How to close AsyncHttpClient in scalaz Task

Question

I am trying to combine AsyncHttpClient and Scalaz Task together. Normally, if I am using AsyncHttpClient, I can invoke client.close to stop the client.

val asyncHttpClient = new AsyncHttpClient()
println(asyncHttpClient.prepareGet("http://www.google.com"))

asyncHttpClient.close()

So current will be stopped. However, if I wrap the api call into the Task. I dont know how to stop it.

  def get(s: String) = Task.async[Int](k => {
    asyncHttpClient.prepareGet(s).execute(toHandler)
    Thread.sleep(5000)
    asyncHttpClient.closeAsynchronously()
  } )

  def toHandler[A] = new AsyncCompletionHandler[Response] {
    def onCompleted(r: Response) = {
      println("get response ", r.getResponseBody)
      r
    }
    def onError(e: Throwable) = {
      println("some error")
      e
    }
  }

println(get("http://www.google.com").run)

The current Process is still running. I am thinking the reason is that Task and AsynClient are both async. I dont know what I should do to close it

Many thanks in advance

Answer 1

The problem is that Task.async takes a function that can register callbacks. This is a little confusing, and the types aren't much help because there's so much damn Unit in there, but what it means here is that you want something more like this:

import com.ning.http.client._
import scalaz.syntax.either._
import scalaz.concurrent.Task

val asyncHttpClient = new AsyncHttpClient()

def get(s: String): Task[Response] = Task.async[Response](callback =>
  asyncHttpClient.prepareGet(s).execute(
    new AsyncCompletionHandler[Unit] {
      def onCompleted(r: Response): Unit = callback(r.right)
      def onError(e: Throwable): Unit = callback(e.left)
    }
  )
)

This doesn't handle closing the client—it's just intended to show the general idea. You could close the client in the handler, but I'd suggest something more like this:

import com.ning.http.client._
import scalaz.syntax.either._
import scalaz.concurrent.Task

def get(client: AsyncHttpClient)(s: String): Task[Response] =
  Task.async[Response](callback =>
    client.prepareGet(s).execute(
      new AsyncCompletionHandler[Unit] {
        def onCompleted(r: Response): Unit = callback(r.right)
        def onError(e: Throwable): Unit = callback(e.left)
      }
    )
  )

def initClient: Task[AsyncHttpClient] = Task(new AsyncHttpClient())
def closeClient(client: AsyncHttpClient): Task[Unit] = Task(client.close())

And then:

val res = for {
  c <- initClient
  r <- get(c)("http://www.google.com")
  _ <- closeClient(c)
} yield r

res.unsafePerformAsync(
  _.fold(
    _ => println("some error"),
    r => println("get response " + r.getResponseBody)
  )
)

This avoids closeAsynchronously (which seems to be going away, anyway).