Add android fallback for background push notifications (#102)

android/app/build.gradle

@@ -1,4 +1,5 @@
 apply plugin: 'com.android.application'
+apply plugin: 'kotlin-android'
 
 android {
     namespace = "social.flotilla"
@@ -35,6 +36,10 @@ dependencies {
     implementation "androidx.appcompat:appcompat:$androidxAppCompatVersion"
     implementation "androidx.coordinatorlayout:coordinatorlayout:$androidxCoordinatorLayoutVersion"
     implementation "androidx.core:core-splashscreen:$coreSplashScreenVersion"
+    implementation "androidx.work:work-runtime:2.10.3"
+    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
+    implementation "com.squareup.okhttp3:okhttp:4.12.0"
+    implementation "fr.acinq.secp256k1:secp256k1-kmp-jni-android:0.22.0"
     implementation project(':capacitor-android')
     testImplementation "junit:junit:$junitVersion"
     androidTestImplementation "androidx.test.ext:junit:$androidxJunitVersion"

android/app/src/main/java/social/flotilla/MainActivity.java

@@ -1,5 +1,15 @@
 package social.flotilla;
 
+import android.os.Bundle;
+
 import com.getcapacitor.BridgeActivity;
 
-public class MainActivity extends BridgeActivity {}
+import social.flotilla.notifications.AndroidPushFallbackPlugin;
+
+public class MainActivity extends BridgeActivity {
+  @Override
+  public void onCreate(Bundle savedInstanceState) {
+    registerPlugin(AndroidPushFallbackPlugin.class);
+    super.onCreate(savedInstanceState);
+  }
+}

android/app/src/main/java/social/flotilla/notifications/AndroidPushFallbackPlugin.kt

@@ -0,0 +1,99 @@
+package social.flotilla.notifications
+
+import android.content.Context
+import android.content.SharedPreferences
+import androidx.work.Constraints
+import androidx.work.ExistingPeriodicWorkPolicy
+import androidx.work.ExistingWorkPolicy
+import androidx.work.NetworkType
+import androidx.work.OneTimeWorkRequest
+import androidx.work.PeriodicWorkRequest
+import androidx.work.WorkManager
+import com.getcapacitor.JSObject
+import com.getcapacitor.Plugin
+import com.getcapacitor.PluginCall
+import com.getcapacitor.PluginMethod
+import com.getcapacitor.annotation.CapacitorPlugin
+import org.json.JSONArray
+import org.json.JSONException
+import org.json.JSONObject
+import java.util.concurrent.TimeUnit
+
+@CapacitorPlugin(name = "AndroidPushFallback")
+class AndroidPushFallbackPlugin : Plugin() {
+  companion object {
+    const val PREFS_NAME = "CapacitorStorage"
+    const val KEY_STATE = "androidPushFallback.state"
+    const val UNIQUE_PERIODIC_WORK = "androidPushFallback.periodic"
+    const val UNIQUE_IMMEDIATE_WORK = "androidPushFallback.immediate"
+  }
+
+  private fun getPrefs(): SharedPreferences {
+    return context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
+  }
+
+  @PluginMethod
+  fun syncState(call: PluginCall) {
+    val state: JSObject? = call.getObject("state")
+
+    if (state != null) {
+      getPrefs().edit().putString(KEY_STATE, state.toString()).apply()
+
+      if (isEnabled(state.toString())) {
+        scheduleWork()
+      } else {
+        cancelWork()
+      }
+    }
+
+    call.resolve()
+  }
+
+  private fun isEnabled(rawState: String?): Boolean {
+    if (rawState == null || rawState.isEmpty()) {
+      return false
+    }
+
+    return try {
+      val state = JSONObject(rawState)
+      val subscriptions: JSONArray? = state.optJSONArray("subscriptions")
+      subscriptions != null && subscriptions.length() > 0
+    } catch (_: JSONException) {
+      false
+    }
+  }
+
+  private fun scheduleWork() {
+    val constraints = Constraints.Builder().setRequiredNetworkType(NetworkType.CONNECTED).build()
+
+    val workManager = WorkManager.getInstance(context)
+
+    val periodic = PeriodicWorkRequest.Builder(
+      AndroidPushFallbackWorker::class.java,
+      15,
+      TimeUnit.MINUTES,
+    ).setConstraints(constraints).build()
+
+    val immediate = OneTimeWorkRequest.Builder(AndroidPushFallbackWorker::class.java)
+      .setConstraints(constraints)
+      .build()
+
+    workManager.enqueueUniquePeriodicWork(
+      UNIQUE_PERIODIC_WORK,
+      ExistingPeriodicWorkPolicy.UPDATE,
+      periodic,
+    )
+
+    workManager.enqueueUniqueWork(
+      UNIQUE_IMMEDIATE_WORK,
+      ExistingWorkPolicy.REPLACE,
+      immediate,
+    )
+  }
+
+  private fun cancelWork() {
+    val workManager = WorkManager.getInstance(context)
+    workManager.cancelUniqueWork(UNIQUE_IMMEDIATE_WORK)
+    workManager.cancelUniqueWork(UNIQUE_PERIODIC_WORK)
+  }
+}

android/app/src/main/java/social/flotilla/notifications/AndroidPushFallbackWorker.kt

@@ -0,0 +1,862 @@
+package social.flotilla.notifications
+
+import android.Manifest
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.util.Log
+import android.app.PendingIntent
+import android.content.Context
+import android.content.Intent
+import android.app.ActivityManager
+import android.content.SharedPreferences
+import android.content.pm.PackageManager
+import android.database.Cursor
+import android.net.Uri
+import android.os.Build
+import androidx.core.app.NotificationCompat
+import androidx.core.app.NotificationManagerCompat
+import androidx.core.content.ContextCompat
+import androidx.work.Worker
+import androidx.work.WorkerParameters
+import fr.acinq.secp256k1.Secp256k1
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.Response
+import okhttp3.WebSocket
+import okhttp3.WebSocketListener
+import org.json.JSONArray
+import org.json.JSONObject
+import social.flotilla.notifications.AndroidPushFallbackPlugin.Companion.KEY_STATE
+import social.flotilla.notifications.AndroidPushFallbackPlugin.Companion.PREFS_NAME
+import java.nio.charset.StandardCharsets
+import java.security.MessageDigest
+import java.security.SecureRandom
+import java.util.Arrays
+import java.util.UUID
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.CountDownLatch
+import java.util.concurrent.TimeUnit
+import android.util.Base64
+
+class AndroidPushFallbackWorker(context: Context, params: WorkerParameters) : Worker(context, params) {
+  companion object {
+    private const val TAG = "PushFallback"
+    private const val CHANNEL_ID = "flotilla_fallback"
+    private const val CURSOR_PREFIX = "androidPushFallback.cursor."
+    private const val SOCKET_TIMEOUT_SECONDS = 20L
+    private const val REJECTED = "__REJECTED__"
+    private const val KIND_RELAY_AUTH = 22242
+    private const val KIND_NIP46_RPC = 24133
+    private val SECP = Secp256k1.get()
+  }
+
+  private val prefs: SharedPreferences =
+    context.getSharedPreferences(PREFS_NAME, Context.MODE_PRIVATE)
+  private val client: OkHttpClient = OkHttpClient.Builder().build()
+
+  // ---- Socket pool ----
+
+  // Opens each relay URL at most once; caller must invoke closeAll() when done.
+  private inner class SocketPool {
+    private val sockets = ConcurrentHashMap<String, WebSocket>()
+
+    fun open(url: String, listener: WebSocketListener): WebSocket =
+      sockets.getOrPut(url) {
+        client.newWebSocket(Request.Builder().url(url).build(), listener)
+      }
+
+    fun closeAll() {
+      for ((_, ws) in sockets) ws.close(1000, "done")
+      sockets.clear()
+    }
+  }
+
+  override fun doWork(): Result {
+    if (isAppInForeground()) {
+      return Result.success()
+    }
+
+    val pool = SocketPool()
+    try {
+      val rawState = prefs.getString(KEY_STATE, "") ?: ""
+      if (rawState.isEmpty()) return Result.success()
+
+      val state = JSONObject(rawState)
+      val sessionInfo = getSessionInfo(state)
+      val subscriptions = parseSubscriptions(state)
+      if (subscriptions.isEmpty()) return Result.success()
+
+      val activeSince = state.optLong("activeSince", 0L)
+      val seen = mutableSetOf<String>()
+      var latestPair: Pair<String, JSONObject>? = null
+
+      for (sub in subscriptions) {
+        val cursorKey = CURSOR_PREFIX + sub.relay + ":" + sub.key
+        val since = maxOf(prefs.getLong(cursorKey, 0L), activeSince)
+        val result = pollRelay(sub, since, sessionInfo, pool)
+
+        if (result.lastCursor > prefs.getLong(cursorKey, 0L)) {
+          prefs.edit().putLong(cursorKey, result.lastCursor).apply()
+        }
+
+        for (event in result.events) {
+          val id = event.optString("id", "")
+          if (id.isNotEmpty() && seen.add(id)) {
+            val createdAt = event.optLong("created_at", 0L)
+            if (latestPair == null || createdAt > latestPair!!.second.optLong("created_at", 0L)) {
+              latestPair = Pair(sub.relay, event)
+            }
+          }
+        }
+      }
+
+      if (latestPair != null) {
+        val (relay, event) = latestPair!!
+        postNotification(relay, event)
+      }
+
+      return Result.success()
+    } catch (e: Exception) {
+      Log.e(TAG, "Worker failed", e)
+      return Result.success()
+    } finally {
+      pool.closeAll()
+      client.dispatcher.executorService.shutdown()
+    }
+  }
+
+  private fun isAppInForeground(): Boolean {
+    val am = applicationContext.getSystemService(ActivityManager::class.java) ?: return false
+    val tasks = am.getRunningAppProcesses() ?: return false
+    val pkg = applicationContext.packageName
+    return tasks.any { it.processName == pkg && it.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND }
+  }
+
+  private fun getSessionInfo(state: JSONObject): SessionInfo {
+    val session = state.optJSONObject("session") ?: return SessionInfo("anonymous", "", JSONObject())
+    return SessionInfo(
+      session.optString("method", "anonymous"),
+      session.optString("pubkey", ""),
+      session,
+    )
+  }
+
+  private fun parseSubscriptions(state: JSONObject): List<Subscription> {
+    val result = mutableListOf<Subscription>()
+    val arr = state.optJSONArray("subscriptions") ?: return result
+
+    for (i in 0 until arr.length()) {
+      val item = arr.optJSONObject(i) ?: continue
+      val relay = item.optString("relay", "").trim()
+
+      if (!relay.startsWith("wss://") && !relay.startsWith("ws://")) continue
+
+      val filters = item.optJSONArray("filters")
+      if (filters == null || filters.length() == 0) continue
+
+      val key = item.optString("key", "").trim()
+      result.add(Subscription(relay, key, filters, item.optJSONArray("ignore")))
+    }
+
+    return result
+  }
+
+  private fun pollRelay(sub: Subscription, since: Long, sessionInfo: SessionInfo, pool: SocketPool): RelayResult {
+    val result = RelayResult()
+    val latch = CountDownLatch(1)
+
+    val listener = RelayListener(sub, since, sessionInfo, result, latch, pool)
+    pool.open(sub.relay, listener)
+
+    if (!latch.await(SOCKET_TIMEOUT_SECONDS, TimeUnit.SECONDS)) {
+      Log.d(TAG, "Relay ${sub.relay} timed out")
+    }
+
+    return result
+  }
+
+  private fun postNotification(relay: String, event: JSONObject) {
+    val context = applicationContext
+
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU &&
+      ContextCompat.checkSelfPermission(context, Manifest.permission.POST_NOTIFICATIONS) != PackageManager.PERMISSION_GRANTED
+    ) return
+
+    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
+      val manager = context.getSystemService(NotificationManager::class.java)
+      if (manager != null && manager.getNotificationChannel(CHANNEL_ID) == null) {
+        val channel = NotificationChannel(CHANNEL_ID, "Fallback Notifications", NotificationManager.IMPORTANCE_DEFAULT)
+        channel.description = "Notifications delivered by Android background fallback"
+        manager.createNotificationChannel(channel)
+      }
+    }
+
+    val id = event.optString("id", "")
+    val encodedRelay = Uri.encode(relay)
+    val url = "https://app.flotilla.social/?relay=$encodedRelay&id=$id"
+    val intent = Intent(Intent.ACTION_VIEW, Uri.parse(url))
+    intent.setPackage(context.packageName)
+    intent.flags = Intent.FLAG_ACTIVITY_NEW_TASK or Intent.FLAG_ACTIVITY_CLEAR_TOP
+
+    val pendingIntent = PendingIntent.getActivity(
+      context, 0, intent,
+      PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE,
+    )
+
+    val body = "New activity"
+
+    val notification = NotificationCompat.Builder(context, CHANNEL_ID)
+      .setSmallIcon(android.R.drawable.stat_notify_chat)
+      .setContentTitle("Flotilla")
+      .setContentText(body)
+      .setAutoCancel(true)
+      .setPriority(NotificationCompat.PRIORITY_DEFAULT)
+      .setContentIntent(pendingIntent)
+      .build()
+
+    NotificationManagerCompat.from(context).notify(1, notification)
+  }
+
+  private fun matchesFilter(filter: JSONObject, event: JSONObject): Boolean {
+    val kinds = filter.optJSONArray("kinds")
+    if (kinds != null && kinds.length() > 0) {
+      val kind = event.optInt("kind", -1)
+      var found = false
+      for (i in 0 until kinds.length()) {
+        if (kinds.optInt(i, -1) == kind) { found = true; break }
+      }
+      if (!found) return false
+    }
+
+    val tags = event.optJSONArray("tags")
+    val iter = filter.keys()
+    while (iter.hasNext()) {
+      val key = iter.next()
+      if (!key.startsWith("#")) continue
+      val tagName = key.substring(1)
+      val allowed = filter.optJSONArray(key) ?: continue
+      if (allowed.length() == 0) continue
+
+      val allowedValues = mutableSetOf<String>()
+      for (i in 0 until allowed.length()) {
+        val v = allowed.optString(i, "")
+        if (v.isNotEmpty()) allowedValues.add(v)
+      }
+
+      var matched = false
+      if (tags != null) {
+        for (i in 0 until tags.length()) {
+          val tag = tags.optJSONArray(i) ?: continue
+          if (tag.optString(0, "") == tagName && allowedValues.contains(tag.optString(1, ""))) {
+            matched = true; break
+          }
+        }
+      }
+      if (!matched) return false
+    }
+
+    return true
+  }
+
+  // ---- Crypto helpers ----
+
+  private fun computeEventId(event: JSONObject): String {
+    return try {
+      val serialized = JSONArray()
+      serialized.put(0)
+      serialized.put(event.optString("pubkey", ""))
+      serialized.put(event.optLong("created_at", 0))
+      serialized.put(event.optInt("kind", 0))
+      serialized.put(event.optJSONArray("tags") ?: JSONArray())
+      serialized.put(event.optString("content", ""))
+      // JSONObject escapes forward slashes (/ -> \/), but NIP-01 event ID hashing
+      // requires unescaped slashes. Replace them before hashing.
+      val serializedStr = serialized.toString().replace("\\/", "/")
+      bytesToHex(sha256(serializedStr.toByteArray(StandardCharsets.UTF_8)))
+    } catch (_: Exception) {
+      ""
+    }
+  }
+
+  private fun deriveXOnlyPubkey(secretHex: String): String {
+    val secret = hexToBytes(secretHex)
+    if (secret.size != 32 || !SECP.secKeyVerify(secret)) return ""
+    val pubkey65 = try { SECP.pubkeyCreate(secret) } catch (_: Exception) { return "" }
+    if (pubkey65.size != 65) return ""
+    return bytesToHex(Arrays.copyOfRange(pubkey65, 1, 33))
+  }
+
+  private fun schnorrSign(secretHex: String, messageHex: String): String {
+    val sk = hexToBytes(secretHex)
+    val msg = hexToBytes(messageHex)
+    if (sk.size != 32 || msg.size != 32 || !SECP.secKeyVerify(sk)) return ""
+    val aux = ByteArray(32).also { SecureRandom().nextBytes(it) }
+    val sig = try { SECP.signSchnorr(msg, sk, aux) } catch (_: Exception) { return "" }
+    if (sig.size != 64) return ""
+    return bytesToHex(sig)
+  }
+
+  private fun sha256(input: ByteArray): ByteArray =
+    try { MessageDigest.getInstance("SHA-256").digest(input) } catch (_: Exception) { ByteArray(32) }
+
+  private fun hexToBytes(hex: String?): ByteArray {
+    var s = hex?.trim()?.lowercase() ?: ""
+    if (s.startsWith("0x")) s = s.substring(2)
+    if (s.length % 2 == 1) s = "0$s"
+    val bytes = ByteArray(s.length / 2)
+    var i = 0
+    while (i < s.length) {
+      val hi = Character.digit(s[i], 16)
+      val lo = Character.digit(s[i + 1], 16)
+      if (hi < 0 || lo < 0) return ByteArray(0)
+      bytes[i / 2] = ((hi shl 4) + lo).toByte()
+      i += 2
+    }
+    return bytes
+  }
+
+  private fun bytesToHex(bytes: ByteArray): String {
+    val hex = "0123456789abcdef".toCharArray()
+    val chars = CharArray(bytes.size * 2)
+    for (i in bytes.indices) {
+      val v = bytes[i].toInt() and 0xFF
+      chars[i * 2] = hex[v ushr 4]
+      chars[i * 2 + 1] = hex[v and 0x0F]
+    }
+    return String(chars)
+  }
+
+  // ---- NIP-44 encryption (v2: ECDH + HKDF + ChaCha20 + HMAC-SHA256) ----
+
+  private fun nip44ConversationKey(clientSecret: String, theirPubkey: String): ByteArray {
+    val sk = hexToBytes(clientSecret)
+    val pk = hexToBytes("02$theirPubkey")
+    if (sk.size != 32 || pk.size != 33) return ByteArray(0)
+    val shared = try { SECP.pubKeyTweakMul(pk, sk) } catch (_: Exception) { return ByteArray(0) }
+    if (shared.size != 65) return ByteArray(0)
+    val sharedX = Arrays.copyOfRange(shared, 1, 33)
+    return hkdfExtract(sharedX, "nip44-v2".toByteArray(StandardCharsets.UTF_8))
+  }
+
+  private fun hkdfExtract(ikm: ByteArray, salt: ByteArray): ByteArray {
+    val mac = javax.crypto.Mac.getInstance("HmacSHA256")
+    mac.init(javax.crypto.spec.SecretKeySpec(salt, "HmacSHA256"))
+    return mac.doFinal(ikm)
+  }
+
+  private fun hkdfExpand(prk: ByteArray, info: ByteArray, length: Int): ByteArray {
+    val mac = javax.crypto.Mac.getInstance("HmacSHA256")
+    val result = ByteArray(length)
+    var prev = ByteArray(0)
+    var offset = 0
+    var counter = 1
+    while (offset < length) {
+      mac.init(javax.crypto.spec.SecretKeySpec(prk, "HmacSHA256"))
+      mac.update(prev)
+      mac.update(info)
+      mac.update(counter.toByte())
+      prev = mac.doFinal()
+      val toCopy = minOf(prev.size, length - offset)
+      System.arraycopy(prev, 0, result, offset, toCopy)
+      offset += toCopy
+      counter++
+    }
+    return result
+  }
+
+  private fun hmacSha256(key: ByteArray, vararg parts: ByteArray): ByteArray {
+    val mac = javax.crypto.Mac.getInstance("HmacSHA256")
+    mac.init(javax.crypto.spec.SecretKeySpec(key, "HmacSHA256"))
+    for (part in parts) mac.update(part)
+    return mac.doFinal()
+  }
+
+  // ChaCha20 block function per RFC 8439
+  private fun chacha20Block(key: ByteArray, counter: Int, nonce: ByteArray): ByteArray {
+    fun Int.rotl(n: Int) = (this shl n) or (this ushr (32 - n))
+    val state = IntArray(16)
+    state[0] = 0x61707865; state[1] = 0x3320646e; state[2] = 0x79622d32; state[3] = 0x6b206574
+    for (i in 0..7) state[4 + i] = (key[i*4].toInt() and 0xFF) or
+      ((key[i*4+1].toInt() and 0xFF) shl 8) or
+      ((key[i*4+2].toInt() and 0xFF) shl 16) or
+      ((key[i*4+3].toInt() and 0xFF) shl 24)
+    state[12] = counter
+    for (i in 0..2) state[13 + i] = (nonce[i*4].toInt() and 0xFF) or
+      ((nonce[i*4+1].toInt() and 0xFF) shl 8) or
+      ((nonce[i*4+2].toInt() and 0xFF) shl 16) or
+      ((nonce[i*4+3].toInt() and 0xFF) shl 24)
+    val working = state.copyOf()
+    repeat(10) {
+      fun quarterRound(a: Int, b: Int, c: Int, d: Int) {
+        working[a] += working[b]; working[d] = (working[d] xor working[a]).rotl(16)
+        working[c] += working[d]; working[b] = (working[b] xor working[c]).rotl(12)
+        working[a] += working[b]; working[d] = (working[d] xor working[a]).rotl(8)
+        working[c] += working[d]; working[b] = (working[b] xor working[c]).rotl(7)
+      }
+      quarterRound(0,4,8,12); quarterRound(1,5,9,13); quarterRound(2,6,10,14); quarterRound(3,7,11,15)
+      quarterRound(0,5,10,15); quarterRound(1,6,11,12); quarterRound(2,7,8,13); quarterRound(3,4,9,14)
+    }
+    val out = ByteArray(64)
+    for (i in 0..15) {
+      val v = working[i] + state[i]
+      out[i*4]   = v.toByte()
+      out[i*4+1] = (v ushr 8).toByte()
+      out[i*4+2] = (v ushr 16).toByte()
+      out[i*4+3] = (v ushr 24).toByte()
+    }
+    return out
+  }
+
+  private fun chacha20(key: ByteArray, nonce: ByteArray, data: ByteArray): ByteArray {
+    val out = ByteArray(data.size)
+    var counter = 0
+    var offset = 0
+    while (offset < data.size) {
+      val block = chacha20Block(key, counter, nonce)
+      val len = minOf(64, data.size - offset)
+      for (i in 0 until len) out[offset + i] = (data[offset + i].toInt() xor block[i].toInt()).toByte()
+      offset += len
+      counter++
+    }
+    return out
+  }
+
+  private fun nip44CalcPaddedLen(len: Int): Int {
+    if (len <= 32) return 32
+    val nextPower = 1 shl (Math.floor(Math.log((len - 1).toDouble()) / Math.log(2.0)).toInt() + 1)
+    val chunk = if (nextPower <= 256) 32 else nextPower / 8
+    return chunk * ((len - 1) / chunk + 1)
+  }
+
+  private fun nip44Pad(plaintext: String): ByteArray {
+    val unpadded = plaintext.toByteArray(StandardCharsets.UTF_8)
+    val len = unpadded.size
+    val padded = ByteArray(2 + nip44CalcPaddedLen(len))
+    padded[0] = (len ushr 8).toByte()
+    padded[1] = len.toByte()
+    System.arraycopy(unpadded, 0, padded, 2, len)
+    return padded
+  }
+
+  private fun nip44Unpad(padded: ByteArray): String {
+    val len = ((padded[0].toInt() and 0xFF) shl 8) or (padded[1].toInt() and 0xFF)
+    if (len == 0 || len > padded.size - 2) return ""
+    return String(padded, 2, len, StandardCharsets.UTF_8)
+  }
+
+  private fun encryptNip44(plaintext: String, conversationKey: ByteArray): String {
+    return try {
+      val nonce = ByteArray(32).also { SecureRandom().nextBytes(it) }
+      val keys = hkdfExpand(conversationKey, nonce, 76)
+      val chachaKey = keys.sliceArray(0 until 32)
+      val chachaNonce = keys.sliceArray(32 until 44)
+      val hmacKey = keys.sliceArray(44 until 76)
+      val padded = nip44Pad(plaintext)
+      val ciphertext = chacha20(chachaKey, chachaNonce, padded)
+      val mac = hmacSha256(hmacKey, nonce, ciphertext)
+      val payload = ByteArray(1 + 32 + ciphertext.size + 32)
+      payload[0] = 2
+      System.arraycopy(nonce, 0, payload, 1, 32)
+      System.arraycopy(ciphertext, 0, payload, 33, ciphertext.size)
+      System.arraycopy(mac, 0, payload, 33 + ciphertext.size, 32)
+      Base64.encodeToString(payload, Base64.NO_WRAP)
+    } catch (_: Exception) {
+      ""
+    }
+  }
+
+  private fun decryptNip44(payload: String, conversationKey: ByteArray): String {
+    return try {
+      if (payload.isEmpty() || payload[0] == '#') return ""
+      val data = Base64.decode(payload, Base64.NO_WRAP)
+      if (data.size < 99 || data[0] != 2.toByte()) return ""
+      val nonce = data.sliceArray(1 until 33)
+      val ciphertext = data.sliceArray(33 until data.size - 32)
+      val mac = data.sliceArray(data.size - 32 until data.size)
+      val keys = hkdfExpand(conversationKey, nonce, 76)
+      val chachaKey = keys.sliceArray(0 until 32)
+      val chachaNonce = keys.sliceArray(32 until 44)
+      val hmacKey = keys.sliceArray(44 until 76)
+      val expectedMac = hmacSha256(hmacKey, nonce, ciphertext)
+      if (!expectedMac.contentEquals(mac)) return ""
+      val padded = chacha20(chachaKey, chachaNonce, ciphertext)
+      nip44Unpad(padded)
+    } catch (_: Exception) {
+      ""
+    }
+  }
+
+  // ---- Signing ----
+
+  private fun signWithNip01Secret(secretHex: String, eventJson: String, expectedPubkey: String): String {
+    return try {
+      val secret = hexToBytes(secretHex)
+      if (secret.size != 32) return ""
+
+      val event = JSONObject(eventJson)
+      var pubkey = event.optString("pubkey", expectedPubkey)
+      if (pubkey.isEmpty()) pubkey = deriveXOnlyPubkey(secretHex)
+      if (pubkey.isEmpty()) return ""
+
+      event.put("pubkey", pubkey)
+      val id = computeEventId(event)
+      if (id.isEmpty()) return ""
+
+      val sig = schnorrSign(secretHex, id)
+      if (sig.isEmpty()) return ""
+
+      event.put("id", id)
+      event.put("sig", sig)
+      event.toString()
+    } catch (_: Exception) {
+      ""
+    }
+  }
+
+  private fun signWithNip55ContentResolver(packageName: String, eventJson: String, pubkey: String): String {
+    val uri = Uri.parse("content://$packageName.SIGN_EVENT")
+    var cursor: Cursor? = null
+    return try {
+      cursor = applicationContext.contentResolver.query(uri, arrayOf(eventJson, "", pubkey), "1", null, null)
+      if (cursor == null || !cursor.moveToFirst()) return ""
+      val rejIdx = cursor.getColumnIndex("rejected")
+      if (rejIdx >= 0) {
+        val v = cursor.getString(rejIdx)
+        if (v == "1" || v.equals("true", ignoreCase = true)) return REJECTED
+      }
+      val eventIdx = cursor.getColumnIndex("event")
+      if (eventIdx >= 0) cursor.getString(eventIdx) ?: "" else ""
+    } catch (_: Exception) {
+      ""
+    } finally {
+      cursor?.close()
+    }
+  }
+
+  // ---- Data types ----
+
+  private data class SessionInfo(
+    val method: String,
+    val pubkey: String,
+    val session: JSONObject,
+  )
+
+  private data class Subscription(
+    val relay: String,
+    val key: String,
+    val filters: JSONArray,
+    val ignore: JSONArray?,
+  )
+
+  private class RelayResult {
+    val events = mutableListOf<JSONObject>()
+    var lastCursor = 0L
+  }
+
+  // ---- Relay listener ----
+
+  private inner class RelayListener(
+    private val sub: Subscription,
+    private val since: Long,
+    private val sessionInfo: SessionInfo,
+    private val result: RelayResult,
+    private val latch: CountDownLatch,
+    private val pool: SocketPool,
+  ) : WebSocketListener() {
+    private val subId = UUID.randomUUID().toString().replace("-", "")
+    private var done = false
+    private var authed = false
+    private var authEventId = ""
+    private var nip46InFlight = false
+    private var pendingDone = false
+
+    override fun onOpen(webSocket: WebSocket, response: Response) {
+      sendReq(webSocket)
+    }
+
+    private fun sendReq(webSocket: WebSocket) {
+      val req = JSONArray()
+      req.put("REQ")
+      req.put(subId)
+
+      for (i in 0 until sub.filters.length()) {
+        val filter = sub.filters.optJSONObject(i) ?: continue
+        val shaped = JSONObject(filter.toString())
+        if (since > 0) shaped.put("since", since + 1)
+        shaped.put("limit", 1)
+        req.put(shaped)
+      }
+
+      if (req.length() <= 2) { finish(); return }
+
+      send(webSocket, req.toString())
+    }
+
+    override fun onMessage(webSocket: WebSocket, text: String) {
+      try {
+        val message = JSONArray(text)
+        Log.d(TAG, "Received message from ${sub.relay}: $text")
+        when (message.optString(0, "")) {
+          "EVENT" -> {
+            val event = message.optJSONObject(2) ?: return
+            if (!matchesAnyFilter(sub.filters, event)) return
+            if (isIgnored(event)) return
+            result.events.add(event)
+            val createdAt = event.optLong("created_at", 0L)
+            if (createdAt > result.lastCursor) result.lastCursor = createdAt
+          }
+          "AUTH" -> {
+            // Only auth once per connection
+            if (!authed) {
+              authed = true
+              tryAuth(webSocket, message.optString(1, ""))
+            }
+          }
+          "OK" -> {
+            val okId = message.optString(1, "")
+            val accepted = message.optBoolean(2, false)
+            if (accepted && okId == authEventId) sendReq(webSocket)
+          }
+          "EOSE" -> {
+            send(webSocket, JSONArray().apply { put("CLOSE"); put(subId) }.toString())
+            finish()
+          }
+        }
+      } catch (_: Exception) {
+        finish()
+      }
+    }
+
+    override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) = finish()
+    override fun onClosed(webSocket: WebSocket, code: Int, reason: String) = finish()
+
+    private fun finish() {
+      if (done) return
+      if (nip46InFlight) { pendingDone = true; return }
+      done = true
+      latch.countDown()
+    }
+
+    private fun isIgnored(event: JSONObject): Boolean {
+      val ignore = sub.ignore ?: return false
+      for (i in 0 until ignore.length()) {
+        val filter = ignore.optJSONObject(i) ?: continue
+        if (matchesFilter(filter, event)) return true
+      }
+      return false
+    }
+
+    private fun matchesAnyFilter(filters: JSONArray, event: JSONObject): Boolean {
+      for (i in 0 until filters.length()) {
+        val filter = filters.optJSONObject(i) ?: continue
+        if (matchesFilter(filter, event)) return true
+      }
+      return false
+    }
+
+    // ---- NIP-42 auth ----
+
+    private fun tryAuth(webSocket: WebSocket, challenge: String) {
+      if (challenge.isEmpty()) return
+      when (sessionInfo.method) {
+        "nip01" -> tryNip01Auth(webSocket, challenge)
+        "nip55" -> tryNip55Auth(webSocket, challenge)
+        "nip46" -> tryNip46Auth(webSocket, challenge)
+        // Pomade background auth is not supported: properly delegating to the Pomade signer
+        // from a background worker is complex, usage is rare, and relays that require auth
+        // may still be readable without it.
+      }
+    }
+
+    private fun buildAuthEvent(challenge: String): JSONObject {
+      return JSONObject().apply {
+        put("kind", KIND_RELAY_AUTH)
+        put("pubkey", sessionInfo.pubkey)
+        put("created_at", System.currentTimeMillis() / 1000L)
+        put("content", "")
+        put("id", "")
+        put("sig", "")
+        put("tags", JSONArray().apply {
+          put(JSONArray().apply { put("relay"); put(sub.relay) })
+          put(JSONArray().apply { put("challenge"); put(challenge) })
+        })
+      }
+    }
+
+    private fun sendAuthMessage(webSocket: WebSocket, signedEventJson: String): Boolean {
+      if (signedEventJson.isEmpty() || signedEventJson == REJECTED) return false
+      return try {
+        val event = JSONObject(signedEventJson)
+        authEventId = event.optString("id", "")
+        send(webSocket, JSONArray().apply { put("AUTH"); put(event) }.toString())
+      } catch (_: Exception) {
+        false
+      }
+    }
+
+    private fun send(webSocket: WebSocket, message: String): Boolean {
+      Log.d(TAG, "Sending message to ${webSocket.request().url}: $message")
+      return webSocket.send(message)
+    }
+
+    private fun tryNip01Auth(webSocket: WebSocket, challenge: String): Boolean {
+      val secret = sessionInfo.session.optString("secret", "")
+      if (secret.isEmpty()) return false
+      val signed = signWithNip01Secret(secret, buildAuthEvent(challenge).toString(), sessionInfo.pubkey)
+      return sendAuthMessage(webSocket, signed)
+    }
+
+    private fun tryNip55Auth(webSocket: WebSocket, challenge: String): Boolean {
+      val signerPackage = sessionInfo.session.optString("signer", "")
+      if (signerPackage.isEmpty()) return false
+      val signed = signWithNip55ContentResolver(signerPackage, buildAuthEvent(challenge).toString(), sessionInfo.pubkey)
+      return sendAuthMessage(webSocket, signed)
+    }
+
+    private fun tryNip46Auth(webSocket: WebSocket, challenge: String): Boolean {
+      val handler = sessionInfo.session.optJSONObject("handler") ?: return false
+      val clientSecret = sessionInfo.session.optString("secret", "")
+      val signerPubkey = handler.optString("pubkey", "")
+      val relays = handler.optJSONArray("relays")
+
+      if (clientSecret.isEmpty() || signerPubkey.isEmpty() || relays == null || relays.length() == 0) return false
+
+      val clientPubkey = deriveXOnlyPubkey(clientSecret)
+      if (clientPubkey.isEmpty()) return false
+
+      val authEventJson = buildAuthEvent(challenge).toString()
+
+      nip46InFlight = true
+      var success = false
+      try {
+        for (i in 0 until relays.length()) {
+          val signerRelay = relays.optString(i, "").trim()
+          if (!signerRelay.startsWith("wss://") && !signerRelay.startsWith("ws://")) continue
+          if (tryNip46ViaRelay(webSocket, signerRelay, clientSecret, clientPubkey, signerPubkey, authEventJson)) { success = true; break }
+        }
+      } finally {
+        nip46InFlight = false
+        if (pendingDone) finish()
+      }
+
+      return success
+    }
+
+    private fun tryNip46ViaRelay(
+      relaySocket: WebSocket,
+      signerRelay: String,
+      clientSecret: String,
+      clientPubkey: String,
+      signerPubkey: String,
+      authEventJson: String,
+    ): Boolean {
+      val localLatch = CountDownLatch(1)
+      val signedEvent = StringBuilder()
+      val requestId = UUID.randomUUID().toString().replace("-", "")
+
+      val signerSocket = pool.open(signerRelay, object : WebSocketListener() {
+        private var done = false
+
+        override fun onOpen(webSocket: WebSocket, response: Response) {
+          try {
+            val rpcEnvelope = JSONObject().apply {
+              put("kind", KIND_NIP46_RPC)
+              put("pubkey", clientPubkey)
+              put("created_at", System.currentTimeMillis() / 1000L)
+              put("content", encryptNip44(
+                JSONObject().apply {
+                  put("id", requestId)
+                  put("method", "sign_event")
+                  put("params", JSONArray().apply { put(authEventJson) })
+                }.toString(),
+                nip44ConversationKey(clientSecret, signerPubkey),
+              ))
+              put("id", "")
+              put("sig", "")
+              put("tags", JSONArray().apply { put(JSONArray().apply { put("p"); put(signerPubkey) }) })
+            }
+
+            val signedEnvelope = signWithNip01Secret(clientSecret, rpcEnvelope.toString(), clientPubkey)
+            if (signedEnvelope.isEmpty()) { finish(); return }
+
+            val sentAt = System.currentTimeMillis() / 1000L
+            send(webSocket, JSONArray().apply { put("EVENT"); put(JSONObject(signedEnvelope)) }.toString())
+            send(webSocket, JSONArray().apply {
+              put("REQ")
+              put(requestId)
+              put(JSONObject().apply {
+                put("#p", JSONArray().apply { put(clientPubkey) })
+                put("kinds", JSONArray().apply { put(KIND_NIP46_RPC) })
+                put("since", sentAt)
+                put("limit", 10)
+              })
+            }.toString())
+          } catch (_: Exception) {
+            finish()
+          }
+        }
+
+        override fun onMessage(webSocket: WebSocket, text: String) {
+          try {
+            val message = JSONArray(text)
+            val msgType = message.optString(0, "")
+            Log.d(TAG, "NIP-46 signer message: $msgType from ${webSocket.request().url}")
+            if (msgType != "EVENT") return
+            val event = message.optJSONObject(2) ?: return
+
+            val tags = event.optJSONArray("tags")
+            var hasP = false
+            if (tags != null) {
+              for (i in 0 until tags.length()) {
+                val tag = tags.optJSONArray(i) ?: continue
+                if (tag.optString(0, "") == "p" && tag.optString(1, "") == clientPubkey) { hasP = true; break }
+              }
+            }
+            if (!hasP) { Log.d(TAG, "NIP-46 event missing p tag for client"); return }
+
+            val decryptedContent = decryptNip44(event.optString("content", ""), nip44ConversationKey(clientSecret, signerPubkey))
+            Log.d(TAG, "NIP-46 decrypted response: $decryptedContent")
+            if (decryptedContent.isEmpty()) return
+            val payload = JSONObject(decryptedContent)
+            if (requestId == payload.optString("id", "")) {
+              val result = payload.optString("result", "")
+              if (result.isNotEmpty()) {
+                signedEvent.setLength(0)
+                signedEvent.append(result)
+                finish()
+              }
+            }
+          } catch (e: Exception) {
+            Log.e(TAG, "NIP-46 signer message error", e)
+          }
+        }
+
+        override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) = finish()
+        override fun onClosed(webSocket: WebSocket, code: Int, reason: String) = finish()
+
+        private fun finish() {
+          if (!done) { done = true; localLatch.countDown() }
+        }
+      })
+
+      try {
+        localLatch.await(5, TimeUnit.SECONDS)
+      } catch (_: InterruptedException) {
+        return false
+      }
+
+      if (signedEvent.isEmpty()) return false
+
+      val authEvent = JSONObject(signedEvent.toString())
+      authEventId = authEvent.optString("id", "")
+      val authMessage = JSONArray().apply { put("AUTH"); put(authEvent) }.toString()
+      Log.d(TAG, "NIP-46 sending AUTH to relay ${relaySocket.request().url}: $authMessage")
+      return try {
+        relaySocket.send(authMessage)
+      } catch (e: Exception) {
+        Log.e(TAG, "NIP-46 failed to send AUTH", e)
+        false
+      }
+    }
+  }
+}

android/build.gradle

@@ -1,6 +1,7 @@
 // Top-level build file where you can add configuration options common to all sub-projects/modules.
 
 buildscript {
+    ext.kotlin_version = '2.2.20'
     
     repositories {
         google()
@@ -9,6 +10,7 @@ buildscript {
     dependencies {
         classpath 'com.android.tools.build:gradle:8.13.2'
         classpath 'com.google.gms:google-services:4.4.4'
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files