Re-implement Discovery

- Convert Discovery class to object
- Simplify cross-thread handling with dedicated executor
- Fixed simultaneous resolution of multiple services
- Acquire multicast lock to improve reliability

app/src/androidTest/java/com/gaurav/avnc/viewmodel/service/DiscoveryTest.kt

@@ -0,0 +1,112 @@
+/*
+ * Copyright (c) 2024  Gaurav Ujjwal.
+ *
+ * SPDX-License-Identifier:  GPL-3.0-or-later
+ *
+ * See COPYING.txt for more details.
+ */
+
+package com.gaurav.avnc.viewmodel.service
+
+import android.net.nsd.NsdManager
+import android.net.nsd.NsdServiceInfo
+import android.util.Log
+import androidx.core.content.ContextCompat
+import com.gaurav.avnc.pollingAssert
+import com.gaurav.avnc.runOnMainSync
+import com.gaurav.avnc.targetContext
+import org.junit.After
+import org.junit.Assert.assertTrue
+import org.junit.Assume
+import org.junit.Before
+import org.junit.Test
+
+class DiscoveryTest {
+    private val TAG = "DiscoveryTest"
+    private var nsdManager: NsdManager? = null
+    private var listeners = mutableListOf<NsdManager.RegistrationListener>()
+
+    /**
+     * If advertisement fails, this method will cause the calling test to be skipped.
+     * Advertisement can fail if there is no suitable network on the device
+     * (e.g. in Airplane mode on newer Android versions).
+     */
+    private fun advertiseService(advertisedName: String, advertisedPort: Int) {
+        var registeredService = false
+        val listener = object : NsdManager.RegistrationListener {
+            override fun onRegistrationFailed(serviceInfo: NsdServiceInfo?, errorCode: Int) {
+                Log.e(TAG, "Registration failed: si: $serviceInfo, error:$errorCode")
+            }
+
+            override fun onUnregistrationFailed(serviceInfo: NsdServiceInfo?, errorCode: Int) {}
+            override fun onServiceRegistered(serviceInfo: NsdServiceInfo?) {
+                Log.d(TAG, "Registered si: $serviceInfo")
+                registeredService = true
+            }
+
+            override fun onServiceUnregistered(serviceInfo: NsdServiceInfo?) {}
+        }
+        val si = NsdServiceInfo().apply {
+            serviceType = "_rfb._tcp"
+            serviceName = advertisedName
+            port = advertisedPort
+        }
+        nsdManager?.registerService(si, NsdManager.PROTOCOL_DNS_SD, listener)
+        listeners.add(listener)
+
+        Assume.assumeTrue(runCatching { pollingAssert { assertTrue(registeredService) } }.isSuccess)
+    }
+
+    private fun assertDiscoveryState(test: Discovery.() -> Boolean) {
+        pollingAssert { runOnMainSync { assertTrue(Discovery.test()) } }
+    }
+
+    @Before
+    fun before() {
+        nsdManager = ContextCompat.getSystemService(targetContext, NsdManager::class.java)
+    }
+
+    @After
+    fun after() {
+        assertDiscoveryState { Log.d(TAG, "AfterTest: state: ${isRunning.value}, list: ${servers.value}"); true }
+        listeners.forEach { nsdManager?.unregisterService(it) }
+        listeners.clear()
+        assertDiscoveryState { servers.value!!.isEmpty() }
+        Discovery.stop()
+        assertDiscoveryState { isRunning.value == false }
+    }
+
+    @Test
+    fun startStop() {
+        assertDiscoveryState { isRunning.value == false }
+        Discovery.start(targetContext)
+        assertDiscoveryState { isRunning.value == true }
+        Discovery.stop()
+        assertDiscoveryState { isRunning.value == false }
+    }
+
+    @Test
+    fun singleService() {
+        Discovery.start(targetContext)
+        advertiseService("Server 1", 5999)
+        assertDiscoveryState {
+            isRunning.value == true && servers.value!!.size == 1 && servers.value!![0].port == 5999
+        }
+    }
+
+    @Test
+    fun multipleServices() {
+        Discovery.start(targetContext)
+
+        val count = 10
+        for (i in 1..count)
+            advertiseService("Server $i", 5900 + i)
+
+        assertDiscoveryState {
+            isRunning.value == true && servers.value!!.size == count &&
+            servers.value!!.find { it.port == 5901 } != null &&
+            servers.value!!.find { it.port == 5904 } != null &&
+            servers.value!!.find { it.port == 5908 } != null
+        }
+    }
+}

app/src/main/AndroidManifest.xml

@@ -10,6 +10,7 @@
     xmlns:tools="http://schemas.android.com/tools">
 
     <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
 
     <application
         android:name=".App"

app/src/main/java/com/gaurav/avnc/viewmodel/HomeViewModel.kt

@@ -12,7 +12,6 @@ import android.app.Application
 import androidx.lifecycle.MediatorLiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.switchMap
-import androidx.lifecycle.viewModelScope
 import com.gaurav.avnc.model.ServerProfile
 import com.gaurav.avnc.util.LiveEvent
 import com.gaurav.avnc.viewmodel.service.Discovery
@@ -33,7 +32,7 @@ class HomeViewModel(app: Application) : BaseViewModel(app) {
     /**
      * Used to find new servers.
      */
-    val discovery by lazy { Discovery(app) }
+    val discovery = Discovery
 
     /**
      * Used for starting new VNC connections.
@@ -72,7 +71,7 @@ class HomeViewModel(app: Application) : BaseViewModel(app) {
 
     fun startDiscovery() {
         autoStopped = false
-        discovery.start(viewModelScope)
+        discovery.start(app)
     }
 
     fun stopDiscovery() {