}
-
-          override fun onCurrentWindowIndexChanged(player: Player) {}
-
-          override fun onCommand(player: Player, controlDispatcher: ControlDispatcher, command: String, extras: Bundle?, cb: ResultReceiver?) = true
-
-          override fun getSupportedQueueNavigatorActions(player: Player): Long {
-            return PlaybackStateCompat.ACTION_PLAY_PAUSE or PlaybackStateCompat.ACTION_SKIP_TO_NEXT or PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS
-          }
-
-          override fun onSkipToNext(player: Player, controlDispatcher: ControlDispatcher) {}
-
-          override fun getActiveQueueItemId(player: Player?) = 0L
-
-          override fun onSkipToPrevious(player: Player, controlDispatcher: ControlDispatcher) {}
-
-          override fun onTimelineChanged(player: Player) {}
-        })
-
         it.setMediaButtonEventHandler { player, _, mediaButtonEvent ->
           mediaButtonEvent.extras?.getParcelable<KeyEvent>(Intent.EXTRA_KEY_EVENT)?.let { key ->
             if (key.action == KeyEvent.ACTION_UP) {
               when (key.keyCode) {
-                KeyEvent.KEYCODE_MEDIA_PLAY -> state(true)
-                KeyEvent.KEYCODE_MEDIA_PAUSE -> state(false)
+                KeyEvent.KEYCODE_MEDIA_PLAY -> setPlaybackState(true)
+                KeyEvent.KEYCODE_MEDIA_PAUSE -> setPlaybackState(false)
                 KeyEvent.KEYCODE_MEDIA_NEXT -> player.next()
-                KeyEvent.KEYCODE_MEDIA_PREVIOUS -> previousTrack()
+                KeyEvent.KEYCODE_MEDIA_PREVIOUS -> skipToPreviousTrack()
               }
             }
           }
@@ -146,12 +131,12 @@ class PlayerService : Service() {
     }
 
     if (queue.current > -1) {
-      player.prepare(queue.datasources, true, true)
+      player.prepare(queue.datasources)
 
       Cache.get(this, "progress")?.let { progress ->
         player.seekTo(queue.current, progress.readLine().toLong())
 
-        val (current, duration, percent) = progress(true)
+        val (current, duration, percent) = getProgress(true)
 
         ProgressBus.send(current, duration, percent)
       }
@@ -179,7 +164,7 @@ class PlayerService : Service() {
             queue.replace(command.queue)
             player.prepare(queue.datasources, true, true)
 
-            state(true)
+            setPlaybackState(true)
 
             CommandBus.send(Command.RefreshTrack(queue.current()))
           }
@@ -193,22 +178,17 @@ class PlayerService : Service() {
             queue.current = command.index
             player.seekTo(command.index, C.TIME_UNSET)
 
-            state(true)
+            setPlaybackState(true)
 
             CommandBus.send(Command.RefreshTrack(queue.current()))
           }
 
-          is Command.ToggleState -> toggle()
-          is Command.SetState -> state(command.state)
+          is Command.ToggleState -> togglePlayback()
+          is Command.SetState -> setPlaybackState(command.state)
 
-          is Command.NextTrack -> {
-            player.next()
-
-            Cache.set(this@PlayerService, "progress", "0".toByteArray())
-            ProgressBus.send(0, 0, 0)
-          }
-          is Command.PreviousTrack -> previousTrack()
-          is Command.Seek -> progress(command.progress)
+          is Command.NextTrack -> skipToNextTrack()
+          is Command.PreviousTrack -> skipToPreviousTrack()
+          is Command.Seek -> seek(command.progress)
 
           is Command.ClearQueue -> queue.clear()
 
@@ -222,10 +202,6 @@ class PlayerService : Service() {
           is Command.PinTrack -> PinService.download(this@PlayerService, command.track)
           is Command.PinTracks -> command.tracks.forEach { PinService.download(this@PlayerService, it) }
         }
-
-        if (player.playWhenReady) {
-          mediaControlsManager.tick()
-        }
       }
     }
 
@@ -243,7 +219,7 @@ class PlayerService : Service() {
       while (true) {
         delay(1000)
 
-        val (current, duration, percent) = progress()
+        val (current, duration, percent) = getProgress()
 
         if (player.playWhenReady) {
           ProgressBus.send(current, duration, percent)
@@ -256,6 +232,8 @@ class PlayerService : Service() {
 
   @SuppressLint("NewApi")
   override fun onDestroy() {
+    scope.cancel()
+
     try {
       unregisterReceiver(headphonesUnpluggedReceiver)
     } catch (_: Exception) {
@@ -272,11 +250,8 @@ class PlayerService : Service() {
         audioManager.abandonAudioFocus(audioFocusChangeListener)
       })
 
-    mediaSession.isActive = false
-    mediaSession.release()
-
     player.removeListener(playerEventListener)
-    state(false)
+    setPlaybackState(false)
     player.release()
 
     stopForeground(true)
@@ -286,9 +261,9 @@ class PlayerService : Service() {
   }
 
   @SuppressLint("NewApi")
-  private fun state(state: Boolean) {
+  private fun setPlaybackState(state: Boolean) {
     if (!state) {
-      val (progress, _, _) = progress()
+      val (progress, _, _) = getProgress()
 
       Cache.set(this@PlayerService, "progress", progress.toString().toByteArray())
     }
@@ -329,11 +304,11 @@ class PlayerService : Service() {
     }
   }
 
-  private fun toggle() {
-    state(!player.playWhenReady)
+  private fun togglePlayback() {
+    setPlaybackState(!player.playWhenReady)
   }
 
-  private fun previousTrack() {
+  private fun skipToPreviousTrack() {
     if (player.currentPosition > 5000) {
       return player.seekTo(0)
     }
@@ -341,7 +316,14 @@ class PlayerService : Service() {
     player.previous()
   }
 
-  private fun progress(force: Boolean = false): Triple<Int, Int, Int> {
+  private fun skipToNextTrack() {
+    player.next()
+
+    Cache.set(this@PlayerService, "progress", "0".toByteArray())
+    ProgressBus.send(0, 0, 0)
+  }
+
+  private fun getProgress(force: Boolean = false): Triple<Int, Int, Int> {
     if (!player.playWhenReady && !force) return progressCache
 
     return queue.current()?.bestUpload()?.let { upload ->
@@ -354,7 +336,7 @@ class PlayerService : Service() {
     } ?: Triple(0, 0, 0)
   }
 
-  private fun progress(value: Int) {
+  private fun seek(value: Int) {
     val duration = ((queue.current()?.bestUpload()?.duration ?: 0) * (value.toFloat() / 100)) * 1000
 
     progressCache = Triple(duration.toInt(), queue.current()?.bestUpload()?.duration ?: 0, value)
@@ -362,6 +344,28 @@ class PlayerService : Service() {
     player.seekTo(duration.toLong())
   }
 
+  private fun buildTrackMetadata(track: Track?): MediaMetadataCompat {
+    track?.let {
+      val coverUrl = maybeNormalizeUrl(track.album.cover.original)
+
+      return mediaMetadataBuilder.apply {
+        putString(MediaMetadataCompat.METADATA_KEY_TITLE, track.title)
+        putString(MediaMetadataCompat.METADATA_KEY_ARTIST, track.artist.name)
+        putLong(MediaMetadata.METADATA_KEY_DURATION, (track.bestUpload()?.duration?.toLong() ?: 0L) * 1000)
+
+        try {
+          runBlocking(IO) {
+            this@apply.putBitmap(MediaMetadataCompat.METADATA_KEY_ALBUM_ART, Picasso.get().load(coverUrl).get())
+          }
+        } catch (e: Exception) {
+        }
+      }.build()
+    }
+
+    return mediaMetadataBuilder.build()
+  }
+
+  @SuppressLint("NewApi")
   inner class PlayerEventListener : Player.EventListener {
     override fun onPlayerStateChanged(playWhenReady: Boolean, playbackState: Int) {
       super.onPlayerStateChanged(playWhenReady, playbackState)
@@ -388,7 +392,11 @@ class PlayerService : Service() {
 
           if (playbackState == Player.STATE_READY) {
             mediaControlsManager.updateNotification(queue.current(), false)
-            stopForeground(false)
+
+            Build.VERSION_CODES.N.onApi(
+              { stopForeground(STOP_FOREGROUND_DETACH) },
+              { stopForeground(false) }
+            )
           }
         }
       }
@@ -441,18 +449,18 @@ class PlayerService : Service() {
         AudioManager.AUDIOFOCUS_GAIN -> {
           player.volume = 1f
 
-          state(stateWhenLostFocus)
+          setPlaybackState(stateWhenLostFocus)
           stateWhenLostFocus = false
         }
 
         AudioManager.AUDIOFOCUS_LOSS -> {
           stateWhenLostFocus = false
-          state(false)
+          setPlaybackState(false)
         }
 
         AudioManager.AUDIOFOCUS_LOSS_TRANSIENT -> {
           stateWhenLostFocus = player.playWhenReady
-          state(false)
+          setPlaybackState(false)
         }
 
         AudioManager.AUDIOFOCUS_LOSS_TRANSIENT_CAN_DUCK -> {
@@ -462,4 +470,33 @@ class PlayerService : Service() {
       }
     }
   }
+
+  inner class OtterQueueNavigator : MediaSessionConnector.QueueNavigator {
+    override fun onSkipToQueueItem(player: Player, controlDispatcher: ControlDispatcher, id: Long) {
+      CommandBus.send(Command.PlayTrack(id.toInt()))
+    }
+
+    override fun onCurrentWindowIndexChanged(player: Player) {}
+
+    override fun onCommand(player: Player, controlDispatcher: ControlDispatcher, command: String, extras: Bundle?, cb: ResultReceiver?) = true
+
+    override fun getSupportedQueueNavigatorActions(player: Player): Long {
+      return PlaybackStateCompat.ACTION_PLAY_PAUSE or
+        PlaybackStateCompat.ACTION_SKIP_TO_NEXT or
+        PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS or
+        PlaybackStateCompat.ACTION_SKIP_TO_QUEUE_ITEM
+    }
+
+    override fun onSkipToNext(player: Player, controlDispatcher: ControlDispatcher) {
+      skipToNextTrack()
+    }
+
+    override fun getActiveQueueItemId(player: Player?) = queue.current.toLong()
+
+    override fun onSkipToPrevious(player: Player, controlDispatcher: ControlDispatcher) {
+      skipToPreviousTrack()
+    }
+
+    override fun onTimelineChanged(player: Player) {}
+  }
 }

app/src/main/java/com/github/apognu/otter/utils/Bus.kt

@@ -11,6 +11,7 @@ import kotlinx.coroutines.flow.conflate
 import kotlinx.coroutines.launch
 
 sealed class Command {
+  class StartService(val command: Command) : Command()
   object RefreshService : Command()
 
   object ToggleState : Command()