Do not use a CDN to get bootstrap, jquery and popper

[LudovicRousseau]

This patch is NOT complete. A better approach would be to add a --no-cdn command line (or something like that). But I do not know Ruby so I am not able to program that myself.

If the assets are downloaded from a CDN then the loading fails with a Content-Security-Policy error in my case.

Content-Security-Policy : Les paramètres de la page ont empêché le chargement d’une ressource à https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css (« style-src »).

I know I could change the server configuration but it is simpler for me to distribute the files myself from the server.
And this is better for my user privacy.

[mishina2228]

Thanks for your PR!

To explain the context, CDN has been used since v2.3.0.
Prior to that, assets bundled with the gem were used.

The reasons for the change to use CDN are as follows:

• To reduce the size of the gem.
• Not want to replace assets every time the JS libraries are updated.

I prefer not to bundle assets with the gem, so I would like to take other approaches.
For example, I came up with the idea that if --no-cdn is added to the command line, assets will be downloaded locally from the internet and the view will use them.

What do you think?

[LudovicRousseau]

Downloading the assets at build time if --no-cdn is used is a very good idea.

I propose to use a cache and download bootstrap & jquery only if not already present (and with the correct hash).

My patch was just a quick hack for my own use.

[mishina2228]

I propose to use a cache and download bootstrap & jquery only if not already present (and with the correct hash).

Great idea!
I'm a little busy right now, but would like to tackle this when I have time.

[LudovicRousseau]

I propose to always download the assets from the CDN (or somewhere else) at run time (and use the cache mechanism). So no need to add a --no-cdn option.

• the gem will still have a small size
• it will work for everybody