lattice_presence

Distributed presence CRDT with topic/key/pid/meta tracking, add-wins merge semantics, replica visibility, and Phoenix-style diff reporting.

Use this package to track which users, devices, or processes are online across distributed nodes without requiring a central coordinator.

Installation

gleam add lattice_presence

Quick example

import gleam/json
import lattice_presence/presence_state

pub fn main() {
  let state =
    presence_state.new("node-a")
    |> presence_state.join(
      pid: "pid-1",
      topic: "room:lobby",
      key: "alice",
      meta: json.object([]),
    )

  presence_state.get_by_topic(state, "room:lobby")
  // -> [#("pid-1", "alice", json.object([]))]
}

Modules

Module	Purpose
`lattice_presence/presence_state`	Presence CRDT state, joins/leaves, merges, diffs, liveness, and queries.
`lattice_presence/state_json`	JSON encoding and decoding for presence state.

Notes

presence_state exposes new, join, leave, leave_by_pid, merge, merge_with_diff, online_list, get_by_topic, and get_by_key.
merge_with_diff reports Phoenix-style joins and leaves while returning the merged state.
Replica liveness is local-only: replica_down, replica_up, and remove_down_replica affect local visibility and are not merged as replicated state.
Use state_json.to_json_string and state_json.from_json for persistence or transport.

License

MIT