Example of asynchronous, cancelable downloading using the Ning AsyncHttpClient (see also https://trello.com/c/KTUBorWF/78-project-4)

asyncDownloader.sc

// long download: https://downloads.gradle.org/distributions/gradle-2.3-src.zip
// short download: https://repo1.maven.org/maven2/com/ning/async-http-client/1.9.20/async-http-client-1.9.20.jar

// dependencies: see build.sbt

// usage: val f = download(url, localFileName)
// to cancel (if desired): f.cancel(true)

import com.ning.http.client._
import com.ning.http.client.listener._
import java.io.{ File, FileOutputStream }

def fileSaver(name: String) = new TransferListener {
  val file = new File(name)
  var stream: Option[FileOutputStream] = None
  def onRequestHeadersSent(headers: FluentCaseInsensitiveStringsMap): Unit = ()
  def onResponseHeadersReceived(headers: FluentCaseInsensitiveStringsMap): Unit = 
    stream = Some(new FileOutputStream(file))
  def onBytesReceived(buffer: Array[Byte]): Unit =
    stream.get.write(buffer)
  def onBytesSent(amount: Long, current: Long, total: Long): Unit = ()
  def onRequestResponseCompleted(): Unit = stream.get.close()
  def onThrowable(t: Throwable): Unit = stream.get.close()
}

val progressReporter = new TransferListener {
  def onRequestHeadersSent(headers: FluentCaseInsensitiveStringsMap): Unit = ()
  def onResponseHeadersReceived(headers: FluentCaseInsensitiveStringsMap): Unit = print("+")
  def onBytesReceived(buffer: Array[Byte]): Unit = print("*")
  def onBytesSent(amount: Long, current: Long, total: Long): Unit = ()
  def onRequestResponseCompleted(): Unit = println("!")
  def onThrowable(t: Throwable): Unit = { }
}

val client = new AsyncHttpClient

def download(url: String, local: String): ListenableFuture[Response] = {
  val t = new TransferCompletionHandler
  t.addTransferListener(fileSaver(local))
  t.addTransferListener(progressReporter)
  client.prepareGet(url).execute(t)
}

build.sbt

scalaVersion := "2.11.8"

scalacOptions in Compile ++= Seq("-feature", "-unchecked", "-deprecation")

libraryDependencies ++= Seq(
  "io.reactivex" %% "rxscala" % "+",
  "com.ning" % "async-http-client" % "+",
  "org.slf4j" % "slf4j-simple" % "+"
)