debianize-mobilizon/docs/contribute/activity_pub.md

Federation

ActivityPub

Mobilizon uses ActivityPub to federate content between instances. It only supports the server-to-server part of the ActivityPub spec.

It implements the HTTP signatures spec for authentication of inbox deliveries, but doesn't implement Linked Data Signatures for forwarded payloads, and instead fetches content when needed.

To match usernames to actors, Mobilizon uses WebFinger.

Instance subscriptions

Instances subscribe to each other through an internal actor named relay@instance.tld that publishes (through Announce) every created content to it's followers. Each content creation share is saved so that updates and deletes are correctly sent to every relay subscriber.

Activities

Supported Activity	Supported Object or Activity
Accept	Follow, Join
Add	Document, ResourceCollection
Announce	any Object
Create	any Object
Delete	any Object
Flag	any Object
Follow	any Object
Invite	Group
Join	Event
Leave	Event, Group
Reject	Follow, Join
Remove	Note, Event, Member
Undo	Announce, Follow
Update	Object

Objects

Person

Every Mobilizon profile is a Person.

Event

Every Mobilizon event is an Event with a few extensions, especially for location information since Place is limited.

Note

Every Mobilizon comment showing under an event is a Note, as well as every element from group discussions, where the context property is used to group messages in discussions.

Group

Every Mobilizon group is a Group.

Member

Every Mobilizon group member is a Member, that conveys the role information that the Person has in the Group.

%{
  "type" => "Member",
  "id" => "https://somemobilizon.instance/member/some-uuid",
  "actor" => "https://somemobilizon.instance/@some-person",
  "object" => "https://somemobilizon.instance/@some-group",
  "role" => "MODERATOR"
    }

The allowed values for role are: invited, not_approved, member, moderator, administrator, rejected.

Document

Attached pictures and other files are represented with Document.

Group resources are also represented with Document.

Article

Every Mobilizon group post is an Article.

ResourceCollection

Mobilizon's group resources (see Document) can be collected into folders named ResourceCollection, which have the same set of properties as a Document, without the url.

Extensions

Event

The vocabulary for Event is based on the Event object in ActivityStreams, extended with :

• the Event Schema from Schema.org
• some properties from iCalendar, such as ical:status (see this issue)

The following properties are added.

repliesModeration

Disabling replies is an ongoing issue with ActivityPub so we use a temporary property.

See the corresponding issue.

Accepted values: allow_all, closed, moderated (not used at the moment)

!!! info We also support PeerTube's commentEnabled property as a fallback. It is set to true only when repliesModeration is equal to allow_all.

Example:

{
  "@context": [
    "...",
    {
      "mz": "https://joinmobilizon.org/ns#",
      "pt": "https://joinpeertube.org/ns#",
      "repliesModerationOption": {
        "@id": "mz:repliesModerationOption",
        "@type": "mz:repliesModerationOptionType"
      },
      "repliesModerationOptionType": {
        "@id": "mz:repliesModerationOptionType",
        "@type": "rdfs:Class"
      },
      "commentsEnabled": {
        "@id": "pt:commentsEnabled",
        "@type": "sc:Boolean"
      }
    }
  ],
  "...": "...",
  "repliesModerationOption": "allow_all",
  "commentsEnabled": true,
  "type": "Event",
  "url": "http://mobilizon1.com/events/8cf76e9f-c426-4912-9cd6-c7030b969611"
}

joinMode

Indicator of how new members may be able to join.

See the corresponding issue.

Accepted values: free, restricted, invite (not used at the moment)

Example:

{
  "@context": [
    "...",
    {
      "mz": "https://joinmobilizon.org/ns#",
      "joinMode": {
        "@id": "mz:joinMode",
        "@type": "mz:joinModeType"
      },
      "joinModeType": {
        "@id": "mz:joinModeType",
        "@type": "rdfs:Class"
      }
    }
  ],
  "...": "...",
  "joinMode": "restricted",
  "type": "Event",
  "url": "http://mobilizon1.com/events/8cf76e9f-c426-4912-9cd6-c7030b969611"
}

location

We use Schema.org's location property on Event. The ActivityStream vocabulary to represent places is quite limited so instead of just using Place from ActivityStreams we also add a few properties from Schema.org's Place vocabulary.

We add an address property, which we assume to be of PostalAddress type.

{
  "@context": [
    "...",
    {
      "PostalAddress": "sc:PostalAddress",
      "address": {
        "@id": "sc:address",
        "@type": "sc:PostalAddress"
      },
      "addressCountry": "sc:addressCountry",
      "addressLocality": "sc:addressLocality",
      "addressRegion": "sc:addressRegion",
      "postalCode": "sc:postalCode",
      "sc": "http://schema.org#",
      "streetAddress": "sc:streetAddress",
    }
  ],
  "id": "http://mobilizon2.com/events/945f350d-a3e6-4bcd-9bf2-0bd2e4d353c5",
  "location": {
      "address": {
        "addressCountry": "France",
        "addressLocality": "Lyon",
        "addressRegion": "Auvergne-Rhône-Alpes",
        "postalCode": "69007",
        "streetAddress": "10 Rue Jangot",
        "type": "PostalAddress"
      },
      "latitude": 4.8425657,
      "longitude": 45.7517141,
      "id": "http://mobilizon2.com/address/bdf7fb53-7177-46f3-8fb3-93c25a802522",
      "name": "10 Rue Jangot",
      "type": "Place"
    },
  "type": "Event"
}

maximumAttendeeCapacity

We use Schema.org's maximumAttendeeCapacity to know how many places there can be for an event.

anonymousParticipationEnabled

We add this boolean field to know whether or not anonymous participants can participate to an event.

!!! note Even though this information is federated, we redirect anonymous participants to the original instance so they can participate.

Join

participationMessage

We add a participationMessage property on a Join activity so that participants may transmit a note to event organizers, to motivate their participation when event participations are manually approved. This field is restricted to plain text.

{
  "type": "Join",
  "object": "http://mobilizon.test/events/some-uuid",
  "id": "http://mobilizon2.test/@admin/join/event/1",
  "actor": "http://mobilizon2.test/@admin",
  "participationMessage": "I want to join !",
  "@context": [
    {
      "participationMessage": {
        "@id": "mz:participationMessage",
        "@type": "sc:Text"
      }
    }
  ]
}