frontier-store

A small runtime for storing garbage-collection acknowledgement frontiers for Sovereignbase CRDT replicas.

• JSR
• NPM
• Typedoc

Compatibility

• Runtimes: Node >= 22, modern browsers, Bun, Deno, Cloudflare Workers, Edge Runtime.
• Module format: ESM + CommonJS.
• Required globals / APIs: none beyond the target JavaScript runtime.
• TypeScript: bundled types.

Goals

• Keep acknowledgement frontiers separated by CRDT kind, CRDT target, and acknowledging entity.
• Provide the exact frontier arrays expected by garbageCollect(frontiers).
• Support CRSet, CRMap, CRList, CRText, and CRStruct acknowledgement types.
• Stay storage-adapter-neutral: persist the JSON snapshot wherever the application already stores metadata.
• Keep the runtime small and explicit; callers that need defensive copies can clone snapshots at the storage boundary.

Installation

npm install @sovereignbase/frontier-store
# or
pnpm add @sovereignbase/frontier-store
# or
yarn add @sovereignbase/frontier-store
# or
bun add @sovereignbase/frontier-store
# or
deno add jsr:@sovereignbase/frontier-store
# or
vlt install jsr:@sovereignbase/frontier-store
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Usage

Copy-paste example

import { CRSet } from '@sovereignbase/convergent-replicated-set'
import { FrontierStore } from '@sovereignbase/frontier-store'

const alice = new CRSet<string>()
const bob = new CRSet<string>()
const frontiers = new FrontierStore()

alice.addEventListener('delta', (event) => {
  bob.merge(event.detail)
})

bob.addEventListener('delta', (event) => {
  alice.merge(event.detail)
})

alice.addEventListener('ack', (event) => {
  frontiers.setFrontier('set', 'shopping-list', 'alice', event.detail)
})

bob.addEventListener('ack', (event) => {
  frontiers.setFrontier('set', 'shopping-list', 'bob', event.detail)
})

alice.add('milk')
alice.delete('milk')
bob.add('coffee')

alice.acknowledge()
bob.acknowledge()

const acknowledged = frontiers.getFrontiers('set', 'shopping-list')

alice.garbageCollect(acknowledged)
bob.garbageCollect(acknowledged)
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Persisting frontier state

import { FrontierStore } from '@sovereignbase/frontier-store'

const store = new FrontierStore(
  JSON.parse(localStorage.getItem('frontiers') ?? '{}')
)

store.setFrontier(
  'text',
  'article:homepage',
  'device:laptop',
  '0198f0a8-1357-7c00-8000-000000000001'
)

localStorage.setItem('frontiers', JSON.stringify(store))
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Snapshots are plain structured-clone-compatible objects:

type FrontierStoreSnapshot = {
  set?: Record<string, Record<string, CRSetAck>>
  map?: Record<string, Record<string, CRMapAck>>
  list?: Record<string, Record<string, CRListAck>>
  text?: Record<string, Record<string, CRTextAck>>
  struct?: Record<string, Record<string, CRStructAck<Record<string, unknown>>>>
}
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Multiple CRDT kinds

import { FrontierStore } from '@sovereignbase/frontier-store'

const store = new FrontierStore()

store.setFrontier('map', 'profile:alice', 'phone', mapAck)
store.setFrontier('text', 'profile:alice/name', 'phone', textAck)
store.setFrontier('struct', 'profile:alice/settings', 'phone', structAck)

profileMap.garbageCollect(store.getFrontiers('map', 'profile:alice'))
nameText.garbageCollect(store.getFrontiers('text', 'profile:alice/name'))
settingsStruct.garbageCollect(
  store.getFrontiers('struct', 'profile:alice/settings')
)
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The kind and targetId are application-level routing keys. Keep them stable for the lifetime of the CRDT object whose acknowledgements they describe.

Removing stale entities

import { FrontierStore } from '@sovereignbase/frontier-store'

const store = new FrontierStore(snapshot)

store.deleteFrontier('set', 'shopping-list', 'old-phone')
store.deleteFrontier('text', 'article:homepage')
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Passing an entityId removes one acknowledging entity. Omitting it removes all frontiers for the target. Empty target and kind buckets are cleaned up.

Runtime behavior

Snapshot semantics

• The constructor uses the provided snapshot as the backing state.
• setFrontier() stores the provided acknowledgement value.
• getFrontiers() returns the currently stored acknowledgement values.
• toJSON(), JSON.stringify(), inspection symbols, and iteration expose the current snapshot model.
• deleteFrontier() is idempotent for missing kinds, targets, and entities.
• The store does not validate CRDT frontier internals; the corresponding CRDT package remains the authority for accepting or ignoring a frontier.
• Clone snapshots before passing them to or reading them from the store when your application needs mutation isolation.

Convergence and compaction

• FrontierStore does not decide when a CRDT may compact history.
• It records the latest acknowledgement frontier per (kind, targetId, entityId).
• Callers should pass the complete frontier set for the target to that target's garbageCollect().
• A partial frontier set is caller misuse for Sovereignbase CRDTs that require every active replica's acknowledgement before compacting safely.
• Store snapshots can be replicated or persisted independently of the CRDT snapshots they describe.

Tests

npm run test
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The test suite covers:

• Core FrontierStore storage, replacement, deletion, cleanup, iteration, inspection, and serialization behavior.
• Snapshot/frontier exposure semantics for constructor input, getFrontiers(), toJSON(), and iteration.
• ESM and CommonJS package interop through JSON snapshots.
• End-to-end runtime matrix for Node ESM/CJS, Bun ESM/CJS, Deno ESM, Cloudflare Workers ESM, Edge Runtime ESM, and browsers via Playwright.
• Integration with CRSet, CRMap, CRList, CRText, and CRStruct: collect ack events, store them by target/entity, retrieve complete frontier arrays, run garbageCollect(), settle replicas, and hydrate snapshots.
• Coverage on built dist/**/*.js with 100% statements, branches, functions, and lines via c8.

Benchmarks

npm run bench
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The benchmark suite measures FrontierStore orchestration paths:

• constructor hydration
• setFrontier() for string and struct acknowledgements
• getFrontiers()
• entity and target deletion
• toJSON()
• iteration

License

Apache-2.0