init. dbus registration works

.gitignore

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+# Ignore Gradle project-specific cache directory
+.gradle
+gradle
+gradlew*
+
+# Ignore Gradle build output directory
+build

build.gradle.kts

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+plugins {
+    id("org.jetbrains.kotlin.jvm") version "1.9.0"
+    application
+}
+
+dependencies {
+    testImplementation("org.jetbrains.kotlin:kotlin-test-junit5")
+    testImplementation("org.junit.jupiter:junit-jupiter-engine:5.9.3")
+    implementation("com.github.hypfvieh:dbus-java-core:4.3.1")
+    runtimeOnly("com.github.hypfvieh:dbus-java-transport-native-unixsocket:4.3.1")
+    implementation("org.slf4j:slf4j-api:2.0.9")
+    runtimeOnly("org.slf4j:slf4j-simple:2.0.9")
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion.set(JavaLanguageVersion.of(17))
+    }
+}
+
+application {
+    mainClass.set("net.eksb.obsdc.Main")
+}
+
+tasks.named<Test>("test") {
+    useJUnitPlatform()
+}

settings.gradle.kts

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+rootProject.name = "obsdc"

src/main/kotlin/net/eksb/obsdc/Main.kt

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+package net.eksb.obsdc
+
+import org.freedesktop.dbus.annotations.DBusInterfaceName
+import org.freedesktop.dbus.connections.impl.DBusConnection
+import org.freedesktop.dbus.connections.impl.DBusConnectionBuilder
+import org.freedesktop.dbus.interfaces.DBusInterface
+import org.freedesktop.dbus.interfaces.DBusSigHandler
+import org.freedesktop.dbus.messages.DBusSignal
+import org.slf4j.LoggerFactory
+
+object Main {
+    @JvmStatic
+    fun main(args:Array<String>) {
+
+        DBusConnectionBuilder.forSessionBus().build().use { dbus ->
+
+            // These lines are not necessary to handle signals, but are necessary to register methods.
+            dbus.requestBusName("net.eksb.obsdc")
+            dbus.exportObject("/", ObsdcDBusInterfaceImpl())
+
+            dbus.addSigHandler<ObsdcDBusInterface.Signal> { signal -> log.info("signal: ${signal.message}") }
+            while (true) {
+                try {
+                    Thread.sleep(60_000)
+                } catch (e:InterruptedException) {
+                    log.info("interrupted")
+                    break
+                }
+            }
+        }
+        log.info("done")
+    }
+
+}
+
+inline fun <reified T:DBusSignal> DBusConnection.addSigHandler(handler:DBusSigHandler<T>) {
+    addSigHandler(T::class.java, handler)
+}
+
+private val log = LoggerFactory.getLogger(Main::class.java)
+
+@DBusInterfaceName("net.eksb.Obsdc")
+interface ObsdcDBusInterface: DBusInterface {
+    fun echo(message:String): String
+    class Signal(path:String, val message:String): DBusSignal(path, message)
+}
+class ObsdcDBusInterfaceImpl: ObsdcDBusInterface {
+    override fun echo(message: String):String {
+        log.info("echo: ${message}")
+        return message
+    }
+    override fun getObjectPath(): String = "/"
+}
+
+/*
+Monitor:
+`dbus-monitor`
+
+See what is registered:
+`qdbus net.eksb.obsdc /`
+
+Send signal:
+`dbus-send --session --type=signal --dest=net.eksb.obsdc / net.eksb.Obsdc.Signal string:a`
+
+Call method:
+`dbus-send --session --type=method_call --print-reply --dest=net.eksb.obsdc / net.eksb.Obsdc.echo string:b`
+`qdbus net.eksb.obsdc / net.eksb.Obsdc.echo hello`
+ */