Kotlin Android Websocket Libraries

Kotlin Android Websocket Libraries

WebSockets are a powerful way to enable two-way communication between the client and the server. Let's dive into some of the best WebSocket libraries for Kotlin on Android and explore how you can use them to supercharge your app with real-time features.

1. OkHttp

OkHttp is a popular HTTP client for Android and Java applications. It's developed by Square and is widely used for its efficiency and ease of use. OkHttp supports WebSocket calls as of version 3.5.0, making it a great choice if you're already using it for HTTP requests in your app.

Features

  • Ease of Use: Integrates seamlessly with Retrofit, another Square library for REST API integration.
  • Connection Pooling: Reuses HTTP/2 connections, which is great for mobile networks.
  • Request Timeouts: Helps prevent battery drain and unnecessary network usage.
  • Response Caching: Reduces latency and saves on data usage.

Installation

Add the OkHttp dependency to your build.gradle file:. 

dependencies {
    implementation("com.squareup.okhttp3:okhttp:4.9.0")
}

Code Example

val client = OkHttpClient()
val request = Request.Builder().url("ws://your.websocket.url").build()
val ws = client.newWebSocket(request, object : WebSocketListener() {
    override fun onOpen(webSocket: WebSocket, response: Response) {
        webSocket.send("Hello, world!")
    }

    override fun onMessage(webSocket: WebSocket, text: String) {
        println("Receiving: $text")
    }

    override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) {
        println("Error: " + t.message)
    }
})

// To close the WebSocket connection
ws.close(1000, "Goodbye, world!")

In this example, we create a WebSocket connection using OkHttp's newWebSocket method. We define callbacks for onOpen, onMessage, and onFailure to handle different stages of the WebSocket lifecycle.

Comparison

OkHttp is a robust choice for those who want a reliable, well-tested library that integrates well with other networking libraries like Retrofit. It might not be the most lightweight option, but it's highly reliable and feature-rich.

2. Jetty

Jetty is an open-source WebSocket server and client that's part of the Eclipse Foundation. It's a full-featured library that can handle complex WebSocket use cases.

Features

  • Full WebSocket Spec Implementation: Supports both WebSocket RFC 6455 and the older Hixie 76 protocols.
  • Servlet Container: Can be used as a WebSocket servlet container if you need to run a server within your app.
  • Extensible: Allows for custom extensions and protocols.

Installation

Add the Jetty WebSocket client dependency to your build.gradle:. 

dependencies {
    implementation("org.eclipse.jetty.websocket:websocket-client:9.4.44.v20210927")
}

Code Example

val factory = WebSocketClientFactory()
val client = factory.newWebSocketClient()
client.start()

val ws = object : WebSocketAdapter() {
    override fun onWebSocketConnect(sess: Session) {
        sess.remote.sendString("Hello, Jetty!")
    }

    override fun onWebSocketText(sess: Session, text: String) {
        println("Received: $text")
    }
}

client.connect(ws, URI("ws://your.websocket.url"))

// To disconnect
client.stop()

In this snippet, we create a WebSocket client and connect it to our server URI. We extend WebSocketAdapter to handle connection and message events.

Comparison

Jetty is a powerful option for those who need a comprehensive WebSocket solution with support for advanced features. However, it might be overkill for simpler use cases and has a steeper learning curve compared to OkHttp.

3. Socket.IO Client for Android

Socket.IO is a library that enables real-time bidirectional event-based communication. It's not strictly a WebSocket library but uses WebSocket as a transport mechanism when possible. It's designed to work seamlessly with the Socket.IO server.

Features

  • Automatic Reconnection: Attempts to reconnect when the connection drops.
  • Event-based Communication: Allows you to emit and listen to events with data payloads.
  • Fallback to Polling: If WebSockets aren't available, it can fall back to HTTP long-polling.

Installation

Add the Socket.IO client dependency to your build.gradle:. 

dependencies {
    implementation("io.socket:socket.io-client:1.0.0")
}

Code Example

val socket = IO.socket("http://your.socket.io.server")
socket.on(Socket.EVENT_CONNECT, object : Emitter.Listener {
    override fun call(vararg args: Any) {
        socket.emit("hello", "world")
    }
})

socket.on("news", object : Emitter.Listener {
    override fun call(vararg args: Any) {
        val data = args[0] as String
        println("Received news: $data")
    }
})

socket.connect()

// To disconnect
socket.disconnect()

Here, we create a Socket.IO client and set up event listeners for connection and message events. We use emit to send messages to the server.

Comparison

Socket.IO is a great choice if you're looking for an easy-to-use library that handles the complexities of real-time communication for you. It's particularly useful if you're using a Socket.IO server. However, it's less suitable for applications that need to adhere strictly to the WebSocket protocol.