RunProgram.scala

import fs2._

case class ProcessState(exitValue: Task[Int],
                        output: Stream[Task, Byte],
                        input: Sink[Task, Byte],
                        error: Stream[Task, Byte])

object RunProgram {
  val waitThreadStrategy = Strategy.fromCachedDaemonPool("wait-threads")
  
  def runProgram(workingDirectory: Path, args: String*)(implicit S: Strategy): ProcessState = {
    val pb      = new ProcessBuilder(args: _*).directory(workingDirectory.toFile)
    val process = pb.start()
    val inStream =
      io.readInputStreamAsync(Task.delay(process.getInputStream), 1024)
    val outStream = io.writeOutputStream(Task.delay(process.getOutputStream))
    val errStream =
      io.readInputStreamAsync(Task.delay(process.getErrorStream), 1024)

    val result = Task(process.waitFor)(waitThreadStrategy)

    ProcessState(result, inStream, outStream, errStream)
  }
}