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
Accept	Follow, Join
Announce	Object
Create	Note, Event
Delete	Object
Flag	Object
Follow	Object
Reject	Follow, Join
Remove	Note, Event
Undo	Announce, Follow
Update	Object

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 using Place from ActivityStreams we use Place from Schema.org.

A Schema.org Place type has an address property, which we assume to be of PostalAddress type and a geo property, which is assumed to be of GeoCoordinates type.

{
  "@context": [
    "...",
    {
      "GeoCoordinates": "sc:GeoCoordinates",
      "Place": "sc:Place",
      "PostalAddress": "sc:PostalAddress",
      "address": {
        "@id": "sc:address",
        "@type": "sc:PostalAddress"
      },
      "addressCountry": "sc:addressCountry",
      "addressLocality": "sc:addressLocality",
      "addressRegion": "sc:addressRegion",
      "geo": {
        "@id": "sc:geo",
        "@type": "sc:GeoCoordinates"
      },
      "location": {
        "@id": "sc:location",
        "@type": "sc:Place"
      },
      "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"
      },
      "geo": {
        "latitude": 4.8425657,
        "longitude": 45.7517141,
        "type": "GeoCoordinates"
      },
      "id": "http://mobilizon2.com/address/bdf7fb53-7177-46f3-8fb3-93c25a802522",
      "name": "10 Rue Jangot",
      "type": "Place"
    },
  "type": "Event"
}