ActivityPub

Manyfold’s ActivityPub implementation is still evolving, and this document may be inaccurate compared to the latest code, or may include sections that are not yet implemented.

Manyfold instances use the ActivityPub protocol to exchange user activity with other instances, and other ActivityPub services, such as Mastodon.

On top of the ActivityPub standard object types, we define an extension specifically for 3D content, and provide alternatives for use when communicating to instances that don’t support it.

NodeInfo

Manyfold supports the NodeInfo standard for exposing server capabilities.

Support for extension types will be indicated in the metadata field of the nodeinfo response. Several metadata fields are known, but we define a new one specifically to indicate 3d model support.

{
  "version": "2.1",
  "software": {
    "name": "manyfold",
    "version": "x.y.z"
  },
  "protocols": [
    "activitypub"
  ],
  "usage": {...},
  "openRegistrations": true|false,
  "metadata": {
    "activitypub": {
      "extensions": [
        "https://w3id.org/activity-streams/extensions/3dModel#v1.0"
      ]
    }
  }
}

Platforms such as Pixelfed and Bookwyrm use the software field to determine support for their custom types, but as we explicitly want to encourage other implementations, using a structure in metadata seems more sensible. We define an IRI for the extension type, as proposed in FEP-6481.

Objects

3DModel

3DModel is a custom ActivityStreams object type, parallel to the similar Audio and Video types, and consistent with the schema.org 3DModel type.

This object type corresponds to Manyfold’s internal Model class. It extends the Document core object type, in the same way as Audio in the core spec.

The standard ActivityStreams activity types will be used in direct correspondence to events in Manyfold. A new Model will results in a Create activity, changes will result in Update activities, and so on.

If available, the preview property of the object includes a URL for both an image and a 3d model file for direct loading by the client, with the appropriate MIME types. Of course, it’s up to the client whether it chooses to display these.

Note

Note is used to represent comments on a model; these could either be local to Manyfold, or remote on a different system such as Mastodon.

Servers such as Mastodon that do not support the 3DModel object type (potentially determined using NodeInfo, above) are sent a Note instead, containing a textual description of the event and the canonical URL of the model’s web page; the 3D preview will not be included. A new Note is created for each event, whether creation, update, etc.

Actors

Manyfold provides individual ActivityPub actors for the following:

Manyfold class	ActvityPub actor type	Notes
User	Person
Creator	Person
Collection	Group
Model	Service	used instead of the more accurate Document for wider compatibility

Any of these can be followed via ActivityPub if they are publicly visible to logged-out users.

Activities

The following activities are supported on the object types shown in the table. In summary:

• Following is supported for users, creators, individual models, and collections;
• Standard microblog-interaction-type activities (create, like, boost) are supported for models and comments;
• Collection-oriented activities are supported for users, models, and other collections.

Activity	Description	object	target	origin
Create	Actor has published a new model or comment	3DModel, Note
Update	Actor has updated the object (including individual files, in the case of a model)	3DModel
Delete	Actor has deleted the object	3DModel
Flag	Actor has flagged the object for moderator attention	3DModel, Note
Follow	Actor has followed the object to get updates	Person, Group, Service
Add	Actor has added the object to the target collection	3DModel, Group	Group
Remove	Actor has removed the object from the target collection	3DModel, Group		Group

Technical implementation

Manyfold’s ActivityPub support will be built using the federails Ruby gem.

Many thanks to Bookwyrm and Pixelfed for their excellent ActivityPub implementation docs, which this page is heavily based on.