Socket.IO - Full Reference

Exhaustive reference for SocketIOServerHelper and SocketIOClientHelper. For a readable introduction and the common tasks, start with the Socket.IO overview.

Files:

• packages/helpers/src/modules/socket/socket-io/server/helper.ts - SocketIOServerHelper
• packages/helpers/src/modules/socket/socket-io/client/helper.ts - SocketIOClientHelper
• packages/helpers/src/modules/socket/socket-io/common/types/ - option and callback types
• packages/helpers/src/modules/socket/socket-io/common/constants.ts - SocketIOConstants, SocketIOClientStates
• packages/helpers/src/modules/socket/socket-io/index.ts - barrel export (@venizia/ignis-helpers/socket-io)

Find what you need

You want to	Go to
See the full server and client call sequence	Architecture
Look up a server method (send(), on(), getClients(), ...)	Server API
Look up a client method (emit(), subscribe(), joinRooms(), ...)	Client API
Follow the auth handshake step by step	Authentication Protocol
Understand the three Redis connections	Redis Adapter
Look up a type, option, or callback signature	Types Reference
Look up an event name, room default, or client state	Constants
Match an error message to its cause	Common Errors

Architecture

SocketIOServerHelper (extends BaseHelper)
  |
  |-- constructor(opts)
  |     |-- setRuntime(opts)                  # validates `server` (Node) or `engine` (Bun)
  |     +-- initRedisClients(opts.redisConnection)
  |           |-- redisPub = duplicateClient()
  |           |-- redisSub = duplicateClient()
  |           +-- redisEmitter = duplicateClient()
  |
  |-- configure()  [async]
  |     |-- ensureRedisClientsConnecting([redisPub, redisSub, redisEmitter])
  |     |-- await Promise.all(waitForRedisReady x3)   # 30s timeout per client
  |     |-- initIOServer()                     # new IOServer(server, serverOptions) | new IOServer() + io.bind(engine)
  |     |-- io.adapter(createAdapter(redisPub, redisSub))
  |     |-- emitter = new Emitter(redisEmitter)
  |     +-- io.on('connection', socket => onClientConnect({ socket }))
  |
  |-- onClientConnect({ socket })
  |     |-- Create ISocketIOClient entry (state: UNAUTHORIZED)
  |     |-- Start authenticateTimeout timer
  |     |-- Register 'disconnect' handler
  |     +-- registerAuthHandler({ socket, handshake, clientId })
  |           +-- socket.on('authenticate', ...)
  |                 |-- state -> AUTHENTICATING
  |                 |-- authenticateFn(handshake)
  |                 |-- true  -> onClientAuthenticated({ socket })
  |                 +-- false or throw -> emit 'unauthenticated', disconnect
  |
  |-- onClientAuthenticated({ socket })
  |     |-- state -> AUTHENTICATED, clear authenticateTimeout
  |     |-- ping({ socket, doIgnoreAuth: true })       # immediate first ping
  |     |-- Join all defaultRooms
  |     |-- registerRoomHandlers({ socket, clientId })  # 'join' / 'leave'
  |     |-- interval = setInterval(ping, pingInterval)
  |     |-- send 'authenticated' to socket.id
  |     +-- invokeHook(clientConnectedFn)
  |
  |-- send({ destination?, payload, doLog?, callback? })
  |     +-- emitter.compress(true).to(destination)?.emit(topic, data)
  |
  +-- shutdown()  [async]
        |-- Disconnect all tracked clients (clears their timers)
        |-- close()                            # io.close()
        +-- Promise.all([redisPub.quit(), redisSub.quit(), redisEmitter.quit()])


SocketIOClientHelper (extends BaseHelper)
  |
  |-- constructor -> configure()
  |     |-- client = io(host, options)
  |     |-- Register 'connect'          -> onConnected
  |     |-- Register 'disconnect'       -> state UNAUTHORIZED, onDisconnected
  |     |-- Register 'connect_error'    -> onError
  |     |-- Register 'authenticated'    -> state AUTHENTICATED, onAuthenticated
  |     |-- Register 'unauthenticated'  -> state UNAUTHORIZED, onUnauthenticated
  |     +-- Register 'ping'             -> debug log
  |
  |-- authenticate()  -> state AUTHENTICATING, client.emit('authenticate')
  |-- subscribe({ event, handler, ignoreDuplicate? })   # wraps handler, tracked in wrappedHandlers
  |-- emit({ topic, data, doLog?, callback? })
  |-- joinRooms({ rooms })  -> client.emit('join', { rooms })
  |-- leaveRooms({ rooms }) -> client.emit('leave', { rooms })
  |
  +-- shutdown()
        |-- client.removeAllListeners()
        |-- disconnect() if connected
        +-- state -> UNAUTHORIZED

Server API

SocketIOServerHelper

Extends BaseHelper. Manages a socket.io server with a Redis adapter, authentication, room management, and heartbeat pings.

constructor(opts: TSocketIOServerOptions)

Validates the runtime-specific server (Node) or engine (Bun) field. Duplicates the provided redisConnection into three independent clients (redisPub, redisSub, redisEmitter). Does not start the IO server - call configure() to complete initialization.

Throws:

Message	Condition
[SocketIOServerHelper] Invalid HTTP server for Node.js runtime!	runtime: 'node' and server is falsy
[SocketIOServerHelper] Invalid @socket.io/bun-engine instance for Bun runtime!	runtime: 'bun' and engine is falsy
[SocketIOServerHelper] Unsupported runtime!	runtime is neither 'node' nor 'bun'
Invalid redis connection to config socket.io adapter!	redisConnection is falsy

configure(): Promise<void>

1. Registers error listeners on all three duplicated Redis clients (logged, not thrown)
2. Kicks off connect() on any client still in 'wait' status
3. await Promise.all([waitForRedisReady(redisPub), waitForRedisReady(redisSub), waitForRedisReady(redisEmitter)])
4. Creates the IOServer - new IOServer(server, serverOptions) for Node.js, or new IOServer() followed by io.bind(engine) for Bun
5. Attaches the Redis adapter via @socket.io/redis-adapter
6. Creates the Redis emitter via @socket.io/redis-emitter
7. Registers the 'connection' handler

Must be called before on(), send(), or any server operation.

NOTE

waitForRedisReady rejects after 30 seconds if a client never reaches ready (or immediately on that client's error event). A broken Redis connection fails configure() instead of hanging boot indefinitely.

getIOServer(): IOServer

Returns the underlying socket.io Server instance for direct access.

const io = socketServer.getIOServer();
io.of('/admin').on('connection', socket => {
  /* ... */
});

getEngine(): any

Returns the Bun engine instance.

Throws: '[getEngine] Engine is only available for Bun runtime!' - runtime is not 'bun'

getClients(opts?: { id?: string }): ISocketIOClient | Map<string, ISocketIOClient> | undefined

Without id, returns the full Map<string, ISocketIOClient>. With { id }, returns that client's entry or undefined.

const allClients = socketServer.getClients() as Map<string, ISocketIOClient>;
const client = socketServer.getClients({ id: 'socket-id' }) as ISocketIOClient | undefined;

on<HandlerArgsType extends unknown[] = unknown[], HandlerReturnType = void>(opts: { topic: string; handler: (...args: HandlerArgsType) => ValueOrPromise<HandlerReturnType> }): void

Registers an event handler directly on the IO server instance (io.on(topic, handler)).

socketServer.on({
  topic: 'custom-event',
  handler: (data: { userId: string }) => console.log('received:', data),
});

Throws:

Message	Condition
[on] Invalid topic to start binding handler	topic is empty/falsy
[on] Invalid event handler | topic: {topic}	handler is missing
[on] IOServer is not initialized yet!	called before configure() completes

onClientConnect(opts: { socket: IOSocket }): void

Handles a new socket connection. Invoked automatically by the 'connection' event, but can also be called manually.

1. Creates an ISocketIOClient entry with state UNAUTHORIZED
2. Starts the authenticateTimeout timer
3. Registers 'disconnect' and 'authenticate' handlers on the socket

No-op if socket is falsy or the client ID already exists in the registry.

onClientAuthenticated(opts: { socket: IOSocket }): void

Runs after successful authentication. Can also be called manually to authenticate a client programmatically.

1. Sets state to AUTHENTICATED
2. Clears and unsets the authenticateTimeout timer
3. Sends an immediate ping (doIgnoreAuth: true)
4. Joins all defaultRooms
5. Registers room handlers ('join', 'leave')
6. Starts the periodic ping interval
7. Emits 'authenticated' to the client with { id, time }
8. Invokes clientConnectedFn - errors are caught and logged, never surfaced to the caller

If the client entry no longer exists (disconnected mid-flow), logs and calls disconnect({ socket }) instead.

ping(opts: { socket: IOSocket; doIgnoreAuth: boolean }): void

Emits 'ping' to the client with { time: ISO string }.

• If doIgnoreAuth is false and the client is not AUTHENTICATED, the client is disconnected instead of pinged
• No-op if the socket or the tracked client is not found

disconnect(opts: { socket: IOSocket }): void

1. Clears the ping interval timer
2. Clears the authenticateTimeout timer
3. Removes the client from the registry
4. Calls socket.disconnect()

No-op if socket is falsy.

send(opts: { destination?: string; payload: { topic: string; data: any }; doLog?: boolean; callback?: () => void }): void

Emits through the Redis emitter with compression enabled (emitter.compress(true)), reaching clients on any server instance.

Parameter	Type	Description
destination	string | undefined	Socket ID or room name. Omit to broadcast to all clients
payload.topic	string	Event name
payload.data	any	Event payload
doLog	boolean	Logs the message details. Default: false
callback	() => void	Invoked via setImmediate after the emit call returns

No-op if payload, payload.topic, or payload.data is falsy. Logs an error and returns if called before configure() (the Redis emitter does not exist yet).

socketServer.send({
  destination: 'some-room',
  payload: { topic: 'update', data: { value: 42 } },
  callback: () => console.log('queued'),
});

shutdown(): Promise<void>

1. Disconnects every tracked client, clearing its interval and authenticateTimeout
2. Clears the clients map
3. Closes the IO server (no-op if configure() never ran)
4. await Promise.all([redisPub.quit(), redisSub.quit(), redisEmitter.quit()]) - runs even if closing the IO server rejects, so the three Redis sockets never leak

Client API

SocketIOClientHelper

Extends BaseHelper. Manages a socket.io-client connection with authentication, event subscriptions, and room operations.

constructor(opts: ISocketIOClientOptions)

Stores the callbacks and calls configure() internally. The client starts connecting immediately.

configure(): void

Creates the socket.io-client connection (io(host, options)) and registers the internal lifecycle handlers below. Called automatically by the constructor. A second call is a no-op if a client instance already exists.

socket.io-client is loaded here, through ModuleUtility.loadSync, not when the subpath is imported. A server that only uses SocketIOServerHelper never needs the client package installed. A bun build --compile binary has no node_modules for that lookup: pass the module as the module option.

Event	Behavior
'connect'	Invokes onConnected
'disconnect'	State -> UNAUTHORIZED, invokes onDisconnected(reason)
'connect_error'	Invokes onError(error)
'authenticated'	State -> AUTHENTICATED, invokes onAuthenticated
'unauthenticated'	State -> UNAUTHORIZED, invokes onUnauthenticated(message)
'ping'	Logs a debug message only

Every callback invocation is wrapped so a rejected promise is caught and logged, never thrown.

getState(): TSocketIOClientState

Returns 'unauthorized', 'authenticating', or 'authenticated'.

if (client.getState() === 'authenticated') {
  client.emit({ topic: 'message', data: { text: 'hello' } });
}

getSocketClient(): Socket

Returns the underlying socket.io-client Socket instance.

const rawSocket = client.getSocketClient();
rawSocket.io.opts.reconnection = false;

authenticate(): void

Emits 'authenticate' to the server to start the handshake.

• No-op if the client is not connected
• No-op if the current state is not 'unauthorized'
• Sets state to AUTHENTICATING before emitting

const client = new SocketIOClientHelper({
  // ...
  onConnected: () => client.authenticate(),
});

subscribe<T>(opts: { event: string; handler: TSocketIOEventHandler<T>; ignoreDuplicate?: boolean }): void

Registers a handler on the client socket. The handler is wrapped with error handling that catches both sync throws and async rejections. That wrapper is tracked in an internal wrappedHandlers map, so unsubscribe() can find and remove it.

Parameter	Type	Default	Description
event	string	-	Event name to listen for
handler	TSocketIOEventHandler<T>	-	Callback receiving the event data
ignoreDuplicate	boolean	true	Skip registration if a handler already exists for this event

subscribeMany(opts: { events: Record<string, TSocketIOEventHandler>; ignoreDuplicate?: boolean }): void

Calls subscribe() for each entry in events.

client.subscribeMany({
  events: {
    'user-joined': data => console.log('joined:', data),
    'user-left': data => console.log('left:', data),
  },
});

unsubscribe(opts: { event: string; handler?: TSocketIOEventHandler }): void

• With handler, removes only that specific handler (looked up in wrappedHandlers). No-op if that handler was not registered through this helper
• Without handler, removes all handlers for the event
• No-op if the event has no listeners

unsubscribeMany(opts: { events: string[] }): void

Calls unsubscribe() for each event, removing all handlers for each.

connect(): void

Manually reconnects the client socket. No-op if the client instance does not exist (i.e. configure() never ran).

disconnect(): void

Manually disconnects the client socket without removing listeners or resetting state. No-op if the client instance does not exist.

TIP

Use shutdown() for a full cleanup that also removes listeners and resets the authentication state.

emit<T>(opts: { topic: string; data: T; doLog?: boolean; callback?: () => void }): void

Emits an event to the server.

Parameter	Type	Default	Description
topic	string	-	Event name
data	T	-	Event payload
doLog	boolean	false	Logs the emission details
callback	() => void	undefined	Invoked via setImmediate after the emit call

Throws (both status 400):

Message	Condition
Invalid socket client state to emit	the client is not connected
Topic is required to emit	topic is empty/falsy

joinRooms(opts: { rooms: string[] }): void

Emits 'join' with { rooms }. The server validates the request through its validateRoomFn. Logs a warning and no-ops if the client is not connected.

leaveRooms(opts: { rooms: string[] }): void

Emits 'leave' with { rooms }. Logs a warning and no-ops if the client is not connected.

NOTE

Unlike joinRooms(), leave requests are not validated server-side. The client can request to leave any room name, including ones it never joined. socket.leave() on a room the socket isn't in is a no-op.

shutdown(): void

1. Removes all event listeners (removeAllListeners())
2. Disconnects if currently connected
3. Resets state to UNAUTHORIZED

Authentication Protocol

Client connects (transport only)
  |
  v
Server creates client entry (state: UNAUTHORIZED)
  |-- Starts authenticateTimeout timer (default: 10s)
  |-- Registers 'disconnect' handler
  |
Client emits 'authenticate'
  |
  v
State -> AUTHENTICATING
Server calls authenticateFn(handshake)
  |
  +-- Resolves true:
  |     |-- State -> AUTHENTICATED, authenticateTimeout cleared
  |     |-- Immediate ping, join defaultRooms, start ping interval
  |     |-- Emit 'authenticated' { id, time } to client
  |     +-- Invoke clientConnectedFn (errors caught and logged)
  |
  +-- Resolves false:
  |     |-- State -> UNAUTHORIZED
  |     |-- Emit 'unauthenticated' { message: 'Invalid token to authenticate! Please login again!', time }
  |     +-- Disconnect (right after the emit on the client's own socket)
  |
  +-- Throws / rejects:
  |     |-- State -> UNAUTHORIZED
  |     |-- Emit 'unauthenticated' { message: 'Failed to authenticate connection! Please login again!', time }
  |     +-- Disconnect (right after the emit on the client's own socket), error logged
  |
  +-- authenticateTimeout elapses first:
        +-- Disconnect - including a client whose authenticateFn is still pending;
            its eventual resolution finds the client already removed and is a no-op

A client that re-emits 'authenticate' while already AUTHENTICATING or AUTHENTICATED is ignored (logged as a warning, authenticateFn is not called again).

Redis Adapter

The server uses @socket.io/redis-adapter and @socket.io/redis-emitter for horizontal scaling. Three Redis connections are created by duplicating the provided redisConnection:

Client	Purpose
redisPub	Publishes adapter messages (room membership, cross-instance socket.io internals)
redisSub	Subscribes to adapter messages
redisEmitter	Powers send() for cross-instance message delivery

• Created in the constructor, connected in configure(). initRedisClients calls duplicateClient() three times while the helper is being built. configure() then attaches the error listeners and awaits all three, before the IO server starts.
• Lazy connect handled explicitly. Duplicated clients inherit lazyConnect but never dial on their own. If the parent redisConnection uses lazyConnect (autoConnect: false), configure() kicks each duplicated client into connect() explicitly.

Types Reference

IHandshake

interface IHandshake {
  headers: IncomingHttpHeaders;
  time: string;
  address: string;
  xdomain: boolean;
  secure: boolean;
  issued: number;
  url: string;
  query: ParsedUrlQuery;
  auth: { [key: string]: any };
}

ISocketIOClient

interface ISocketIOClient {
  id: string;
  socket: IOSocket;
  state: TSocketIOClientState;
  interval?: NodeJS.Timeout;           // Ping interval timer, set after authentication
  authenticateTimeout?: NodeJS.Timeout; // Cleared (set to undefined) after authentication
}

TSocketIOClientState

type TSocketIOClientState = 'unauthorized' | 'authenticating' | 'authenticated';

TSocketIOAuthenticateFn

type TSocketIOAuthenticateFn = (args: IHandshake) => ValueOrPromise<boolean>;

TSocketIOValidateRoomFn

type TSocketIOValidateRoomFn = (opts: { socket: IOSocket; rooms: string[] }) => ValueOrPromise<string[]>;

TSocketIOClientConnectedFn

type TSocketIOClientConnectedFn = (opts: { socket: IOSocket }) => ValueOrPromise<void>;

TSocketIOEventHandler<T>

type TSocketIOEventHandler<T = unknown> = (data: T) => ValueOrPromise<void>;

IOptions

Client connection options. Extends SocketOptions from socket.io-client; path and extraHeaders are required by the type.

interface IOptions extends SocketOptions {
  path: string;
  extraHeaders: Record<string | symbol | number, any>;
}

ISocketIOClientOptions

Option	Type	Default	Description
identifier	string	-	Unique identifier for this client (used as logger scope)
host	string	-	Server URL to connect to (e.g. 'http://localhost:3000')
options	IOptions	-	Socket.IO client options
module	typeof import('socket.io-client')	loaded by name	socket.io-client itself, for a compiled binary. Omitted, it is loaded on configure()
onConnected	() => ValueOrPromise<void>	undefined	Called when the transport connection is established
onDisconnected	(reason: string) => ValueOrPromise<void>	undefined	Called on disconnect; state resets to 'unauthorized' first
onError	(error: Error) => ValueOrPromise<void>	undefined	Called on 'connect_error'
onAuthenticated	() => ValueOrPromise<void>	undefined	Called when the server confirms authentication
onUnauthenticated	(message: string) => ValueOrPromise<void>	undefined	Called when the server rejects authentication

TSocketIOServerOptions

Discriminated union on runtime.

type TSocketIOServerOptions = ISocketIOServerNodeOptions | ISocketIOServerBunOptions;

interface ISocketIOServerBaseOptions {
  identifier: string;
  serverOptions: Partial<ServerOptions>;   // socket.io ServerOptions - required by the type, pass {} if unused
  redisConnection: IRedisHelper;
  defaultRooms?: string[];                 // Default: ['io-default', 'io-notification']
  authenticateTimeout?: number;            // Default: 10000 (10s)
  pingInterval?: number;                   // Default: 30000 (30s)

  authenticateFn: TSocketIOAuthenticateFn;
  validateRoomFn?: TSocketIOValidateRoomFn;
  clientConnectedFn?: TSocketIOClientConnectedFn;
}

interface ISocketIOServerNodeOptions extends ISocketIOServerBaseOptions {
  runtime: 'node';
  server: HTTPServer; // node:http Server
}

interface ISocketIOServerBunOptions extends ISocketIOServerBaseOptions {
  runtime: 'bun';
  engine: any; // @socket.io/bun-engine Server instance - typed `any` since it's an optional peer dep
}

WARNING

If no validateRoomFn is provided, all custom room join requests are rejected with a warning log. Clients still get defaultRooms automatically.

Constants

SocketIOConstants

Constant	Value	Description
EVENT_PING	'ping'	Heartbeat event emitted by the server at pingInterval
EVENT_CONNECT	'connection'	Server-side connection event
EVENT_DISCONNECT	'disconnect'	Disconnect event (server and client)
EVENT_JOIN	'join'	Room join request event
EVENT_LEAVE	'leave'	Room leave request event
EVENT_AUTHENTICATE	'authenticate'	Client -> server authentication request
EVENT_AUTHENTICATED	'authenticated'	Server -> client authentication success
EVENT_UNAUTHENTICATE	'unauthenticated'	Server -> client authentication failure
ROOM_DEFAULT	'io-default'	Default room name
ROOM_NOTIFICATION	'io-notification'	Default notification room name

SocketIOClientStates

Constant	Value	Description
UNAUTHORIZED	'unauthorized'	Initial state; not yet authenticated
AUTHENTICATING	'authenticating'	Authentication in progress
AUTHENTICATED	'authenticated'	Successfully authenticated

SocketIOClientStates.isValid(input: string): input is TConstValue<typeof SocketIOClientStates> - checks membership against the backing SCHEME_SET.

SocketIOClientStates.isValid('authenticated'); // true
SocketIOClientStates.isValid('invalid');       // false

Internal defaults

Constant	Value	Description
CLIENT_AUTHENTICATE_TIMEOUT	10_000 (10s)	Default authenticateTimeout
CLIENT_PING_INTERVAL	30_000 (30s)	Default pingInterval

Common Errors

Error	Cause	Fix
[SocketIOServerHelper] Invalid HTTP server for Node.js runtime!	server missing/falsy with runtime: 'node'	Pass a valid http.Server instance
[SocketIOServerHelper] Invalid @socket.io/bun-engine instance for Bun runtime!	engine missing/falsy with runtime: 'bun'	Pass a valid @socket.io/bun-engine Server instance
[SocketIOServerHelper] Unsupported runtime!	runtime is neither 'node' nor 'bun'	Use RuntimeModules.NODE, RuntimeModules.BUN, or RuntimeModules.detect()
Invalid redis connection to config socket.io adapter!	redisConnection missing, null, or undefined	Pass a valid IRedisHelper (e.g. RedisSingleHelper, RedisClusterHelper)
[on] Invalid topic to start binding handler	Empty/falsy topic passed to on()	Provide a non-empty string topic
[on] IOServer is not initialized yet!	on() called before configure() completed	await configure() before registering handlers
Invalid socket client state to emit (client)	emit() called while not connected	Check getState() / connection status, or emit inside onConnected
Topic is required to emit (client)	emit() called with an empty/falsy topic	Provide a non-empty string topic

See also

• Socket.IO overview - getting started, constructor options, and common tasks
• Socket.IO Component - DI-managed lifecycle wrapper around this helper
• WebSocket Helper - Bun-native alternative with no socket.io dependency
• Redis Helper - duplicateClient() and the topology classes used as redisConnection