Handle pac files that return a list of proxies by taking the first one

[JohnAdders]

It's valid for pac files to return a list to allow for failures, this patch simply always takes the first one

[genotrance]

Instead of just picking the first, it will be better to change the ; separator to ,. That way, it will be parsed correctly in caller get_destination() which calls parse_proxy() later and Px will attempt to failover to the next one in the list if the first proxy doesn't work.

I think you could also have DIRECT in the list so if PAC doesn't send the exact string DIRECT (which is handled in get_destination()), it will be incorrectly treated as a proxy hostname. It might be helpful to remove DIRECT from a list response but accept it only if it is an exact string. Thoughts?

[JohnAdders]

Update to take into account your comments, thinking about it I'm not sure it handles the case where DIRECT is the first element of a list but I'm not sure that makes sense, do you want me to try and handle that case?

[genotrance]

If DIRECT is the first in list, we could probably just treat it as a simple DIRECT case and give up otherwise. I don't think Px can handle the DIRECT or proxy fallback case right now as it is. And it makes little sense to have DIRECT,proxy anyway so I wouldn't want to invest too much time on that unless we get more info.

I have no way to test any of these changes, is this something you can test?

[JohnAdders]

Have added removal of first item being DIRECT, I'm testing it with a PAC that either returns a list of 2 proxies or DIRECT

[JohnAdders]

Code seems to work as expected with winhttp_find_proxy_for_url returning
DIRECT;fake_proxy;real_proxy
fake_proxy;DIRECT;real_proxy
fake_proxy;real_proxy;DIRECT
fake_proxy;real_proxy
real_proxy
DIRECT

[genotrance]

Thank you for verifying. 👍