def compare_stream(a, b)
    bsize = fu_stream_blksize(a, b)
    sa = sb = nil
    while sa == sb
      sa = a.read(bsize)
      sb = b.read(bsize)
      unless sa and sb
        if sa.nil? and sb.nil?
          return true
        end
      end
    end
    false
  end
Returns true if the contents of a stream +a+ and +b+ are identical.