new-feature: Broken link checker

[CookieSource]

Hugo doesn't seem to have a native way to check for broken links.
We should however implement a way to check for these.

I currently found 3 different solutions:

https://github.com/marketplace/actions/hugo-broken-link-check
https://discourse.gohugo.io/t/tutorial-how-to-check-broken-links-in-hugo/54750
https://www.veriphor.com/articles/link-and-image-render-hooks/#link-render-hook

This is to make sure our content stays relevant without people running into broken links.

[NomadicCore]

Do you have a preference?

Whilst we are on GitHub, my preference would be the GitHub action approach but I don't know if you take a different view?

[jplatte]

There's also https://lychee.cli.rs/ as a standalone solution (that checks both internal and external links in the built site).

[NomadicCore]

Thanks, will also have a look at that

[NomadicCore]

Aside from broken links, we should also be checking whether links have been hijacked over time.

Thanks to @livingsilver94 for highlighting links in these two by way of example:

1. https://aerynos.com/blog/2020/07/01/the-great-experiment/
2. https://aerynos.com/blog/2020/08/08/stage1-complete/

[CookieSource]

hmm that may be difficult.

Do we wish to check for domain owner changes or how do we define hijacked. Perhaps check for redirects 301 and 302 http codes? as that's this issue.

[CookieSource]

It seems there's a couple of options available now.
https://github.com/stevenvachon/broken-link-checker

I will do further research when I look further down the line. However I am still unsure how one might want to check for hijacking. As redirects are very common that wouldn't immediately indicate bad behavior.

although we could write a thing that checks if a redirect goes to a different domain. To validate those manually.

https://github.com/JustinBeckwith/linkinator
https://github.com/lycheeverse/lychee
https://github.com/linkchecker/linkchecker

[CookieSource]

I've added a couple of options I will test these later. To confirm they work and handle the implementation. I will see if I can add something like a compare for 301 and 302 http events. So we can get an alert if a redirect moves to a different domain.

Lychy can output in Json so we could write a small shell script to compare each run if the domain on a redirect has changed to verify manually that's fine. Should be a reasonable simple implementation I'm partial to just doing the compare in Bash as everyone pretty much understands how to work with that.