According to the specification, tar should finish with two zero blocks, but "reasonable system must not assume that such a block exists when reading an archive". Therefore, the Zig standard library recommends to not call this function.
pub fn finishPedantically(w: *Writer) Io.Writer.Error!void
pub fn finishPedantically(w: *Writer) Io.Writer.Error!void {
try w.underlying_writer.splatByteAll(0, block_size * 2);
}