AsynchronousIo

The following readAll is a Task to read file content with the help of AsynchronousIo.ReadFile

import java.nio._, file._, channels._
import com.thoughtworks.dsl.domains.task.Task
import com.thoughtworks.dsl.keywords._
import com.thoughtworks.dsl.keywords.Shift._
import com.thoughtworks.dsl.keywords.AsynchronousIo.ReadFile
import scala.collection.mutable.ArrayBuffer
import scala.io.Codec
def readAll(channel: AsynchronousFileChannel, temporaryBufferSize: Int = 4096): Task[ArrayBuffer[CharBuffer]] = Task {
  val charBuffers = ArrayBuffer.empty[CharBuffer]
  val decoder = Codec.UTF8.decoder
  val byteBuffer = ByteBuffer.allocate(temporaryBufferSize)
  var position: Long = 0L
  while (!ReadFile(channel, byteBuffer, position) != -1) {
    position += byteBuffer.position()
    byteBuffer.flip()
    charBuffers += decoder.decode(byteBuffer)
    byteBuffer.clear()
  }
  charBuffers
}

Tasks created from !-notation can be used in for-comprehension, and other keywords can be used together in the same for block. For example, the following cat function contains a single for block to concatenate file contents. It asynchronously iterates elements Seq, ArrayBuffer and String with the help of keywords.Each, managed native resources with the help of keywords.Using, performs previously created readAll task with the help of keywords.Shift, and finally converts the return type as a Task[Vector[Char]].

import com.thoughtworks.dsl.comprehension._
import com.thoughtworks.dsl.keywords._
import com.thoughtworks.dsl.keywords.Shift._
import com.thoughtworks.dsl.domains.task.Task
import java.net.URL
def cat(paths: Path*) = {
  for {
    path <- Each(paths)
    channel <- Using(AsynchronousFileChannel.open(path))
    charBuffers <- readAll(channel)
    charBuffer <- Each(charBuffers)
    char <- Each(charBuffer.toString)
  } yield char
}.as[Task[Vector[Char]]]

Then the cat function is used to concatenate files from this project, as shown below:

Task.toFuture(Task {
  (!cat(Paths.get(".sbtopts"), Paths.get(".scalafmt.conf"))).mkString should be(
    "-J-XX:MaxMetaspaceSize=512M\n-J-Xmx5G\n-J-Xss6M\nversion = \"1.5.1\"\nmaxColumn = 120"
  )
})