ActivityPub

Manyfold instances use the ActivityPub protocol to exchange user activity with other instances, and other ActivityPub services, such as Mastodon. We use ActivityPub standard object types to directly federate content, and also post activities as Notes for use by microblog-style instances (e.g. Mastodon).

ActivityPub extensions

Manyfold uses the following extensions in its ActivityPub messages, specified in the JSON-LD @context:

Namespace	URI	Notes
as	https://www.w3.org/ns/activitystreams	used for hashtags and [sensitive]https://swicg.github.io/miscellany/#sensitive).
f3di	http://purl.org/f3di/ns#	a custom namespace for federation of 3d content; see next section for details.
sec	https://w3id.org/security/v1	used for public keys.
spdx	http://spdx.org/rdf/terms#	used to specify license information.
toot	http://joinmastodon.org/ns#	used for attributionDomains.

JSON-LD f3di namespace

In order to support 3d content over ActivityPub, we extend the vocabulary to support required concepts. The namespace is called f3di instead of a more application-specific one like manyfold, because we hope that other platforms will also adopt and help shape this specification to federate 3d content.

f3di:concreteType

In ActivityPub, an Actor is (basically) any Object that can perform an activity, and which has an inbox and outbox. In theory, Actors can have any type; they could be any defined object type, or a custom one. However, in practice, some Fediverse software only handles messages from certain types of Actor. Specifically, Mastodon (the dominant platform at present) only supports a limited set of Actors. Because of this, for compatibility, we choose to use Actor types from this limited subset.

However, we still need to know exactly what type of object is being represented, so concreteType is used to distingish between domain-specific types at a finer level of detail than Actor type allows. It also allows us to detect whether the remote Actor is a type relevant to Manyfold.

For examples, see the actor documentation below.

f3di:compatibilityNote

A boolean flag to indicate if a Note is posted for compatibility reasons. See the Notes section below for details.

Actors

Manyfold exposes the following ActivityPub actors, any of which can be discovered and followed if they are publicly visible to logged-out users.

Actor type	f3di:concreteType	Manyfold class	Description
Service	3DModel	Model	A 3d model (a coherent set of files and metadata)
Person	Creator	Creator	An entity (individual or organisation) that publishes models
Group	Collection	Collection	A collection of models
Person	User	User	A login account on a Manyfold instance; not necessarily a Creator

Using a combination of the Actor type and the concreteType, a remote Manyfold-compatible Actor can be identified and mapped to the appropriate domain-specific class.

Model

A 3D model, which in Manyfold terms is a collection of one or more 3d files that are intended to be used together, along with associated metadata.

Property	Data type	Description	Manyfold DB field	Example	Note
type	string	Actor type		always "Service"
f3di:concreteType	string	Domain-specific type		always "3DModel"
name	string	Display name	name	"Tablet Stand"
preferredUsername	string	Fediverse account username	username	"fjtcb1xl"	Manyfold randomly generates these for models at present, as they are not intended to be used directly.
summary	string	Short-form textual description; allows HTML	caption		Manyfold creates HTML from Markdown. Appears as bio on Mastodon.
content	string	Longer-form description; allows HTML	notes		Manyfold creates HTML from Markdown. Not shown on Mastodon.
attachment	object[]	standard ActivityStreams attachment	links	[  {   "type": "Link",   "href": "https://example.com"  } ]	Manyfold only creates and parses Link attachments at present
as:sensitive	boolean	Used to indicate sensitive content that some viewers may wish to hide by default.	sensitive	true
as:tag	Hashtag[]		tags	[  {   "type": "Hashtag",   "href": "...",   "name": "#Household"  } ]	Manyfold attempts to turn multiword tags into CamelCase, for accessibility.
attributedTo	id	A link to an actor for the model creator, if available	creator
context	id	A link to an actor for a collection that contains the model, if any	collection
spdx:license	License	A license definition from SPDX		{  "@id": "http://spdx.org/licenses/CC-BY-SA-4.0",  "spdx:licenseId": "CC-BY-SA-4.0" }	Manyfold uses LicenseRef-Commercial to identify paid-for models; this isn’t a proper SPDX license, so won’t have the @id property.

Standard Actor properties (e.g. inbox) are also included and use the standard semantics.

Creator

An entity which creates and publishes models; i.e. a content creator or author. Not necessarily related to an actual individual or user of an instance.

Property	Data type	Description	Manyfold database field	Example	Note
type	string	Actor type		always "Person"
f3di:concreteType	string	Domain-specific type		always "Creator"
name	string	Display name	name	"Floppy"
preferredUsername	string	Fediverse account username	username	"floppy"
summary	string	Short-form textual description; allows HTML	caption		Manyfold creates HTML from Markdown. Appears as bio on Mastodon.
content	string	Longer-form description; allows HTML	notes		Manyfold creates HTML from Markdown. Not shown on Mastodon.
attachment	object[]	standard ActivityStreams attachment	links	[  {   "type": "Link",   "href": "https://example.com"  } ]	Manyfold only creates and parses Link attachments at present
toot:attributionDomains	string[]	A list of domains that are valid for fediverse:creator opengraph tags		["try.manyfold.app"]	Will always be set to the account domain

Standard Actor properties (e.g. inbox) are also included and use the standard semantics.

Collection

A collection of models.

Property	Data type	Description	Manyfold database field	Example	Note
type	string	Actor type		always "Group"
f3di:concreteType	string	Domain-specific type		always "Collection"
name	string	Display name	name	"Household items"
preferredUsername	string	Fediverse account username	username	"fjtcb1xl"	Manyfold randomly generates these at present, as they are not intended to be used directly.
summary	string	Short-form textual description; allows HTML	caption		Manyfold creates HTML from Markdown. Appears as bio on Mastodon.
content	string	Longer-form description; allows HTML	notes		Manyfold creates HTML from Markdown. Not shown on Mastodon.
attachment	object[]	standard ActivityStreams attachment	links	[  {   "type": "Link",   "href": "https://example.com"  } ]	Manyfold only creates and parses Link attachments at present

Standard Actor properties (e.g. inbox) are also included and use the standard semantics.

User

An individual user account. These will follow the above actors, but in general, they’re not currently expected to be followed by others.

Property	Data type	Description	Manyfold database field	Example	Note
type	string	Actor type		always "Person"
f3di:concreteType	string	Domain-specific type		always "User"
name	string	Display name	name	"James"
preferredUsername	string	Fediverse account username	username	"fjtcb1xl"	Manyfold randomly generates these at present, as they are not intended to be used directly.

Standard Actor properties (e.g. inbox) are also included and use the standard semantics.

Activities

Manyfold will post and receive activities as follows.

	3DModel	Creator	Collection	User	Note (see below)
Create	both	both	both		send
Update	both	both	both		send
Delete	both	both	both		send
Flag	recv	recv	recv	both	recv
Follow	recv	recv	recv	send
Accept	send	send	send	recv
Undo	recv	recv	recv	send

Notes

Much of Manyfold’s activity is based around actions that are happening to the Actors themselves; for instance “This Creator has been updated”. However, in a microblog-style application, this would not be visible, or at best would just appear as a change in the profile information. Therefore, for compatibility with microblog-style services, Manyfold also posts Note objects, just as an application such as Mastodon would.

These notes contain a textual summary of an activity, which can be displayed in lieu of the actual activity itself. For instance, in the scenario where a new Model is added by a particular Creator:

1. The creator posts a Create activity, where the object is the new Service/3DModel. It will be posted to the creator’s followers, and Manyfold (and compatible) instances can respond can create their own Model object with the received information.
2. The creator also posts a Create activity with a Note object. The note contains a text description of the change, in this case announcing that a new model has been posted, including a link to the model and other microblog compatible data. The note is posted with the f3di:compatibilityNote property set to true, which lets Manyfold-compatible instances ignore it, while other Fediverse platforms will receive and display it in timelines.

Note that by default, this means that each change will be posted twice to all followers. An instance may use NodeInfo extension data (see below) to determine which activities and actors a remote server supports, and only send the appropriate activity. Manyfold has not yet implemented this filtering, but will do soon.

NodeInfo

Manyfold supports the NodeInfo standard for exposing server capabilities.

The following extension definition method is proposed, and not yet implemented by Manyfold.

Support for extension types is indicated in the operations field of the nodeinfo response following the method proposed in FEP-9fde

Currently f3di.accept.3dmodel is proposed as the extension name, though this is subject to change as the FEP and behaviour evolves.

{
  "version": "2.1",
  "software": {
    "name": "manyfold",
    "version": "x.y.z"
  },
  "protocols": [
    "activitypub"
  ],
  "usage": {...},
  "openRegistrations": true|false,
  "operations": {
    "f3di.accept.3dmodel": ["0.1.0"]
  }
}

Technical implementation

Manyfold’s ActivityPub support is built using the Federails Ruby gem, which is a reusable Rails engine for adding ActivityPub support to existing Rails apps.

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