Scala example source code file (SourceReader.scala)

This example Scala source code file (SourceReader.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

abstractfile, array, bytebuffer, charbuffer, charsetdecoder, coderresult, compiler, entry, exception, jfile, nsc, sourcereader

The SourceReader.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */


package scala.tools.nsc
package io

import java.io.{ FileInputStream, InputStream, IOException }
import java.nio.{ByteBuffer, CharBuffer}
import java.nio.channels.{ ReadableByteChannel, Channels }
import java.nio.charset.{CharsetDecoder, CoderResult}
import scala.tools.nsc.reporters._

/** This class implements methods to read and decode source files. */
class SourceReader(decoder: CharsetDecoder, reporter: Reporter) {

  import SourceReader.{decode, flush}

  //########################################################################
  // Private Fields

  /** The input byte buffer (small enough to fit in cache) */
  private val bytes: ByteBuffer = ByteBuffer.allocate(0x4000)

  /** The output character buffer */
  private var chars: CharBuffer = CharBuffer.allocate(0x4000)

  private def reportEncodingError(filename:String) = {
    reporter.error(scala.reflect.internal.util.NoPosition,
                   "IO error while decoding "+filename+" with "+decoder.charset()+"\n"+
                   "Please try specifying another one using the -encoding option")
  }

  /** Reads the specified file. */
  def read(file: JFile): Array[Char] = {
    val c = new FileInputStream(file).getChannel

    try read(c)
    catch { case e: Exception => reportEncodingError("" + file) ; Array() }
    finally c.close()
  }

  /** Reads the specified file.
   */
  def read(file: AbstractFile): Array[Char] = {
    try file match {
      case p: PlainFile        => read(p.file)
      case z: ZipArchive#Entry => read(Channels.newChannel(z.input))
      case _                   => read(ByteBuffer.wrap(file.toByteArray))
    }
    catch {
      case e: Exception => reportEncodingError("" + file) ; Array()
    }
  }

  /** Reads the specified byte channel. */
  protected def read(input: ReadableByteChannel): Array[Char] = {
    val decoder: CharsetDecoder = this.decoder.reset()
    val bytes: ByteBuffer       = this.bytes; bytes.clear()
    var chars: CharBuffer       = this.chars; chars.clear()
    var endOfInput              = false

    while (!endOfInput ) {
      endOfInput = input.read(bytes) < 0
      bytes.flip()
      chars = decode(decoder, bytes, chars, endOfInput)
    }
    terminate(flush(decoder, chars))
  }

  /** Reads the specified byte buffer. */
  protected def read(bytes: ByteBuffer): Array[Char] = {
    val decoder: CharsetDecoder = this.decoder.reset()
    val chars: CharBuffer = this.chars; chars.clear()
    terminate(flush(decoder, decode(decoder, bytes, chars, endOfInput = true)))
  }

  //########################################################################
  // Private Methods

  /**
   * Sets the specified char buffer as the new output buffer and
   * reads and returns its content.
   */
  private def terminate(chars: CharBuffer): Array[Char] = {
    val result = new Array[Char](chars.length())
    chars.get(result)
    this.chars = chars
    result
  }

}

object SourceReader {

  /**
   * Decodes the content of the specified byte buffer with the
   * specified decoder into the specified char buffer, allocating
   * bigger ones if necessary, then compacts the byte buffer and
   * returns the last allocated char buffer. The "endOfInput"
   * argument indicates whether the byte buffer contains the last
   * chunk of the input file.
   */
  def decode(decoder: CharsetDecoder, bytes: ByteBuffer, chars: CharBuffer,
             endOfInput: Boolean): CharBuffer =
  {
    val result: CoderResult = decoder.decode(bytes, chars, endOfInput)
    if (result.isUnderflow()) {
      bytes.compact()
      chars
    } else {
      if (result.isError()) throw new IOException(result.toString())
      assert(result.isOverflow())
      decode(decoder, bytes, increaseCapacity(chars), endOfInput)
    }
  }

  /**
   * Flushes the specified decoder into the specified char buffer,
   * allocating bigger ones if necessary and then flips and returns
   * the last allocated char buffer.
   */
  def flush(decoder: CharsetDecoder, chars: CharBuffer): CharBuffer = {
    val result: CoderResult = decoder.flush(chars)
    if (result.isUnderflow()) {
      chars.flip()
      chars
    } else {
      if (result.isError()) throw new IOException(result.toString())
      assert(result.isOverflow())
      flush(decoder, increaseCapacity(chars))
    }
  }

  /**
   * Flips the specified buffer and returns a new one with the same
   * content but with an increased capacity.
   */
  private def increaseCapacity(buffer: CharBuffer): CharBuffer = {
    buffer.flip()
    val capacity = 2 * buffer.capacity()
    CharBuffer.allocate(capacity).put(buffer)
  }

}