Let nikola serve work together with non-root BASE_URL or SITE_URL. Fixes #3726

[aknrdureegaesr]

Pull Request Checklist

• I’ve read the guidelines for contributing.
• I updated AUTHORS.txt and CHANGES.txt (if the change is non-trivial) and documentation (if applicable).
• I tested my changes.

Description

With the previous implementation, check out nikola-site, edit config.py to say something like SITE_URL = "https://getnikola.com/documentation" and build anew, then run nikola serve --browser . This breaks in several ways, which is exactly the point of #3726 .

Now apply this pull request to nikola, and do the same again: It works.

I have also added some tests. They let the nikola server functionality run in a different thread, opening up an HTTP port. The main thread sends HTTP requests to the server and checks whether the answers are as expected.

Doing so exposed an assumption of the server plugin: "When I'm running, I'm the only thing that matters, so when I'm done, I might as well shut down the entire application." I don't like that from an architectural point of view. To put application-level shutdown into the hands of one of several components feels wrong to me. Essentially, such a component is not testable.

I left it in there, but guarded: This now happens only if running on the main thread. My tests runs the functionality on a different thread, so then the guard sees to it that the whole application is not shut down. In the process, I found the plugin didn't even try to stop the internal HTTP server when shutdown was called. This is somewhat improved now, at least for the case when the HTTP server runs in a thread of its own.