API docs

Please check the clients and API docs for reference

Warning: Use client versions compatible with Socket.IO Server v4. Previous versions may not be supported and may not work correctly

Language	Website
Java	https://github.com/socketio/socket.io-client-java
JavaScript (browser, Node.js or React Native)	- Installation steps - API - Source code
JavaScript (for WeChat Mini-Programs)	https://github.com/weapp-socketio/weapp.socket.io
C++	https://github.com/socketio/socket.io-client-cpp
Swift	https://github.com/socketio/socket.io-client-swift
Dart	https://github.com/rikulo/socket.io-client-dart
Python	https://github.com/miguelgrinberg/python-socketio
.Net	https://github.com/doghappy/socket.io-client-csharp
Rust	https://github.com/1c3t3a/rust-socketio
Kotlin	https://github.com/icerockdev/moko-socket-io
PHP	https://github.com/ElephantIO/elephant.io
Golang	https://github.com/maldikhan/go.socket.io

Not all client-side APIs may be available in the server implementation, and vice versa.

Compatibility Matrix

Client API	Netty‑SocketIO Support	JavaScript Client	Java Client	Python Client	C++ Client	Swift Client	Dart/Flutter Client	.NET Client	PHP Client	Go Client	Notes
Connect	✅ Yes	io(url, opts)	IO.socket(url)	sio.connect(url)	socket.connect()	socket.connect()	socket.connect()	socket.Connect()	client->Connect()	socket.Connect()	Standard connect method
Disconnect	✅ Yes	socket.disconnect()	socket.disconnect()	sio.disconnect()	socket.disconnect()	socket.disconnect()	socket.disconnect()	socket.Disconnect()	client->Disconnect()	socket.Disconnect()	Client disconnects from server
Event listen	✅ Yes	socket.on(event, cb)	socket.on(EVENT, listener)	@sio.on(event)	socket.on(event, cb)	socket.on(event, cb)	socket.on(event, cb)	socket.On(event, cb)	client->On(event, cb)	socket.On(event, cb)	Standard event handler
One‑time listener	✅ Yes	socket.once(event, cb)	socket.once(EVENT, listener)	@sio.once(event)	socket.once(event, cb)	socket.once(event, cb)	socket.once(event, cb)	socket.Once(event, cb)	client->Once(event, cb)	socket.Once(event, cb)	Some clients don’t have built‑in once
Remove listener	✅ Yes	socket.off() / socket.removeListener()	socket.off(EVENT)	sio.off(event)	socket.off(event)	socket.off(event)	socket.off(event)	socket.Off(event)	client->Off(event)	socket.Off(event)	Most clients support listener removal cycles
Emit event	✅ Yes	socket.emit(event, …args)	socket.emit(event, …args)	sio.emit(event, data)	socket.emit(event, data)	socket.emit(event, data)	socket.emit(event, data)	socket.Emit(event, data)	client->Emit(event, data)	socket.Emit(event, data)	Standard emit
Emit with ack	✅ Yes	socket.emit(event, …, callback) / emitWithAck()	socket.emit(event, …args, AckCallback)	sio.call(event, data) / await sio.emit(event, data, callback)	socket.emit(event, data, cb)	socket.emit(event, data, cb)	socket.emit(event, data, cb)	socket.Emit(event, data, cb)	client->Emit(event, data, cb)	socket.Emit(event, data, cb)	Ack support varies
Namespace API	✅ Yes	io(url/ns) / socket.nsp	socket.of("/ns")	sio.connect(url, namespaces=["/ns"])	socket.of("/ns")	socket.of("/ns")	socket.of("/ns")	socket.Of("/ns")	client->Of("/ns")	socket.Of("/ns")	Most multi‑namespace clients support
Query / Auth	⚠️ Limited	io(url, { auth, query })	IO.Options.query/setAuth(Map<String,Object>)	sio.connect(url, auth={…})	socket.setAuth(data)	socket.setAuth(data)	socket.setAuth(data)	socket.SetAuth(data)	client->SetAuth(data)	socket.SetAuth(data)	Handshake params pass through
Reconnection control	⚠️ Partial	Managed by client options	socket.io().reconnection(true/false)	sio.reconnect() or handled by sio.connect()	Client library dependent	Client library dependent	Client library dependent	Client library dependent	Client library dependent	Client library dependent	Auto reconnect logic client
Volatile emit	⚠️ Limited	socket.volatile.emit()	JS-only / no standard in Java client	⚠️ Rare / not standard	Varies	Varies	Varies	Varies	Varies	Varies	Not consistently implemented
Compression flags	⚠️ Internal	socket.compress()	Not standard	Not standard	Not standard	Varies	Varies	Varies	Varies	Varies	Usually internal
Client middleware (use())	❌ No	JS only	❌	❌	❌	❌	❌	❌	❌	❌	Middleware API largely JS only
Engine/Manager internals	❌ No	socket.io / Manager	Internal	Internal	Internal	Internal	Internal	Internal	Internal	Internal	Client internals not mirrored on server