Add MqttManager for broker connection lifecycle (CATROID-1671)

catroid/build.gradle

@@ -157,6 +157,7 @@ android {
         buildConfigField "boolean", "FEATURE_NFC_ENABLED", "true"
         buildConfigField "boolean", "FEATURE_POCKETMUSIC_ENABLED", "true"
         buildConfigField "boolean", "FEATURE_RASPI_ENABLED", "true"
+        buildConfigField "boolean", "FEATURE_MQTT_ENABLED", "true"
         buildConfigField "boolean", "FEATURE_SCRATCH_CONVERTER_ENABLED", "true"
         buildConfigField "boolean", "FEATURE_USER_REPORTERS_ENABLED", "true"
         buildConfigField "boolean", "FEATURE_MULTIPLAYER_VARIABLES_ENABLED", "true"
@@ -423,6 +424,9 @@ dependencies {
     implementation 'com.google.guava:guava:28.2-android'
     implementation 'com.google.code.gson:gson:2.8.7'
 
+    // MQTT
+    implementation 'org.eclipse.paho:org.eclipse.paho.client.mqttv3:1.2.5'
+
     implementation 'com.koushikdutta.async:androidasync:2.2.1'
     implementation 'com.squareup.picasso:picasso:2.71828'
     implementation 'ar.com.hjg:pngj:2.1.0'

catroid/src/androidTest/java/org/catrobat/catroid/uiespresso/ui/activity/SettingsFragmentTest.java

@@ -85,6 +85,7 @@
 import static org.catrobat.catroid.ui.settingsfragments.SettingsFragment.SETTINGS_SHOW_PHIRO_BRICKS_CHECKBOX_PREFERENCE;
 import static org.catrobat.catroid.ui.settingsfragments.SettingsFragment.SETTINGS_SHOW_PLOT_BRICKS;
 import static org.catrobat.catroid.ui.settingsfragments.SettingsFragment.SETTINGS_SHOW_RASPI_BRICKS;
+import static org.catrobat.catroid.ui.settingsfragments.SettingsFragment.SETTINGS_SHOW_MQTT_BRICKS;
 import static org.hamcrest.Matchers.hasToString;
 import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.core.AllOf.allOf;
@@ -123,7 +124,7 @@ public class SettingsFragmentTest {
 			SETTINGS_CAST_GLOBALLY_ENABLED, SETTINGS_SHOW_AI_SPEECH_RECOGNITION_SENSORS,
 			SETTINGS_SHOW_AI_SPEECH_SYNTHETIZATION_SENSORS,
 			SETTINGS_SHOW_AI_FACE_DETECTION_SENSORS, SETTINGS_SHOW_AI_POSE_DETECTION_SENSORS,
-			SETTINGS_SHOW_AI_TEXT_RECOGNITION_SENSORS));
+			SETTINGS_SHOW_AI_TEXT_RECOGNITION_SENSORS, SETTINGS_SHOW_MQTT_BRICKS));
 	private Map<String, Boolean> initialSettings = new HashMap<>();
 	private Matcher<Intent> expectedBrowserIntent;
 
@@ -258,6 +259,15 @@ public void rasPiSettingsTest() {
 		checkPreference(R.string.preference_title_enable_raspi_bricks, SETTINGS_SHOW_RASPI_BRICKS);
 	}
 
+	@Category({Cat.AppUi.class, Level.Smoke.class, Cat.Gadgets.class})
+	@Test
+	public void mqttSettingsTest() {
+		onData(PreferenceMatchers.withTitle(R.string.preference_title_enable_mqtt_bricks))
+				.perform(click());
+
+		checkPreference(R.string.preference_title_enable_mqtt_bricks, SETTINGS_SHOW_MQTT_BRICKS);
+	}
+
 	@Category({Cat.AppUi.class, Level.Smoke.class, Cat.Gadgets.class})
 	@Test
 	public void aiSettingsTest() {

catroid/src/main/AndroidManifest.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <!--
   ~ Catroid: An on-device visual programming system for Android devices
-  ~ Copyright (C) 2010-2025 The Catrobat Team
+  ~ Copyright (C) 2010-2026 The Catrobat Team
   ~ (<http://developer.catrobat.org/credits>)
   ~
   ~ This program is free software: you can redistribute it and/or modify

catroid/src/main/java/org/catrobat/catroid/devices/mqtt/MqttClientInterface.kt

@@ -0,0 +1,35 @@
+/*
+ * Catroid: An on-device visual programming system for Android devices
+ * Copyright (C) 2010-2026 The Catrobat Team
+ * (<http://developer.catrobat.org/credits>)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * An additional term exception under section 7 of the GNU Affero
+ * General Public License, version 3, is available at
+ * http://developer.catrobat.org/license_additional_term
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.catrobat.catroid.devices.mqtt
+
+import org.eclipse.paho.client.mqttv3.MqttCallback
+import org.eclipse.paho.client.mqttv3.MqttConnectOptions
+
+interface MqttClientInterface {
+    val isConnected: Boolean
+    fun connect(options: MqttConnectOptions)
+    fun disconnect()
+    fun close()
+    fun setCallback(callback: MqttCallback)
+}

catroid/src/main/java/org/catrobat/catroid/devices/mqtt/MqttConnectionConfig.kt

@@ -0,0 +1,47 @@
+/*
+ * Catroid: An on-device visual programming system for Android devices
+ * Copyright (C) 2010-2026 The Catrobat Team
+ * (<http://developer.catrobat.org/credits>)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * An additional term exception under section 7 of the GNU Affero
+ * General Public License, version 3, is available at
+ * http://developer.catrobat.org/license_additional_term
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.catrobat.catroid.devices.mqtt
+
+import android.content.Context
+import org.catrobat.catroid.ui.settingsfragments.SettingsFragment
+
+data class MqttConnectionConfig(
+    val host: String,
+    val port: Int,
+    val clientId: String,
+    val username: String,
+    val password: String,
+    val useTls: Boolean
+) {
+    companion object {
+        fun fromContext(context: Context) = MqttConnectionConfig(
+            host = SettingsFragment.getMqttHost(context),
+            port = SettingsFragment.getMqttPort(context),
+            clientId = SettingsFragment.getMqttClientId(context),
+            username = SettingsFragment.getMqttUsername(context),
+            password = SettingsFragment.getMqttPassword(context),
+            useTls = SettingsFragment.isMqttTlsEnabled(context)
+        )
+    }
+}

catroid/src/main/java/org/catrobat/catroid/devices/mqtt/MqttManager.kt

@@ -0,0 +1,115 @@
+/*
+ * Catroid: An on-device visual programming system for Android devices
+ * Copyright (C) 2010-2026 The Catrobat Team
+ * (<http://developer.catrobat.org/credits>)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * An additional term exception under section 7 of the GNU Affero
+ * General Public License, version 3, is available at
+ * http://developer.catrobat.org/license_additional_term
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.catrobat.catroid.devices.mqtt
+
+import android.content.Context
+import android.util.Log
+import org.eclipse.paho.client.mqttv3.IMqttDeliveryToken
+import org.eclipse.paho.client.mqttv3.MqttCallback
+import org.eclipse.paho.client.mqttv3.MqttClient
+import org.eclipse.paho.client.mqttv3.MqttConnectOptions
+import org.eclipse.paho.client.mqttv3.MqttException
+import org.eclipse.paho.client.mqttv3.MqttMessage
+
+class MqttManager(private var mqttClient: MqttClientInterface? = null) {
+
+    val isConnected: Boolean
+        get() = mqttClient?.isConnected == true
+
+    companion object {
+        private val TAG = MqttManager::class.simpleName
+        private const val TCP_SCHEME = "tcp"
+        private const val SSL_SCHEME = "ssl"
+        private const val CONNECTION_TIMEOUT = 5
+
+        @JvmStatic
+        val instance: MqttManager by lazy { MqttManager() }
+    }
+
+    fun connectFromContext(context: Context) = connect(MqttConnectionConfig.fromContext(context))
+
+    fun connect(config: MqttConnectionConfig): Boolean {
+        if (isConnected) return true
+        if (config.host.isBlank()) {
+            Log.e(TAG, "Cannot connect: host is blank")
+            return false
+        }
+        return try {
+            val brokerUrl = buildServerUri(config.host, config.port, config.useTls)
+            val resolvedClientId = config.clientId.ifEmpty { MqttClient.generateClientId() }
+            val client = mqttClient ?: PahoMqttClient(brokerUrl, resolvedClientId).also { mqttClient = it }
+            client.setCallback(callback)
+            client.connect(buildConnectOptions(config.username, config.password))
+            val connected = client.isConnected
+            Log.d(TAG, "Connect result for clientId=$resolvedClientId at $brokerUrl: connected=$connected")
+            connected
+        } catch (e: MqttException) {
+            Log.e(TAG, "Failed to connect to ${config.host}:${config.port}", e)
+            try {
+                mqttClient?.close()
+            } catch (closeEx: MqttException) {
+                Log.e(TAG, "Failed to close client after connect error", closeEx)
+            }
+            mqttClient = null
+            false
+        }
+    }
+
+    fun disconnect() {
+        if (!isConnected) return
+        try {
+            mqttClient?.disconnect()
+            mqttClient?.close()
+            Log.d(TAG, "Disconnected and closed client")
+        } catch (e: MqttException) {
+            Log.e(TAG, "Error during disconnect", e)
+        } finally {
+            mqttClient = null
+        }
+    }
+
+    internal fun buildServerUri(host: String, port: Int, useTls: Boolean): String {
+        val scheme = if (useTls) SSL_SCHEME else TCP_SCHEME
+        return "$scheme://$host:$port"
+    }
+
+    internal fun buildConnectOptions(username: String, password: String) = MqttConnectOptions().apply {
+        isCleanSession = true
+        connectionTimeout = CONNECTION_TIMEOUT
+        if (username.isNotBlank()) {
+            this.userName = username
+            this.password = password.toCharArray()
+        }
+    }
+
+    private val callback = object : MqttCallback {
+        override fun connectionLost(cause: Throwable?) {
+            Log.e(TAG, "Connection lost: ${cause?.message}")
+        }
+        // Message handling is implemented in a later ticket.
+        override fun messageArrived(topic: String, message: MqttMessage) = Unit
+        // Delivery tokens are not used until publish is implemented in a later ticket.
+        override fun deliveryComplete(token: IMqttDeliveryToken?) = Unit
+    }
+}

catroid/src/main/java/org/catrobat/catroid/devices/mqtt/PahoMqttClient.kt

@@ -0,0 +1,38 @@
+/*
+ * Catroid: An on-device visual programming system for Android devices
+ * Copyright (C) 2010-2026 The Catrobat Team
+ * (<http://developer.catrobat.org/credits>)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * An additional term exception under section 7 of the GNU Affero
+ * General Public License, version 3, is available at
+ * http://developer.catrobat.org/license_additional_term
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.catrobat.catroid.devices.mqtt
+
+import org.eclipse.paho.client.mqttv3.MqttCallback
+import org.eclipse.paho.client.mqttv3.MqttClient
+import org.eclipse.paho.client.mqttv3.MqttConnectOptions
+import org.eclipse.paho.client.mqttv3.persist.MemoryPersistence
+
+class PahoMqttClient(brokerUrl: String, clientId: String) : MqttClientInterface {
+    private val client = MqttClient(brokerUrl, clientId, MemoryPersistence())
+    override val isConnected get() = client.isConnected
+    override fun connect(options: MqttConnectOptions) = client.connect(options)
+    override fun disconnect() = client.disconnect()
+    override fun close() = client.close()
+    override fun setCallback(callback: MqttCallback) = client.setCallback(callback)
+}