@colibri-social/space-sync

Keeps a local, up-to-date copy of an atproto permissioned space.

Push and sweep

SpaceSyncEngine runs both:

• Push. registerNotify subscribes this service on the space host. When a member writes, their host tells the authority, which forwards to registered syncers. notifyWrite(space, repo) enqueues that repo
• Sweep. Every sweepIntervalMs, listRepos gives the authority's view of the writer set with each repo's revision. Anything ahead of our cursor is enqueued, and anything that has disappeared is dropped

Fail handling

A repo that fails records consecutiveFailures and a retryAfter, backing off exponentially to an hour. The sweep skips a repo that is still backing off.

| | | | --------------------------------------------------------- | ---------------------------------------- | | the host no longer retains our since revision | full recovery from the CAR | | the account is gone, taken down, suspended or deactivated | drop the repo | | the set hash disagrees with a verified commit | full recovery | | the authority says the space is deleted | drop the space and forget the credential | | anything else | back off and retry, keeping the copy |

Treating an outage as a deletion would throw away a correct copy, so an unrecognised error is never allowed to mean "gone".

Seeing it in context

Colibri's own write-up of this algorithm is in the docs.