ssb-crut-authors

Basically ssb-crut but adds authors field and rules which go with that to control who can publish valid updates to a record.

Example usage

const CRUT = require('ssb-crut-authors')
const Overwrite = require('@tangle/overwrite')

const server = Server() // some scuttlebutt instance
const spec = {
  type: 'gathering',
  props: {
    title: Overwrite({ type: 'string' }),
    description: Overwrite({ type: 'string' }),
    date: Overwrite({ type: 'string', pattern: '^2020-\d\d-\d\d' }),
    // authors    <-- automatically added
  },
  // isValidNextStep    <-- auto-adds authoship logic, you can add more logic on top
}

const crut = new CRUT(serve, spec)

const details = {
  title: 'party',
  authors: { add: [server.id] }
}
crut.create(details, (err, gatheringId) => {
  //
})

Authorship Rules

1. You must add at least one author when creating a record
2. A valid update is one which
   • a) is authored by someone in the list of active authors on the tip(s) the update is extending
   • b) leaves the record with > 1 author (after update is applied)
3. An Author must be one of:
   • a FeedId
   • * (wildcard), and means anyone can author
4. If * is active (has been added and not removed) then anyone can update, regardless of whehter they have been removed.

Rare edge cases:

Edge Case (A) - authors simultaneously remove one another

An example of edge case (A) would be:

• there are two authors added in initial message A
• update B removes one author, C removes the other
• one of those authors tries to publish M

graph TB
A-->B-.->M
A-->C-.->M

classDef default fill: purple, color: white, stroke: none;
classDef proposed fill: hotpink, color: white, stroke: none;
class M proposed

Diagram of a branched state (tips B, C) and you're trying to publish an update (merge node M)

This could be a block because of rule (2.a), as to extend two tips you must be an active author according to each tip, (and no author is valid for both tips).

Special Rule: in this case the "original author" is considered a valid author to publish a resolving message

Notes:

• this special rule only applies if there exists no valid author who could merge
• publishing an "empty" transformation M is insufficient as merging these authors state would violate rule (2.b)
  • i.e. M here must contain add at least one author

Requirements

Same as ssb-crut: https://gitlab.com/ahau/lib/ssb-crut#requirements

API

Same as ssb-crut except authors is a reserved variable:

• spec.props cannot include authors
• spec.staticProps cannot include authors

TODO

This was extracted from ssb-profile in order to generalise it to more records.

• Need to review if we've extracted all the relevant tests about authorship from there

We might want to consider modifying ssb-crut to take "plugins" to extend core functionality and make this a plugin