Emissary supports many standard ways of following and sharing content. The goal is to accept the highest-fidelity connections from as many sites as possible, whatever specific protocols they are using at the time. In many cases, Emissary will support several competing standards, defaulting to its preferred methods, but accepting connections in whatever form they are offered.
The ActivityPub standard is currently the most common and popular protocol for sharing information between users on various websites. Emissary currently supports the following Activities defined in the ActivityPub spec. Other unrecognized activities are ignored.
| Activity | Sending | Receiving |
|---|---|---|
| Accept/Follow | When Emissary receives a follow request, it adds a new "Follower" record and sends a corresponding Accept activity to the original server. |
When Emissary receives an Accept activity tied to a Follow activity, it mark the corresponding Following record as active. Other forms of Accept are ignored. |
| Block | Emissary sends a Block activity to all followers whenever a user creates a Block in their profile that is shared publicly. |
When Emissary receives a Block activity from a remote actor it follows, it creates a block recommendation for the current user that includes the reason the remote actor provided for the block. |
| Create/* | Emissary's publisher service sends Create activities to all followers whenever a new Stream is created. The object type is determined by the Stream's Template. |
When Emissary receives a "Create" activity, it adds a new message to that user's Inbox. |
| Delete/* | Emissary's publisher service sends a Delete activity to all followers whenever a Stream is unpublished. |
When Emissary receives a Delete activity, it soft-deletes the corresponding message from the User's inbox. |
| Dislike | Emissary sends a Dislike activity to a remote Inbox whenever a person responds NEGATIVELY to an external post. |
When Emissary receives a Dislike activity, creates a new Response record for the corresponding Stream. |
| Follow | Emissary sends a Follow activity to a remote Inbox whenever a person requests to follow another ActivityPub Actor. |
When Emissary receives a Follow activity, it validates the request, creates a new Follower record in the user's inbox, and then sends a corresponding Accept message to the originating server. Emissary does not currently allow user's to manually approve/disapprove follow requests. |
| Like | Emissary sends a Like activity to a remote Inbox whenever a person responds POSITIVELY to an external post. |
When Emissary receives a Like activity, creates a new Response record for the corresponding Stream. |
| Undo/Block | Emissary sends an Undo activity whenever a user deletes or un-publishes a Block record in their profile. |
When Emissary receives an Undo activity linked to a Block, it deletes the corresponding Block recommendation record from that user's profile. |
| Undo/Dislike | Emissary sends an Undo activity whenever a user deletes a NEGATIVE Response record in their profile. |
When Emissary receives an Undo activity linked to a Dislike, it deletes the corresponding Response record from that user's profile. |
| Undo/Follow | Emissary sends an Undo activity whenever a user deletes a Following record in their profile. |
When Emissary receives an Undo activity linked to a follow request, it deletes the corresponding Follower record from that user's profile. |
| Undo/Like | Emissary sends an Undo activity whenever a user deletes a POSITIVE Response record in their profile. |
When Emissary receives an Undo activity linked to a Like, it deletes the corresponding Response record from that user's profile. |
| Update/* | Emissary's publisher service sends an Update activity whenever a currently-published Stream is published again. |
When Emissary receives an Update activity, it updates the corresponding message in that user's Inbox. |
Emissary supports but does not require WebFinger protocol. Every Emissary instance includes a WebFinger server that provides the publicly-available metadata about the people on that server, and is a WebFinger client that can use WebFinger to look up metadata from remote servers.
Emissary can read and write feeds in RSS 2.0, [Atom](https://en.wikipedia.org/wiki/Atom_(web_standard\)), and JSONFeed formats. The specific format is auto-negotiated, preferring: JSONFeed, then Atom, then RSS.
Creating Feeds: The view-feed step adds an RSS feed to any Stream, listing its children
Reading Feeds: Users can follow any feed on the Internet by entering the site's URL into the "Follow" dialog.
Emissary sends and receives real-time feed updates via WebSub protocol. The publisher service works as its own WebSub hub, sending updates whenever a Stream us published or republished.
Emissary's publisher service sends WebMentions whenever a Stream is published or re-published.
Default templates also include meta-data that points to Emissary's WebMention receiver, which receives WebMentions from external servers, which are stored a "Mentions" in Emissary's database and are accessible to all Stream Templates.
Emissary's default templates all include standard MicroFormats for all available data points.
Emissary can also parse MicroFormats as a feed when following a URL.
Emisary implements a subset of the Mastodon API, allowing third-party Mastodon clients to interact with Emissary for all features commonly supported by both Emissary and Mastodon.
This is a placeholder for writing FEDERATION.md documentation, similar to the entries listed here: https://socialhub.activitypub.rocks/t/guide-for-new-activitypub-implementers/479#federationmd-25