Add server & shared module and remove the serveur from the client app.

server/src/main/kotlin/com/pixelized/server/lwa/Application.kt

@@ -0,0 +1,7 @@
+package com.pixelized.server.lwa
+
+import com.pixelized.server.lwa.server.LocalServer
+
+fun main() {
+    LocalServer().create().start()
+}

server/src/main/kotlin/com/pixelized/server/lwa/extention/JsonExt.kt

@@ -0,0 +1,17 @@
+package com.pixelized.server.lwa.extention
+
+import com.pixelized.server.lwa.protocol.Message
+import io.ktor.websocket.Frame
+import io.ktor.websocket.readText
+import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.encodeToJsonElement
+
+fun Json.decodeFromFrame(frame: Frame.Text): Message {
+    val json = frame.readText()
+    return decodeFromString<Message>(json)
+}
+
+fun Json.encodeToFrame(message: Message): Frame {
+    val json = encodeToJsonElement(message)
+    return Frame.Text(text = json.toString())
+}

server/src/main/kotlin/com/pixelized/server/lwa/server/Server.kt

@@ -0,0 +1,101 @@
+package com.pixelized.server.lwa.server
+
+import com.pixelized.server.lwa.SERVER_PORT
+import com.pixelized.server.lwa.extention.decodeFromFrame
+import io.ktor.server.application.install
+import io.ktor.server.engine.EmbeddedServer
+import io.ktor.server.engine.embeddedServer
+import io.ktor.server.netty.Netty
+import io.ktor.server.netty.NettyApplicationEngine
+import io.ktor.server.routing.routing
+import io.ktor.server.websocket.DefaultWebSocketServerSession
+import io.ktor.server.websocket.WebSockets
+import io.ktor.server.websocket.pingPeriod
+import io.ktor.server.websocket.timeout
+import io.ktor.server.websocket.webSocket
+import io.ktor.websocket.Frame
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.channels.consumeEach
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import kotlinx.serialization.json.Json
+import kotlin.time.Duration.Companion.seconds
+
+// https://ktor.io/docs/server-websockets.html#handle-multiple-session
+typealias Server = EmbeddedServer<NettyApplicationEngine, NettyApplicationEngine.Configuration>
+
+class LocalServer {
+    private var server: Server? = null
+    private val scope = CoroutineScope(Dispatchers.IO)
+    private var networkJob: Job? = null
+    private val outgoingMessageBuffer = MutableSharedFlow<Frame>()
+
+    fun create(): LocalServer {
+        server = build {
+            println("Server launched")
+
+            val job = launch {
+                // send local message to the clients
+                outgoingMessageBuffer.collect { frame ->
+                    send(frame)
+                }
+            }
+            runCatching {
+                // watching for clients incoming message
+                incoming.consumeEach { frame ->
+                    if (frame is Frame.Text) {
+                        val message = Json.decodeFromFrame(frame = frame)
+                        println(message)
+                        // broadcast to clients the message
+                        outgoingMessageBuffer.emit(frame)
+                    }
+                }
+            }.onFailure { exception ->
+                println("WebSocket exception: ${exception.localizedMessage}")
+            }.also {
+                job.cancel()
+            }
+        }
+        return this
+    }
+
+    fun start() {
+        runBlocking {
+            try {
+                server?.start(wait = true)
+            } catch (exception: Exception) {
+                // TODO
+                println("WebSocket exception: ${exception.localizedMessage}")
+            } finally {
+                println("Server close")
+            }
+        }
+    }
+
+    private fun build(
+        port: Int = SERVER_PORT,
+        handler: suspend DefaultWebSocketServerSession.() -> Unit
+    ): EmbeddedServer<NettyApplicationEngine, NettyApplicationEngine.Configuration> {
+        return embeddedServer(
+            factory = Netty,
+            port = port,
+            module = {
+                install(WebSockets) {
+                    pingPeriod = 15.seconds
+                    timeout = 15.seconds
+                    maxFrameSize = Long.MAX_VALUE
+                    masking = false
+                }
+                routing {
+                    webSocket(
+                        path = "/ws",
+                        handler = handler,
+                    )
+                }
+            },
+        )
+    }
+}