When install the Plone-5.2.1,the err log 'Error: Download error for https://files.pythonhosted.org/packages/c5/da/cab04479eb7c64b52ff197c32bc92fb3b04d11ab1d6f818f68d7431b8524/z3c.zcmlhook-1.0b1.tar.gz#sha256=f0456020738a921d68b488c453e76d7dc8b5e8c890593116854f54dfcd3c1302: EOF occurred in violation of protocol (_ssl.c:645)' 
It looks like we should provide a zip of the eggs directory as an additional download.
what's time can support this feature,I can't wait any more 
I'm going crazy because of it
you can try to use an Chinese PyPI mirror. With a quick search I found
https://pypi.tuna.tsinghua.edu.cn/simple - probably there are more out there.
In file buildout.cfg in the [buildout] section use index = https://pypi.tuna.tsinghua.edu.cn/simple
(replace a eventually existing index= line).
I've tried, but I still make mistakes, and I suggest should provide a zip of the eggs directory as an additional download.It will be a lot more convenient 
~