server: added loading page while model loading

[VJHack]

Fix #9158

• I have read the contributing guidelines
• Self-reported review complexity:
  • Low
  • Medium
  • High

[VJHack]

Resolves #9158

[ngxson]

We cannot return HTML for JSON API endpoint (please don't change the test file)

[BradHutchings]

We cannot return HTML for JSON API endpoint (please don't change the test file)

This was not the intent of the request. The intent was when an html file was requested, and the model was loading, that the server not substitute a JSON error result.

I'm sorry that I don't have experience with pull requests and couldn't submit this myself. There is a discussion of what I was trying to accomplish here:

#9158

[VJHack]

We cannot return HTML for JSON API endpoint (please don't change the test file)

Sorry about that. There was a bit of confusion but it should be resolved now. @BradHutchings, now when you visit the page it displays the loading message without interfering with api calls that return JSON.

@ngxson, I ran the CI checks in my forked repo and they all pass.

[ngxson]

You're missing one requirement from the original issue #9158

Here only / is catched, not *.html. I leave a suggestion on my comment #9401 (comment) , but I'll apply it myself.

[ngxson]

I can't push to your repo, so I created a PR to replace this.
See #9468