Tag: programming

Spring ’83 Came And Went

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Just in time for Robin Sloan to give up on Spring ’83, earlier this month I finally got aroud to launching STS-6 (named for the first mission of the Space Shuttle Challenger in Spring 1983), my experimental Spring ’83 server. It’s been a busy year; I had other things to do. But you might have guessed that something like this had been under my belt when I open-sourced a keygenerator for the protocol the other day.

If you’ve not played with Spring ’83, this post isn’t going to make much sense to you. Sorry.

Introducing STS-6

Screenshots showing STS-6, listing the most-recent blog posts on DanQ.me, in two different display styles.
My output looks distinctly different in The Kingswood Palimpsest then in The Oakland Follower-Sentinel (two key reference Spring ’83 clients), and that’s fine and expected.

My server is, as far as I can tell, very different from any others in a few key ways:

  • It does not allow third-party publishing at all. Some might argue that this undermines the aim of the exercise, but I disagree. My IndieWeb inclinations lead me to favour “self-hosted” content, shared from its owners’ domain. Also: the specification clearly states that a server must implement a denylist… I guess my denylist simply includes all keys that are not specifically permitted.
  • It’s geared towards dynamic content. My primary board self-publishes whenever I produce a new blog post, listing the most recent blog posts published. I have another half-implemented which shows a summary of the most-recent post, and another which would would simply use a WordPress page as its basis – yes, this was content management, but published over Spring ’83.
  • It provides helpers to streamline content production. It supports internal references to other boards you control using the format {{board:123}}which are automatically converted to addresses referencing the public key of the “current” keypair for that board. This separates the concept of a board and its content template from that board’s keypairs, making it easier to link to a board. To put it another way, STS-6 links are self-healing on the server-side (for local boards).
  • It helps automate content-fitting. Spring ’83 strictly requires a maximum board size of 2,217 bytes. STS-6 can be configured to fit a flexible amount of dynamic content within a template area while respecting that limit. For my posts list board, the number of posts shown is moderated by the size of the resulting board: STS-6 adds more and more links to the board until it’s too big, and then removes one!
  • It provides “hands-off” key management features. You can pregenerate a list of keys with different validity periods and the server will automatically cycle through them as necessary, implementing and retroactively-modifying <link rel="next"> connections to keep them current.

I’m sure that there are those who would see this as automating something that was beautiful because it was handcrafted; I don’t know whether or not I agree, but had Spring ’83 taken off in a bigger way, it would always only have been a matter of time before somebody tried my approach.

From a design perspective, I enjoyed optimising an SVG image of my header so it could meaningfully fit into the board. It’s pretty, and it’s tolerably lightweight.

If you want to see my server in action, patch this into your favourite Spring ’83 client: https://s83.danq.dev/10c3ff2e8336307b0ac7673b34737b242b80e8aa63ce4ccba182469ea83e0623

A dead end?

Without Robin’s active participation, I feel that Spring ’83 is probably coming to a dead end. It’s been a lot of fun to play with and I’d love to see what ideas the experience of it goes on to inspire next, but in its current form it’s one of those things that’s an interesting toy, but not something that’ll make serious waves.

In his last lab essay Robin already identified many of the key issues with the system (too complicated, no interpersonal-mentions, the challenge of keys-as-identifiers, etc.) and while they’re all solvable without breaking the underlying mechanisms (mentions might be handled by Webmention, perhaps, etc.), I understand the urge to take what was learned from this experiment and use it to help inform the decisions of the next one. Just as John Postel’s Quote of the Day protocol doesn’t see much use any more (although maybe if my finger server could support QotD?) but went on to inspire the direction of many subsequent “call-and-response” protocols, including HTTP, it’s okay if Spring ’83 disappears into obscurity, so long as we can learn what it did well and build upon that.

Meanwhile: if you’re looking for a hot new “like the web but lighter” protocol, you should probably check out Gemini. (Incidentally, you can find me at gemini://danq.me, but that’s something I’ll write about another day…)

Debugging Mysteries

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This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

Just wanted to share with you something I found ages ago but only just got around to mentioning – Julia Evans‘ (of Wizard Zines fame) Debugging Mysteries:

There are five mysteries here right now:

The Case of the Slow Websites
The Case of the Connection Timeout
The Case of the DNS Update that Didn’t Work
The Case of the 50ms Request
The Case of the Failed Docker Connection

Go back to wizardzines.com

GitHub repository: jvns/twine-stories
Blog post about this project: Notes on building debugging puzzles

Each mystery is a Twine-powered “choose your own adventure” game in which you must diagnose the kind of issue that a software developer might, for real. I think these are potentially excellent tools for beginner programmers, not just because they provide some information about the topic of each, but because they encourage cultivating a mindset of the kind of thinking that’s required to get to the bottom of gnarly problems.

Better yet, she’s open-sourced the entire thing (and I was excited to see she wrote in Twee, which is very dear to my heart).

Beating Children at Mastermind [Video]

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This video accompanies a blog post of the same title. The content is basically the same – if you prefer videos, watch this video. If you prefer blog posts, go read the blog post. You might also like to play with my Mastermind solver or view the source code.

Also available on YouTube and Facebook.

Beating Children at Mastermind

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This blog post is also available as a video. Would you prefer to watch/listen to me tell you about how I’ve implemented a tool to help me beat the kids when we play Mastermind?

I swear that I used to be good at Mastermind when I was a kid. But now, when it’s my turn to break the code that one of our kids has chosen, I fail more often than I succeed. That’s no good!

Black, white, brown, blue, green, orange and yellow Mastermind pegs in a disordered heap.
If you didn’t have me pegged as a board gamer… where the hell have you been?

Mastermind and me

Maybe it’s because I’m distracted; multitasking doesn’t help problem-solving. Or it’s because we’re “Super” Mastermind, which differs from the one I had as a child in that eight (not six) peg colours are available and secret codes are permitted to have duplicate peg colours. These changes increase the possible permutations from 360 to 4,096, but the number of guesses allowed only goes up from 8 to 10. That’s hard.

A plastic Mastermind board in brown and green; it has twelve spots for guessing and shows six coloured pegs. The game has been won on the sixth guess.
The set I had as a kid was like this, I think. Photo courtesy ZeroOne; CC-BY-SA license.

Or maybe it’s just that I’ve gotten lazy and I’m now more-likely to try to “solve” a puzzle using a computer to try to crack a code using my brain alone. See for example my efforts to determine the hardest hangman words and make an adverserial hangman game, to generate solvable puzzles for my lock puzzle game, to cheat at online jigsaws, or to balance my D&D-themed Wordle clone.

Hey, that’s an idea. Let’s crack the code… by writing some code!

Screenshot showing Mastermind game from WebGamesOnline.com. Seven guesses have been made, each using only one colour for each of the four pegs, and no guesses are corect; only red pegs have never been guessed.
This online edition plays a lot like the version our kids play, although the peg colours are different. Next guess should be an easy solve!

Representing a search space

The search space for Super Mastermind isn’t enormous, and it lends itself to some highly-efficient computerised storage.

There are 8 different colours of peg. We can express these colours as a number between 0 and 7, in three bits of binary, like this:

Decimal Binary Colour
0 000 Red
1 001 Orange
2 010 Yellow
3 011 Green
4 100 Blue
5 101 Pink
6 110 Purple
7 111 White

There are four pegs in a row, so we can express any given combination of coloured pegs as a 12-bit binary number. E.g. 100 110 111 010 would represent the permutation blue (100), purple (110), white (111), yellow (010). The total search space, therefore, is the range of numbers from 000000000000 through 111111111111… that is: decimal 0 through 4,095:

Decimal Binary Colours
0 000000000000 Red, red, red, red
1 000000000001 Red, red, red, orange
2 000000000010 Red, red, red, yellow
…………
4092 111111111100 White, white, white, blue
4093 111111111101 White, white, white, pink
4094 111111111110 White, white, white, purple
4095 111111111111 White, white, white, white

Whenever we make a guess, we get feedback in the form of two variables: each peg that is in the right place is a bull; each that represents a peg in the secret code but isn’t in the right place is a cow (the names come from Mastermind’s precursor, Bulls & Cows). Four bulls would be an immediate win (lucky!), any other combination of bulls and cows is still valuable information. Even a zero-score guess is valuable- potentially very valuable! – because it tells the player that none of the pegs they’ve guessed appear in the secret code.

A plastic Mastermind board in blue and yellow with ten guess spaces and eight pegs. The sixth guess is unscored but looks likely to be the valid solution.
If one of Wordle‘s parents was Scrabble, then this was the other. Just ask its Auntie Twitter.

Solving with Javascript

The latest versions of Javascript support binary literals and bitwise operations, so we can encode and decode between arrays of four coloured pegs (numbers 0-7) and the number 0-4,095 representing the guess as shown below. Decoding uses an AND bitmask to filter to the requisite digits then divides by the order of magnitude. Encoding is just a reduce function that bitshift-concatenates the numbers together.

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/**
 * Decode a candidate into four peg values by using binary bitwise operations.
 */
function decodeCandidate(candidate){
  return [
    (candidate & 0b111000000000) / 0b001000000000,
    (candidate & 0b000111000000) / 0b000001000000,
    (candidate & 0b000000111000) / 0b000000001000,
    (candidate & 0b000000000111) / 0b000000000001
  ];
}

/**
 * Given an array of four integers (0-7) to represent the pegs, in order, returns a single-number
 * candidate representation.
 */
function encodeCandidate(pegs) {
  return pegs.reduce((a, b)=>(a << 3) + b);
}

With this, we can simply:

  1. Produce a list of candidate solutions (an array containing numbers 0 through 4,095).
  2. Choose one candidate, use it as a guess, and ask the code-maker how it scores.
  3. Eliminate from the candidate solutions list all solutions that would not score the same number of bulls and cows for the guess that was made.
  4. Repeat from step #2 until you win.

Step 3’s the most important one there. Given a function getScore( solution, guess ) which returns an array of [ bulls, cows ] a given guess would score if faced with a specific solution, that code would look like this (I’m convined there must be a more-performant way to eliminate candidates from the list with XOR bitmasks, but I haven’t worked out what it is yet):

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/**
 * Given a guess (array of four integers from 0-7 to represent the pegs, in order) and the number
 * of bulls (number of pegs in the guess that are in the right place) and cows (number of pegs in the
 * guess that are correct but in the wrong place), eliminates from the candidates array all guesses
 * invalidated by this result. Return true if successful, false otherwise.
 */
function eliminateCandidates(guess, bulls, cows){
  const newCandidatesList = data.candidates.filter(candidate=>{
    const score = getScore(candidate, guess);
    return (score[0] == bulls) && (score[1] == cows);
  });
  if(newCandidatesList.length == 0) {
    alert('That response would reduce the candidate list to zero.');
    return false;
  }
  data.candidates = newCandidatesList;
  chooseNextGuess();
  return true;
}

I continued in this fashion to write a full solution (source code). It uses ReefJS for component rendering and state management, and you can try it for yourself right in your web browser. If you play against the online version I mentioned you’ll need to transpose the colours in your head: the physical version I play with the kids has pink and purple pegs, but the online one replaces these with brown and black.

Testing the solution

Let’s try it out against the online version:

As expected, my code works well-enough to win the game every time I’ve tried, both against computerised and in-person opponents. So – unless you’ve been actively thinking about the specifics of the algorithm I’ve employed – it might surprise you to discover that… my solution is very-much a suboptimal one!

A young boy sits cross-legged on the floor, grinning excitedly at a Mastermind board (from the code-maker's side).
My code has only failed to win a single game… and that turned out to because my opponent, playing overexcitedly, cheated in the third turn. To be fair, my code didn’t lose either, though: it identified that a mistake must have been made and we declared the round void when we identified the problem.

My solution is suboptimal

A couple of games in, the suboptimality of my solution became pretty visible. Sure, it still won every game, but it was a blunt instrument, and anybody who’s seriously thought about games like this can tell you why. You know how when you play e.g. Wordle (but not in “hard mode”) you sometimes want to type in a word that can’t possibly be the solution because it’s the best way to rule in (or out) certain key letters? This kind of strategic search space bisection reduces the mean number of guesses you need to solve the puzzle, and the same’s true in Mastermind. But because my solver will only propose guesses from the list of candidate solutions, it can’t make this kind of improvement.

Animation showing how three clues alone are sufficient to derive a unique answer from the search space of the original "break into us" lock puzzle.
My blog post about Break Into Us used a series of visual metaphors to show search space dissection, including this one. If you missed it, it might be worth reading.

Search space bisection is also used in my adverserial hangman game, but in this case the aim is to split the search space in such a way that no matter what guess a player makes, they always find themselves in the larger remaining portion of the search space, to maximise the number of guesses they have to make. Y’know, because it’s evil.

Screenshot showing a single guess row from Online Mastermind, with the guess Red, Red, Green, Green.
A great first guess, assuming you’re playing against a random code and your rules permit the code to have repeated colours, is a “1122” pattern.

There are mathematically-derived heuristics to optimise Mastermind strategy. The first of these came from none other than Donald Knuth (legend of computer science, mathematics, and pipe organs) back in 1977. His solution, published at probably the height of the game’s popularity in the amazingly-named Journal of Recreational Mathematics, guarantees a solution to the six-colour version of the game within five guesses. Ville [2013] solved an optimal solution for a seven-colour variant, but demonstrated how rapidly the tree of possible moves grows and the need for early pruning – even with powerful modern computers – to conserve memory. It’s a very enjoyable and readable paper.

But for my purposes, it’s unnecessary. My solver routinely wins within six, maybe seven guesses, and by nonchalantly glancing at my phone in-between my guesses I can now reliably guess our children’s codes quickly and easily. In the end, that’s what this was all about.

Bash+Batch In One File

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Today I wanted to write a script that I could execute from both *nix (using Bash or a similar shell) and on Windows (from a command prompt, i.e. a batch file). I found Max Norin’s solution which works, but has a few limitations, e.g. when run it outputs either the word “off” when run in *nix or the word “goto” when run on Windows. There’s got to be a sneaky solution, right?

Here’s my improved version:

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@goto(){
  # Linux code here
  uname -o
}

@goto $@
exit

:(){
@echo off
rem Windows script here
echo %OS%

Mine exploits the fact that batch files can prefix commands with @ to suppress outputting them as they execute. So @goto can be a valid function name in bash/zsh etc. but is interpreted as a literal goto command in a Windows Command Prompt. This allows me to move the echo off command – which only has meaning to Windows – into the Windows section of the script and suppress it with @.

The file above can be saved as e.g. myfile.cmd and will execute in a Windows Command Prompt (or in MS-DOS) or your favourite *nix OS. Works in MacOS/BSD too, although obviously any more-sophisticated script is going to have to start working around the differences between GNU and non-GNU versions of core utilities, which is always a bit of a pain! Won’t work in sh because you can’t define functions like that.

But the short of it is you can run this on a stock *nix OS and get:

$ ./myfile.cmd
GNU/Linux

And you can run it on Windows and get:

> .\myfile.cmd
Windows_NT

You can’t put a shebang at the top because Windows hates it, but there might be a solution using PowerShell scripts (which use hashes for comments: that’s worth thinking about!). In any case: if the interpreter strictly matters you’ll probably want to shell to it on line 3 with e.g. bash -c.

Why would you want such a thing? I’m not sure. But there is is, if you do.

Pronouns in Three Rings

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The Old Way

Prior to 2018, Three Rings had a relatively simple approach to how it would use pronouns when referring to volunteers.

If the volunteer’s gender was specified as a “masculine” gender (which particular options are available depends on the volunteer’s organisation, but might include “male”, “man”, “cis man”, and “trans man”), the system would use traditional masculine pronouns like “he”, “his”, “him” etc.

If the gender was specified as a “feminine” gender (e.g .”female”, “woman”, “cis women”, “trans woman”) the system would use traditional feminine pronouns like “she”, “hers”, “her” etc.

For any other answer, no specified answer, or an organisation that doesn’t track gender, we’d use singular “they” pronouns. Simple!

Three Rings' "Gender" drop-down, with "Female" selected.This selection was reflected throughout the system. Three Rings might say:

  • They have done 7 shifts by themselves.
  • She verified her email address was hers.
  • Would you like to sign him up to this shift?

Unfortunately, this approach didn’t reflect the diversity of personal pronouns nor how they’re applied. It didn’t support volunteer whose gender and pronouns are not conventionally-connected (“I am a woman and I use ‘them/they’ pronouns”), nor did it respect volunteers whose pronouns are not in one of these three sets (“I use ze/zir pronouns”)… a position it took me an embarrassingly long time to fully comprehend.

So we took a new approach:

The New Way

Three Rings' "Pronouns" drop-down, with "ze/zir/zir/zirs/zemself" selected.

From 2018 we allowed organisations to add a “Pronouns” property, allowing volunteers to select from 13 different pronoun sets. If they did so, we’d use it; failing that we’d continue to assume based on gender if it was available, or else use the singular “they”.

Flowchart showing how the pronouns used by Three Rings for a volunteer are contingent on what properties their org records, whether the volunteer has specified pronouns, failing that whether they've specified a gender, falling back to "singular they" pronouns.
The process has some further complexities to cover the fact that we say “they are” but “he is“, but this broadly covers it.

Let’s take a quick linguistics break

Three Rings‘ pronoun field always shows five personal pronouns, separated by slashes, because you can’t necessarily derive one from another. That’s one for each of five types:

  1. the subject, used when the person you’re talking about is primary argument to a verb (“he called”),
  2. object, for when the person you’re talking about is the secondary argument to a transitive verb (“he called her“),
  3. dependent possessive, for talking about a noun that belongs to a person (“this is their shift”),
  4. independent possessive, for talking about something that belongs to a person potentially would an explicit noun (“this is theirs“), and the
  5. reflexive (and intensive), two types which are generally the same in English, used mostly in Three Rings when a person is both the subject and indeirect of a  verb (“she signed herself up to a shift”).

Let’s see what those look like – here are the 13 pronoun sets supported by Three Rings at the time of writing:

Subject Object Possessive Reflexive/intensive
Dependent Independent
he him his himself
she her hers herself
they them their theirs themselves
e em eir eirs emself
ey eirself
hou hee hy hine hyself
hu hum hus humself
ne nem nir nirs nemself
per pers perself
thon thons thonself
ve ver vis verself
xe xem xyr xyrs xemself
ze zir zirs zemself

That’s all data-driven rather than hard-coded, by the way, so adding additional pronoun sets is very easy for our developers. In fact, it’s even possible for us to apply an additional “override” on an individual, case-by-case basis: all we need to do is specify the five requisite personal pronouns, separated by slashes, and Three Rings understands how to use them.

Writing code that respects pronouns

Behind the scenes, the developers use a (binary-gendered, for simplicity) convenience function to produce output, and the system corrects for the pronouns appropriate to the volunteer in question:

<%= @volunteer.his_her.capitalize %>
account has been created for
<%= @volunteer.him_her %>
so
<%= @volunteer.he_she %>
can now log in.

The code above will, dependent on the pronouns specified for the volunteer @volunteer, output something like:

  • His account has been created for him so he can now log in.
  • Her account has been created for her so she can now log in.
  • Their account has been created for them so they can now log in.
  • Eir account has been created for em so ey can now log in.
  • Etc.

We’ve got extended functions to automatically detect cases where the use of second person pronouns might be required (“Your account has been created for you so you can now log in.”) as well as to help us handle the fact that we say “they are” but “he/she/ey/ze/etc. is“.

It’s all pretty magical and “just works” from a developer’s perspective. I’m sure most of our volunteer developers don’t think about the impact of pronouns at all when they code; they just get on with it.

Is that a complete solution?

Does this go far enough? Possibly not. This week, one of our customers contacted us to ask:

Is there any way to give the option to input your own pronouns? I ask as some people go by she/them or he/them and this option is not included…

You can probably see what’s happened here: some organisations have taken our pronouns property – which exists primarily to teach the system itself how to talk about volunteers – and are using it to facilitate their volunteers telling one another what their pronouns are.

What’s the difference? Well:

When a human discloses that their pronouns are “she/they” to another human, they’re saying “You can refer to me using either traditional feminine pronouns (she/her/hers etc.) or the epicene singular ‘they’ (they/their/theirs etc.)”.

But if you told Three Rings your pronouns were “she/her/their/theirs/themselves”, it would end up using a mixture of the two, even in the same sentence! Consider:

  • She has done 7 shifts by themselves.
  • She verified her email address was theirs.

That’s some pretty clunky English right there! Mixing pronoun sets for the same person within a sentence is especially ugly, but even mixing them within the same page can cause confusion. We can’t trivially meet this customer’s request simply by adding new pronoun sets which mix things up a bit! We need to get smarter.

A Newer Way?

Ultimately, we’re probably going to need to differentiate between a more-rigid “what pronouns should Three Rings use when talking about you” and a more-flexible, perhaps optional “what pronouns should other humans use for you”? Alternatively, maybe we could allow people to select multiple pronoun sets to display but Three Rings would only use one of them (at least, one of them at a time!): “which of the following sets of pronouns do you use: select as many as apply”?

Even after this, there’ll always be more work to do.

For instance: I’ve met at least one person who uses no pronouns! By this, they actually mean they use no third-person personal pronouns (if they actually used no pronouns they wouldn’t say “I”, “me”, “my”, “mine” or “myself” and wouldn’t want others to say “you”, “your”, “yours” and “yourself” to them)! Semantics aside… for these people Three Rings should use the person’s name rather than a pronoun.

Maybe we can get there one day.

Three Rings' "Pronouns" drop-down, with "Dan/Dan/Dan/Dan's/Dan's self" selected.
Three Rings is already capable of supporting people who use no pronouns, but we don’t yet have a user interface to help them specify this! Maybe it’d look like this?

But so long as Three Rings continues to remain ahead of the curve in its respect for and understanding of pronoun use then I’ll be happy.

Our mission is to focus on volunteers and make volunteering easier. At the heart of that mission is treating volunteers with respect. Making sure our system embraces the diversity of the 65,000+ volunteers who use it by using pronouns correctly might be a small part of that, but it’s a part of it, and I for one am glad we make the effort.

Making an RSS feed of YOURLS shortlinks

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As you might know if you were paying close attention in Summer 2019, I run a “URL shortener” for my personal use. You may be familiar with public URL shorteners like TinyURL and Bit.ly: my personal URL shortener is basically the same thing, except that only I am able to make short-links with it. Compared to public ones, this means I’ve got a larger corpus of especially-short (e.g. 2/3 letter) codes available for my personal use. It also means that I’m not dependent on the goodwill of a free siloed service and I can add exactly the features I want to it.

Diagram showing the relationships of the DanQ.me ecosystem. Highlighted is the injection of links into the "S.2" link shortener and the export of these shortened links by RSS into FreshRSS.
Little wonder then that my link shortener sat so close to me on my ecosystem diagram the other year.

For the last nine years my link shortener has been S.2, a tool I threw together in Ruby. It stores URLs in a sequentially-numbered database table and then uses the Base62-encoding of the primary key as the “code” part of the short URL. Aside from the fact that when I create a short link it shows me a QR code to I can easily “push” a page to my phone, it doesn’t really have any “special” features. It replaced S.1, from which it primarily differed by putting the code at the end of the URL rather than as part of the domain name, e.g. s.danq.me/a0 rather than a0.s.danq.me: I made the switch because S.1 made HTTPS a real pain as well as only supporting Base36 (owing to the case-insensitivity of domain names).

But S.2’s gotten a little long in the tooth and as I’ve gotten busier/lazier, I’ve leant into using or adapting open source tools more-often than writing my own from scratch. So this week I switched my URL shortener from S.2 to YOURLS.

Screenshot of YOURLS interface showing Dan Q's list of shortened links. Six are shown of 1,939 total.
YOURLs isn’t the prettiest tool in the world, but then it doesn’t have to be: only I ever see the interface pictured above!

One of the things that attracted to me to YOURLS was that it had a ready-to-go Docker image. I’m not the biggest fan of Docker in general, but I do love the convenience of being able to deploy applications super-quickly to my household NAS. This makes installing and maintaining my personal URL shortener much easier than it used to be (and it was pretty easy before!).

Another thing I liked about YOURLS is that it, like S.2, uses Base62 encoding. This meant that migrating my links from S.2 into YOURLS could be done with a simple cross-database INSERT... SELECT statement:

INSERT INTO yourls.yourls_url(keyword, url, title, `timestamp`, clicks)
  SELECT shortcode, url, title, created_at, 0 FROM danq_short.links

But do you know what’s a bigger deal for my lifestack than my URL shortener? My RSS reader! I’ve written about it a lot, but I use RSS for just about everything and my feed reader is my first, last, and sometimes only point of contact with the Web! I’m so hooked-in to my RSS ecosystem that I’ll use my own middleware to add feeds to sites that don’t have them, or for which I’m not happy with the feed they provide, e.g. stripping sports out of BBC News, subscribing to webcomics that don’t provide such an option (sometimes accidentally hacking into sites on the way), and generating “complete” archives of series’ of posts so I can use my reader to track my progress.

One of S.1/S.2’s features was that it exposed an RSS feed at a secret URL for my reader to ingest. This was great, because it meant I could “push” something to my RSS reader to read or repost to my blog later. YOURLS doesn’t have such a feature, and I couldn’t find anything in the (extensive) list of plugins that would do it for me. I needed to write my own.

Partial list of Dan's RSS feed subscriptions, including Jeremy Keith, Jim Nielson, Natalie Lawhead, Bruce Schneier, Scott O'Hara, "Yahtzee", BBC News, and several podcasts, as well as (highlighted) "Dan's Short Links", which has 5 unread items.
In some ways, subscribing “to yourself” is a strange thing to do. In other ways… shut up, I’ll do what I like.

I could have written a YOURLS plugin. Or I could have written a stack of code in Ruby, PHP, Javascript or some other language to bridge these systems. But as I switched over my shortlink subdomain s.danq.me to its new home at danq.link, another idea came to me. I have direct database access to YOURLS (and the table schema is super simple) and the command-line MariaDB client can output XML… could I simply write an XML Transformation to convert database output directly into a valid RSS feed? Let’s give it a go!

I wrote a script like this and put it in my crontab:

mysql --xml yourls -e                                                                                                                     \
      "SELECT keyword, url, title, DATE_FORMAT(timestamp, '%a, %d %b %Y %T') AS pubdate FROM yourls_url ORDER BY timestamp DESC LIMIT 30" \
    | xsltproc template.xslt -                                                                                                            \
    | xmllint --format -                                                                                                                  \
    > output.rss.xml

The first part of that command connects to the yourls database, sets the output format to XML, and executes an SQL statement to extract the most-recent 30 shortlinks. The DATE_FORMAT function is used to mould the datetime into something approximating the RFC-822 standard for datetimes as required by RSS. The output produced looks something like this:

<?xml version="1.0"?>
<resultset statement="SELECT keyword, url, title, timestamp FROM yourls_url ORDER BY timestamp DESC LIMIT 30" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <row>
        <field name="keyword">VV</field>
        <field name="url">https://webdevbev.co.uk/blog/06-2021/perfect-is-the-enemy-of-good.html</field>
        <field name="title"> Perfect is the enemy of good || Web Dev Bev</field>
        <field name="timestamp">2021-09-26 17:38:32</field>
  </row>
  <row>
        <field name="keyword">VU</field>
        <field name="url">https://webdevlaw.uk/2021/01/30/why-generation-x-will-save-the-web/</field>
        <field name="title">Why Generation X will save the web  Hi, Im Heather Burns</field>
        <field name="timestamp">2021-09-26 17:38:26</field>
  </row>

  <!-- ... etc. ... -->
  
</resultset>

We don’t see this, though. It’s piped directly into the second part of the command, which  uses xsltproc to apply an XSLT to it. I was concerned that my XSLT experience would be super rusty as I haven’t actually written any since working for my former employer SmartData back in around 2005! Back then, my coworker Alex and I spent many hours doing XML backflips to implement a system that converted complex data outputs into PDF files via an XSL-FO intermediary.

I needn’t have worried, though. Firstly: it turns out I remember a lot more than I thought from that project a decade and a half ago! But secondly, this conversion from MySQL/MariaDB XML output to RSS turned out to be pretty painless. Here’s the template.xslt I ended up making:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <xsl:template match="resultset">
    <rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">
      <channel>
        <title>Dan's Short Links</title>
        <description>Links shortened by Dan using danq.link</description>
        <link> [ MY RSS FEED URL ] </link>
        <atom:link href=" [ MY RSS FEED URL ] " rel="self" type="application/rss+xml" />
        <lastBuildDate><xsl:value-of select="row/field[@name='pubdate']" /> UTC</lastBuildDate>
        <pubDate><xsl:value-of select="row/field[@name='pubdate']" /> UTC</pubDate>
        <ttl>1800</ttl>
        <xsl:for-each select="row">
          <item>
            <title><xsl:value-of select="field[@name='title']" /></title>
            <link><xsl:value-of select="field[@name='url']" /></link>
            <guid>https://danq.link/<xsl:value-of select="field[@name='keyword']" /></guid>
            <pubDate><xsl:value-of select="field[@name='pubdate']" /> UTC</pubDate>
          </item>
        </xsl:for-each>
      </channel>
    </rss>
  </xsl:template>
</xsl:stylesheet>

That uses the first (i.e. most-recent) shortlink’s timestamp as the feed’s pubDate, which makes sense: unless you’re going back and modifying links there’s no more-recent changes than the creation date of the most-recent shortlink. Then it loops through the returned rows and creates an <item> for each; simple!

The final step in my command runs the output through xmllint to prettify it. That’s not strictly necessary, but it was useful while debugging and as the whole command takes milliseconds to run once every quarter hour or so I’m not concerned about the overhead. Using these native binaries (plus a little configuration), chained together with pipes, had already resulted in way faster performance (with less code) than if I’d implemented something using a scripting language, and the result is a reasonably elegant “scratch your own itch”-type solution to the only outstanding barrier that was keeping me on S.2.

All that remained for me to do was set up a symlink so that the resulting output.rss.xml was accessible, over the web, to my RSS reader. I hope that next time I’m tempted to write a script to solve a problem like this I’ll remember that sometimes a chain of piped *nix utilities can provide me a slicker, cleaner, and faster solution.

Update: Right as I finished writing this blog post I discovered that somebody had already solved this problem using PHP code added to YOURLS; it’s just not packaged as a plugin so I didn’t see it earlier! Whether or not I use this alternate approach or stick to what I’ve got, the process of implementing this YOURLS-database ➡ XML ➡  XSLT ➡ RSS chain was fun and informative.

Quickly Solving Jigidi Puzzles

327 comments

tl;dr? Just want instructions on how to solve Jigidi puzzles really fast with the help of your browser’s dev tools? Skip to that bit.

I don’t enjoy jigsaw puzzles

I enjoy geocaching. I don’t enjoy jigsaw puzzles. So mystery caches that require you to solve an online jigsaw puzzle in order to get the coordinates really don’t do it for me. When I’m geocaching I want to be outdoors exploring, not sitting at my computer gradually dragging pixels around!

A completed 1000-piece "Where's Wally?" jigsaw.
Don’t let anybody use my completion of this 1000-piece jigsaw puzzle over New Year as evidence that I’m lying and actually like jigsaws.

Many of these mystery caches use Jigidi to host these jigsaw puzzles. An earlier version of Jigidi was auto-solvable with a userscript, but the service has continued to be developed and evolve and the current version works quite hard to make it hard for simple scripts to solve. For example, it uses a WebSocket connection to telegraph back to the server how pieces are moved around and connected to one another and the server only releases the secret “you’ve solved it” message after it detects that the pieces have been arranged in the appropriate relative configuration.

A nine-piece jigsaw puzzle with the pieces numbered 1 through 9; only the ninth piece is detached.
I made a simple Jigidi puzzle for demonstration purposes. Do you think you can manage a nine-piece jigsaw?

If there’s one thing I enjoy more than jigsaw puzzles – and as previously established there are about a billion things I enjoy more than jigsaw puzzles – it’s reverse-engineering a computer system to exploit its weaknesses. So I took a dive into Jigidi’s client-side source code. Here’s what it does:

  1. Get from the server the completed image and the dimensions (number of pieces).
  2. Cut the image up into the appropriate number of pieces.
  3. Shuffle the pieces.
  4. Establish a WebSocket connection to keep the server up-to-date with the relative position of the pieces.
  5. Start the game: the player can drag-and-drop pieces and if two adjacent pieces can be connected they lock together. Both pieces have to be mostly-visible (not buried under other pieces), presumably to prevent players from just making a stack and then holding a piece against each edge of it to “fish” for its adjacent partners.
Javascirpt code where the truthiness of this.j affects whether or not the pieces are shuffled.
I spent some time tracing call stacks to find this line… only to discover that it’s one of only four lines to actually contain the word “shuffle” and I could have just searched for it…

Looking at that process, there’s an obvious weak point – the shuffling (point 3) happens client-side, and before the WebSocket sync begins. We could override the shuffling function to lay the pieces out in a grid, but we’d still have to click each of them in turn to trigger the connection. Or we could skip the shuffling entirely and just leave the pieces in their default positions.

An unshuffled stack of pieces from the nine-piece jigsaw. Piece number nine is on top of the stack.
An unshuffled jigsaw appears as a stack, as if each piece from left to right and then top to bottom were placed one at a time into a pile.

And what are the default positions? It’s a stack with the bottom-right jigsaw piece on the top, the piece to the left of it below it, then the piece to the left of that and son on through the first row… then the rightmost piece from the second-to-bottom row, then the piece to the left of that, and so on.

That’s… a pretty convenient order if you want to solve a jigsaw. All you have to do is drag the top piece to the right to join it to the piece below that. Then move those two to the right to join to the piece below them. And so on through the bottom row before moving back – like a typewriter’s carriage return – to collect the second-to-bottom row and so on.

How can I do this?

If you’d like to cheat at Jigidi jigsaws, this approach works as of the time of writing. I used Firefox, but the same basic approach should work with virtually any modern desktop web browser.

  1. Go to a Jigidi jigsaw in your web browser.
  2. Pop up your browser’s developer tools (F12, usually) and switch to the Debugger tab. Open the file game/js/release.js and uncompress it by pressing the {} button, if necessary.
  3. Find the line where the code considers shuffling; right now for me it’s like 3671 and looks like this:
    return this.j ? (V.info('board-data-bytes already exists, no need to send SHUFFLE'), Promise.resolve(this.j)) : new Promise(function (d, e) {

    Javascirpt code where the truthiness of this.j affects whether or not the pieces are shuffled.
    I spent some time tracing call stacks to find this line… only to discover that it’s one of only four lines to actually contain the word “shuffle” and I could have just searched for it…
  4. Set a breakpoint on that line by clicking its line number.
  5. Restart the puzzle by clicking the restart button to the right of the timer. The puzzle will reload but then stop with a “Paused on breakpoint” message. At this point the application is considering whether or not to shuffle the pieces, which normally depends on whether you’ve started the puzzle for the first time or you’re continuing a saved puzzle from where you left off.
    Paused on breakpoint dialog with play button.
  6. In the developer tools, switch to the Console tab.
  7. Type: this.j = true (this ensures that the ternary operation we set the breakpoint on will resolve to the true condition, i.e. not shuffle the pieces).
    this.j = true
  8. Press the play button to continue running the code from the breakpoint. You can now close the developer tools if you like.
  9. Solve the puzzle as described/shown above, by moving the top piece on the stack slightly to the right, repeatedly, and then down and left at the end of each full row.
    Jigsaw being solved by moving down-and-right.

Update 2021-09-22: Abraxas observes that Jigidi have changed their code, possibly in response to this shortcut. Unfortunately for them, while they continue to perform shuffling on the client-side they’ll always be vulnerable to this kind of simple exploit. Their new code seems to be named not release.js but given a version number; right now it’s 14.3.1977. You can still expand it in the same way, and find the shuffling code: right now for me this starts on line 1129:

Put a breakpoint on line 1129. This code gets called twice, so the first time the breakpoint gets hit just hit continue and play on until the second time. The second time it gets hit, move the breakpoint to line 1130 and press continue. Then use the console to enter the code d = a.G and continue. Only one piece of jigsaw will be shuffled; the rest will be arranged in a neat stack like before (I’m sure you can work out where the one piece goes when you get to it).

Higher/Lower Datepicker

3 comments

I’ve written before about the trend in web development to take what the web gives you for free, throw it away, and then rebuild it in Javascript. The rebuilt version is invariably worse in many ways – less-accessible, higher-bandwidth, reduced features, more fragile, etc. – but it’s more convenient for developers. Personally, I try not to value developer convenience at the expense of user experience, but that’s an unpopular opinion lately.

Screenshot showing a hovered hyperlink to "Digital Forest" on a list of green hosting providers in France.
Here’s a perfect example I bumped into earlier this week, courtesy of The Green Web Foundation. This looks like a hyperlink… but if you open it in a new tab/window, you see a page (not even a 404 page!) with the text “It looks like nothing was found at this location.”

In the site shown in the screenshot above, the developer took something the web gave them for free (a hyperlink), threw it away (by making it a link-to-nowhere), and rebuilt its functionality with Javascript (without thinking about the fact that you can do more with hyperlinks than click them: you can click-and-drag them, you can bookmark them, you can share them, you can open them in new tabs etc.). Ugh.

Date pickers

Particularly egregious are the date pickers. Entering your date of birth on a web form ought to be pretty simple: gov.uk pretty much solved it based on user testing they did in 2013.

Here’s the short of it:

  • Something you can clearly type a numeric day, month and year into is best.
  • Three dropdowns are slightly worse, but at least if you use native HTML <select> elements keyboard users can still “type” to filter.
  • Everything else – including things that look like <select>s but are really funky React <div>s, is pretty terrible.
Calendar datepicker with slider-based timepicker and no text-based fallback.
Calendars can be great for choosing your holiday date range. But pressing “Prev” ~480 times to get to my month of birth isn’t good. Also: what’s with the time “sliders”? (Yes, I know I’ve implemented these myself, in the past, and I’m sorry.)

My fellow Automattician Enfys recently tweeted:

People designing webforms that require me to enter my birthdate:

I am begging you: just let me type it in.

Typing it in is 6-8 quick keystrokes. Trying to navigate a little calendar or spinny wheels back to the 1970s is time-consuming, frustrating and unnecessary.

They’re right. Those little spinny wheels are a pain in the arse if you’ve got to use one to go back 40+ years.

Date "spinner" currently showing 20 December 2012.
These things are okay (I guess) on mobile/touchscreen devices, though I’d still prefer the option to type in my date of birth. But send one to my desktop and I will curse your name.

Can we do worse?

If there’s one thing we learned from making the worst volume control in the world, the other year, it’s that you can always find a worse UI metaphor. So here’s my attempt at making a date of birth field that’s somehow even worse than “date spinners”:

My datepicker implements a game of “higher/lower”. Starting from bounds specified in the HTML code and a random guess, it narrows-down its guess as to what your date of birth is as you click the up or down buttons. If you make a mistake you can start over with the restart button.

Amazingly, this isn’t actually the worst datepicker into which I’ve entered my date of birth! It’s cognitively challenging compared to most, but it’s relatively fast at narrowing down the options from any starting point. Plus, I accidentally implemented some good features that make it better than plenty of the datepickers out there:

  • It’s progressively enhanced – if the Javascript doesn’t load, you can still enter your date of birth in a sensible way.
  • Because it leans on a <input type="date"> control, your browser takes responsibility for localising, so if you’re from one of those weird countries that prefers mm-dd-yyyy then that’s what you should see.
  • It’s moderately accessible, all things considered, and it could easily be improved further.

It turns out that even when you try to make something terrible, so long as you’re building on top of the solid principles the web gives you for free, you can accidentally end up with something not-so-bad. Who knew?

Getting Twitter Avatars (without the Twitter API)

5 comments

Among Twitter’s growing list of faults over the years are various examples of its increasing divergence from open Web standards and developer-friendly endpoints. Do you remember when you used to be able to subscribe to somebody’s feed by RSS? When you could see who follows somebody without first logging in? When they were still committed to progressive enhancement and didn’t make your browser download ~5MB of Javascript or else not show any content whatsoever? Feels like a long time ago, now.

Lighthouse Performance score for Twitter's Twitter account page on mobile, scoring 50%.
For one of the most-popular 50 websites in the world, this score is frankly shameful.

But those complaints aside, the thing that bugged me most this week was how much harder they’ve made it to programatically get access to things that are publicly accessible via web pages. Like avatars, for example!

If you’re a human and you want to see the avatar image associated with a given username, you can go to twitter.com/that-username and – after you’ve waited a bit for all of the mandatory JavaScript to download and run (I hope you’re not on a metered connection!) – you’ll see a picture of the user, assuming they’ve uploaded one and not made their profile private. Easy.

If you’re a computer and you want to get the avatar image, it used to be just as easy; just go to twitter.com/api/users/profile_image/that-username and you’d get the image. This was great if you wanted to e.g. show a Facebook-style facepile of images of people who’d retweeted your content.

But then Twitter removed that endpoint and required that computers log in to Twitter, so a clever developer made a service that fetched avatars for you if you went to e.g. twivatar.glitch.com/that-username.

But then Twitter killed that, too. Because despite what they claimed 5½ years ago, Twitter still clearly hates developers.

Dan Q's Twitter profile header showing his avatar image.
You want to that image? Well you’ll need a Twitter account, a developer account, an OAuth token set, a stack of code…

Recently, I needed a one-off program to get the avatars associated with a few dozen Twitter usernames.

First, I tried the easy way: find a service that does the work for me. I’d used avatars.io before but it’s died, presumably because (as I soon discovered) Twitter had made things unnecessarily hard for them.

Second, I started looking at the Twitter API documentation but it took me in the region of 30-60 seconds before I said “fuck that noise” and decided that the set-up overhead in doing things the official way simply wasn’t justified for my simple use case.

So I decided to just screen-scrape around the problem. If a human can just go to the web page and see the image, a computer pretending to be a human can do exactly the same. Let’s do this:

/* Copyright (c) 2021 Dan Q; released under the MIT License. */

const Puppeteer = require('puppeteer');

getAvatar = async (twitterUsername) => {
  const browser = await Puppeteer.launch({args: ['--no-sandbox', '--disable-setuid-sandbox']});
  const page = await browser.newPage();
  await page.goto(`https://twitter.com/${twitterUsername}`);
  await page.waitForSelector('a[href$="/photo"] img[src]');
  const url = await page.evaluate(()=>document.querySelector('a[href$="/photo"] img').src);
  await browser.close();
  console.log(`${twitterUsername}: ${url}`);
};

process.argv.slice(2).forEach( twitterUsername => getAvatar( twitterUsername.toLowerCase() ) );
The code is ludicrously simple. It took less time, energy, and code to write this than to follow Twitter’s “approved” procedure. You can download the code via Gist.

Obviously, using this code would violate Twitter’s terms of use for automation, so… don’t, I guess?

Given that I only needed to run it once, on a finite list of accounts, I maintain that my approach was probably kinder on their servers than just manually going to every page and saving the avatar from it. But if you set up a service that uses this approach then you’ll certainly piss off somebody at Twitter and history shows that they’ll take their displeasure out on you without warning.

$ node get-twitter-avatar.js alexsdutton richove geohashing TailsteakAD LilFierce1 ninjanails
alexsdutton: https://pbs.twimg.com/profile_images/740505937039986688/F9gUV0eK_200x200.jpg
lilfierce1: https://pbs.twimg.com/profile_images/1189417235313561600/AZ2eLjAg_200x200.jpg
richove: https://pbs.twimg.com/profile_images/1576438972/2011_My_picture4_200x200.jpeg
geohashing: https://pbs.twimg.com/profile_images/877137707939581952/POzWWV2d_200x200.jpg
ninjanails: https://pbs.twimg.com/profile_images/1146364466801577985/TvCfb49a_200x200.jpg
tailsteakad: https://pbs.twimg.com/profile_images/1118738807019278337/y5WWkLbF_200x200.jpg
This output shows the avatar URLs of a half a dozen Twitter accounts. It took minutes to write the code and takes seconds to run, but if I’d have done it the “right” way I’d still be unnecessarily wading through Twitter’s sprawling documentation.

But it works. It was fast and easy and I got what I was looking for.

And the moral of the story is: if you make an API and it’s terrible, don’t be surprised if people screen-scape your service instead. (You can’t spell “scraping” without “API”, amirite?)

Ireland and the UK Aren’t In The Same Timezone!

109 comments

This weekend, while investigating a bug in some code that generates iCalendar (ICS) feeds, I learned about a weird quirk in the Republic of Ireland’s timezone. It’s such a strange thing (and has so little impact on everyday life) that I imagine that even most Irish people don’t even know about it, but it’s important enough that it can easily introduce bugs into the way that computer calendars communicate:

Most of Europe put their clocks forward in Summer, but the Republic of Ireland instead put their clocks backward in Winter.

If that sounds to you like the same thing said two different ways – or the set-up to a joke! – read on:

Map showing timezones of Europe. The UK and Ireland are grouped (along with Iceland) in a zone labelled as being UTC+0.
The timezones of Europe look pretty simple compared to some parts of the world, but the illustration of the British Isles hides an interesting eccentricity.

A Brief History of Time (in Ireland)

Poster titled "Time (Ireland) Act 1916", advising that "On and after Sunday 1st October 1916 Western European Time will be ovserved throughout Ireland" asking people to set their clocks and watches back 35 minutes.
Spring forward, fall back… just a little bit back, though. Not too much.

After high-speed (rail) travel made mean solar timekeeping problematic, Great Britain in 1880 standardised on Greenwich Mean Time (UTC+0) as the time throughout the island, and Ireland standardised on Dublin Mean Time (UTC-00:25:21). If you took a ferry from Liverpool to Dublin towards the end of the 19th century you’d have to put your watch back by about 25 minutes. With air travel not yet being a thing, countries didn’t yet feel the need to fixate on nice round offsets in the region of one-hour (today, only a handful of regions retain UTC-offsets of half or quarter hours).

That’s all fine in peacetime, but by the First World War and especially following the Easter Rising, the British government decided that it was getting too tricky for their telegraph operators (many of whom operated out of Ireland, which provided an important junction for transatlantic traffic) to be on a different time to London.

1885 GPO telegraph instrument from the Porthcurno Telegraph Museum, which Dan almost visited the other week but it was closed.
It’s widely believed that the world’s first “U UP? [STOP]” message never got a response as a direct result of Anglo-Irish timezone confusion.
So the Time (Ireland) Act 1916 was passed, putting Ireland on Greenwich Mean Time. Ireland put her clocks back by 35 minutes and synched-up with the rest of the British Isles. And from then on, everything was simple and because nothing ever went wrong in Ireland as a result of the way it was governed by by Britain, nobody ever had to think about the question of timezones on the island again.

Ah. Hmm.

December 1920 photograph showing St Patrick's Street, Cork, following the burning of the city by British forces.
“Those Irish people want to govern their own country, do they? After we so kindly shared our king with them? Right-ho: let’s set fire to their cities and see how they feel then.”

Following Irish independence, the keeping of time carried on in much the same way for a long while, which will doubtless have been convenient for families spread across the Northern Irish border. But then came the Second World War.

Summers in the 1940s saw Churchill introduce Double Summer Time which he believed would give the UK more daylight, saving energy that might otherwise be used for lighting and increasing production of war materiel.

Ireland considered using the emergency powers they’d put in place to do the same, as a fuel saving measure… but ultimately didn’t. This was possibly because aligning her time with Britain might be seen as undermining her neutrality, but was more likely because the government saw that such a measure wouldn’t actually have much impact on fuel use (it certainly didn’t in Britain). Whatever the reason, though, Britain and Northern Ireland were again out-of-sync with one another until the war ended.

Newspaper clipping advising that "Double Summer Time comes to an end on Saturday night, August 8-9, when all clocks and watches should be put back one hour, thus reverting to British Summer Time, which will probably be maintained throughout the winter."
I like to imagine that the development of powerful computers by the folks at Bletchley Park was a result of needing to keep track of timezones across the British Isles.

From 1968 to 1971 Britain experimented with “British Standard Time” – putting the clocks forward in Summer once, to UTC+1, and then leaving them there for three years. This worked pretty well except if you were Scottish in which case you’ll have found winter mornings to be even gloomier than you were used to, which was already pretty gloomy. Conveniently: during much of this period Ireland was also on UTC+1, but in their case it was part of a different experiment. Ireland were working on joining the European Economic Community, and aligning themselves with “Paris time” year-round was an unnecessary concession but an interesting idea.

But here’s where the quirk appears: the Standard Time Act 1968, which made UTC+1 the “standard” timezone for the Republic of Ireland, was not repealed and is still in effect. Ireland could have started over in 1971 with a new rule that made UTC+0 the standard and added a “Summer Time” alternative during which the clocks are put forward… but instead the Standard Time (Amendment) Act 1971 left UTC+1 as Ireland’s standard timezone and added a “Winter Time” alternative during which the clocks are put back.

Two clocks, both showing the same time. One has a sign reading "LONDON", the other "DUBLIN, I GUESS?"
It all seems so simple until you actually think about it.

(For a deeper look at the legal history of time in the UK and Ireland, see this timeline. Certainly don’t get all your history lessons from me.)

So what?

You might rightly be thinking: so what! Having a standard time of UTC+0 and going forward for the Summer (like the UK), is functionally-equivalent to having a standard time of UTC+1 and going backwards in the Winter, like Ireland, right? It’s certainly true that, at any given moment, a clock in London and a clock in Dublin should show the same time. So why would anybody care?

Perl Data::ICal::TimeZone implementation of Dublin timezone, incorrectly showing summer DST at +1 rather than winter DST of -1.
This code for Europe/Dublin, from the Perl module Data::ICal::TimeZone, is technically-incorrect because it states that the winter time is the standard and daylight savings of +1 hour apply in the summer, rather than the opposite.

But declaring which is “standard” is important when you’re dealing with computers. If, for example, you run a volunteer rota management system that supports a helpline charity that has branches in both the UK and Ireland, then it might really matter that the computer systems involved know what each other mean when they talk about specific times.

The author of an iCalendar file can choose to embed timezone information to explain what, in that file, a particular timezone means. That timezone information might say, for example, “When I say ‘Europe/Dublin’, I mean UTC+1, or UTC+0 in the winter.” Or it might say – like the code above! – “When I say ‘Europe/Dublin’, I mean UTC+0, or UTC+1 in the summer.” Both of these declarations would be technically-valid and could be made to work, although only the first one would be strictly correct in accordance with the law.

Stressed programmer hunched over a MacBook. Photo by Anna Shvets from Pexels.
Clients who need solid timezone support represent 50% of a programmer’s production of stress hormones. See also Falsehoods Programmers Believe About Time.

But if you don’t include timezone information in your iCalendar file, you’re relying  on the feed subscriber’s computer (e.g. their calendar software) to make a sensible interpretation.. And that’s where you run into trouble. Because in cases like Ireland, for which the standard is one thing but is commonly-understood to be something different, there’s a real risk that the way your system interprets and encodes time won’t necessarily be the same as the way somebody else’s does.

If I say I’ll meet you at 12:00 on 1 January, in Ireland, you rightly need to know whether I’m talking about 12:00 in Irish “standard” time (i.e. 11:00, because daylight savings are in effect) or 12:00 in local-time-at-the-time-of-the-meeting (i.e. 12:00). Humans usually mean the latter because we think in terms of local time, but when your international computer system needs to make sure that people are on a shift at the same time, but in different timezones, it needs to be very clear what exactly it means!

And when your daylight savings works “backwards” compared to everybody else’s… that’s sure to make a developer somewhere cry. And, possibly, blog about your weird legislation.

Big List of Naughty Strings

0 comments

This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

# Reserved Strings
#
# Strings which may be used elsewhere in code
undefined
undef
null
NULL

…

then
constructor
\
\\

# Numeric Strings
#
# Strings which can be interpreted as numeric
0
1
1.00
$1.00
1/2
1E2

…

Max Woolf

Max has produced a list of “naughty strings”: things you might try injecting into your systems along with any fuzz testing you’re doing to check for common errors in escaping, processing, casting, interpreting, parsing, etc. The copy above is heavily truncated: the list is long!

It’s got a lot of the things in it that you’d expect to find: reserved keywords and filenames, unusual or invalid unicode codepoints, tests for the Scunthorpe Problem, and so on. But perhaps my favourite entry is this one, a test for “human injection”:

# Human injection
#
# Strings which may cause human to reinterpret worldview
If you're reading this, you've been in a coma for almost 20 years now. We're trying a new technique. We don't know where this message will end up in your dream, but we hope it works. Please wake up, we miss you.

Beautiful.

OpenAI-powered Linux shell uses AI to Do What You Mean

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This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

It’s like Alexa/Siri/Cortana for your terminal!

This is a basic Python shell (really, it’s a fancy wrapper over the system shell) that takes a task and asks OpenAI for what Linux bash command to run based on your description. For safety reasons, you can look at the command and cancel before actually running it.

…

Of all the stupid uses of OpenAI’s GPT-3, this might be the most-amusing. It’s really interesting to see how close – sometimes spot-on – the algorithm comes to writing the right command when you “say what you mean”. Also, how terribly, terribly ill-advised it would be to actually use this for real.

The most important feature of Sublime Text

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This article is a repost promoting content originally published elsewhere. See more things Dan's reposted.

The most important feature of Sublime Text is that it doesn’t change. In the modern world, everything changes at a crazy pace. We get new OSes and new phones every year, Google opens and closes its products monthly, many physical devices get announced, produced, and disappear in an interval shorter than the Sublime Text release cycle. I have two problems with that.

…

I love Sublime Text. It was the editor for which I finally broke my long, long emacs habit (another editor that “doesn’t change”). Like emacs, Sublime is simple but powerful. Unlike Atom, it doesn’t eat all the RAM in the universe. And unlike VS Code, I can rely on it being fundamentally the same today, tomorrow, and next year.

Break Into . Us (lock puzzle game)

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I’ve made a puzzle game about breaking open padlocks. If you just want to play the game, go play the game. Or read on for the how-and-why of its creation.

About three months ago, my friend Claire, in a WhatsApp group we both frequent, shared a brainteaser:

WhatsApp message from Claire, challenging people to solve her puzzle.
Was this way back at the beginning of April? Thank heavens for WhatsApp scrollback.

The puzzle was to be interpreted as follows: you have a three-digit combination lock with numbers 0-9; so 1,000 possible combinations in total. Bulls and Cows-style, a series of clues indicate how “close” each of several pre-established “guesses” are. In “bulls and cows” nomenclature, a “bull” is a correctly-guessed digit in the correct location and a “cow” is a correctly-guessed digit in the wrong location, so the puzzle’s clues are:

  • 682 – one bull
  • 614 – one cow
  • 206 – two cows
  • 738 – no bulls, no cows
  • 380 – one cow
"Can you open the lock using these clues?" puzzle
Feel free to stop scrolling at this point and solve it for yourself. Or carry on; there are no spoilers in this post.

By the time I’d solved her puzzle the conventional way I was already interested in the possibility of implementing a general-case computerised solver for this kind of puzzle, so I did. My solver uses a simple “brute force” technique, as follows:

  1. Put all possible combinations into a search space.
  2. For each clue, remove from the search space all invalid combinations.
  3. Whatever combination is left is the correct answer.
Animation showing how the first three clues alone are sufficient to derive a unique answer from the search space of Claire's puzzle.
The first three clues of Claire’s puzzle are sufficient alone to reduce the search space to a single answer, although a human is likely to need more.

Visualising the solver as a series of bisections of a search space got me thinking about something else: wouldn’t this be a perfectly reasonable way to programatically generate puzzles of this type, too? Something like this:

  1. Put all possible combinations into a search space.
  2. Randomly generate a clue such that the search space is bisected (within given parameters to ensure that neither too many nor too few clues are needed)
  3. Repeat until only one combination is left

Interestingly, this approach is almost the opposite of what a human would probably do. A human, tasked with creating a puzzle of this sort, would probably choose the answer first and then come up with clues that describe it. Instead, though, my solution would come up with clues, apply them, and then see what’s left-over at the end.

Sample output of the puzzle generator for an alphabet of 0-9 and a combination length of 3.
Sometimes it comes up with inelegant or unchallenging suggestions, but for the most part my generator produces adequate puzzles.

I expanded my generator to go beyond simple bulls-or-cows clues: it’s also capable of generating clues that make reference to the balance of odd and even digits (in a numeric lock), the number of different digits used in the combination, the sum of the digits of the combination, and whether or not the correct combination “ascends” or “descends”. I’ve ideas for other possible clue types too, which could be valuable to make even tougher combination locks: e.g. specifying how many numbers in the combination are adjacent to a consecutive number, specifying the types of number that the sum of the digits adds to (e.g. “the sum of the digits is a prime number”) and so on.

A single solution in a search space derived in multiple ways.
Like the original puzzle, puzzles produced by my generator might have redundancies. In the picture above, the black square can be defined by the light blue, dark blue, and green bisections only: the yellow bisection is rendered redundant by the light blue one. I’ve left this as a deliberate feature.

Next up, I wanted to make a based interface so that people could have a go at the puzzles in their web browser, track their progress through the levels, get a “score” based on the number and difficulty of the locks that they’d cracked (so they can compare it to their friends), and save their progress to carry on next time.

I implemented in pure vanilla HTML, CSS, SVG and JS, with no dependencies. Compressed, it delivers to your browser and is ready-to-play in a little under 10kB, most of which is the puzzles themselves (which are pregenerated and stored in a JSON file). Naturally, it lends itself well to running offline, so it’s PWA-enhanced with a service worker so it can be “installed” onto your device, too, and it’ll check for bonus puzzles and other updates periodically.

The original puzzle shown via BreakInto.Us.
Naturally, the original puzzle appears in the web-based game, too.

Honestly, the hardest bit of implementing the frontend was the “spinnable” digits: depending on your browser, these are an endless-scrolling <ul> implemented mostly in CSS and with snap points set, and then some JS to work out “what you meant” based on where you span to. Which feels like the right way to implement such a thing, but was a lot more work than putting together my own control, not least because of browser inconsistencies in the implementation of snap points.

Anyway: you should go and play the game, now, and let me know what you think. Is it worth expanding and improving? Should I leave it as it is? I’m open to ideas (and if you don’t like that I’m not implementing your suggestions, you can always fork a copy of the code and change it yourself)!

Or if you’d like to see some of the other JavaScript experiments I’ve done, you might enjoy my “cheating” hangman game, my recreation of the lunar lander game I wrote in college, or rediscover that time I was ill and came up the worst conceivable tool to calculate Pi.