Scala example source code file (BasicIO.scala)

This example Scala source code file (BasicIO.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

annotation, boolean, collection, immutable, inputstream, ioexception, left, outputstream, processio, streamed, string, uncloseable, unit

The BasicIO.scala Scala example source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2003-2013, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala
package sys
package process

import processInternal._
import java.io.{ BufferedReader, InputStreamReader, FilterInputStream, FilterOutputStream }
import java.util.concurrent.LinkedBlockingQueue
import scala.collection.immutable.Stream
import scala.annotation.tailrec

/**
  * This object contains factories for [[scala.sys.process.ProcessIO]],
  * which can be used to control the I/O of a [[scala.sys.process.Process]]
  * when a [[scala.sys.process.ProcessBuilder]] is started with the `run`
  * command.
  *
  * It also contains some helper methods that can be used to in the creation of
  * `ProcessIO`.
  *
  * It is used by other classes in the package in the implementation of various
  * features, but can also be used by client code.
  */
object BasicIO {
  /** Size of the buffer used in all the functions that copy data */
  final val BufferSize = 8192

  /** Used to separate lines in the `processFully` function that takes `Appendable`. */
  final val Newline    = props("line.separator")

  private[process] final class Streamed[T](
    val process:   T => Unit,
    val    done: Int => Unit,
    val  stream:  () => Stream[T]
  )

  private[process] object Streamed {
    def apply[T](nonzeroException: Boolean): Streamed[T] = {
      val q = new LinkedBlockingQueue[Either[Int, T]]
      def next(): Stream[T] = q.take match {
        case Left(0)    => Stream.empty
        case Left(code) => if (nonzeroException) scala.sys.error("Nonzero exit code: " + code) else Stream.empty
        case Right(s)   => Stream.cons(s, next())
      }
      new Streamed((s: T) => q put Right(s), code => q put Left(code), () => next())
    }
  }

  private[process] trait Uncloseable extends Closeable {
    final override def close() { }
  }
  private[process] object Uncloseable {
    def apply(in: InputStream): InputStream      = new FilterInputStream(in) with Uncloseable { }
    def apply(out: OutputStream): OutputStream   = new FilterOutputStream(out) with Uncloseable { }
    def protect(in: InputStream): InputStream    = if (in eq stdin) Uncloseable(in) else in
    def protect(out: OutputStream): OutputStream = if ((out eq stdout) || (out eq stderr)) Uncloseable(out) else out
  }

  /** Creates a `ProcessIO` from a function `String => Unit`. It can attach the
    * process input to stdin, and it will either send the error stream to
    * stderr, or to a `ProcessLogger`.
    *
    * For example, the `ProcessIO` created below will print all normal output
    * while ignoring all error output. No input will be provided.
    * {{{
    * import scala.sys.process.BasicIO
    * val errToDevNull = BasicIO(false, println(_), None)
    * }}}
    *
    * @param withIn True if the process input should be attached to stdin.
    * @param output A function that will be called with the process output.
    * @param log    An optional `ProcessLogger` to which the output should be
    *               sent. If `None`, output will be sent to stderr.
    * @return A `ProcessIO` with the characteristics above.
    */
  def apply(withIn: Boolean, output: String => Unit, log: Option[ProcessLogger]) =
    new ProcessIO(input(withIn), processFully(output), getErr(log))

  /** Creates a `ProcessIO` that appends its output to a `StringBuffer`. It can
    * attach the process input to stdin, and it will either send the error
    * stream to stderr, or to a `ProcessLogger`.
    *
    * For example, the `ProcessIO` created by the function below will store the
    * normal output on the buffer provided, and print all error on stderr. The
    * input will be read from stdin.
    * {{{
    * import scala.sys.process.{BasicIO, ProcessLogger}
    * val printer = ProcessLogger(println(_))
    * def appendToBuffer(b: StringBuffer) = BasicIO(true, b, Some(printer))
    * }}}
    *
    * @param withIn True if the process input should be attached to stdin.
    * @param buffer A `StringBuffer` which will receive the process normal
    *               output.
    * @param log    An optional `ProcessLogger` to which the output should be
    *               sent. If `None`, output will be sent to stderr.
    * @return A `ProcessIO` with the characteristics above.
    */
  def apply(withIn: Boolean, buffer: StringBuffer, log: Option[ProcessLogger]) =
    new ProcessIO(input(withIn), processFully(buffer), getErr(log))

  /** Creates a `ProcessIO` from a `ProcessLogger` . It can attach the
    * process input to stdin.
    *
    * @param withIn True if the process input should be attached to stdin.
    * @param log    A `ProcessLogger` to receive all output, normal and error.
    * @return A `ProcessIO` with the characteristics above.
    */
  def apply(withIn: Boolean, log: ProcessLogger) =
    new ProcessIO(input(withIn), processOutFully(log), processErrFully(log))

  /** Returns a function `InputStream => Unit` given an optional
    * `ProcessLogger`. If no logger is passed, the function will send the output
    * to stderr. This function can be used to create a
    * [[scala.sys.process.ProcessIO]].
    *
    * @param log An optional `ProcessLogger` to which the contents of
    *            the `InputStream` will be sent.
    * @return A function `InputStream => Unit` (used by
    *          [[scala.sys.process.ProcessIO]]) which will send the data to
    *          either the provided `ProcessLogger` or, if `None`, to stderr.
    */
  def getErr(log: Option[ProcessLogger]) = log match {
    case Some(lg) => processErrFully(lg)
    case None     => toStdErr
  }

  private def processErrFully(log: ProcessLogger) = processFully(log err _)
  private def processOutFully(log: ProcessLogger) = processFully(log out _)

  /** Closes a `Closeable` without throwing an exception */
  def close(c: Closeable) = try c.close() catch { case _: IOException => () }

  /** Returns a function `InputStream => Unit` that appends all data read to the
    * provided `Appendable`. This function can be used to create a
    * [[scala.sys.process.ProcessIO]]. The buffer will be appended line by line.
    *
    * @param buffer An `Appendable` such as `StringBuilder` or `StringBuffer`.
    * @return A function `InputStream => Unit` (used by
    *          [[scala.sys.process.ProcessIO]] which will append all data read
    *          from the stream to the buffer.
    */
  def processFully(buffer: Appendable): InputStream => Unit = processFully(appendLine(buffer))

  /** Returns a function `InputStream => Unit` that will call the passed
    * function with all data read. This function can be used to create a
    * [[scala.sys.process.ProcessIO]]. The `processLine` function will be called
    * with each line read, and `Newline` will be appended after each line.
    *
    * @param processLine A function that will be called with all data read from
    *                    the stream.
    * @return A function `InputStream => Unit` (used by
    *          [[scala.sys.process.ProcessIO]] which will call `processLine`
    *          with all data read from the stream.
    */
  def processFully(processLine: String => Unit): InputStream => Unit = in => {
    val reader = new BufferedReader(new InputStreamReader(in))
    try processLinesFully(processLine)(reader.readLine)
    finally reader.close()
  }

  /** Calls `processLine` with the result of `readLine` until the latter returns
   *  `null` or the current thread is interrupted.
   */
  def processLinesFully(processLine: String => Unit)(readLine: () => String) {
    def working = (Thread.currentThread.isInterrupted == false)
    def halting = { Thread.currentThread.interrupt(); null }
    def readFully(): Unit =
      if (working) {
        val line =
          try readLine()
          catch {
            case _: InterruptedException    => halting
            case e: IOException if !working => halting
          }
        if (line != null) {
          processLine(line)
          readFully()
        }
      }
    readFully()
  }

  /** Copy contents of stdin to the `OutputStream`. */
  def connectToIn(o: OutputStream): Unit = transferFully(Uncloseable protect stdin, o)

  /** Returns a function `OutputStream => Unit` that either reads the content
    * from stdin or does nothing. This function can be used by
    * [[scala.sys.process.ProcessIO]].
    */
  def input(connect: Boolean): OutputStream => Unit = { outputToProcess =>
    if (connect) connectToIn(outputToProcess)
    outputToProcess.close()
  }

  /** Returns a `ProcessIO` connected to stdout and stderr, and, optionally, stdin. */
  def standard(connectInput: Boolean): ProcessIO = standard(input(connectInput))

  /** Retruns a `ProcessIO` connected to stdout, stderr and the provided `in` */
  def standard(in: OutputStream => Unit): ProcessIO = new ProcessIO(in, toStdOut, toStdErr)

  /** Send all the input from the stream to stderr, and closes the input stream
   * afterwards.
   */
  def toStdErr = (in: InputStream) => transferFully(in, stderr)

  /** Send all the input from the stream to stdout, and closes the input stream
   * afterwards.
   */
  def toStdOut = (in: InputStream) => transferFully(in, stdout)

  /** Copy all input from the input stream to the output stream. Closes the
    * input stream once it's all read.
    */
  def transferFully(in: InputStream, out: OutputStream): Unit =
    try transferFullyImpl(in, out)
    catch onInterrupt(())

  private[this] def appendLine(buffer: Appendable): String => Unit = line => {
    buffer append line
    buffer append Newline
  }

  private[this] def transferFullyImpl(in: InputStream, out: OutputStream) {
    val buffer = new Array[Byte](BufferSize)
    @tailrec def loop() {
      val byteCount = in.read(buffer)
      if (byteCount > 0) {
        out.write(buffer, 0, byteCount)
        // flush() will throw an exception once the process has terminated
        val available = try { out.flush(); true } catch { case _: IOException => false }
        if (available) loop()
      }
    }
    loop()
    in.close()
  }
}