Retry a future on failure, with a delay, up to n times

futureRetry.scala

import scala.concurrent.{Promise, Future, ExecutionContext}
import scala.concurrent.duration.FiniteDuration
import java.util.{TimerTask, Timer}

// Inspired by https://gist.github.com/viktorklang/9414163, but modified to not depend on Akka, works with just Scala's standard library
def retry[T](block: => T, delay: FiniteDuration, retries: Int)(implicit ec: ExecutionContext): Future[T] =
  Future(block).recoverWith { case _ if retries > 0 =>
    after(delay)(retry(block, delay, retries - 1))
  }

def after[T](delay: FiniteDuration)(block: => Future[T])(implicit ec: ExecutionContext): Future[T] = {
  val promise = Promise[T]()
  new Timer().schedule(
    new TimerTask {
      override def run(): Unit =
        block.onComplete { case x => promise.complete(x) }
    },
    delay.toMillis
  )
  promise.future
}