Kotlin WebSocket Libraries for Creating Real-Time in Web Applications

Kotlin WebSocket Libraries: Creating Real-Time Applications

WebSocket is a protocol that provides a persistent two-way connection between a client and a server. Unlike HTTP, where a request is sent by the client and the server responds, WebSocket allows the server to initiate data sending without a request. This makes it ideal for chats, online games, stock quotes, notifications, and other systems that require instant data transfer.

Kotlin, being a modern JVM language, offers several powerful libraries for working with WebSocket. In this article, we will look at three of the most popular options: Ktor, OkHttp, and kweb.

1. Ktor – Framework for Servers and Clients

Ktor is an asynchronous framework from JetBrains, written entirely in Kotlin. It supports WebSocket on both the server and client sides. Ktor uses coroutines, making the code concise and efficient.

Installation (Gradle)

dependencies {    implementation("io.ktor:ktor-server-core:2.3.0")    implementation("io.ktor:ktor-server-netty:2.3.0")    implementation("io.ktor:ktor-server-websockets:2.3.0")    implementation("io.ktor:ktor-client-core:2.3.0")    implementation("io.ktor:ktor-client-cio:2.3.0")    implementation("io.ktor:ktor-client-websockets:2.3.0")}

Ktor Server Example

import io.ktor.server.engine.*import io.ktor.server.netty.*import io.ktor.server.routing.*import io.ktor.server.websocket.*import io.ktor.websocket.*

fun main() {    embeddedServer(Netty, port = 8080) {        install(WebSockets)        routing {            webSocket("/chat") {                send(Frame.Text("Welcome to the chat!"))                for (frame in incoming) {                    if (frame is Frame.Text) {                        val text = frame.readText()                        send(Frame.Text("You wrote: $text"))                    }                }            }        }    }.start(wait = true)}

Ktor Client Example

import io.ktor.client.*import io.ktor.client.engine.cio.*import io.ktor.client.plugins.websocket.*import io.ktor.websocket.*import kotlinx.coroutines.*

fun main() = runBlocking {    val client = HttpClient(CIO) {        install(WebSockets)    }    client.webSocket("ws://localhost:8080/chat") {        send(Frame.Text("Hello, server!"))        for (frame in incoming) {            if (frame is Frame.Text) {                println("Response: ${frame.readText()}")            }        }    }    client.close()}

Advantages of Ktor:

• Full support for Kotlin coroutines
• Asynchronous processing without blocking
• Unified syntax for server and client
• Built-in support for SSL, compression, and other protocols

2. OkHttp – Reliable HTTP/WebSocket Client

OkHttp is a popular library from Square, originally focused on HTTP but with excellent WebSocket support. It is used in Android development and server applications. OkHttp works synchronously and asynchronously, supports reconnection and connection pooling.

Installation (Gradle)

dependencies {    implementation("com.squareup.okhttp3:okhttp:4.12.0")}

OkHttp Client Example

import okhttp3.*

fun main() {    val client = OkHttpClient()    val request = Request.Builder().url("ws://echo.websocket.org").build()    val ws = client.newWebSocket(request, object : WebSocketListener() {        override fun onOpen(webSocket: WebSocket, response: Response) {            webSocket.send("Hello from OkHttp!")        }        override fun onMessage(webSocket: WebSocket, text: String) {