fep/feps/fep-fffd.md

authors, status, dateReceived

authors	status	dateReceived
Adam R. Nelson <adam@nels.onl>	DRAFT	2023-04-29

FEP-fffd: Proxy Objects

Summary

A proxy object is an [ActivityPub] object that is semantically identical to an entity on another, non-ActivityPub protocol. For example, an ActivityPub-to-Nostr bridge creates Actors and Notes that are proxies for Nostr users and notes.

This document describes a data format to identify proxy objects and to describe the non-ActivityPub entities that they are equivalent to, with the intention that multi-protocol clients will automatically merge objects with their proxies, hiding the implementation details of bridges and cross-protocol publishing from users.

Requirements

The key words "MUST", "SHOULD", and "MAY" are to be interpreted as described in [RFC2119].

Rationale

Many Fediverse servers speak multiple protocols besides ActivityPub, such as Zot or Diaspora, and simultaneously publish posts across multiple protocols. Additionally, bridge servers exist to relay posts between ActivityPub and other protocols such as Nostr.

There is currently no standard way to communicate that an ActivityPub activity is a copy (or proxy) of a post on another protocol.

Consider this scenario:

• Alice's server speaks both ActivityPub and Diaspora protocols. She publishes a post, which is syndicated on both protocols.
• Bob's server speaks only ActivityPub. He replies to the ActivityPub version of Alice's post.
• Charlie's server speaks only Diaspora. He replies to the Diaspora version of Alice's post.
• Dee's server speaks both ActivityPub and Diaspora. She receives Alice's, Bob's, and Charlie's posts. How does Dee's server know that Bob's reply and Charlie's reply belong to the same post?

Proxy objects provide a potential solution to this problem.

Format

FEP-fffd uses the w3id.org/fep namespace as defined in [FEP-9606]. Conforming ActivityPub JSON-LD messages MUST include a context that maps the terms proxyOf, protocol, proxied, and authoritative to the same IRIs and types as in this context:

{
  "@context": {
    "xsd": "http://www.w3.org/2001/XMLSchema#",
    "fep": "https://w3id.org/fep/",
    "proxyOf": {
      "@id": "fep:fffd/proxyOf",
      "@type": "@id",
      "@container": "@set"
    },
    "protocol": {
      "@id": "fep:fffd/protocol",
      "@type": "@id"
    },
    "proxied": {
      "@id": "fep:fffd/proxied",
      "@type": "xsd:string"
    },
    "authoritative": {
      "@id": "fep:fffd/authoritative",
      "@type": "xsd:boolean"
    }
  }
}

The property proxyOf may be included in any ActivityPub Object, such as an Actor or a Note. If proxyOf is present, its value MUST be an array of objects, and each object in this array MUST include the properties protocol and proxied, and additionally MAY include the property authoritative. An object with a nonempty proxyOf property is called a proxy object.

Each entry in proxyOf names a non-ActivityPub entity, called a proxied object, which should be considered semantically identical to the parent proxy object. protocol is an IRI that identifies the non-ActivityPub protocol being used, and proxied is a freeform string (usually, but not necessarily, a URL) that identifies an entity in whatever format the protocol in question uses.

If authoritative is present and its value is true, it indicates that the proxied object is the original, authoritative version of the proxy object. The proxyOf array MUST NOT contain more than one object with authoritative: true. This property SHOULD be used by bridges that relay posts made by third parties, to indicate that the bridged post is not the original. It SHOULD NOT be used by servers that publish to multiple protocols at once; in this case no one version of an object is more authoritative than another.

Protocols

This document defines two protocol names, but more may be included in either future FEPs or future revisions of this document.

Nostr

protocol: "https://nostr.com"

proxied format: A [NIP-19] string identifying a pubkey or note.

Diaspora

protocol: "https://joindiaspora.com/protocol"

proxied format: A URI with the [diaspora:// URI scheme].

Freeform Prefix IRIs

In addition to the above specified protocol IRIs, protocol MAY be any other IRI if proxied is also an IRI and protocol is a prefix of proxied.

This allows an ActivityPub object to proxy any non-federated Web content; for example, a Twitter-to-ActivityPub bridge may use a protocol of "https://twitter.com" and a proxied value that is a Twitter URL, to identify a Note as a proxy object for a Twitter post.

Examples

(This section is non-normative. The JSON-LD @context property is omitted for brevity.)

A post relayed by a third-party Twitter-to-ActivityPub bridge:

{
  "id": "http://twitter-bridge.example/status/1234",
  "type": "Note",
  "actor": "http://twitter-bridge.example/@jack",
  "content": "just setting up my twttr",
  "proxyOf": [{
    "protocol": "https://twitter.com",
    "proxied": "https://twitter.com/jack/status/20",
    "authoritative": true
  }]
}

A post published to ActivityPub, Diaspora, and Nostr simultaneously:

{
  "id": "http://fediverse.example/status/1234",
  "type": "Note",
  "actor": "http://fediverse.example/@alice",
  "content": "Hello, world!",
  "proxyOf": [{
    "protocol": "https://joindiaspora.com/protocol",
    "proxied": "diaspora://alice@fediverse.example/post/deadbeefdeadbeefdeadbeefdeadbeef"
  }, {
    "protocol": "https://nostr.com",
    "proxied": "note1gwdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeefdeadbeef"
  }]
}

References

• [RFC-2119] S. Bradner, Key words for use in RFCs to Indicate Requirement Levels
• [ActivityPub] Christine Lemmer Webber, Jessica Tallon, ActivityPub, 2018
• [FEP-9606] a, FEP-9606 : Using w3id.org/fep as a namespace for extension terms and for FEP documents, 2023
• [NIP-19] jb55, fianjaf, Semisol, NIP-19: bech32-encoded entities, 2023
• [diaspora:// URI scheme] Benjamin Neff, diaspora* federation protocol, 2017

Copyright

CC0 1.0 Universal (CC0 1.0) Public Domain Dedication

To the extent possible under law, the authors of this Fediverse Enhancement Proposal have waived all copyright and related or neighboring rights to this work.