Apr 12, 2020

#082

Work

A standard week in Platform Health, which means I worked on a bunch of different things. Probably the most interesting was a bug1 to do with attachment replacements.

What are attachment replacements? Well, pages on GOV.UK can have files attached to them by the publisher, and new versions of a page can replace existing attachments, making the old attachment redirect to the replacement. However, there was a problem with how this mechanism interacted with draft pages.

Pages on GOV.UK can be either draft or live. Draft content isn’t accessible to normal people (like you), only live content is. So it’s very important that attachments don’t redirect to their replacement if that replacement is still a draft!

There’s a bit of logic for handling redirections in asset-manager:

if asset.replacement.present? && (!asset.replacement.draft? || requested_from_draft_assets_host?)
  set_default_expiry
  redirect_to_replacement_for(asset)
  return
end

So, if a publisher creates a new draft of a document, and replaces some attachments, the live attachments won’t redirect until the document is published and the replacements become live. So far so good.

But there’s a problem with asset.replacement.

To avoid long chains of redirects (which many browsers won’t follow after a certain point), whenever an attachment is replaced, anything transitively replaced by it is updated to refer directly to it.

Say you have two attachments:

A1 -> A2

Where -> means “is replaced by”. Assuming A2 is live, visiting A1 redirects you to it. Good stuff. But then the publisher makes a new draft, and replaces A2. We get this situation:

A1 -> A3
A2 -> A3

Until the document is published, A3 is a draft. So neither A1 nor A2 will redirect to it. That’s good, but now the redirect from A1 to A2 is broken! Oh no!

It turned out to be not too tricky to fix, but did have to be changed in two apps to be fully fixed: in asset-manager and in whitehall.

Now to wait another few years to discover a bug in how I did it.

The Plague

The shops are still out of flour.

Miscellaneous

Books

I read Uzumaki, a horror manga by Junji Ito about spirals. I’ve read it before, but not for a long time, so while I remembered the basics of most of the stories I’d forgotten a lot of the detail. Junji Ito writes some really good stuff.

I also got a few new books:

Games

It’s Apocalypse World week again. This time I tried to introduce some more NPCs, as the players said that the lack of them was causing difficulties: in Apocalypse World you have to pay for your character’s living expenses at the start of a session, and the main way to make more money is to do jobs for NPCs. I got to introduce some new NPCs and flesh out some old ones, and everyone made some money.

Towards the end of the session, I got to reveal a plot twist I’ve had in mind (two NPCs turned out to be the same person), which I thought had been obvious for a while, but a couple of the players hadn’t picked up on it (some had), so it worked pretty well. Now I need to think of the next plot twist and get some foreshadowing in.

I also ran a game of Golden Sky Stories for two people who’d not played it before, and who had limited RPG experience: one had played a bit of D&D, the other hadn’t played any games before but had read a bunch of rulebooks. I spent the session thinking “this is going terribly, they’re hating this” but, actually, it seems they quite enjoyed it, and they want another session.

The session was slightly marred by Steam’s voice chat echoing everything anyone said. Discord voice chat works fine, so it must be a software issue.

  1. Introduced by me a couple of years ago, as it turns out.↩︎