@lsync/server

Cloudflare Durable Object server support for lsync.

pnpm add @lsync/server @lsync/definitions

The package exports the reusable Durable Object, worker handler, collection configuration helpers, and the @lsync/server/client subpath for server-side clients.

SQLite JSON collections use server-sequence last-write-wins conflict resolution. previousValue is available to access rules and history consumers, but is not a compare-and-swap precondition. Mutation IDs are recorded durably, so retrying the same update is idempotent; reusing an ID with a different payload is rejected.

Safeguards

Each WebSocket may subscribe to at most 100 collection scopes by default. Override or disable the cap when building the shard options:

const options = CollectionShardDurableObject.from(collections)
  .limits({ maxSubscriptionsPerWebSocket: 250 }) // or false
  .build();

Cloudflare's managed Rate Limiting binding can protect WebSocket message handling:

import { cloudflareRateLimiter } from "@lsync/server";

const options = CollectionShardDurableObject.from(collections)
  .rateLimit(
    cloudflareRateLimiter({
      key: ({ auth, clientId }) => String(auth.userId ?? clientId),
    }),
  )
  .build();

Configure the matching binding in wrangler.toml (the period must be 10 or 60 seconds):

[[ratelimits]]
name = "RATE_LIMITER"
namespace_id = "1001"

[ratelimits.simple]
limit = 100
period = 60

The managed limiter is intentionally permissive, eventually consistent, and local to a Cloudflare location. Use it for abuse protection rather than billing or exact accounting. Prefer an authenticated user or tenant key; clientId is only the fallback.