simple scala socket program - talks to one client only? - scala

Question

I'm trying to make a very simple scala socket program that will "echo" out any input it recieves from multiple clients
This program does work but only for a single client. I think this is because execution is always in while(true) loop
import java.net._
import java.io._
import scala.io._
//println(util.Properties.versionString)
val server = new ServerSocket(9999)
println("initialized server")
val client = server.accept
while(true){
val in = new BufferedReader(new InputStreamReader(client.getInputStream)).readLine
val out = new PrintStream(client.getOutputStream)
println("Server received:" + in) // print out the input message
out.println("Message received")
out.flush
}
I've tried
making this modification
while(true){
val client = server.accept
val in = new BufferedReader(new InputStreamReader(client.getInputStream)).readLine
val out = new PrintStream(client.getOutputStream)
println("Server received:" + in)
}
But this does'nt work beyond "echo"ing out a single message
I'd like multiple clients to connect to the socket and constantly receive the output of whatever they type in

Answer 1

Basically you should accept the connection and create a new Future for each client. Beware that the implicit global ExecutionContext might be limited, you might need to find a different one that better fits your use cases.
You can use Scala async if you need more complex tasks with futures, but I think this is probably fine.
Disclaimer, I have not tried this, but something similar might work (based on your code and the docs):
import scala.concurrent._
import ExecutionContext.Implicits.global
...
while(true){
val client = server.accept
Future {
val inReader = new BufferedReader(new InputStreamReader(client.getInputStream))
val out = new PrintStream(client.getOutputStream)
do {
val in = inReader.readLine
println("Server received:" + in)
} while (true/*or a better condition to close the connection */)
client.close
}
}

Answer 2

Here you can find an example for the scala language:
[http://www.scala-lang.org/old/node/55][1]
And this is also a good example from scala twitter school, that works with java libraries:
import java.net.{Socket, ServerSocket}
import java.util.concurrent.{Executors, ExecutorService}
import java.util.Date
class NetworkService(port: Int, poolSize: Int) extends Runnable {
val serverSocket = new ServerSocket(port)
def run() {
while (true) {
// This will block until a connection comes in.
val socket = serverSocket.accept()
(new Handler(socket)).run()
}
}
}
class Handler(socket: Socket) extends Runnable {
def message = (Thread.currentThread.getName() + "\n").getBytes
def run() {
socket.getOutputStream.write(message)
socket.getOutputStream.close()
}
}
(new NetworkService(2020, 2)).run