@kontsedal/olas-realtime

Two primitives over a consumer-supplied RealtimeService: createRealtimePatcher for the "WebSocket event → cache write" pattern, and createLiveStream for tail-mode buffers (logs, metrics, presence) with capacity + coalesced flush. createConnectionState and onReconnect follow the transport's connection. SPEC §16.5.

The package ships no default transport. Apps wire their own (WebSocket, Pusher, Supabase Realtime, Ably, …) and pass it through ctx.deps.realtime after augmenting AmbientDeps.

Install

pnpm add @kontsedal/olas-realtime @kontsedal/olas-core @preact/signals-core

30-second example

import { bindQuery, defineController, defineQuery } from '@kontsedal/olas-core'
import {
  createLiveStream,
  createRealtimePatcher,
  type RealtimeService,
} from '@kontsedal/olas-realtime'

// Augment AmbientDeps once in your app's top-level types.
declare module '@kontsedal/olas-core' {
  interface AmbientDeps {
    realtime: RealtimeService
  }
}

type Post = { id: string; title: string; likes: number }
type Comment = { id: string; text: string }

type FeedEvent =
  | { type: 'post-updated'; post: Post }
  | { type: 'comment-added'; postId: string; comment: Comment }

const postQuery = defineQuery({
  id: 'post',
  key: (id: string) => ['post', id],
  fetcher: async ({ signal }, id: string) =>
    (await fetch(`/api/posts/${id}`, { signal })).json() as Promise<Post>,
})
const commentsQuery = defineQuery({
  id: 'post/comments',
  key: (postId: string) => ['post', postId, 'comments'],
  fetcher: async ({ signal }, postId: string) =>
    (await fetch(`/api/posts/${postId}/comments`, { signal })).json() as Promise<Comment[]>,
})

const feed = defineController((ctx) => {
  // The `origin` tags these writes, so cross-tab leaves them alone: every tab
  // receives the same push from the server itself.
  const posts = bindQuery(ctx, postQuery, { origin: 'realtime' })
  const comments = bindQuery(ctx, commentsQuery, { origin: 'realtime' })

  // Dispatch realtime events to type-keyed handlers. Each handler receives
  // its own variant of `FeedEvent`, so `ev.post` and `ev.comment` need no check.
  createRealtimePatcher<FeedEvent>(ctx, 'feed', {
    'post-updated': (ev) => posts.replace(ev.post.id, ev.post),
    'comment-added': (ev) => comments.write(ev.postId, (list = []) => [...list, ev.comment]),
  })

  // Or buffer a live tail with backpressure.
  const logs = createLiveStream<string>(ctx, 'logs', {
    capacity: 1000,
    flushMs: 16,
  })

  return { logs }
})

A server push is data that is already true, so the handlers use the canonical writes. replace takes a whole record and supersedes a fetch in flight. write patches an entry. setData is the optimistic write for a mutation's onMutate: a push applied with it leaves a live snapshot behind on every call.

API

function createRealtimePatcher<TEvent extends { type: string }>(
  ctx: Ctx<RealtimeDeps>,
  channel: string | ReadSignal<string>,
  handlers: PatcherHandlers<TEvent>,
): void

function createLiveStream<TEvent>(
  ctx: Ctx<RealtimeDeps>,
  channel: string | ReadSignal<string>,
  options?: {
    capacity?: number                              // default 1000
    flushMs?: number                               // default 16
    rafFlush?: boolean                             // default false
    onDrop?: (dropped: readonly TEvent[]) => void
  },
): LiveStream<TEvent>

function createConnectionState(ctx: Ctx<RealtimeDeps>): ReadSignal<ConnectionState>

function onReconnect(ctx: Ctx<RealtimeDeps>, fn: () => void): void

// Each key's handler receives that key's variant; '*' receives the union.
type PatcherHandlers<TEvent extends { type: string }> = {
  [K in TEvent['type']]?: (event: Extract<TEvent, { type: K }>) => void
} & { '*'?: (event: TEvent) => void }

type LiveStream<TEvent> = {
  events: ReadSignal<readonly TEvent[]>
  isPaused: ReadSignal<boolean>
  pause(): void
  resume(): void
  clear(): void
}

type ConnectionState = 'connected' | 'reconnecting' | 'offline' | 'unknown'

Name	What
createRealtimePatcher	Subscribe; dispatch by event.type. Each handler receives its own variant of the union. A '*' handler also sees every event, after the specific one. Handlers run inside untracked. Auto-unsubscribes on dispose.
createLiveStream	Tail buffer. capacity caps memory (oldest drops, and onDrop receives them); flushMs coalesces bursts into one signal write; flushMs <= 0 flushes synchronously. rafFlush coalesces on requestAnimationFrame instead, and falls back to setTimeout(0) where there is none.
createConnectionState	A ReadSignal of the transport's connection state. It is 'unknown' for a transport without onConnectionChange. With one, it starts at 'connected' until the first report, or at the latest report when another user already holds the subscription. A resume starts it the same way.
onReconnect	Call fn when the connection returns to 'connected' from another state. It does not fire for the initial 'connected'. A resume that moves the state back to 'connected' counts too. Pair it with a query invalidate to refetch what a disconnect missed.
RealtimeService	The consumer-implemented contract — subscribe(channel, handler) → { unsubscribe }, plus an optional onConnectionChange.

RealtimeService contract

type RealtimeSubscription = { unsubscribe(): void }

type RealtimeService = {
  subscribe<TEvent = unknown>(
    channel: string,
    handler: (event: TEvent) => void,
  ): RealtimeSubscription
  onConnectionChange?(handler: (state: ConnectionState) => void): () => void
}

Most transports already match this shape (Pusher, Ably, Supabase, raw WebSocket wrappers). Adapt yours into a tiny RealtimeService object and inject via RootOptions.deps.

Lifecycle notes

• Subscriptions live inside ctx.effect(...). They are unsubscribed on controller dispose.
• channel is a name or a ReadSignal<string>. When the signal changes, the patcher and the stream unsubscribe from the old channel and subscribe to the new one. So a per-route room is computed(() => `room:${params.value.roomId}`). A stream also empties its buffer on the change, as clear() does, because the buffered events came from the old channel.
• Every createConnectionState and onReconnect on one RealtimeService shares one onConnectionChange subscription. The first one opens it, and the last one to dispose or suspend closes it. The transport is called as a method, so a class-based one keeps its this.
• pause() flips a tracked signal — the effect re-runs and the subscription is torn down. resume() restores it. Already-buffered events are preserved across a pause, but events that arrive during the pause are lost — the subscription is gone, so nothing is received (let alone buffered) until resume(). To recover a gap, pair with onReconnect(...) + a query invalidate (refetch authoritative state) rather than relying on the buffer.
• clear() empties both the visible buffer and the pending-flush queue without touching the subscription.

What's NOT included

• Default transport. Bring your own.
• Multi-channel patcher sugar. Call createRealtimePatcher per channel.
• Backpressure beyond capacity, flushMs and rafFlush (e.g. sampling, downsampling, priority queues).

Further reading

• ../../.wiki/modules/realtime.md
• SPEC §16.5 (real-time → cache patches; tail-buffer pattern).