Fix reverse proxy subpath support using External_Webserver_address

[Leolebleis]

Your checklist for this pull request

• Make sure your name is added to Contributors file /Plan/common/src/main/java/com/djrapitops/plan/delivery/rendering/html/Contributors.java
• No locale changes

Description

When Plan runs behind a reverse proxy at a subpath (e.g. /minecraft/stats/), External_Webserver_address was only consulted when the webserver was disabled. With the webserver running, both HTML asset paths and PLAN_BASE_ADDRESS used the internal address (e.g. http://localhost:8804), breaking static asset loading, React Router navigation, and API calls (wrong protocol/path).

Changes:

• Addresses.getExternalAddress() — new method returning External_Webserver_address when set to a non-default value
• BundleAddressCorrection.getWebserverBasePath() — prefers external address base path for HTML/JS/CSS path rewriting
• ResponseFactory.replaceMainAddressPlaceholder() — prefers external address for PLAN_BASE_ADDRESS injection

Tested on a live deployment (Plan v5.7 b3288 behind nginx HTTPS proxy at a subpath). Unit tests included.

[AuroraLS3]

Alternative_IP.Address is used for this purpose - External address is intended for use when Export is being used

[Leolebleis]

Alternative_IP.Address is used for this purpose - External address is intended for use when Export is being used

@AuroraLS3 Ah I see, thanks! I originally tried Alternative_IP but ran into two issues with HTTPS reverse proxy setups:

1. Mixed content: Alternative_IP gets prepended with Plan's webserver protocol (http://), so PLAN_BASE_ADDRESS becomes http://example.com/plan. On an HTTPS page, API calls to http://... are blocked as mixed content by browsers.
2. getMainAddress() checks DB first: BundleAddressCorrection.getWebserverBasePath() uses getMainAddress(), which queries plan_servers before checking getAccessAddress(). The DB stores the internal address (http://localhost:8804), so Alternative_IP never affects path correction.

External_Webserver_address avoids both issues since it includes the correct protocol (https://) and isn't overridden by the DB lookup.

Would you prefer a different approach — e.g. making Alternative_IP protocol-aware, or having getMainAddress() also consider Alternative_IP?

[AuroraLS3]

When using reverse-proxy based https you can set up Plan to assume https with proxy-mode: https://github.com/plan-player-analytics/Plan/wiki/SSL-Certificate-%28HTTPS%29-Set-Up#if-behind-a-proxy

[AuroraLS3]

This test covers regressions for reverse-proxy behind subdirectory
https://github.com/plan-player-analytics/Plan/blob/master/Plan/common/src/test/java/com/djrapitops/plan/delivery/webserver/ReverseProxyRegressionTest.java

[Leolebleis]

Ah ok thank you :) I need to AFK for a bit but will check later, I think I tried that and ran into issues

Will get back to you asap!