Share what's playing in any Android music app

A local Expo module listens to system media sessions (the only way Android exposes other apps' playback, gated by notification access; we never read notifications). It filters to known music apps, debounces and deduplicates changes, sends a heartbeat while playing, and delivers reports through WorkManager so they survive the app being closed. - One-screen onboarding that doubles as Google Play's prominent disclosure, opening straight to the app's toggle in Android settings - Only media notifications are pre-ticked on that settings screen - Device registration is single-flight (several screens react to the same permission change) and self-heals if the server revokes a token - Sign-out revokes the phone's token; resuming sharing re-sends the current track immediately - Pause controls in Settings and on the feed - Fix invisible tab icons and labels on Android - Keep Metro out of build output so it doesn't exhaust file watchers Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MzFywujuH9TiuXbr9vjoX8
2026-10-03 17:37:30 -04:00
parent 23faffc251
commit 15ab815df6
26 changed files with 865 additions and 8 deletions
@@ -0,0 +1,23 @@
+plugins {
+  id 'com.android.library'
+  id 'expo-module-gradle-plugin'
+}
+
+group = 'tech.chrisedwards.musicshare.nowplaying'
+version = '0.1.0'
+
+android {
+  namespace "tech.chrisedwards.musicshare.nowplaying"
+  defaultConfig {
+    versionCode 1
+    versionName "0.1.0"
+  }
+  lintOptions {
+    abortOnError false
+  }
+}
+
+dependencies {
+  // Delivers reports even if the app process is killed, and retries when the network returns.
+  implementation "androidx.work:work-runtime-ktx:2.10.5"
+}
@@ -0,0 +1,25 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+  <uses-permission android:name="android.permission.INTERNET" />
+
+  <application>
+    <!--
+      Holding notification access is the only way Android lets an app see other apps'
+      media sessions. We never read notification contents; the service only uses its
+      binding to call MediaSessionManager.getActiveSessions().
+    -->
+    <service
+      android:name=".MediaListenerService"
+      android:label="@string/now_playing_listener_label"
+      android:permission="android.permission.BIND_NOTIFICATION_LISTENER_SERVICE"
+      android:exported="false">
+      <intent-filter>
+        <action android:name="android.service.notification.NotificationListenerService" />
+      </intent-filter>
+      <!-- Only media ("real-time") notifications are relevant, so the settings screen
+           doesn't pre-tick Conversations etc. We still never read notification contents. -->
+      <meta-data
+        android:name="android.service.notification.default_filter_types"
+        android:value="ongoing" />
+    </service>
+  </application>
+</manifest>
@@ -0,0 +1,162 @@
+package tech.chrisedwards.musicshare.nowplaying
+
+import android.content.ComponentName
+import android.content.Context
+import android.content.pm.PackageManager
+import android.media.MediaMetadata
+import android.media.session.MediaController
+import android.media.session.MediaSessionManager
+import android.media.session.PlaybackState
+import android.os.Handler
+import android.os.Looper
+import android.service.notification.NotificationListenerService
+
+/**
+ * Bound by the system once the user grants notification access. We don't
+ * override onNotificationPosted: notification access is only the key that
+ * unlocks MediaSessionManager.getActiveSessions(), which tells us what music
+ * apps are playing. Changes are debounced (apps publish title and artist in
+ * separate updates), deduplicated, and handed to Reporter.
+ */
+class MediaListenerService : NotificationListenerService() {
+  private val handler = Handler(Looper.getMainLooper())
+  private val callbacks = mutableMapOf<MediaController, MediaController.Callback>()
+  private var sessionManager: MediaSessionManager? = null
+  private var lastReported: Playback? = null
+
+  private val component by lazy { ComponentName(this, MediaListenerService::class.java) }
+  private val prefs by lazy { Prefs(this) }
+
+  private val sessionsChanged = MediaSessionManager.OnActiveSessionsChangedListener { controllers ->
+    track(controllers.orEmpty())
+  }
+  private val evaluateRunnable = Runnable { evaluate() }
+  private val heartbeatRunnable = object : Runnable {
+    override fun run() {
+      // Re-send while playing so the server knows we're still here (it expires silent phones).
+      lastReported?.takeIf { it.state == PlayState.PLAYING }?.let { Reporter.report(this@MediaListenerService, it) }
+      handler.postDelayed(this, HEARTBEAT_MS)
+    }
+  }
+
+  override fun onListenerConnected() {
+    super.onListenerConnected()
+    instance = this
+    val manager = getSystemService(Context.MEDIA_SESSION_SERVICE) as MediaSessionManager
+    sessionManager = manager
+    try {
+      manager.addOnActiveSessionsChangedListener(sessionsChanged, component, handler)
+      track(manager.getActiveSessions(component))
+    } catch (e: SecurityException) {
+      // Access was revoked between binding and now.
+    }
+    handler.postDelayed(heartbeatRunnable, HEARTBEAT_MS)
+  }
+
+  override fun onListenerDisconnected() {
+    instance = null
+    handler.removeCallbacksAndMessages(null)
+    sessionManager?.removeOnActiveSessionsChangedListener(sessionsChanged)
+    untrackAll()
+    NowPlayingBus.emitPlayback(null)
+    super.onListenerDisconnected()
+  }
+
+  /** Called when JS changes configuration (e.g. which apps to share). */
+  internal fun refresh() {
+    val manager = sessionManager ?: return
+    try {
+      track(manager.getActiveSessions(component))
+    } catch (e: SecurityException) {
+      return
+    }
+  }
+
+  private fun track(controllers: List<MediaController>) {
+    untrackAll()
+    for (controller in controllers) {
+      val callback = object : MediaController.Callback() {
+        override fun onPlaybackStateChanged(state: PlaybackState?) = scheduleEvaluate()
+        override fun onMetadataChanged(metadata: MediaMetadata?) = scheduleEvaluate()
+        override fun onSessionDestroyed() = scheduleEvaluate()
+      }
+      controller.registerCallback(callback, handler)
+      callbacks[controller] = callback
+    }
+    scheduleEvaluate()
+  }
+
+  private fun untrackAll() {
+    callbacks.forEach { (controller, callback) -> controller.unregisterCallback(callback) }
+    callbacks.clear()
+  }
+
+  private fun scheduleEvaluate() {
+    handler.removeCallbacks(evaluateRunnable)
+    handler.postDelayed(evaluateRunnable, DEBOUNCE_MS)
+  }
+
+  private fun evaluate() {
+    val allowed = prefs.allowedPackages
+    val candidates = callbacks.keys
+      .filter { it.packageName in allowed }
+      .mapNotNull { snapshot(it) }
+    // Prefer whatever is actually playing; otherwise a paused session in an allowed app.
+    val current = candidates.firstOrNull { it.state == PlayState.PLAYING } ?: candidates.firstOrNull()
+    NowPlayingBus.emitPlayback(current)
+
+    val next = when {
+      current != null -> current
+      // The app we were reporting went away entirely: tell the server it stopped.
+      lastReported != null && lastReported!!.state != PlayState.STOPPED ->
+        Playback.stopped(lastReported!!.packageName, lastReported!!.appName)
+      else -> return
+    }
+    if (next.identity == lastReported?.identity) return
+    lastReported = next
+    if (prefs.isConfigured) Reporter.report(this, next)
+  }
+
+  private fun snapshot(controller: MediaController): Playback? {
+    val metadata = controller.metadata
+    val title = metadata?.text(MediaMetadata.METADATA_KEY_TITLE) ?: metadata?.text(MediaMetadata.METADATA_KEY_DISPLAY_TITLE)
+    val artist = metadata?.text(MediaMetadata.METADATA_KEY_ARTIST)
+      ?: metadata?.text(MediaMetadata.METADATA_KEY_ALBUM_ARTIST)
+      ?: metadata?.text(MediaMetadata.METADATA_KEY_DISPLAY_SUBTITLE)
+    val playbackState = controller.playbackState
+    val state = when (playbackState?.state) {
+      PlaybackState.STATE_PLAYING, PlaybackState.STATE_BUFFERING,
+      PlaybackState.STATE_FAST_FORWARDING, PlaybackState.STATE_REWINDING,
+      PlaybackState.STATE_SKIPPING_TO_NEXT, PlaybackState.STATE_SKIPPING_TO_PREVIOUS,
+      PlaybackState.STATE_CONNECTING -> PlayState.PLAYING
+      PlaybackState.STATE_PAUSED -> PlayState.PAUSED
+      else -> PlayState.STOPPED
+    }
+    if (title.isNullOrBlank() && state != PlayState.STOPPED) return null // between tracks / ads with no metadata
+    return Playback(
+      packageName = controller.packageName,
+      appName = appLabel(controller.packageName),
+      state = state,
+      title = title,
+      artist = artist,
+      album = metadata?.text(MediaMetadata.METADATA_KEY_ALBUM),
+      durationMs = metadata?.getLong(MediaMetadata.METADATA_KEY_DURATION)?.takeIf { it > 0 },
+      positionMs = playbackState?.position?.takeIf { it >= 0 },
+    )
+  }
+
+  private fun MediaMetadata.text(key: String): String? = getString(key)?.trim()?.takeIf { it.isNotEmpty() }
+
+  private fun appLabel(packageName: String): String? = try {
+    packageManager.getApplicationLabel(packageManager.getApplicationInfo(packageName, 0)).toString()
+  } catch (e: PackageManager.NameNotFoundException) {
+    null
+  }
+
+  companion object {
+    private const val DEBOUNCE_MS = 1_500L
+    private const val HEARTBEAT_MS = 4 * 60_000L
+
+    @Volatile internal var instance: MediaListenerService? = null
+  }
+}
@@ -0,0 +1,26 @@
+package tech.chrisedwards.musicshare.nowplaying
+
+/** Bridges the listener service (system-bound, no JS) to the JS module when the app is open. */
+internal object NowPlayingBus {
+  @Volatile var current: Playback? = null
+    private set
+
+  private val listeners = mutableSetOf<Listener>()
+
+  interface Listener {
+    fun onPlayback(playback: Playback?)
+    fun onStatus(status: String)
+  }
+
+  @Synchronized fun add(listener: Listener) { listeners.add(listener) }
+  @Synchronized fun remove(listener: Listener) { listeners.remove(listener) }
+
+  @Synchronized fun emitPlayback(playback: Playback?) {
+    current = playback
+    listeners.forEach { it.onPlayback(playback) }
+  }
+
+  @Synchronized fun emitStatus(status: String) {
+    listeners.forEach { it.onStatus(status) }
+  }
+}
@@ -0,0 +1,90 @@
+package tech.chrisedwards.musicshare.nowplaying
+
+import android.content.ComponentName
+import android.content.Intent
+import android.os.Build
+import android.provider.Settings
+import androidx.core.app.NotificationManagerCompat
+import expo.modules.kotlin.exception.Exceptions
+import expo.modules.kotlin.modules.Module
+import expo.modules.kotlin.modules.ModuleDefinition
+
+class NowPlayingReaderModule : Module() {
+  private val context get() = appContext.reactContext ?: throw Exceptions.ReactContextLost()
+
+  private val busListener = object : NowPlayingBus.Listener {
+    override fun onPlayback(playback: Playback?) {
+      sendEvent("onPlaybackChange", mapOf("playback" to playback?.toMap()))
+    }
+    override fun onStatus(status: String) {
+      sendEvent("onStatusChange", mapOf("status" to status))
+    }
+  }
+
+  override fun definition() = ModuleDefinition {
+    Name("NowPlayingReader")
+
+    Events("onPlaybackChange", "onStatusChange")
+
+    OnStartObserving { NowPlayingBus.add(busListener) }
+    OnStopObserving { NowPlayingBus.remove(busListener) }
+
+    /** Whether the user has granted notification access (required to see media sessions). */
+    Function("isPermissionGranted") {
+      NotificationManagerCompat.getEnabledListenerPackages(context).contains(context.packageName)
+    }
+
+    /** Opens the system screen with our toggle (directly on Android 11+, the list before that). */
+    Function("openPermissionSettings") {
+      val intent = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+        Intent(Settings.ACTION_NOTIFICATION_LISTENER_DETAIL_SETTINGS).putExtra(
+          Settings.EXTRA_NOTIFICATION_LISTENER_COMPONENT_NAME,
+          ComponentName(context, MediaListenerService::class.java).flattenToString(),
+        )
+      } else {
+        Intent(Settings.ACTION_NOTIFICATION_LISTENER_SETTINGS)
+      }
+      intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK)
+      try {
+        context.startActivity(intent)
+      } catch (e: android.content.ActivityNotFoundException) {
+        context.startActivity(Intent(Settings.ACTION_NOTIFICATION_LISTENER_SETTINGS).addFlags(Intent.FLAG_ACTIVITY_NEW_TASK))
+      }
+    }
+
+    /** Where and how to report, and which apps' sessions to share. */
+    Function("configure") { apiUrl: String, deviceToken: String, allowedPackages: List<String> ->
+      val prefs = Prefs(context)
+      val tokenChanged = prefs.deviceToken != deviceToken
+      prefs.apiUrl = apiUrl
+      prefs.deviceToken = deviceToken
+      prefs.allowedPackages = allowedPackages.toSet()
+      if (tokenChanged) prefs.unauthorized = false
+      MediaListenerService.instance?.refresh()
+    }
+
+    /** Re-send what's playing now (after resuming sharing). */
+    Function("resend") {
+      // Use the last snapshot the listener published rather than the service instance,
+      // which isn't reachable from here if the system rebound the service.
+      val prefs = Prefs(context)
+      NowPlayingBus.current?.let { if (prefs.isConfigured) Reporter.report(context, it) }
+    }
+
+    /** Stop reporting (sign out). */
+    Function("clear") {
+      Prefs(context).clear()
+      NowPlayingBus.emitPlayback(null)
+    }
+
+    /** True when the server rejected this device's token; JS should register a new device. */
+    Function("needsReregistration") {
+      Prefs(context).unauthorized
+    }
+
+    /** What the listener currently sees, for showing "Sharing: X in Spotify" in settings. */
+    Function("getCurrent") {
+      NowPlayingBus.current?.toMap()
+    }
+  }
+}
@@ -0,0 +1,50 @@
+package tech.chrisedwards.musicshare.nowplaying
+
+import org.json.JSONObject
+
+internal enum class PlayState(val wire: String) { PLAYING("playing"), PAUSED("paused"), STOPPED("stopped") }
+
+/** A snapshot of what one app is playing. */
+internal data class Playback(
+  val packageName: String,
+  val appName: String?,
+  val state: PlayState,
+  val title: String?,
+  val artist: String?,
+  val album: String?,
+  val durationMs: Long?,
+  val positionMs: Long?,
+) {
+  /** Fields that matter for "did anything change": not position, which ticks constantly. */
+  val identity: String get() = listOf(packageName, state.wire, title, artist).joinToString("\u0000")
+
+  fun toJson(): JSONObject = JSONObject().apply {
+    put("app", packageName)
+    appName?.let { put("appName", it) }
+    put("state", state.wire)
+    if (state != PlayState.STOPPED && !title.isNullOrBlank()) {
+      put("track", JSONObject().apply {
+        put("title", title)
+        put("artist", artist ?: "")
+        album?.let { put("album", it) }
+        durationMs?.takeIf { it > 0 }?.let { put("durationMs", it) }
+      })
+    }
+    positionMs?.takeIf { it >= 0 }?.let { put("positionMs", it) }
+  }
+
+  fun toMap(): Map<String, Any?> = mapOf(
+    "app" to packageName,
+    "appName" to appName,
+    "state" to state.wire,
+    "title" to title,
+    "artist" to artist,
+    "album" to album,
+    "durationMs" to durationMs?.toDouble(),
+  )
+
+  companion object {
+    fun stopped(packageName: String, appName: String?) =
+      Playback(packageName, appName, PlayState.STOPPED, null, null, null, null, null)
+  }
+}
@@ -0,0 +1,30 @@
+package tech.chrisedwards.musicshare.nowplaying
+
+import android.content.Context
+
+/** Configuration written by JS (configure) and read by the listener service, which may run without the app UI. */
+internal class Prefs(context: Context) {
+  private val prefs = context.applicationContext.getSharedPreferences("musicshare.now_playing", Context.MODE_PRIVATE)
+
+  var apiUrl: String?
+    get() = prefs.getString("api_url", null)
+    set(value) = prefs.edit().putString("api_url", value).apply()
+
+  var deviceToken: String?
+    get() = prefs.getString("device_token", null)
+    set(value) = prefs.edit().putString("device_token", value).apply()
+
+  var allowedPackages: Set<String>
+    get() = prefs.getStringSet("allowed_packages", emptySet()) ?: emptySet()
+    set(value) = prefs.edit().putStringSet("allowed_packages", value).apply()
+
+  /** Set when the server rejects the token (device revoked); JS re-registers. */
+  var unauthorized: Boolean
+    get() = prefs.getBoolean("unauthorized", false)
+    set(value) = prefs.edit().putBoolean("unauthorized", value).apply()
+
+  val isConfigured: Boolean
+    get() = !apiUrl.isNullOrEmpty() && !deviceToken.isNullOrEmpty() && !unauthorized
+
+  fun clear() = prefs.edit().clear().apply()
+}
@@ -0,0 +1,77 @@
+package tech.chrisedwards.musicshare.nowplaying
+
+import android.content.Context
+import androidx.work.BackoffPolicy
+import androidx.work.Constraints
+import androidx.work.CoroutineWorker
+import androidx.work.ExistingWorkPolicy
+import androidx.work.NetworkType
+import androidx.work.OneTimeWorkRequestBuilder
+import androidx.work.WorkManager
+import androidx.work.WorkerParameters
+import androidx.work.workDataOf
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import java.net.HttpURLConnection
+import java.net.URL
+import java.util.concurrent.TimeUnit
+
+internal object Reporter {
+  private const val WORK_NAME = "musicshare.now_playing.report"
+
+  /** Queue the latest state. REPLACE drops any older unsent report: only the newest state matters. */
+  fun report(context: Context, playback: Playback) {
+    val request = OneTimeWorkRequestBuilder<ReportWorker>()
+      .setInputData(workDataOf(ReportWorker.KEY_BODY to playback.toJson().toString()))
+      .setConstraints(Constraints.Builder().setRequiredNetworkType(NetworkType.CONNECTED).build())
+      .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, 15, TimeUnit.SECONDS)
+      .build()
+    WorkManager.getInstance(context).enqueueUniqueWork(WORK_NAME, ExistingWorkPolicy.REPLACE, request)
+  }
+}
+
+internal class ReportWorker(context: Context, params: WorkerParameters) : CoroutineWorker(context, params) {
+  override suspend fun doWork(): Result = withContext(Dispatchers.IO) {
+    val prefs = Prefs(applicationContext)
+    val apiUrl = prefs.apiUrl
+    val token = prefs.deviceToken
+    if (!prefs.isConfigured || apiUrl == null || token == null) return@withContext Result.success()
+    val body = inputData.getString(KEY_BODY) ?: return@withContext Result.success()
+
+    val connection = (URL("${apiUrl.trimEnd('/')}/devices/now-playing").openConnection() as HttpURLConnection).apply {
+      requestMethod = "POST"
+      connectTimeout = 10_000
+      readTimeout = 10_000
+      doOutput = true
+      instanceFollowRedirects = false
+      setRequestProperty("Content-Type", "application/json")
+      setRequestProperty("Authorization", "Bearer $token")
+    }
+    try {
+      connection.outputStream.use { it.write(body.toByteArray(Charsets.UTF_8)) }
+      when (val code = connection.responseCode) {
+        in 200..299 -> Result.success()
+        401 -> {
+          // Device was revoked or the account deleted: stop reporting until JS re-registers.
+          prefs.unauthorized = true
+          NowPlayingBus.emitStatus("unauthorized")
+          Result.failure()
+        }
+        429, in 500..599 -> Result.retry()
+        else -> {
+          android.util.Log.w(TAG, "report rejected: HTTP $code")
+          Result.failure()
+        }
+      }
+    } catch (e: java.io.IOException) {
+      Result.retry()
+    } finally {
+      connection.disconnect()
+    }
+  }
+
+  companion object {
+    const val KEY_BODY = "body"
+    private const val TAG = "MusicshareNowPlaying"
+  }
+}
@@ -0,0 +1,3 @@
+<resources>
+  <string name="now_playing_listener_label">musicshare: share what you\'re playing</string>
+</resources>