解决问题的方法是显式设置Content-Type为undefined，这样你的浏览器或者您使用的任何客户端都可以设置它并为您添加该边界值.令人失望但真实.

The solution to the problem is to explicitly set Content-Type to undefined so that your browser or whatever client you're using can set it and add that boundary value in there for you. Disappointing but true.