action: Add action to check bridge connectivity

[logmanoriginal]

It is currently not simply possible to check if the remote server for a bridge is reachable or not, which means some of the bridges might no longer work because the server is no longer on the internet.

In order to find those bridges we can either check each bridge individually (which takes a lot of effort), or use an automated script to do this for us.

If a server is no longer reachable it could mean that it is temporarily unavailable, or shutdown permanently. The results of this script will at least help identifying such servers.

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This PR adds a new action connectivity which returns a page that checks each bridge individually. It only checks bridges on the whitelist and uses JavaScript to make the page somewhat responsive.

Note that I didn't use PHPUnit for the testing because it doesn't make sense to fail tests on bridges unrelated to fixes. There might also be some benefit for administrators if they want to check if a bridge works on their servers.

The implementation is still very rough (more like a proof of concept). This is what the process looks like (on my end at least).

Pressing [Show] opens a new tab to the bridge on our front page.

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Disclaimer
I'm no JS programmer, so don't get too irritated by the implementation.

What is your opinion on this?
Should this be part of the repository?
Let me know if you have a better idea of detecting inoperable bridges.

[logmanoriginal]

I added a few things to make it respond better to user input.

• Split into multiple files to separate JavaScript and CSS code
• This action now only works in debug mode (because it has no value to "normal" users)
• The process can be aborted by pressing "x" on the status message
• Added status icons to the message (processing, aborted, done)
• Added a new status (yellow) if the process is aborted
• The page now always responds to user input while processing in the background

I'm currently thinking about adding one more status for bridges where the server redirects requests.
Let me know if you have further suggestions.

Here are a few impressions

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[logmanoriginal]

Added two more features.

• Mark redirected bridges (blue) => This requires a change in lib/contents.php
• Show tool tip for icons

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By the way, this is what inactive bridges (not on the whitelist) look like

[teromene]

I am good with this !
The only downside I see is that it kinda acts as a replacement to real tests, but it's definitely better than nothing.

[teromene]

I am not sure about linking to bootstap's CDNs tbh. If needed I'll do a CSS in another PR

[logmanoriginal]

Do you mean to include the CSS files in the repository, or to replace Bootstrap entirely?

[teromene]

Maybe include the CSS for now

[logmanoriginal]

Thanks for your feedback @teromene

I am good with this !
The only downside I see is that it kinda acts as a replacement to real tests, but it's definitely better than nothing.

I agree that the border between real tests and this action is somewhat blurry, but there is an important difference. Real tests run on Travis, while this action can be used on any server without having to install any third-party software.

This has become very helpful to me for detecting bridges that simply don't work on my server (although they seem to work for others). I could even use this action to filter inaccessible sites/bridges from my whitelist.

That said, we clearly need to limit the amount of functionality to keep it maintainable. Let me know if you find anything that should rather be left out.

[teromene]

Appart from the CSS thing, LGTM