iterator runes*(s: Stream, buffSize=64000): Rune =
  ## reads runes from a stream. Resuming is not supported.
  ## It must be ran until completion, otherwise it
  ## may've consumed more than what was yielded. Raises
  ## `EIO` if an error occurred.
  var buff = newString(buffSize)
  var rune: Rune
  var n = 0
  var safeBoundary = buffSize - 4
  while not s.atEnd:
    let read = readData(s, addr(buff[n]), buff.len - n)
    if read != buff.len - n:
      assert s.atEnd
      buff.setLen(read + n)
      safeBoundary = buff.len
    n = 0
    while n < safeBoundary:
      fastRuneAt(buff, n, rune, true)
      yield rune
    copyMem(addr(buff[0]), addr(buff[n]), buff.len - n)
    n = buff.len - n