A Scala Object to do simple RFC3986 URL encoding.

PercentEncoder

package com.sabrelabs.twitter.auth

import scala.collection.BitSet
import scala.annotation.tailrec
import scala.runtime.RichInt
import scala.collection.mutable.ListBuffer

object PercentEncoder {

  def encodeRFC3986(str: String): String = {
    val strBytes = str.getBytes("UTF-8").toList
    val encodedBytes = new ListBuffer[Byte]
    strBytes.foreach(byte => {
      if(allowedBytes.contains(byte)){
        encodedBytes += byte
      } else {
        encodedBytes += PercentByte
        new RichInt(byte.toInt).toHexString.takeRight(2).foreach({
          char => encodedBytes += char.toUpper.toByte
        })
      }
    })
    stringFromByteList("", encodedBytes.toList)
  }

  private[this] val PercentByte = "%".charAt(0).toByte
  private[this] val allowedAsciiChars = strListToCharList(Nil, List(
    "0", "1", "2", "3", "4", "5", "6", "7", "8", "9",
    "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S",
    "T", "U", "V", "W", "X", "Y", "Z",
    "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s",
    "t", "u", "v", "w", "x", "y", "z",
    "-", ".", "_", "~"
  ))
  private[this] val allowedBytes = buildAllowedAsciiByteSet(BitSet.empty, byteListFromCharList(Nil, allowedAsciiChars))

  @tailrec
  private[this] def byteListFromCharList(bytes: List[Byte], chars: List[Char]): List[Byte] = {
    if(chars.isEmpty) return bytes
    byteListFromCharList(bytes.::(chars.head.toByte), chars.tail)
  }

  @tailrec
  private[this] def buildAllowedAsciiByteSet(set: BitSet, bytes: List[Byte]): BitSet = {
    if(bytes.isEmpty) return set
    buildAllowedAsciiByteSet(set + bytes.head, bytes.tail)
  }

  @tailrec
  private[this] def strListToCharList (chars: List[Char], strings: List[String]): List[Char] = {
    if(strings.isEmpty) return chars
    strListToCharList(chars ::: strings.head.toCharArray.toList, strings.tail)
  }

  @tailrec
  private[this] def stringFromByteList(str: String, bytes: List[Byte]): String = {
    if(bytes.isEmpty) return str
    stringFromByteList(str + bytes.head.toChar, bytes.tail)
  }
}