@molecule/api-realtime

Auto-generated, AI-first package reference for the molecule.dev ecosystem. It is written to be read by coding agents as much as by people, and is generated from this package's source — edit src/index.ts JSDoc, not this file.

Realtime core interface for molecule.dev.

Defines the standard interface for real-time communication providers (WebSocket, SSE, Socket.io, etc.), including the client-initiated room-join protocol with pluggable authorization.

Client-initiated room-join protocol

Connected clients join rooms by name (any string, e.g. channel:<uuid>) with the reserved molecule:join event (payload { room }). The server replies molecule:joined { room } on success or molecule:join-denied { room, reason? } on rejection, sends molecule:leave acks as molecule:left { room }, and emits molecule:presence { room, presence: [{ clientId }] } to the room on every join/leave/disconnect. Clients send app messages into a joined room with molecule:room-send { room, event, data }, which dispatches to server onMessage handlers. Protocol room names live in the same namespace broadcast(roomId, ...) uses, so server code pushes to a protocol room by its name. The managed createRoom()/joinRoom() API (server-driven, room_N ids) is unchanged and coexists.

Authorization is pluggable via {@link onJoinRequest} guards: no guards → every join is allowed; multiple guards → ALL must return true (AND); a guard that throws → the join is denied (the bond logs the error).

Quick Start

import {
  setProvider,
  createRoom,
  broadcast,
  onMessage,
  onJoinRequest,
} from '@molecule/api-realtime'

// Bond a provider at startup
setProvider(socketioProvider)

// Authorize client-initiated joins (REQUIRED for apps with private rooms)
onJoinRequest(async ({ clientId, room, auth }) => {
  const userId = await verifyToken(auth.token)
  return userId !== undefined && (await canAccessRoom(userId, room))
})

// Push to a client-joined room by NAME
await broadcast('channel:general', 'message', { text: 'Hello!' })

// Managed (server-driven) rooms still work unchanged
const room = await createRoom('chat')
await broadcast(room.id, 'message', { text: 'Hello!' })

// Listen for incoming messages (including molecule:room-send dispatches)
onMessage((roomId, clientId, event, data) => {
  console.log(`${clientId} sent ${event} in ${roomId}:`, data)
})

Type

core

Installation

npm install @molecule/api-realtime @molecule/api-bond @molecule/api-i18n

API

Interfaces

JoinRequest

A client's request to join a room by name via the client-initiated room-join protocol (the reserved molecule:join event).

interface JoinRequest {
  /** The connected client's identifier (e.g. the Socket.io socket id). */
  clientId: string

  /** The room NAME the client wants to join (arbitrary string, e.g. `channel:<uuid>`). */
  room: string

  /**
   * The client's handshake auth payload. Socket.io: `socket.handshake.auth`;
   * ws/SSE: the connection URL's query params. `{}` when the transport
   * carries no auth.
   */
  auth: Record<string, unknown>

  /**
   * The HTTP headers of the transport request that established the
   * connection (Socket.io handshake / ws upgrade / SSE subscribe), when the
   * transport exposes them. Apps whose sessions live in an httpOnly cookie
   * (browser JS never sees the token, so it can't be sent in `auth`)
   * authenticate joins from `headers.cookie` — the browser attaches the
   * session cookie to the same-origin handshake request automatically.
   */
  headers?: Record<string, string | string[] | undefined>
}

PresenceInfo

Presence information for a connected client.

interface PresenceInfo {
  /** The client's unique identifier. */
  clientId: string

  /** When the client joined the room. */
  joinedAt: Date

  /** Arbitrary metadata attached to the client's presence. */
  metadata?: Record<string, unknown>
}

RealtimeProvider

Realtime provider interface.

All realtime providers must implement this interface to provide room-based, bidirectional real-time communication.

interface RealtimeProvider {
  /**
   * Creates a new room.
   *
   * @param name - Human-readable room name.
   * @param options - Optional room configuration.
   * @returns The created room.
   */
  createRoom(name: string, options?: RoomOptions): Promise<Room>

  /**
   * Adds a client to a room.
   *
   * @param roomId - The room to join.
   * @param clientId - The client joining the room.
   */
  joinRoom(roomId: string, clientId: string): Promise<void>

  /**
   * Removes a client from a room.
   *
   * @param roomId - The room to leave.
   * @param clientId - The client leaving the room.
   */
  leaveRoom(roomId: string, clientId: string): Promise<void>

  /**
   * Sends an event to all clients in a room.
   *
   * @param roomId - The target room.
   * @param event - The event name.
   * @param data - The event payload.
   */
  broadcast(roomId: string, event: string, data: unknown): Promise<void>

  /**
   * Sends an event to a specific client.
   *
   * @param clientId - The target client.
   * @param event - The event name.
   * @param data - The event payload.
   */
  sendTo(clientId: string, event: string, data: unknown): Promise<void>

  /**
   * Registers a handler for incoming messages.
   *
   * @param handler - The message handler callback.
   */
  onMessage(handler: MessageHandler): void

  /**
   * Registers a handler for client connections.
   *
   * @param handler - The connection handler callback.
   */
  onConnection(handler: ConnectionHandler): void

  /**
   * Registers a handler for client disconnections.
   *
   * @param handler - The disconnection handler callback.
   */
  onDisconnection(handler: DisconnectionHandler): void

  /**
   * Optionally registers an authorization guard for the client-initiated
   * room-join protocol (`molecule:join`). Providers that implement the
   * protocol evaluate every registered guard for each join request: with no
   * guards every join is allowed; with multiple guards ALL must return `true`;
   * a guard that throws denies the join. Providers whose transport has no
   * client-initiated join path may leave this undefined.
   *
   * @param guard - The join guard to register.
   */
  onJoinRequest?(guard: JoinGuard): void

  /**
   * Returns presence information for all clients in a room.
   *
   * @param roomId - The room to query.
   * @returns Array of presence info for each connected client.
   */
  getPresence(roomId: string): Promise<PresenceInfo[]>

  /**
   * Returns all active rooms.
   *
   * @returns Array of active rooms.
   */
  getRooms(): Promise<Room[]>

  /**
   * Optionally attach the provider's transport to an already-created HTTP(S)
   * server (e.g. the API's server) so realtime shares the API's port — rather
   * than binding a separate standalone port that a containerized/proxied
   * deployment may not expose. Providers that bind their transport eagerly at
   * creation may leave this undefined. When present it is called once, with the
   * real HTTP(S) server, before the server starts listening.
   *
   * @param server - The HTTP(S) server to attach the realtime transport to.
   */
  attachHttpServer?(server: HttpServer | HttpsServer): void

  /**
   * Shuts down the realtime provider and cleans up resources.
   */
  close(): Promise<void>
}

Room

A real-time communication room.

interface Room {
  /** Unique room identifier. */
  id: string

  /** Human-readable room name. */
  name: string

  /** Client IDs currently in the room. */
  clients: string[]

  /** Arbitrary metadata attached to the room. */
  metadata?: Record<string, unknown>
}

RoomOptions

Options for creating a room.

interface RoomOptions {
  /** Maximum number of clients allowed in the room. */
  maxClients?: number

  /** Arbitrary metadata to attach to the room. */
  metadata?: Record<string, unknown>

  /** Whether the room should persist after all clients leave. */
  persistent?: boolean
}

Types

ConnectionHandler

Handler invoked when a client connects.

type ConnectionHandler = (clientId: string, metadata?: Record<string, unknown>) => void

DisconnectionHandler

Handler invoked when a client disconnects.

type DisconnectionHandler = (clientId: string, reason: string) => void

JoinGuard

Authorization guard for client-initiated room joins.

Semantics: no guards registered → every join is allowed; multiple guards → ALL must return true (AND); a guard that throws → the join is denied (bonds log the error — never silently).

type JoinGuard = (request: JoinRequest) => boolean | Promise<boolean>

MessageHandler

Handler invoked when a message is received in a room.

type MessageHandler = (roomId: string, clientId: string, event: string, data: unknown) => void

Functions

broadcast(roomId, event, data)

Sends an event to all clients in a room using the bonded realtime provider.

function broadcast(roomId: string, event: string, data: unknown): Promise<void>

• roomId — The target room.
• event — The event name.
• data — The event payload.

Returns: Resolves when the broadcast completes.

close()

Shuts down the bonded realtime provider and cleans up resources.

function close(): Promise<void>

Returns: Resolves when sockets and timers are torn down.

createRoom(name, options)

Creates a new room using the bonded realtime provider.

function createRoom(name: string, options?: RoomOptions): Promise<Room>

• name — Human-readable room name.
• options — Optional room configuration.

Returns: The created room.

getPresence(roomId)

Returns presence information for all clients in a room.

function getPresence(roomId: string): Promise<PresenceInfo[]>

• roomId — The room to query.

Returns: Array of presence info for each connected client.

getProvider()

Retrieves the bonded realtime provider, throwing if none is configured.

function getProvider(): RealtimeProvider

Returns: The bonded realtime provider.

getRooms()

Returns all active rooms.

function getRooms(): Promise<Room[]>

Returns: Array of active rooms.

hasProvider()

Checks whether a realtime provider is currently bonded.

function hasProvider(): boolean

Returns: true if a realtime provider is bonded.

joinRoom(roomId, clientId)

Adds a client to a room using the bonded realtime provider.

function joinRoom(roomId: string, clientId: string): Promise<void>

• roomId — The room to join.
• clientId — The client joining the room.

Returns: Resolves when the join operation completes.

leaveRoom(roomId, clientId)

Removes a client from a room using the bonded realtime provider.

function leaveRoom(roomId: string, clientId: string): Promise<void>

• roomId — The room to leave.
• clientId — The client leaving the room.

Returns: Resolves when the leave operation completes.

onConnection(handler)

Registers a handler for client connections. Buffered + flushed on setProvider if no provider is bonded yet, so it is safe to call before the realtime bond binds at server-creation (e.g. presence handlers in postBondsSetup).

function onConnection(handler: ConnectionHandler): void

• handler — The connection handler callback.

onDisconnection(handler)

Registers a handler for client disconnections. Buffered + flushed on setProvider if no provider is bonded yet, so it is safe to call before the realtime bond binds at server-creation (e.g. in postBondsSetup).

function onDisconnection(handler: DisconnectionHandler): void

• handler — The disconnection handler callback.

onJoinRequest(guard)

Registers an authorization guard for the client-initiated room-join protocol (molecule:join). Buffered + flushed on setProvider if no provider is bonded yet, so it is safe to call before the realtime bond binds at server-creation (e.g. in postBondsSetup).

Guard semantics: no guards registered → every join is allowed; multiple guards → ALL must return true (AND); a guard that throws → the join is denied (the bond logs the error). The guard receives the client id, the requested room NAME, and the client's handshake auth payload.

function onJoinRequest(guard: JoinGuard): void

• guard — The join guard callback.

onMessage(handler)

Registers a handler for incoming messages. Buffered + flushed on setProvider if no provider is bonded yet, so it is safe to call before the realtime bond binds at server-creation (e.g. in postBondsSetup).

function onMessage(handler: MessageHandler): void

• handler — The message handler callback.

registerConnection(handler)

Register a connection handler now if a provider is bonded, else buffer it for flush on the next setProvider(). Order-independent (see the buffer comment).

function registerConnection(handler: ConnectionHandler): void

• handler — The connection handler to register or buffer.

registerDisconnection(handler)

Register a disconnection handler now if bonded, else buffer it.

function registerDisconnection(handler: DisconnectionHandler): void

• handler — The disconnection handler to register or buffer.

registerJoinGuard(guard)

Register a join guard now if bonded, else buffer it for flush on the next setProvider(). Order-independent (see the buffer comment), so apps can register room authorization in postBondsSetup before the realtime bond binds at server-creation.

function registerJoinGuard(guard: JoinGuard): void

• guard — The join guard to register or buffer.

registerMessage(handler)

Register a message handler now if bonded, else buffer it.

function registerMessage(handler: MessageHandler): void

• handler — The message handler to register or buffer.

sendTo(clientId, event, data)

Sends an event to a specific client using the bonded realtime provider.

function sendTo(clientId: string, event: string, data: unknown): Promise<void>

• clientId — The target client.
• event — The event name.
• data — The event payload.

Returns: Resolves when the message is delivered to the transport layer.

setProvider(provider)

Registers a realtime provider as the active singleton. Called by bond packages during application startup. Flushes any connection/disconnection/ message handlers that were registered before the provider was bonded.

function setProvider(provider: RealtimeProvider): void

• provider — The realtime provider implementation to bond.

Available Providers

Provider	Package
Realtime	@molecule/api-realtime-socketio
Realtime	@molecule/api-realtime-sse
Realtime	@molecule/api-realtime-ws
Realtime (Yjs CRDT)	@molecule/api-realtime-yjs

Injection Notes

Requirements

Peer dependencies:

• @molecule/api-bond ^1.0.1
• @molecule/api-i18n ^1.0.1

Runtime Dependencies

• @molecule/api-bond

• @molecule/api-i18n

• Pick the provider by your host's server model (read this FIRST). SSE (@molecule/api-realtime-sse) is HTTP-native: it streams from an ordinary route/endpoint and needs NO long-lived socket server, so it is the ONLY realtime that fits a serverless / no-persistent-server host — e.g. Next.js App Router or edge. There, mount its endpoint in a route handler and publish from server code (Next's instrumentation.ts runs at server start). Reach for WS (-ws) or Socket.io (-socketio) ONLY where you own a persistent Node server (a standalone process, or a separate API on its own port). Do NOT bolt a WS/Socket.io server onto Next.js App Router with a custom server.ts — you give up Next's managed server and fight its lifecycle. The interface below is identical for every provider; only the bond and where you attach its transport change.

• A broadcast(room, event, …) reaches ONLY clients that already joined that EXACT room and registered a handler for that EXACT event name. Broadcasting is half the feature — the client half is a separate, easy-to- forget step: wire @molecule/app-realtime-* and have the relevant screen connect() → joinRoom(room) → on(event, …) with the SAME room + event strings this call uses (usually a template literal like `listing:${id}`). A server that broadcasts to a room no client joined — or under an event name no client listens for — is a SILENT no-op (nothing errors). Verify the live two-session check below; do NOT assume a compiling broadcast works.

• Without a registered join guard ANY connected client may join ANY room by name — apps with private rooms MUST register onJoinRequest and validate the request's auth payload (e.g. verify a token grants access to request.room). auth is the client's handshake auth (Socket.io: socket.handshake.auth; ws/SSE: connection query params).

• onJoinRequest (like onMessage/onConnection) is buffered when called before a provider is bonded and flushed on setProvider() — safe to call in postBondsSetup.

• molecule:room-send only dispatches to server onMessage handlers — there is NO automatic relay to the room. Server code decides what (if anything) to broadcast back.

• Reserved molecule:* events are never dispatched to onMessage.

• RealtimeProvider.onJoinRequest is optional: providers whose transport has no client-initiated join path (e.g. the yjs bond with its injected transport) leave it undefined, and guards registered against them are logged as unenforceable rather than silently dropped.

E2E Tests

Integration checklist — drive the real UI (live preview, no mocks), adapt each item to this app's actual screens/flows, and check every box off one by one. A box you can't check is an integration bug to fix — not a skip:

• With the app open in TWO sessions (separate browser contexts/users), an action in one (send a message, update a shared record) appears in the other WITHOUT a manual reload.
• Updates reach only the sessions in the same room/scope — a session viewing a different room/record receives nothing.
• Private rooms enforce the join guard: an unauthorized session's join is denied and no data leaks to it. If ANY client can join any private room, onJoinRequest was never registered — an integration bug.
• Presence (if surfaced) updates when a participant joins and leaves.
• After a dropped connection (offline/online toggle or server restart), the client reconnects and live events flow again.