Bcodr.scala

packagetorrent

importcollection.mutable.ListBuffer

objectBcodr {
/**
 * Returns a List containing Strings, Ints, Lists or Maps[String,Any]
 * Any<|BcodeAny where BcodeAny in Int, String, List[BcodeAny], Map[String,BcodeAny]
 * 3:abc => "abc" (where # is the length of the string)
 * i123e => 123
 * li123e3:abc => List(123, "abc)
 * di123e3:abc4:frooi45e => Map
*/
defbdecode(stream:Stream[Char]):Any= bdecode(stream, ListBuffer()).toList(0)
defbdecode(string:String):Any= bdecode(string.toStream, ListBuffer()).toList(0)
privatedefbdecode(stream:Stream[Char], acc:ListBuffer[Any]):ListBuffer[Any] = stream match {
case s if (s.isEmpty) => acc
case ch #:: chs => ch match {
// beginning of a String
case n if (n.isDigit) => {
valstrlen= stream.takeWhile(p =>':'!= p).mkString
// length + 1 because next char is ':'
val (str, next) = stream.drop(strlen.length +1).splitAt(strlen.toInt)
 bdecode(next, acc += str.mkString)
 }
// end of a list or dictionary 
case'e'=> acc
// beginning of an Int
case'i'=> {
valnum= chs.takeWhile(p =>'e'!= p).mkString
// len + 1 pulls the e off the end
 bdecode(chs.splitAt(num.length +1)._2, acc += num.toInt)
 }
// beginning of a list
case'l'=> {
// drop l and get a sublist ending at outer 'e'
vallist= bdecode(chs, ListBuffer()).toList
 bdecode(stream.drop(size(list)), acc += list)
 }
// beginning of a dictionary
case'd'=> {
// drop d and get a sublist ending at outer 'e'
vallist= bdecode(chs, ListBuffer()).toList
// convert each consecutive pair in the list to a key -> value pair
valmap:Map[String,Any] = list.sliding(2, 2).collect{caseList(a,b) => (a.toString,b)}.toMap
valbytes= size(map)
 bdecode(stream.drop(bytes), acc += map)
 }
case _ =>thrownewIllegalArgumentException("unmatched char in bdecode")
 }
 }
/**
 * Determines the number of characters required to represent an item
 * Any<|BcodeAny where BcodeAny in Int, String, List[BcodeAny], Map[String,BcodeAny]
 * 3:abc => "abc" (where # is the length of the string)
 * i123e => 123
 * li123e3:abc => List(123, "abc)
 * di123e3:abc4:frooi45e => Map
*/
privatedefsize(item:Any):Int= item match {
case i:Int=> {
// if negative, need +1 for the '-'
valneg=if (i <0) 1else0
2+ neg +Math.ceil(Math.log10(Math.abs(i))).toInt
 }
// +1 is for ':', log(len + 1) b/c log(10) = 1
case s:String=>1+Math.ceil(Math.log10(s.length +1)).toInt + s.length 
case l:List[Any] => l.foldLeft(2)((a,i) => a + size(i)) // +2 'l', 'e'
case m:Map[_,_] => m.foldLeft(2)((a, kv) => a + size(kv._1) + size(kv._2)) // +2 'd' 'e'
 }
/**
 * Encodes an item to a String
 * Any<|BcodeAny where BcodeAny in Int, String, List[BcodeAny], Map[String,BcodeAny]
 * 3:abc => "abc" (where # is the length of the string)
 * i123e => 123
 * li123e3:abc => List(123, "abc)
 * di123e3:abc4:frooi45e => Map
*/
defbencode(item:Any):String= bencode(item, "")
privatedefbencode(item:Any, acc:String):String= item match {
case i:Int=> acc +"i"+ i.toString +"e"
case s:String=> acc + s.length +":"+ s
case l:List[Any] => l.foldLeft(acc +"l")((a, i) => bencode(i, a)) +"e"
case m:Map[String@unchecked,_] => {
// keys must appear in sorted order
valkeys:List[String] = m.keys.toList.sorted
 keys.foldLeft(acc +"d")((a, k) => bencode(k, a) + bencode(m(k))) +"e"
 }
case _ =>thrownewIllegalArgumentException("item must be in (Int, String, List, Map[String,_]")
 }

}