Android Kotlin Web Server

Sample code below is a very simple web server written in Kotlin. A [Start] button to start listening, a [Stop] button to stop listening and text view to display WiFi address.

Remember to add these 2 permissions else the app will crash upon start.

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />

Codes for the 2 class variable and in my example I had the port hard coded to 8888.

val hash : ConcurrentHashMap<String, String> = ConcurrentHashMap()
val server = ServerSocket(8888)

Codes for getting WiFi address can be found at “Android Kotlin Get WiFi IP” post. And the codes for the button listener below.

btnStart?.setOnClickListener {
    hash["is_started"]="true"
    thread {
        while (hash["is_started"].toBoolean()) {
            val client = server.accept()
            thread { ClientHandler(client).run() }
        }
    }
}
btnStop?.setOnClickListener {
    hash["is_started"]="false"
}

After that you will also be needing a client handler class. Codes below the screenshot. Content length HTTP header is very important else it will not know when to stop.

class ClientHandler(client: Socket) {
    private val client: Socket = client
    var isr = InputStreamReader(client.getInputStream())
    var reader = StringBuilder()
    private val writer: OutputStream = client.getOutputStream()

    fun run() {
        try {
            var br = BufferedReader(isr)
            while (br.ready()) {
                reader.append(br.read().toChar())
            }
            val body = "OOFnivek\n"
            val response = String.format(
                "HTTP/1.1 200 OK\nContent-Length: %d\r\n\r\n%s",
                body.length,
                body
            )
            writer.write(response.toByteArray())
        } catch (ex: Exception) {
            client.close()
        }
    }
}

Successful test with the apps listed below.
1. curl in Mac terminal
2. Chrome in Mac

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