def completedLength
      num = @completeBlocks.countSet
      # Last block may be smaller
      extra = 0
      if @completeBlocks.set?(@completeBlocks.length-1)
        num -= 1
        extra = @lastBlockLength
      end
      num*@blockSize + extra
    end
def completedLength
      num = @completeBlocks.countSet
      # Last block may be smaller
      extra = 0
      if @completeBlocks.set?(@completeBlocks.length-1)
        num -= 1
        extra = @lastBlockLength
      end
      num*@blockSize + extra
    end
Number of bytes we have downloaded and verified.