Skip Navigation
Fediverse @lemmy.world farcaller @fstab.sh

Why fediverse clients reinvent the C2S APIs and don't use ActivityPub?

I’m reading the ActivityPub spec here and it seems pretty fit for client-to-server communications. Yeah, it might be somewhat bulkier than your typical rest api, but it's more universal, which begs the question: why do mastodon and lemmy both decided to implement custom (and incompatible) APIs for their clients to talk to the servers? Wouldn’t it be more straightforward if e.g. my voyager app talked ActivityPub to lemmy.world which then talked ActivityPub to lemmy.ml or something.

What am I missing?

9
9 comments

  • It could probably work but would quickly turn into a mess of custom extensions.

    For example, ActivityPub has no concept of sorting by hot or active or new. ActivityPub also doesn't specify how a client would authenticate to a server to post on your behalf. There's definitely no ActivityPub message for registering a user account.

    So it makes sense that S2S only does the bare minimum for the purpose of federation of content, while instances with varying implementations can implement whatever C2S protocol makes the most sense.

    For example, should ActivityPub expose a Lemmy post as a nested thread, or a Mastodon microblogging-like format and let the clients reassemble the thread? How should a Mastodon client present a Lemmy community and threads? How about a Lemmy client connecting to a Mastodon server?

    If we put that in ActivityPub, you're pretty much bound to supporting it forever because other servers will eventually expect those protocol extensions, whereas it's much safer to change a C2S protocol.

    Keeping the ActivityPub simple has a lot of benefits if we don't want the fediverse to remain really interoperable. A Lemmy client can reasonably expect that a given server supports a given set of features, providing a much more reliable experience than basically spaguetti of supporting every possible features and presenting the data weirdly.

    • Postel's Law is relevant here. Conservative in what you send (simplify the schema of the data on the wire) and liberal in what you receive (put the complexity for interpreting that data in the client).

    • The underlying assumption is that we need to have separate applications. Why is that? Why can't the client define how to present/ sort/act on the data?

      • In that case, why don't everyone just use a generic fediverse server and let the clients make it into Mastodon/Lemmy/Kbin/Pixelfed/Friendica/Firefish/PeerTube/whatever else?

        The reason is all those server implementations work differently, have different features, different goals, even different cultures and etiquette, or even just for the heck of it. That's the point of the fediverse, it's interoperable but you're also not limited by one single standard as to how you want to expand. Lets say we settle for Mastodon's implementation. Cool, now people want downvotes. Mastodon doesn't do downvotes, but it's the reference implementation. You can't have downvotes, you'll never have downvotes unless you convince everyone to implement downvotes. Nobody will want to make a server that does everything. Maybe the Mastodon guys don't want to implement downvotes because it promotes negativity and they'd rather posts just stay at zero likes. Maybe a site is implementing an additional score for funny/serious. What do we do, do we just allow clients to include any data they want?

        Even if it worked that way, eventually, people would still make servers with proprietary UIs and proprietary features and APIs. You just can't stop it, developers gonna develop.

        Also, if every client supported every format, it would be a nightmare to make clients. And still, there would always be clients with different takes on how to present the data anyway, because again, developers gonna develop. People get creative and do their own thing, and it's how cool stuff gets born.

        If you make a rigid spec outlining every possible feature, then you need a group of people to decide what the spec is, and eventually, people are gonna get tired and make an entirely different protocol anyway, but this time it may not be interoperable.

        You're always gonna end up with specialized servers, and matching specialized clients.

        If you want to make a superserver and superclient that supports everything, go ahead and make one. It may take off, it may not.

        Ultimately, the fediverse will grow organically, custom implementations will happen if not only for personal toys, because there's no governing body making a hard spec. And it's a good thing for things to have a chance to last, or inenevitably there will be disagreements and lead to forks.

        How is pushing for a single megaimplementation a good thing?

  • My assumption would be that, yes Lemmy, Kbin and Mastodon use the same underlying communication protocol called ActivityPub but those have some additions which make their whole featureset incompatible to each other. So instead of writing a combined super Fediverse Browser/Explorer/whatever you get specialised Applications for Lemmy/Kbin and Mastodon.

  • [This comment has been deleted by an automated system]

You've viewed 9 comments.