Improper encoding of reserved characters

This was originally reported as a Cabal bug, but I believe it belongs here:

The value of HTTP_PROXY has as format
http://user:pass@host:80/

In the password special characters can occur, like @ and !.
According to wiki (http://en.wikipedia.org/wiki/Percent-escape)
these characters must be percent-encoded, like %40 and %21.

Cabal doesn't accept percent-encoded characters.
And cabal errs on these characters (if password is a@b, Cabal doesn't look to the right site, but >probably to "b@host:80" (error message is not clear enough to be certain)

该 issue 未指定文件或测试；首先跟踪 HTTP_PROXY 值的解析方式，并复现一个包含 %40 和 %21 等百分号编码保留字符的密码。完成的标准是接受这些字符，并且请求使用预期的主机，同时为代理 URL 场景添加回归覆盖。