Report 404s and such with Canonical referers as LP errors

[Jeroen T. Vermeulen]

My apologies if this is something we already do.

We treat "not found" and "permission denied" errors as a lesser kind of failure. I rarely look at them, if ever, because they'll be full of users (including myself) manipulating URLs themselves and failing, bots chasing down broken links on the internet, and so on. No way we'll ever get rid of those without getting rid of visitors.

But there is one case where I definitely want to know about them: if the referrer is under Canonical's control. If a Translations page links the user to a Code page that doesn't exist, that's a bug. If the help wiki links to a form whose URL has changed, the help wiki needs fixing. If a project description contains a broken URL to a Launchpad page, it'd be sensible to point it out to the project owners.

I'd love to say we could do the same for "permission denied" errors. But that may be harder because it'd produce oopses whenever we said "admins can fix this at http://[...]/".

[Robert Collins (lifeless)]

We already separate out referrals from LP to LP and generate an OOPS for them.

We don't treat links from e.g. www.canonical.com as needing to
generate an OOPS, but its a good idea and we should do that.