What are the activity_id formats for various platforms?

Submitted ⁨⁨6⁩ ⁨months⁩ ago⁩ by ⁨admiralpatrick@lemmy.world⁩ to ⁨fediverse@lemmy.world⁩

So, I’ve rewritten the search / search boxes in Tesseract to skip the search and directly resolve activity pub URLs for users, posts, comments, and communities. I’m loving this as it makes things so much faster and easier.

To make that work, and reduce false positives/negatives, I have to do some pre-flight checks on the URL that’s submitted to the search.

Currently, it checks if the domain is to a known federated instance and looks for specific paths in the URL. If it detects the URL is an AP_ID URL, it will only resolve the object and redirect you to it (skipping the lengthy search step). For false negatives, it will pass it to the regular search but still try a federated lookup along with the search.

For Lemmy and Piefed, those are:

/u/ for users
/c/ for communities
/post/ for posts
/comment/ for comments.

For Mbin, I think it’s the same except it uses /m/ for communities (they call them “magazines” I believe).

I think mastoon uses /user or maybe /username/ in the AP identifiers?

Any of you who are more familiar with Fediverse platforms that aren’t Lemmy/Piefed, can you let me know what the AP_IDs look like for users, posts, comments, and, if applicable, communities?

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moseschrute@lemmy.world ⁨6⁩ ⁨months⁩ ago
I maintain my own Lemmy client (Blorp), and this sounds like a cool idea. How do you get your known list of federated instances?

I currently have my own threadiverse crawler I wrote, but I disgusted any Lemmy/PieFed instance with <20 monthly active users. That brings the list down to about 63 Lemmy instances and 7 PieFed. I wonder if that list is extensive enough to implement the resolve object mechanism you mentioned.

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- admiralpatrick@lemmy.world ⁨6⁩ ⁨months⁩ ago
  At startup, it calls /api/v3/federated_instances and stores the result to a lookup variable. Then I’ve got a couple of helper functions that accept either an instance ID or a domain name which looks them up from the lookup variable.
  
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  - moseschrute@lemmy.world ⁨6⁩ ⁨months⁩ ago
    Ahh that makes sense. I guess you couldn’t search anything your instance doesn’t federate with anyway.
    
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julian@activitypub.space ⁨6⁩ ⁨months⁩ ago
@admiralpatrick@lemmy.world I think you would be better served by checking for the Link header. NodeBB and WordPress do it, if that gives you some idea of implementation?

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- julian@activitypub.space ⁨6⁩ ⁨months⁩ ago
  @admiralpatrick@lemmy.world it took me a minute to find, but it is detailed in @evan@cosocial.ca's write up about HTTP Discovery of ActivityPub Objects.
  
  This is probably exactly what you're looking for.
  
  https://swicg.github.io/activitypub-html-discovery/
  
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  - admiralpatrick@lemmy.world ⁨6⁩ ⁨months⁩ ago
    
    I think you would be better served by checking for the Link header
    
    Can’t really do that, client-side. CORS is a perpetual cockblock (though I understand why it is), and I’d rather not make an internal API endpoint to do the lookup.
    
    The application polls Lemmy’s getFederatedInstances API endpoint at startup, so it has a list of every activity pub server your instance knows about. That’s the first and primary check for the URL that’s being searched.
    
    The second check is just to rule out non activity pub URLs that point to a federated instance (e…g. lemmy.world/modlog, lemm.world/pictrs/image/blah.webp, etc).
    
    Goal isn’t to “catch 'em all” but to catch the most used ones. If there’s one I don’t account for, either by omission or because the federated platform didn’t exist when I made the patterns, then it will just fall back to a regular search which also includes trying to resolve it as a federated URL (which is the current behavior in all prior versions).
    
    The goal is just to simply short-circuit the search behavior if the query is a known ap_id URL in order to avoid a lengthy search process and quickly redirect you to your instance’s local copy.
    
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rglullis@communick.news ⁨6⁩ ⁨months⁩ ago

So, I’ve rewritten the search / search boxes in Tesseract to skip the search and directly resolve activity pub URLs for users, posts, comments, and communities. I’m loving this as it makes things so much faster and easier.

Isn’t that the whole point of webfinger? Moreover, why would you paint yourself into a corner and hardcode the logic for all the different types of services, if ActivityPub uses JSON-LD and therefore provides a straightforward method for document dereferencing?

I’m not trying to be snarky. It’s just that I’m writing ActivityPub server where the id of each object is just an ULID, because to the server there is zero difference between serving the information about an actor or an activity.

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- admiralpatrick@lemmy.world ⁨6⁩ ⁨months⁩ ago
  We’ve had this discussion :)
  
  This application is written against the Lemmy API. It only speaks API. Eventually it’ll speak Piefed API as well, but right now, only Lemmy API.
  
  Lemmy and Piefed only do server-to-server Activity Pub and not client-to-server AP. Clients have to use the API to interact with them. This is a Lemmy (and eventually Piefed) client.
  
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  - rglullis@communick.news ⁨6⁩ ⁨months⁩ ago
    But then why do you worry about the ap_id patterns from other software?
    
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Jayjader@jlai.lu ⁨6⁩ ⁨months⁩ ago
From my own experience querying public mastodon timelines via API:

Mastodon user accounts have an ActivityPub URI of https://<instance.domain.tld>/api/v1/users/<username>

Mastodon posts have an ActivityPub URI of https://<instance.domain.tld>/api/v1/users/<post_author_username>/statuses/<post_id> (they also have a url property of https://<instance.domain.tld>/@<post_author_username>/<post_id> but that tends to serve the html view of the post)

To see for yourself, pick an instance that allows viewing their public timeline without logging in (mastodon.social is perfect for this) and follow the “Playing with public data” section of the docs. That page ellides most of the info you’re looking for in the example payloads they give (as the JSON payloads themself are quite large and nested), but I can assure you that AP_IDs for user accounts and posts can be found pretty quickly from a single timeline query.

I don’t think Mastodon has any notion of community, nor does it distinguish between posts and comments (when following a lemmy community, both posts and comments show up in my masto feed as “top-level” statuses (ie posts)).
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- admiralpatrick@lemmy.world ⁨6⁩ ⁨months⁩ ago
  Cool, thanks. I was close with /user guessing from memory.
  
  I think the /users/…/post_id will be sufficient. It just needs to know that the given URL is an AP_ID before passing it off to the API call to resolveObject. Since it already knows instance.domain.tld is a federated instance, it just needs to see if the path is an AP_ID or the HTML (or something else). Thus, I don’t have to parse the whole thing, just check that enough of it matches.
  
  Thanks!
  
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