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ActivityPub URI Schema Proposal

This is a Draft proposal of URI schema meant to be used across federated applications using ActivityPub protocol to improve people's experience and increase interoperability.

Definitions

Fediverse
A network of interconnected applications using ActivityPub protocol to exchange information.
Actor
Defined in ActivityStreams Vocabulary.

Rationale

Federated applications in current state do exchange information effectively among servers if both Actors established a subscription. Many applications implemented in-app views of links in Fediverse so that people do not have to leave their application and most of them implement Follow button in such views. But people might explore web outside of their beloved application or their application may not implement such in-app views and ask people to see pages or posts on original website. In both cases people are not able to interact with such federated content or Actors. Usually people are forced to copy link to the content or Actor they are interested and paste it inside their application to perform actions from this application.

URI schema in this document is meant to improve people's interaction with content and Actors and to improve applications interoperability. Proposal also tries to make URI schema extensible.

URI Schema 'web+activitypub:' definition

activitypub-schema  = "web+activitypub:" activity-type activity-properties
activity-type       = achars
activity-properties = "?" activity-property *( "&" activity-property )
activity-property   = property-name "=" property-value
property-name       = achars
property-value      = achars
achars              = *( unreserved / pct-encoded )

<activity-type> defines an Activity Type. Activity Type can used either one of defined in ActivityStreams Vocabulary or can be percent-encoded compact URI.

<activity-property> defines Activity properties. Both <property-name> and <property-value> are percent-encoded. Properties should be interpreted as described in ActivityStreams 2.0 with following considerations:

  • <property-name> MUST NOT be type since it's defined by <activity-type>,
  • values are always strings and can't represent complex types,
  • values should be casted from strings to type depending on JSON-LD expected term type,
  • all embedded objects should be referenced by URI,
  • property can define compact URI prefix with key syntax @context:<prefix>.

NOTE: web+ prefix rationale

Currently most fedirated applications are operated using Web Browsers which only allow registration of safelisted or prefixed schemes.

URI Schema consuming

Application MUST handle object property in every supported Activity. Application MAY skip handling any properties it doesn't support.

ActivityPub Activities

Application consuming described URI schema MUST implement Follow Activity Type as defined in ActivityPub.

Application MAY consume Client Activities defined in ActivityPub Client to Server interaction.

Announce Activity

Application MAY consume type Announce with properties defined in ActivityStreams Vocabulary. Application MUST interpret Announce as a command to announce content referenced in object property.

Extended Activities and properties

Application MAY support additional Activity Types and property extensions defined in compact IRI definitions. Application MUST check support of IRI-defined activities and properties only by IRI and not by prefix.

Examples

Follow Activity URI

web+activitypub:Follow?object=https%3A%2F%2Fmastodon.ml%2Fusers%2Fbano

This URI represents following Activity:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Follow",
  "object": "https://mastodon.ml/users/bano"
}

Given Activity asks application to follow Actor with id https://mastodon.ml/users/bano.

web+activitypub:Follow?object=acct%3Abano%40mastodon.ml

This URI represents following Activity:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Follow",
  "object": "acct:bano@mastodon.ml"
}

URI asks application to follow Actor with acct:bano@mastodon.ml which will be resolved to https://mastodon.ml/users/bano using WebFinger.

Announce Activity URI

web+activitypub:Announce?object=https%3A%2F%2Fexample.org%2Fstatus%2Fcat-greeting

This URI represents following Activity:

{
  "@context": "https://www.w3.org/ns/activitystreams",
  "type": "Announce",
  "object": "https://example.org/status/cat-greeting"
}

Which asks application to announce (share/boost/repost) cat-greeting Activity.

Extended Activities

NOTE: URIs in this section are split in lines to be readable.

Next URI shows how to use extended Activity Types and extended properties

web+activitypub:cat%3AHug?
%40context%3Acat=https%3A%2F%2Fexample.com%2Fcat-lovers%23&
object=https%3A%2F%2Fexample.org%2Fstatus%2Fcat-greeting&
cat%3Aname=Snowball

After parsing URI we can get data:

{
  "type": "cat:Hug",
  "properties": [
    { "@context:cat": "https://example.com/cat-lovers#" },
    { "object": "https://example.org/status/cat-greeting" },
    { "cat:name": "Snowball" }
  ]
}

which should be interpreted as following Activity:

{
  "@context": [
    "https://www.w3.org/ns/activitystreams",
    {"cat": "https://example.com/cat-lovers#"}
  ],
  "type": "cat:Hug",
  "object": "https://example.org/status/cat-greeting",
  "cat:name": "Snowball"
}

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