Gregory's ServerActivityPub, as it turns out, follows the actor model of computation. Okay, many people implementing the fediverse don't know about the actor model aspect of ActivityPub but I am here to tell YOU, dear reader, that it is an important thing, not a detail
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 Oh god Christine said "the lambda calculus" did you know she's into lisp and functional programming, what's she going to talk about next monads?!?! I am not going to talk about monads. Not TODAY But we do need to get a better architectural idea of how these systems work because it matters a lot!  @cwebber your spooky Halloween name next year should be Christine "Leibniz"-Webber So let me introduce two models of communication which we can use to analyze these two systems. It's important! - Fediverse/ActivityPub: "message passing" Okay, cool, terms established, let's talk about them and why they matter because they matter A LOT "Message passing" is what ActivityPub uses. It's "like email", people say, and that's true. Actually it's even a lot like physical mail. You write a letter, you say where it should go, it gets delivered to your house. Message passing. The world runs on it. Now I can use message passing to send a message to you *directly* and indeed, that's "like email". For one-to-one correspondence, that's enough. But it's not enough for a followers/following type mechanism. But we can build it on top! Thank *you* computational abstractions! On top of "message passing" we will build "publish-subscribe" as a second-layer abstraction "Your ideas are interesting and I'd like to subscribe to your newsletter." You send me a letter saying you'd like to hear the things I have to say, okay, you're part of the reader list. That's how it works. On top of that we can build even more abstractions and the net result is that this is how federation works in pretty much every "federated" system I know. ActivityPub does some extra work to help you see replies on a thread, think "letters to the editor". This is a bit lossy sometimes though It's true that sometimes users click over to a thread and see some replies but not all on their instance's UI. There's things that could be done to improve it, but it's sometimes mildly confusing, but not so bad, and you can click over typically to see whatever else is happening, and people learn to I actually think this is improvable but I mostly don't care because this isn't as big a complaint as people tend to think it is on the fediverse, the other concerns like "what instance do I pick" tend to be bigger and "oh no my server went down" That can be improved, we'll talk about that later So okay, the federation is "message passing" and like email, or physical mail. You have an idea how it works. Now we need to get to that other thing, a "shared heap" architecture. What on earth does that mean? If "message passing" is like "mail comes to your house", a "shared heap" system works differently In a "shared heap" system, all the mail gets dumped at the post office, and in the most naive version, you go over there and read through every single piece of mail to see which one is relevant to you There is no "directed delivery" in a "shared heap" system, which means you are stuck with two things: either a "god's eye view" (Bluesky) or "even lossier about replies than ActivityPub" (Secure Scuttlebutt/Nostr) The Bluesky approach to the "shared heap" is that *everything* goes into the big, centralized shared heap. Bluesky takes a "god's eye" view: it knows everything, and so knows what all your replies are, and can give you perfect search. Secure Scuttlebutt / Nostr... well long story. Lossier, I'll say You can imagine the physical world version of "message passing" already because you already live in this world. Messages come to your house or apartment building or whatever For Bluesky's "shared heap" architecture, you'd have to build a whole addition to your house for everyone's mail That's exactly why running a Relay or AppView is expensive: you're building an addition to your house for all the world's mail. Eeep! That ain't cheap. That's why I'm saying: decentralization also means the ability to *scale down*. Look, I know that I've been hitting this nail on the head for a while but: the web is open, blogs are open, but Google isn't open But you could run your own Google, in theory. You could index the web. So why aren't you? Ah yeah. Same thing here. That's what I mean, that's why it's centralized Now as I have said, this is a *design decision*. And remember: most users of Bluesky really *don't care*. Decentralization is not their focus, they're trying to get the hell off the nazi hellscape that Musk's toxic reign of Twitter has become. Bluesky's architecture, actually, is great for them. If what your *goal* is to get off Twitter, then Bluesky has solved it. They solved it by building another Twitter, and this time it's open source, which is cool! And it might have this "credible exit" thing. But god damnit it's not decentralized and it's not federated stop TELLING people that "Oh Christine you're being sensitive" Maybe, but there are real consequences to this. What if Bluesky/ATProto fails? "Oh well we tried decentralization and that didn't work." If people think something is something that it isn't, then that's a real problem. Users, clearly, think a lot more of Bluesky is decentralized than it is, and realize less of the consequences than they should. This really worries me. Blocks and DMs are both great examples of this. Blocking first. Bluesky's decision to have *everything* public means that it is expected that every participating node knows *everything* about who's blocking *everyone*. "This is consistent with how blocking works on Twitter/X" their paper says But wait, I'm pretty sure that one's not true though  @cwebber@social.coop https://clearsky.app/ is creepy as shit lol and it shows just how much is public It is ONE thing to be able to block JK Rowling and for you to see that JK Rowling is blocking you. It is an ENTIRELY DIFFERENT THING for ANYONE to see who is blocking JK Rowling and who JK Rowling is blocking This one is shocking to me: this seems like a vector for abusive actors  @cwebber@social.coop Already happening, bots scrape and harass people who sub to a labeller marking transphobes or something Now to be completely fair this is something that Bluesky's devs are interested in potentially changing: there is an open issue to discuss the possibility of private blocks https://github.com/bluesky-social/atproto/discussions/1131 What I am saying is there are architectural consequences to fundamental design abstractions Yes, I may sometimes seem silly over here, SICP-hugging fangirl, come on we're just trying to build things that *work* over here Look I'm a lisp lady, I know the realities of "Worse Is Better" more than most, I now the right CS designs don't win But Conway's Law flows in two directions! You know what, we'll come back to "bidirectional Conway's Law", let's talk about Direct Messages for a minute because I think those are telling Direct Messages in Bluesky, wait how do they work if ATProto is public? Did you guess? DMs are centralized! All DMs flow through Bluesky Now to be completely fair Bluesky is clear about this *in their blogpost announcing DMs*, but just like this thread, I doubt nearly anyone has read that far (am I talking to the void? I don't know, if you actually have gotten to this message reply with "I found the easter egg" or something)     @cwebber i found the easter egg! (Actually readin this thread in semi-realtime)   @cwebber@social.coop i mean you're on my timeline every 2 seconds, it's hard to miss  The thing that is telling to me about DMs is that we *have* federated direct message protocols like XMPP which have been around for ages; if Bluesky wanted to they could have tacked that on pretty quickly, E2EE or not. It still would have been decentralized at least The point is that I have *seen in the wild* people saying "Oh yeah Bluesky added DMs to their decentralized protocol" and augh I know they aren't claiming this but it's very clear to me that people are reading things as being completely different architecture than it is @cwebber this entire thread is enlightening so far! (and i figure liking each post manually would be kind of insane to do.)   @cwebber yeah, I haven't been on Twitter in a hot minute but I lived there for years and you could see things like follows and the most telling was Likes, even before they started getting put in people's TLs, you could look it up -- which were legit the first way we found out JKR was a terf, she wasn't posting it yet or RTing even but she was constantly liking terf shit. However that was the most detailed info you could get on someone, the one thing they didn't necessarily intend to share.  @cwebber honestly kind of shocking that it's not fully encrypted, but then I suppose they would have to solve key management in a decentralized network problem ... Who cares if you block anyone ? They can still get the data , blocking is for fun I guess?  @cwebber I just saw this one comment, and then... clicked it and started scrolling up. Woo, time to read.  @cwebber My gourds, this thread has been a wild, insightful ride so far! |
I'll take one more note about federation which is that often time the message passing mechanism of the fediverse is often called "federation", but theoretically another mechanism could exist, but I'm actually not so sure of that.
There's a reason the actor model and the lambda calculus are undying