Signalling "open in app" behaviour for AP content
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Does anyone know what the most broadly implemented standard is for signalling that a web page has an alternative ActivityPub endpoint?
What I found online (and with @[email protected] and @[email protected]'s input) was to deliver a
Linkheader and set a<link>tag, but it doesn't seem to work (at least with Megalodon)... -
@julian @evan @silverpill I found Link tag to suffice. Do you also have webfinger implemented?
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@[email protected] thanks for the response. While I implemented the link tag for all user, post, topic, and category routes (basically, anything that had a corresponding AP endpoint), I only checked a link to a post, which should have returned a Note object.
I didn't check a link to a user profile, so maybe that's it.
AIUI, webfinger wouldn't apply for other object types.
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@julian @evan @silverpill Cool mind sending a link to the post json-ld and maybe the source code? I'd love to test it against my implementations and see what's up.
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@[email protected] Yeah, sure thing! This is the source code for one of them, it adds the link header when loading a topic.
You can try viewing the source of
https://community.nodebb.org/post/99307or making aHEADcall against it to see the meta tag and Link header, respectively. -
@[email protected] Also tested a user link, and that also didn't work — shrug maybe it'll work in yours?
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fedilinks web+ap is probably the most widely supported, depending on how you count.
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Thanks @[email protected], in my case while making the call is definitely an option, I was hoping for something I could do pre-flight (e.g. an opportunistic HEAD call).
This issue provides some good guidance (with comments from @[email protected] and @[email protected] too!), so I'll have to see.
Perhaps it's just the app I'm using and it'll work fine via the web app for Mastodon.
NodeBB will implement a pre-flight HEAD call I think, although we don't yet.
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@julian @mauve @snarfed.org Content negotiation is a standard procedure described in the ActivityPub spec. Supporting other discovery methods might be a good idea (and a good topic for a FEP), but I don't recommend relying on them exclusively.
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julian: Thanks @[email protected], in my case while making the call is definitely an option, I was hoping for something I could do pre-flight (e.g. an opportunistic HEAD call). Can you explain what you mean by this? Making a GET or HEAD request with Accept: activity+json as the highest priority and HTML as the fallback should work fine and wouldn't require any extra round trips (like a preflight or Link header would)
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@silverpill @julian @[email protected] I don't think content negotiation can be the be-all end-all. The <link> element and Link: HTTP headers are good to use. Julian, I will write it up and we'll see where it lands.
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[email protected]replied to Evan Prodromou on last edited by@evan1 I agree in theory but in this specific instance I'm not sure I understand where the Link header or meta tag would be helpful (I can definitely see where it'd be helpful for the case of e.g. a browser extension though)
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Thanks @[email protected] — that'd be appreciated!
@[email protected], this would be helpful in NodeBB's case where we have a web app, so rendering a link to something is just an anchor.
I could theoretically override the anchor click handler to do a backend round-trip to check whether we could load the content in-app, otherwise fall back to a regular browser behaviour (a page navigation).
For example, let's say I link out to Evan's profile here. If NodeBB knew that this link had an alternative AP endpoint, then we could redirect the user instead to the local representation of his profile
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@julian @nightpool agreed. That's positive behaviour.
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julian: I could theoretically override the anchor click handler to do a backend round-trip to check whether we could load the content in-app, otherwise fall back to a regular browser behaviour (a page navigation). i believe this is what mastodon does, but it's also worth mentioning fep-e232 Object Links as a way to tag a given Link with the appropriate mediaType used for content negotiation: { "@context": "https://www.w3.org/ns/activitystreams", "content": "
This is an object link.
", "tag": { "type": "Link", "name": "object link", "href": "https://example.com/some-object", "mediaType": "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"" } } -
@[email protected] Thanks! That's helpful (the link was purple, so I must've at least looked at it in the past...)
For those implementations using FEP-e232 I can then at least proactively update the anchor.
It's sounding more and more like I'll need to piece together multiple strategies:
- Object Links if provided
- On click, check with backend to see if a local representation can be navigated to
- Otherwise, standard browser navigation
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@evan @julian @nightpool for what it's worth, webfinger should be (re: is) able to do this, even if the implementations in the wild don't. The intent at the time was for webfinger to be the "DNS records" for "social addresses", and the main reasons we didn't just use DNS was because (1) DNS doesn't support anything but bare domain names, (2) management of DNS records at scale is hard, and (3) it wasn't possible to query DNS via the web.
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@evan @julian @nightpool lots of folks advocated to support any URI scheme in a webfinger lookup, and that's why we have the "acct" scheme at all - so that email-style addresses could be used alongside http etc URIs!
The <Link> approach definitely works, but feels a bit reinventing-webfinger/creating more complexity in lookups (on the client side).
Hope the context is helpful!
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Evan Prodromoureplied to blaine on last edited by [email protected]
So, for finding the AP equivalent of an URL that I think is a Web page, I'd take these steps:
- Link header: HEAD and look for the Link: header (easy, fast)
- Webfinger: Webfinger the URL (a little more complicated)
- Content negotiation: GET with Accept header set to AS2 type
- Parsing: GET and look for Link: header or <link> element
