Buffered FileTailer in scala.

FileTailer.scala

import java.io.{File, RandomAccessFile}
import java.nio.{ByteBuffer, CharBuffer}
import java.nio.charset.Charset

/**
 * Read lines from the end of a file.
 * 
 * Partial lines that don't terminate with a newline will be lost
 * Lines bigger than the buffer size will also be lost
 */
class FileTailer(val path: String) {
  val charset = Charset.forName("utf-8")
  
  val buffer = ByteBuffer.allocate(8192)
  var charBuffer: CharBuffer = null

  val file = {
    val f = new File(path)
    val raf = new RandomAccessFile(f, "r")
    raf.seek(math.max(0, f.length - buffer.capacity))
    raf
  }

  def readLine: CharSequence = {
    if (charBuffer == null || !charBuffer.hasRemaining) {
      buffer.clear
      file.getChannel.read(buffer)
      buffer.flip
      charBuffer = charset.decode(buffer)
    }
    var foundNewLine = false
    charBuffer.mark
    while (charBuffer.hasRemaining && !foundNewLine) {
      if (charBuffer.get == '\n') {
        foundNewLine = true
      }
    }
    if (foundNewLine) {
      val copy = charBuffer.duplicate
      copy.limit(copy.position - 1)
      copy.reset
      copy
    } else {
      null
    }
  }
  
  def close = file.close
}

Apparently, FileInputStream.skip may or may not work for a "variety of reasons" http://docs.oracle.com/javase/6/docs/api/java/io/FileInputStream.html#skip(long)

RandomAccessFile seeks as expected, but the readLine method is unbuffered and doesn't seem to correctly handle unicode.

Inspired by http://stackoverflow.com/questions/4305094/java-reading-strings-from-a-random-access-file-with-buffered-input