Windows: Try all configured proxy resolution types

[davids-work]

On Windows, WPAD, PAC and manual proxy settings are not mutually exclusive. They can all be set and should be tried in that order.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (dff9a60) 72.67% compared to head (a35525a) 72.67%.

Additional details and impacted files

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  Coverage   72.67%   72.67%           
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  Files          16       16           
  Lines         849      849           
  Branches      241      241           
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  Hits          617      617           
  Misses        137      137           
  Partials       95       95           

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[janbrummer]

libproxy is using a specific configuration logic, and it should be the same among all systems: https://libproxy.github.io/libproxy/configuration-logic.html

[davids-work]

The problem is that this makes libproxy a LOT less useful on Windows. "Automatically detect settings" (the switch that controls whether or not WPAD is used) seems to be turned on by default on many installations, and when/if manual settings are configured, it won't get turned off unless the configurator explicitly does so. This prevents libproxy from picking up the manual proxy settings. I have unfortunately encountered systems configured exactly like this in the wild.

The current behavior of libproxy is different from e.g. Edge or Chrome in this regard (which do try all options if enabled and if necessary). My expectation for a Windows application using system proxy settings would be for it to behave in the same manner as the built-in browser.

For reference, this is what the settings GUI looks like (on Windows 10):

Note how all options can be enabled.

[janbrummer]

So we talked about this internally and we agreed to follow the system logic then. Will merge it.